ft 75-652 •
550/8-76-001
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An Experimental Investigation with Application to Noise
from Portable Air Compressors
Curtis I. Holiner
National Bureau of Standards
July 1975
\
Approved for public release; distribution unlimited
Applied Acoustics Section
Institute for Basic Standards
National Bureau of Standards
Washington, D. C. 20234
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NBSIR 75-652
EPA-550/8-76-001
PROCEDURES FOR ESTIMATING SOUND
POWER FROM MEASUREMENTS OF SOUND
PRESSURE
An Experimental Investigation with Application to Noise
from Portable Air Compressors
Curtis I. Holmer
Applied Acoustics Section
National Bureau of Standards
Washington. D. C. 20234
July 1975
Final Report
Prepared for
Office of Noise Abatement and Control
U. S. Environmental Protection Agency
Washington, D. C. 20460
<•***
/ w
•**««•
U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary
James A. Baker, III. Under Secretary
Dr. Betsy Ancker-Johnson. Assistant Secretary for Science and Technology
NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director
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Table of Contents
Page
1. Introduction 1
2. Experimental Program 3
2.1. Program Objectives and Implementation 3
2.2. Experimental Plan 3
2.3. Measurement Procedures 3
2.3.1. Measurement Site 3
2.3.2. Instrumentation It
2.3.3. Test Plan 7
2.3-1*. Data Acquisition 9
2.3.5. Data Reduction and Corrections 11
2.1». Description of Compressor Sample lit
2.5. Compressor Operation 15
2.6. Measurement Locations and A-veighted Sound Level Data 16
2.6.1. Far Field Measurements 16
2.6.2. Near Field Measurements 17
3- Sound Power Level Calculations 37
3.1. Far Field Sound Power Calculation Procedures 37
3.1.1. Systematic Errors in the Far Field Array 37
3.1.2. Far Field Sound Power Calculations 1)0
3.2. Near Field Sound Power Calculation Procedures l»i
3-3. Sound Power Level Data UU
1*. Discussion of Kxperimental Results 62
lt.1. Sound Pressure Level Data 62
It. 1.1. Directivity of Compressor Noise 62
4.1.2. Systematic Variation of Hoise with Position 62
1».2. Sound Power Level Data 62
5. Analysis of Measurement Error Gk
5-1. Introduction 6to
5.2. Error in Sound Power Measurement Methodologies 6U
5-3. Instrumentation Accuracy 68
5-1*. Total Measurement Error 69
6. Conclusions 71
7. Acknowledgements 72
8. Beferences 73
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List of Tables
Test Number 1
Test Number 2
Test Number 3
Test Humber U
Test Number 5
Test Number 6
Test Kumber 7
Test Number 8
Test Number 9
Test Number 10
Test Number 11
Test Number 12
Test Number 13
Test Number ik
Test Number 15
Test Number 16
Test Number 17
Test Number 18
Test Number 19,
Table 1 Instrumentation data
Table 2 Description of sources
Table 3.1 A-weighted sound pressure level data.
Table 3.2 A-weighted sound pressure level data.
Table 3-3 A-weighted sound pressure level data.
Table 3-^ A-weighted sound pressure level data.
Table 3-5 A-weighted sound pressure level data.
Table 3-6 A-weighted sound pressure level data.
Table 3-7 A-weighted sound pressure level data.
Table 3.8 A-weighted sound pressure level data.
Table 3-9 A-weighted sound pressure level data.
Table 3.10 A-weighted sound pressure level data.
Table 3.11 A-weighted sound pressure level data.
Table 3.12 A-weighted sound pressure level data.
Table 3.13 A-weighted sound pressure level data.
Table 3-1^ A-weighted sound pressure level data.
Table. 3.15 ATweighted sound pressure level data.
Table 3.16 A-weighted sound pressure level data.
Table 3.17 A-weighted sound pressure level data.
Table 3.18 A-weighted sound pressure level data.
(Broad band reference sound source)
Table 3.19, A-weighted sound pressure level data.
20, 21 20, 21 (Pure-tone loudspeaker source, 500 Hz, 1000 Hz,
2000 Hz) .
Table l*.l Systematic error in estimation of sound power from a
compact source using SPL values from a 73 point array
on a 7 metre hemisphere (source: pure tone)
Table \.Z Systematic error in estimation of sound power from a
compact source using SPL values from a 73 point array
on a 7 metre hemisphere (source: pink noise).
Sound power level data. Test number 1
Test number 2
Test number 3
Test number k
Test number 5
Test number 6
Test number 7
Test cumber 8
Test number 9
Test number 10
Test number 11
Test number 12
Test number 13
Test number lU
Test number 15
Test number 16
Test number 17
Average deviation and standard deviation of average
deviation of near field sound power level from far
field sound power level for seventeen portable air
compressors. Six near field procedures are shown plus
similar statistics for far field methodology
Table 7 Instruments imprecision (two standard deviations)
associated with commercially available precision
(Type I) sound level meters
Table 8 Estimated achievable measurement error (90% confidence
for measurement of A-weighted sound power level of portable
air compressors in a field test environment using a
measurement surface 1 metre from the source surface,
excluding operator error.
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
Table
5.1
5.2
5-3
5.*
5-5
5-6
5.7
5.8
5-9
5.10
5.11
5.12
5.13
5.1k
5.15
5.16
5.17
6
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Sound power level data.
Page
11
s
19
20
21
22
23
2l»
25
26
27
28
29
30
31
32
33
3fc
35
36
39
39
J.5
U6
1»7
U8
»*9
50
51
52
53
5"»
55
56
57
58
59
60
61
63
69
70
ii
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List of Figures
Page
Figure 1 Field test site It
Figure 2 Photographs of test site 5
Figure 3 Equipment configuration for pulse echo tests of 6
test site
Figure U Schematic block diagram of data acquisition and 7
analysis instrumentation
Figure 5 Far-field measurement array 8
Figure 6 Representative near-field measurement positions 9
Figure 7 Microphone correction factor (Type !»llt5 cartridge) 13
Figure 8 Confonnal surface at a distance r from a rectangular box 1»2
Figure 9 Plot of average deviation of near field from far field 6U
sound power level
Figure 10 "Bias" and "precision of A-weighted soxmd ppver level vs 67
number of measurement positions (17 compressors)
Figure 11 A-weighted sound power level deviation vs source size 68
ill
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PROCEDURES FOR ESTIMATING SOUND POWER FROM
MEASUREMENTS OK SOUND PRESSURE
An Experimental Investigation vith Application
to Noise From Portable Air Compressors
Curtis I. Holmer
Applied Acoustics Section
Mechanics Division
National Bureau of Standards
Washington, D. C. 20231*
ABSTRACT
This report describes investigations of the accuracy and precision of various measurement
methodologies for determining the estimated sound power output of "large" machines in 'the free field
over a reflecting plane. One purpose of this investigation is to place empirical error bounds on many
of the free field measurement procedures currently proposed or in use; and in particular, compare the
results of "near-field" and "far-field" measurements. The sources used for the investigation included
17 portable air compressors of various types (powered by internal combustion engines), a "reference"
sound source, and a loudspeaker driven by a pure tone source. The data recorded include sound
pressure level (A-veighted, linear, and 1/3-c.rtave band) on an 8U point hemispherical array of seven
metre radius, and "near-field" measurements, sampled every square metre, on a rectangular surface one
metre from the machine surface. These data were reduced to provide information on the deviation of
"near field" sound power determinations from "far-field" power level (using subsets of the data as
appropriate to various methodologies). The measured data for seventeen sources suggests that the
value of a sound power estimate based on "near-field" sound pressure level measurements msy be an
upper bound to the sound power level estimated from far field measurements, subject to the limitations
of sampling error. Estimates of total achievable measurement error of A-weighted sound power level of
near field determinations relative to far field determinations are made for several measurement
methodologies, based on the experimental data.
1. INTRODUCTION
This report presents the results of an experimental investigation undertaken by the national
Bureau of Standards; of measurement procedures for the determination of sound power output of portable
air compressors.
These results are preliminary in the sense that the potential information available from the data
bank established in the measurement program has only been partially evaluated. Much additional
information remains to be retrieved from the data. The conclusions reached concerning the accuracy
and precision of "near-field" sound power measurements are substantiated as far as they go. However,
additional analysis of the data may lead to reinterpretation of these findings.
This study was jointly funded by the U. S. Environmental Protection Agency Office of Noise
Abatement and Control (EPA/OHAC) and the National Bureau of Standards (NBS) to provide background
information for a measurement methodology appropriate for the regulation of noise emission from newly
manufactured portable air compressors. EPA supported the cost of data collection and NBS the cost of
data reduction and analysis.
True sound power output is conventionally defined as the integral of the normal component of time
average acoustic intensity over a surface completely enclosing the source. (See discussion in Section
5.2.) Since the actual measurement process must involve point sampling of the sound field due to the
source, and to be widely useful must employ commercially available instrumentation, such measurements
can only yield an estimate of true sound power. Present commercially available instrumentation
measures mean square sound pressure rather than intensity, so standardized measurement procedures for
the estimation of sound power employ measurements of sound pressure under particular controlled
situations where the measurements provide data which is known to at least asymptotically approach (in
the large radius limit) the scalar magnitude of true intensity.
Present ISO and ANSI standard methodsfl]-' of determination of sound power in the free field over
a reflecting plane involve measurements of sound pressure level at points on a hemisphere whose radius
is large compared with the largest source dimension ("far field"). Recent draft standards[2] and some
—'Numbers in brackets refer to references at the end of this report.
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current research!3] suggest that measurements made near the surface of a large machine ("near-field")
can also be utilized as the basis for estimates of radiated sound pover. This study was intended to:
(1) provide empirical evaluation of the suitability of close-in measurements of sound pressure level
to infer the "farfield" estimate of sound power output of a portable air compressor; (2) provide
empirical estimates of measurement precision and accuracy as a function of the methodology used; and
(3) contribute additional data on noise emission from portable air compressors.
The measurement program consisted of determinations of time averaged sound pressure level at a
large number of positions on two different measurement surfaces (one in the "far field" and one in the
"near field") surrounding each of seventeen sources. From the data for each source an estimate of the
sound power radiated by that source was made for each surface, and the difference between the two
measurements was used to infer the validity and accuracy of "near field" measurement procedures
relative to the far field procedures. The precision of the measurement procedure was inferred from
the statistics of these differences for the set of sources investigated. Since several proposed
methodologies include measurement positions which are subsets of the complete set of measurement
positions, the accuracy and precision of these methodologies could be inferred in a similar manner.
We recognize that neither of the above measurement procedures provide the absolute sound power
level for the reasons already mentioned. As such we recognize that we cannot state with any
certainty, the degree to vhich either sound power determination approximates the absolute sound power
output. In the following sections it is emphasized that the phrase "sound power" should be
interpreted as refering to the estimate of sound power obtained from measurement of sound pressure
levels at large distances from a source. Further, the use of the term "accuracy" is used to describe
the relative bias of a determination from the estimate of sound power described above.
The following sections of this report present detailed discussions of: the experimental program,
including results of the sound pressure level measurements; the computation of sound power level for a
limited number of measurement methodologies, and the results of these computations; estimates of
measurement accuracy and precision for the methodologies evaluated; and conclusions regarding the
various methodologies.
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2. EXPERIMENTAL PROGRAM
2.1. Program Objectives and Implementation
The principal objectives of the program were:
1. Test experimentally, the validity of using "near-field" measurements of sound pressure level
to predict the "far-field" sound pressure level for large machines. (The computation
procedure used involves the intermediate concept of sound power output as a characterization
of the source emission.)
2. Provide a data base from which the accuracy and precision of sound power determinations may
be estimated based on limited sampling of the sound field.
3. Generate baseline data of noise emission from portable air compressors.
The implementation of these objectives is briefly discussed below.
2.2. Experimental Plan
The experiment consisted of the measurement of sound pressure level on two surfaces surrounding
the sound source. The larger surface (yielding the "far field" measurement data) was a hemisphere of
a fixed 7 metre radius. The sound pressure level was sampled at seven locations utilizing a
semicircular microphone array. The array was rotated around a vertical axis to twelve different
positions during the tests thus providing a total of 81* measurement positions. The smaller
measurement surface, which yielded the "near field" data, consisted of a rectangular box surrounding
the source at a distance of one metre from the surface of the source. These measurements were
recorded for a series of seventeen air compressors, one broad-band reference sound source and one
enclosed loudspeaker excited by three different pure tone signals. The complete set of data from the
compressors was used to compute sound power level for each of the sources to provide a test of the
validity of near field measurements. The data were reprocessed using subsets of the near field data
in order to evaluate the effects of sampling error. These results are used to provide a portion of
the estimate of error of measurement, for various measurement methodologies.
2.3. Measurement Procedures
In this section we discuss the measurement site, the data acquisition and analysis
instrumentation, the data reduction procedures and the detailed test procedures for taking "far field"
and "near field" sound pressure level data. In the following, the term "far field" will be used
without quotes to denote the 7 m radius test data, while "near field" will be similarly used to denote
the measurement at 1 m from the source surface. In so doing, no claim is made or intended that these
data are, in fact, in the acoustic far-field or near-field, respectively.
2-3.1. Measurement Site An agreement was reached with the U. S. Army for utilization of a hard
surface test pad at Fort Belvoir, Virginia, for the data acquisition phase of this program. A plan
view of the measurement site is shown in Figure 1. The test pad consisted of a 27 m. diameter
concrete surface, of roughly conical shape pitched to a drain (which was covered with a 6 mm thick
steel plate throughout the tests) in the center. An estimate of the half-angle of the cone is 89.2°.
An annular-shaped rolled clay area of about 60 m total diameter, surrounded the test pad, and provided
increased clear area. This clay surface varied in elevation from 0 to .3m below the surface of the
concrete test pad. The nearest major reflecting surfaces were a one-story corrugated steel building
about ho m northeast of the test pad, and the test equipment truck located, about 50 m southeast of the
test pad.
Other significant topographic details within a 75 m radius of the center of the test pad included
a creek bed approximately 30 m south of the test site whose surface was 3 to 5 metres below the
surface of the test pad, and a tree covered hill to the northwest of the test site which had a slope
of 20-30°. The photographs in Figure 2 present views of the site from the south edge looking north
and from the west edge looking east.
A pulse echo test, using the equipment shown in Figure 3, was used to quantitatively evaluate the
effect of reflections. The worst case reflection, in the sense of poorest direct-to-reflected signal
ratio, is that which returns to a point behind the major lobe of a directive source. A 10 in.
diameter loudspeaker in an "infinite" baffle enclosure was used to simulate a directive source. Tone
bursts at octave center frequencies from 125 Hz to h kHz were used to investigate the strength of
reflections in twelve directions at 30° increments in angle around the test site. The one story
building was found to produce significant mid and high frequency reflections, and was covered with a 3
in. glass fiber, building insulation, absorber (shown in Figure 2). With this modification, the
strength of reflections was more than 15dB below the direct signal at 180° behind the loudspeaker (see
Table 3.19 for directivity information on the loudspeaker at 500 Hz, 1000 Hz and 2000 Hz). Since the
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GLASS FIBER ABSORB
CALLED
NORTH
60 m DIAMETER AREA (ROLLED
CLAY), 0-0.3 m BELOW PAD
SURFACE
27m DIAMETER TEST
PAD (CONCRETE)
-TELEPHONE
POLES TO
SUPPORT
OARRAY
CREEK BED
(3-5 m BELOW TEST PAD)
Figure 1 Field test site
directivity of the other test sources was found to be less than or equal to that of the loudspeaker,
this leads us to state with confidence that the contribution of unwanted reflected signals was
negligible at all test frequencies at all microphone positions.
The acoustic ambient of the test site was determined by three major sources — steady traffic
noise from a four-lane interstate highway approximately 1 km southeast of the site, aircraft and
helicopter overflights from nearby airports, and rural fauna (principally birds and insects).
2.3.2 Instrumentation Figure U shows a schematic block diagram of the instrumentation used for the
measurements reported here. The eight microphone channels each included a 1-inch diameter Bruel &
KJaer (B & K) Type Itl31— condenser microphone cartridge with standard protection grid (fitted with a
—^
Commercial instruments are identified in this report in order to adequately specify the experimental
procedure. In no case does such identification imply recommendation or endorsement by the National
Bureau of Standards, nor does it imply that the equipment identified is necessarily the best
available for the purpose.
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l"
,
.•
r.
4
i - -
a) South edge looking north showing far field array in place (test no. 9)
-v
b) West edge looking east showing near field microphones in place (test No. 11)
Figure 2 Photographs of test site
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-7m-
1.5m
MICROPHONE
1m
LOUDSPEAKER
CENTER OF
TEST PAD
Figure 3 Equipment configuration for pulse echo tests of
test site
desiccant dehumidifier to control humidity in the microphone cavity) and 10 cm diameter polyurethane
foam windscreen, with B & K Type 2619 FET cathode-follower preamplifier. Each pair of channels was
driven by a battery-operated power supply. The signal from each channel was fed to a
computer-controlled multiplexer (NBS designed and fabricated) which was used to electrically switch
from one channel to another (over the frequency range 20 Hz- 20 kHz, crosstalk between any two
channels is greater than -65 dB, and channel gain is 0 dB +_ 0.2 dB). The signal from the multiplexer
was transmitted via coaxial cable to a B & K Type 33^7 real-time one-third-octave band analyzer where
the signal was analyzed in A-weighted, linear (2 Kz-20 kHz) and one-third octave bands from 12.5 Hz to
20 kHz. Output from the analyzer, in the form of digitally coded sound pressure levels, was sent on
demand to a Raytheon type 10h minicomputer for manipulation and storage. Control of the computer was
accomplished through an initial data acquisition and reduction program, with system operator
interaction through a CRT terminal.
The signal being processed was continuously monitored, both audibly through a headset, and
visually through the spectrum displayed on the analyzer. If (a) non-stationarity of spectra on a
given channel, (b) significant level or spectrum change from channel to channel or, (c) non
characteristic sound in the audible monitor was observed, the data processing was interrupted and the
cause investigated.
Using these techniques, aircraft overflights were typically sensed prior to a visible
identification, and stability and speed of the compressor in operation were monitored as well, thus
permitting the operator to prevent processing of unwanted signals.
An eighth microphone was placed at a fixed height (-v-lm) and distance (-vlim) from the source for
both the near and far field measurements. This position was used as a reference to verify constant
source output throughout both tests.
Additional acoustic instrumentation included a sound level meter and octave band filter set for
recording additional sound level data. Other instruments included a vane-type wind speed indicator,
an optically-coupled tachometer for checking operating speed of the engine and fan, and a mercury
column thermometer for monitoring test site temperature.
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B&K 4145 MICROPHONE
CARTRIDGE, UA 0310
DEHUMIDIFIER,
2619 FET PREAMPLIFIER
B&K 2804
POWER SUPPLY
NBS8 CHANNEL
COMPUTER CONTROLLED
SWITCH (MULTIPLEXER)
B&K 3347 REAL
TIME ONE-THIRD
OCTAVE BAND
ANALYZER
RAYTHEON
704
MINICOMPUTER
TEKTROWIX
CRT TERMINAL
DATA
PROCESSING
> AND
VISUAL
MONITOR
AUDIO
MONITOR
HEADSET
Figure 1» Schematic block diagram of data acquisition and
analysis instrumentation
2.3.3 Test Plan The measurements on all sources vere made according to the following test plan.
Figure 5 shows the far field array, while Figure 6 shows a schematic illustration of the near field
measurement positions referred to in the plan.
a) Assemble and check far field measurement array.
b) Load computer program and check.
c) Record frequency response of all channels for electrical pink noise input.
d) Record channel response to pistonphone calibration signal. If response between channels
differs by more than 0.5 dB plus difference between microphone sensitivities, investigate problem
and complete repair.
e) Erect far field array.
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f) Record first far field ambient noise for first array position (all channels).
g) Record far field data for source (12 array positions). During these runs, wind speed war,
monitored and no data recorded vhen speed exceeded Vim/sec.(12 mph). Signal vas monitored and no data
recorded when acoustic events occurred which were not represented in the ambient noise
measurement (such as aircraft flyovers, etc.).
h) Record second far field ambient noise, for first array position.
i) Take down the array.
j) Record second pistonphone calibration.
k) Disassemble far field array and assemble near field array.
1) Record third pistonphone calibration.
m) Record first near field ambient noise.
n) Record near field data observing same limitations on wind and ambient noise as in g) above.
o) Record second near field ambient noise.
p) Record fourth pistonphone calibration.
q) Tisassemble and store equipment.
MICROPHONE ANGLEtfj Xj Zj
NO.
(DEGREES) (METRES)
CABLES TO POLE
SUPPORT
1
2
3
4
5
6
7
14.2
35.1
65.5
90.0
47.6
24.2
4.7
6.79
5.71
2.89
0.00
4.71
6.33
6.98
1.73
4.03
6.33
7.00
5.18
2.88
.58
MIC 2
MIC1
Figure 5 Far-field measurement array
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1 m
Figure 6 Representative near-field measurement positions
2.3.U. Data Acquisition.
The incorporation of a minicomputer into the data acquisition system permits considerable
flexibility in manipulating information prior to storage, over that of the analyzer operating alone.
The data acquisition program was structured to facilitate this. One major area vhere this facility
vas used was in the area of signal integration.
The digital coded signal available from the analyzer represents the R-C integrated sound pressure
level rounded to the nearest 0.2 dB. Three R-C integration periods for the filters are provided in
•the analyzer, referred to by the manufacturer as "sine", "fast random" and "slow random",
corresponding to nominally 0.2 second, 2.0 second and 20 second integration times. In the first two
modes, the integration time constant is varied with frequency at low frequencies to maintain
confidence levels of the same order of magnitude. For direct display of noise data extending to low
frequencies, the "slow random" mode, because of its long integration time, should be selected in order
to provide data with maximum precision. In order to obtain data which ore not affected by startup
transients, it is necessary to wait a period of 5 time constants after presenting the signal to the
analyzer, prior to recording data. This implies that, per measurement, a . tal observation period of
120 to lUo seconds should be aljowed for noise signals. Our measurement i.rogram included as many as
175 measurements per source, which would require about seven hours of observation time to complete.
This situation forced the evaluation of alternate methods.
After some experimentation, the procedure finally selected involved using the "sine" time
constant and summing repetitive samples (30 samples taken at one second intervals) to obtain an
estimate of the average level. While performing this procedure, the temporal variance of the signal
was also computed, permitting additional inquiries into the temporal "quality" of the signal. The
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algorithms used for these computations were as follows:
p (i) = Antilog (SPL(i)/10)
n
P = ^
12.1)
(n-l)(p2)2
AVG SPL = 10 Log10 (p2)
where SPL(i) is the ith sample of sound pressure level in a band
2
p (i) is the ith mean-square pressure in the band
~2
p is the average mean-square pressure in the band
2
s is the estimated temporal variance of mean-square pressure in the band normalized
by the mean—square pressure squared.
AVG SPL is the average sound pressure level in the band.
The observation time is thus the number of samples taken times the time between samples. Allowing
five seconds (5 time constants at low frequencies) prior to the start of data acquisition gives a
total data acquisition time per measurement point of 35 seconds (considerably below that required by
the "slow random" mode). Table 1 shows the results of some sampling tests using electrical pink noise
as a source. The first line of the table shows the average standard error of the measured mean
voltage level based on eight determinations of the mean using 30 saiaples per observation. The second
line shows the pooled estimate of normalized temporal variance (s eq. 2.1) obtained in seps.ra.te
tests (total number of samples = 2800). The third line shows the computed standard error of a
determination of the mean from the temporal variance values using a propagation of error formulation;
i.e.,
n 2
AVG SPL = 10 Log
STD ERROR = __,„._., _ .
(2.2)
As might be expected, the standard deviation of levels computed from the mean values rounded to
the nearest 0.1 dB is typically larger than that estimated from the temporal variance of the signal,
since the latter values are known to a higher precision.
The values of line 3, Table 1.1, represent our current best estimate of the standard error for
the sampling procedure for sound pressure level. However, because of roundoff error in the display of
sound pressure level, the lower limit for standard error should be taken as 0.1 dB for A-weighted,
linear, and 1.6 kHz through 10 kHz one-third octave band sound pressure levels.
Ho gain change corrections were made in the instrument system during data acquisition, but rather
the overall system gain was determined from the pistonphone calibration. The precision of this
calibration is estimated to be +0.1 dB for comparison of relative levels between channels or runs.
10
-------
TABLE 1. INSTRUMENTATION DATA
1.1. Sampling Procedure Evaluation (see
Pink Noise Excitation, "Sine" Time
Eight Repetitions
text, Section 2.2.U)
Constant, 30 Samples, 1 sec. apart.
Frequency/
Weighting
Standard error
of mean
Value (dB)
Mean Value of
Normalized
Temporal
Variance
(2800 samples)
Computed
Standard error
12.5 16
A-wt. Lin. 1*00 500
.25 .32
.05 .07 .18 .l!*
.11 .11
.0028 .010 .01*0 .031
from Mean Value ! .25 .25
of Variance (dB)i .01*2 .078 .16 Tit
20 25 31.5
630 800 1000
.25 -llO .21
.11 aU .11
ao .090 .o8i*
.027 .023 .016
_.25_ .21. .23
.13 .12 .10
<*0 50
1250 1600
.21 .1*0
.11 .10
.082 .09!*
.013 .011
.23 .21*
.10 .090
2000
.18
.11
.077
.0087
.22
.075
80
2500
.18
.11
.078
.0090
.075
100
3150
.28
.11
.079
.0065
.22
.063
1)000
• 25
.11
.090
.001*7
.05!*
160
5000
.18
.10
.091
.001*2
.21*
.051
200
6300
.21
.10
.085
.0030
^23
.01*3
250
8000
.25
.10
.068
.0029
.21
.01*2
10000
.18
.10
.058
.0220
.035
1.2. Frequency Response Corrections
Factor/Frequency A-vt. Lin
System Frequency
Response
Correction (dB)
Microphone plus
System Frequency
Response Corrections
(1500 Hz - 10 kHz)
12.5 16
. 1*00 500
-.8 .3
-a -.2
20
630
7
0
25
800
1
.?
31.5
1000
2
__
1*0 50 63
1250 1600 2000
722
80
2500
g
_
100
3150
.,
125
1*000
u
— —
160
5000
200
6300
—
250
8000
0
315
10000
-1 0
Channel 1
Channel 2
Channel 3
Channel 1*
Channel 5
Channel 6
Channel 7
0
+ .2
0
+ .1
0
-.2
+ .1
• 3
.1*
.2
.1*
.3
.1
.U
.5 -9
.7 1.1
.5 -9
.6 1.0
.6 i.o
.1* .8
.8 1.2
.3
.5
.5
.6
.2
.8
1.2
1.2
1.3
1.3
1.3
• 9
1.7
.U
.1*
.5
.5
.5
.1
1.0
-1.
• 9
.0
- .3
-1.0
- .6
-1.2
- .6
2.3.5. Data Reduction and Corrections
The rav data (consisting of indicated sound pressure levels) vere corrected for four bias effects
vhich included
1. Microphone cartridge frequency response
2. Measurement system gain calibration
3. Measurement system (other than microphone cartridge) frequency
response
1». Influence of background noise.
The microphone cartridge frequency response was determined by measurement of the free field
normal incidence frequency response (vith windscreen in place) in the small UBS anechoic chamber.
(The frequency response with the windscreen was significantly different from the frequency response
without the windscreen. See Figure 7.)
The measurement system gain calibration was performed separately for each channel for both the
far field and near field data sets. The value used was the average of the before and after
pistonphone calibrations for measurement. The range of the before and after calibrations was 0.5 dB
or less, with a typical value being 0.2 dB or less.
11
-------
The measurement system frequency response calibration was made using electrical pink noise
excitation separately on each channel (flat spectrum within +. 0.1 dB in 1/10 octave bands). Thin
calibration, performed at the beginning and end of the measurement series, was found to bo identical
between channels within the accuracy of the calibration for the frequency range 12.5 llz-2 kllz. The
variations of frequency response above 2 kHz were incorporated into the microphone frequency response
correction. The calibration is based on 1(00 samples per channel, and is accurate to within +0.1 dB.
Table 1.2 provides the frequency response calibrations used. ~
Correction for the influence of background noise was made more difficult by the fact that values
could not be simply deleted if in error, because of programming difficulties created in sound power
level computations. As a result, the measured data were corrected and coded for validity according to
the following scheme. The background noise used is the average of the before and after measurements.
Difference between
signal and
background (dB)
>20
20-3.0
2.9-0.0
<0
Correction
Hone
Standard Correction
to nearest 0.1 dB
SPL = SPL -3dB
SPL = 0
Code
None
Hone
« For cases where the band level equaled the lower limit of the display scale, the level was also
set to zero. Use of the coding will be further discussed under sound power level computations.
There was a need for a further correction to the near field data, due to the fact that the
frequency response of a microphone to a sound pressure field at high frequencies is a function of the
angle of incidence of the sound field. This is of little or no significance in the far field
measurement since the angle subtended by the source at the measurement position is relatively small
(half angle on the order of 15° or less) so that, for microphones directed at the source, incidence
perpendicular to the diaphragm can be assumed.
For the near field case, the microphone is not necessarily directed at the principal source, nor
is the angle subtended by the source necessarily small. An expression which is appropriate for
determining the true pressure if the distribution of intensity as a function of angle is known is
Ptrue ~ p-
1(0.») Sine dp d »
(2.3)
where l(0,) is the scalar magnitude of the intensity at the angle 6,$ from the normal to the
microphone.
g(0) is the microphone fractional response for plane wave incidence at the frequency f and
angle 0 from the normal to the microphone (assumed to be symmetric about the normal to
the microphone), defined by the free field response of the microphone to a plane wave
at the angle -0.
M(9) is the free field response of the microphone at the angle 0.
Figure 7 provides a plot of -20 log g(0) versus frequency. Two of the curves are manufacturer's data
for the microphone cartridge with protecting grid and no windscreen. Two curves represent data
measured at NBS on one of the microphones with a windscreen.
While it would be desirable to make a relatively exact correction for this effect, it is also
clear that this requires much more detailed information than is available (such as distribution of
intensity with angle as a function of frequency at each near-field microphone position for each
compressor, and microphone directiona.1 characteristics throughout the range of angles). In lieu of
this exact correction, and in order to place bounds on this error, let us try to find an approximate
correction which might be applicable (in an average sense) to all the compressor data. One possible
form for such a correction is to postulate a correction at an "equivalent angle of incidence" for the
intensity, which is the same on the average for all microphones, defined by:
12
-------
jfJl(0,»).SinG dO
SinO' dO
(Averaged over near field
microphone position, sources
and frequency)
ip o
Under the assumptions of small angle (such that sin X = X ), spherical source and measurement surface
shape, uniform distribution of 1(0,) over solid angle subtended by the source, microphone directed at
the center of the source, and a weighting function of the form g(0) = l/(l-(ka/3)sintO) (a=microphonc
radius), which fits the data of Figure 7 up to 10 kHz within 10/5, it can be shown that .
ee-ev 2
where 0' is the half-angle subtended by the source.
(2.5)
Since the average linear dimensions (£,w,2h) of the sources are in the range of 2 to 2.5 m the
subtended half-angle is in the range
arctan
-
<_ Q <_ arctan
1*5° <_ 6 <_ 55°
30° <_ 0 <_ ltO°
o
CVJ
6.0
5.0
4.0
3.0
2.0
1.0
0
-1.0
S3
J L
1Z5
MANUFACTURERS DATA 30° WITH PROTECTING GRID
MANUFACTURERS DATA 60° WITH PROTECTING GRID
NBSMEASURED DATA 45°-WITH PROTECTING GRID
AND WIND SCREEN
NBS MEASURED DATA 0°- WITH PROTECTING GRID
AND WIND SCREEN
lit I 1
I
I I i I
250
SOD
Ik
FREQUENCY. Hz
2k
4k
8k
16k
Figure 7 Microphone correction factor (Type l»ll»5 cartridge)
13
-------
Thus when comparing near and far field sound power level data we urge that the near-field data be
corrected by the amount shown in Fipure 7 using the curve for 0=30°. This correction will not be
applied to the data as presented as sound power data on an individual machine.
In passing, we note that using the same figures for a 7 metre microphone position, we find
Ge(far-field) < 7°
and using the analytic form of g(o) given above
-20 Log g(0e) £ 0,1 dB
throughout the frequency range of interest.
We further note that this problem can be minimized by using a smaller microphone. With a
half-inch microphone, for instance, the curves for g(0) are shifted one octave higher in frequency, so
that the estimated value of the correction would be less than about 1.0 dB at the highest test
frequency. Unfortunately, such microphones (with dehumidifiers) were unavailable during these tests.
2.U. Description of Compressor Sample
Table 2 provides descriptions of the pertinent parameters of the individual sources tested.
In terms of the relevant acoustic parameters, the sample was intended to complement tests by
others[l4]. The total compressor sample (including these and other tests) is a sample reflecting
several factors according to current economic data on the industry as previously compiled!?]. The
factors vhich determined the relative number of compressors in the sample vere as follows:
a) Manufacturer: weighted by estimated share of air compressor market.
b) Compressor type: weighted by estimated number of Units produced.
c) Compressor size and power source: weighted according to estimated number of units produced in
each of five ranges:
1. gas, 75-121* cfm
2. gas, 125-25C cfm
3. diesel, 125-2^9 cfm
1*. diesel, 250-500 cfm
5. diesel, over 500 cfm.
Our portion of the sample consisted of smaller size machines which were more readily transportable to
a common test site while other tests on larger machines were more conveniently tested at the site of
manufacture.
The test sample has the following parameters.
a) A total of 17 compressors.
b) Three reciprocating compressors of capacity 100-200 cfm — one gasoline-powered engine, two
diesel-powered, none quieted.
c) Seven rotary screw compressors of capacity 85-185 cfm — five gasoline-powered, two diesel
powered, four quieted.
d) Seven rotary vans compressors of capacity 125-900 cfm — three gasoline-powered, four diesel
powered, four quieted.
e) Seven manufacturers represented; nine gasoline engine powered; eight diesel-powered; eight
standard, while nine were quieted by the manufacturer; total capacity range 85-900 cfm.
All compressors were obtained through rental in the Washington, D. C. metropolitan area, and were
tested as received. Age of the machines varied from new to 1UOO hours, with most in the range of less
than 500 hours. No special preparation by the manufacturer was nade that we are aware of.
Ill
-------
TABLE 2. DESCRIPTION OF SOUBCES
Test
No.
1
2
3
1»
5
6
7
8
9
10
11
12
13
ll»
15
16
17
18
19
Nominal Com- ;Type*
pressor /Vol-
ume Flow/
Rated
Pressure '
(cfm/psi) 1
|
185/100 S
150/100
160/100
150/100
200/100
100/iOO
160/100
125/100
365/100
900/125
100/100
175/100
175/100
185/100
175/100
85/100
150/100
R
V
S
R
R
V
V
V
Engine
Type**/
No. of
Cyl.
GA
G/2
D/HR
DA
DA
D/2
GA
GA
DA
V |D/8
S GA
S GA
S
S
S
DA
DA
Size of (Engine
Enclosure Speed
(L.W.H in (rpm)
metres )
1
1.97,1.28,1.14 2350
1.73,177,1.1*7
2. 07,1- Ht ,1.77
1.71,1. 2>4, l.Uc
1.83, .98, 1.50
1.52, .67, 1.1*2
2.16,1.28,1.76
1.78.1.30,1.85
3. 66, 1.82, 2. lit
1*. 29, 2. 19, 2. 51
1.78,1.22,1.37
2.70,1.29,1.1*3
2.70,1.29,1.1*3
2.70,1.29,1.!*3
GA 1-99, 1.27,1- >*5
2300
2350
1950
1750
1650
2250
1850
1800
2100
2150
Engine] Cooling
Firing] Fan
Freq.
(Hz)
78
38
NRtt
130
116
55
75
62
120
280
72
2300 Ik
2300 '153
2200 73
2150 72
S !GA !l. 96,1. 10,1.3V 2000 66
S
NAt !NA
HA
NA
I
GA -1.93,1.2li,1.36' 3000 100
HA .35 dia x .7 1750 NA
NA r 50, .50,1. 25 NA NA
i
i
Blade
Passage
Freq.
(Hz)
Est.2UO
Est.2llO
300
300
210
150
225
250
Usage 1 Stan- Notes
at
Start
dard
Vs.
of Quieted
Test '•
(Hours)
HR S
1011 S
NR Q
5i*7 S
6.1
NR
2.3
1U.5
1267 1,11.8
307i 1.0
250 :ii*i*o
S
S
Q
... .,..,.-,— ,—,_.-.-— — ,, ., . — .
1* cyl. in-line block
8 cyl. V-8 block
1* cyl. in-line block
Q
Q '20 blade fan g 3800 rpm
Q
S
235 1086 Q
250
NR Q
280 776
i
250
230
S
398 s
1300 S
300 297 ; S
NR ' i —
Governed at less than
rated speed
Broad band reference
(sound source
NA
1
—
.25 m dia. loudspeaker
(tone source) center-
line of speaker 1 m
above ground
• R=Reciprocating compressor
S=Rotary screw compressor
V=Rotary vane compressor
»» G=Gasoline engine
D=Diesel engine
tNA=Not applicable ttNR=Not recorded
2.5. Compressor Operation
The major problems associated with compressor operation for these tests were providing for
acoustically controlled discharge of the compressed air, to assure insignificant contribution to the
measured noise, and ensuring constancy of operation at rated capacity.
Discharge air from the compressor was fed through a 30 m length of commercial high pressure
rubber hose to a commercial automobile muffler, where it was discharged to the atmosphere. The
muffler was placed in the creek bed (see Figure 2) so that the bank of the creek would provide
shielding of the discharge noise from the test site. Measurements of octave band sound pressure
levels near the discharge were made for each test, and extrapolations of the measured levels, assuming
hemispherical spreading and ignoring shielding, indicated that the discharge noise from the muffler
vas more than 10'dB below the compressor noise at all measurement locations. In some cases more than
one hose line and silencer had to be used to accommodate the compressor volume flow. For the two
larger machines (tests 9 and 10) a blow-down silencer of undetermined manufacture (obtained from the
rental source), and large diameter hose was used in place of the above air discharge silencing
arrangement.
The operating point for the test was the condition of the compressor supplying rated flow. This
condition occurs when the compressor is operated at rated speed and pressure. Establishment of this
point was made simpler by the fact that most of the compressors had an engine speed governor which
operated on the difference between receiving tank pressure and rated pressure. Rated speed was thus
obtained by throttling the flow of discharge air until the compressor held a constant receiving tank
pressure near rated pressure (-as indicated on the compressor air pressure gauge) and verifying that
the engine vas operating at rated speed (as measured by an independent tachometer). At this point, a
reduction in air flow will be followed by a reduction in engine speed (for a proportional controller),
while an increase in air flow will be followed by a reduction in receiving tank pressure. This
operating point was easily established once the compressor had been operated for 15-20 minutes and
conditions approached a thermal steady-state.
Once at this point, engine speed could be monitored within about ±50 rpm by inspection of the
displayed noise spectrum at bands near the engine firing rate frequency. Since the firing rate tone
15
-------
typically excited one or the other of the adjacent bands in addition to the band containing the tone,
the difference in decibels between these tvo bands could "be taken as a sensitive indicator of firing
rate frequency. This procedure can not be used if the spectrum of broad band noise is vithin HK1B or
so of the indicated tone level in each band. In this case, engine speed was monitored audibly, with
frequent tachometer checks.
2.6. Measurement Locations and A-Weighted Sound Level Data
2.6.1. Far Field Measurements
The far field sound pressure level data vere taken using the array shown in Figure 5 (also
visible in Figure 2a). The seven microphones were located on nominal one-half metre long standoffs
from a semi-circular arc constructed of steel pipe and tubing. The arc was supported from above by
two cables from the arc center to poles located on the east arid west edge of the test pad. The ends
of the arc were supported on casters to facilitate rotation. Positioning was accomplished by pins at
the end of the arc which fit into holes drilled in the concrete test pad. The maximum radia3
positioning error of a microphone in the array is estimated from sample measurements of positions; to
be less than + 0.1 m (1.14/5) including all array positioning effects such as changing arc shape from
change in proportion of weight supported by overhead cables. Angular positioning error is estimated
to be less than +1° in both azirrmthal and polar angles. In terms of inverse square spreading, the
radial error translates into a possible error in sound pressure level estimation of less than +_ 0.1
dB, per observation. Since the principal source of radial error arises from change of shape of the
arc — which leads to positive errors at some positions vhile there are negative errors at other
positions — this source of error is believed to average out in the estimate of power rather than
produce a systematic bias. The angular positioning error leads to random sampling on the
hemispherical surface (i.e., imprecision in directivity) as opposed to a systematic bias in sound
power determination
In addition to these array data, octave-band sound pressure level data vere also taken using a
hand-held sound level raeter employing a modified form of the present industry methodology[6]. The
intent of the NBS Far Field methodology initially recommended to EPA was to provide an upper bound
estimate of sound power level based on measurements made at six locations. The six locations include:
1. Four positions perpendicular to the center of each side of the
compressor at a distance of 7 metres from the jsr.ter of the compressor (data taken at the
elevation in the range 0.8 to 1.6 m which yields the highest A-veighted sound level).
2. One location at an elevation of 1 metre above the ground, on the 7 metre radius circle
centered on the machine, at the location giving the maximum A-weighted sound level.
3. One location directly above the center of the compressor, at a height of seven metres above
the gound plane (data from microphone four of the array vas used for this location).
The data, using this procedure, vere taken in the same time interval as the data from the
far-field array, and are reported here as "Far-Field Methodology" data. Far-field array and
methodology data were recorded for the seventeen compressors, and also tvo known sources, to
investigate the effectiveness of the far field test procedures for these sources. The first of these
was a broad band "reference sound source" consisting of an electric motor-driven centrifugal fan with
cylindrical symmetry, which is nominally omnidirectional. The second source was a 0.25 m diameter
loudspeaker, mounted in a 0.^* m cubical sealed baffle. The baffle was located at the center of the
test pad vith the loudspeaker axis horizontal, 1 m above the test pad, pointed at approximately 220
degrees from north. The speaker was driven in different tests with tones of 500 Hz, 1 kHz and 2 kHz.
The principal purpose of this test vas -.to give example data of the measurement problem associated vith
tones.
A tabulation of the A-weighted far-field sound level data is given in Tables 3.1 to 3.19- The
"Far-Field Data" are given in tabular form in the form of a directivity pattern, with columns
corresponding to azimuthal angle from Oc to 330° from north (compressors were aligned on the test pad
vith the tov bar pointing north and sides oriented in the north, east, south and west directions).
The "Far-Field Methodology" data are given in tabular form underneath these data. Also given is the
A-veighted sound pover level computed from the far-field and "far-field methodology" data, for
reference purposes (see Section 3 for calculation procedures). The sound level corresponding to the
average mean square pressure over the hemisphere (frequently referred to as the "energy average") may
be calculated from the sound power level according to:
I, (r) = Ly - 10 Log 2irr2
—12
Ly is pover level, dB re 10 vatt _
L is the sound pressure level, dB re 2.10 pascal
r is the radius of the hemisphere, metres
A nominal value of impedence equal to UOO mks rayls Is assumed.
16
-------
At seven metre radius, the average A-weighted sound level thus is
LpA(7m) =LWA- 2l4'9dB
2.6.2. Near Field Measurements
The near-field data were taken using seven microphone channels with nix of the microphone;;
mounted on tripods, and the seventh suspended from a "skyhook" formed by the support cable:; ur.ed to
position the far-field microphone array. Figure 6 shows representative measurement positions on a
measurement surface. The microphone positions were determined according to the following rules.
1. The measurement surface was a rectangular box of dimensions
L x W x H where L = !H-2, W = w+2, H = h+1 and where H, w and h are the length width and height of
the compressor excluding tow bar, tires and fenders, and other small projections with linear
dimensions less than 0.5 metres (such ss exhaust pipes, etc.). The four vertical plane surfaces
were located at distances of +L/2 and +W/2 from the geometric center of the compressor, and
perpendicular to the longitudinal and lateral centerlines. The horizontal plane surface was
located at the distance H above the reflecting plane. These surfaces are nominally 1 metre from
the surface of a compressor with a rectangular enclosure.
2. The microphone positions on the measurement surface were located on a 1 x 1 metre square
grid. The grids were located on the vertical sides so that a measurement position was on the
center of each side at a height of 1.5 metres. This grid location yields measurements positions
at heights of 0.5, 1.5, 2.5 m, above the ground plane, spaced 1 m apart In either direction from
the center of that side. The grid on the horizontal measurement surface was centered in the
center of that surface. For all compressors the measurement positions near the engine exhaust
were displaced along a grid line to the closest point 1 metre from the end of the exhaust pipe.
3. Microphones were oriented with the plane of the microphone diaphragm in the plane of the
measurement surface.
U. Near edges or corners where pairs of measurement locations from adjacent surfaces were less
than 0.25 m apart, one of the pair (usually on the vertical surface) was deleted.
The rectangular measurement surface was chosen because it was the only surface being considered
by ISO working groups on sound power measurement standards, at the time of the tests (May-July, 197^0.
The lower half of Tables 3.1-3.18 titled "near-field data presentation" presents the A-weiehted
sound level data from these tests in a format which facilitates relating level and position. Note
that levels measured closest to the ground plane are furthest from the center of the table.
17
-------
Test Number 1
Table 3.1
A-WEIGHTED SOUND PRESSURE LEVEL DATA
Compressor Output: 185 cfra
Engine/Compressor Type: Rotary screw,
Compressor Size: 1.97x1.28x1.4m
»** FAR FIELD DATA 17 HETRE RADIUS)
A WEIGHTED LEVEL IOBI
ANGULAR
HIC HEIGHT
(METRFSI
.575
1.725
2.875
4.025
5.175
6.375
7.000
HIC HEIGHT
(METRES 1
0-8-1.6
0.8-1.6
0. 8-1. 6
0.8-1.6
7.0
1.0
ORlENTATlON(OtG) 0 30
MUM ELEVATION
IOEG)
7 4.7 80.4 81.5
1 14.4 78.4 79.3
6 24.2 78.8 79.9
2 35.2 79. 5 80. 0
5 47.6 78.2 80=2
3 65.7 77.3 77.6
4 90.0 76.2 76.5
FAR FIELD METHODOLOGY DATA
POSITION LEVEL
(OB)
N 80.5
E 83.0
S 82.5
M 79.0
OVERHEAD 76.2 (AVG.
MAX 84.5
60
82.8
79.8
79.4
80.2
79.2
78.0
76.4
OF HIC4
90
120
80.6 81.0
80.9 80.8
79.4 80.0
79.5 80.2
79.1 79.?
78.4 79.5
76.6 76.1
ABOVE)
150
84.9
82.4
83.0
82.5
82. 1
80.7
76.2
180
83.0
81.5
79.9
PI. 3
77.9
80.3
75.8
210
84.5
82.9
82.7
83.1
82.2
80.7
76.6
240
82.4
80.6
81.0
81.5
80.7
78.4
76.0
270
78.8
77.2
77.8
78.4
77.9
77.4
75.9
300
79.
77.
76.
77.
76.
7o.
76.
0
S
9
2
4
5
0
330
80. 3
79.4
78. 1
79.1
77.2
77.0
76.5
** A WEIGHTED SOUND POWER LEVEL = 105.l DB RE 1 PlCOWATT (BASED ON 73 POINTS)
JULIAN DAY 144
TEST
NEAR
NUMBER 1
MIC
HEIGHT
2M
H
FIELD DATA PRESENTATION
*NORTH SIDE*
1M CENTER IM 2M
U LINE E E
*WEST SIDE*
MIC
HEIGHT O.S 1.5
3M NORTH *»*»* ***»«
?H NORTH ***** *****
1M NORTH 89.1 83.1
CENTERLINE 88.4 85.3
1M SOUTH 89.3 86.6
2M SOUTH ***** *****
3M SOUTH ***** *****
.5 ***** 90.8 91.4 90.'7 *****
X.5 ***** 86.3 86.4 89.6 *****
2.5 ***** ***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
*TOP*
2.5
*****
*****
*****
*****
*****
*****
*****
3.5
*****
*****
*****
*****
*****
*****
*****
*****
85
90
83
86
89
.2
.5
.7
.4
.3
*****
*****
84.
62.
82.
85.
90.
5
•t
0
3
4
*****
*****
85.3
84.5
83.8
87.3
89.3
*****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** *****
***** ***** ***** *****
***** ***** 87.2 92.1
***** ***** 88.2 92.1
***** ***** 88.0 91.0
***** ***** ***** *****
***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
2.5 ***** ***** ***** ***** *****
1.5 ***** 90.6 92.3 93.2 *****
.5 ***** 93.4 95.1 94.7 *****
SOUTH SIDE*
-------
Test Mumber 2
Table 3.2
A-WEIGHTED SOUND PRESSURE LEVtL DATA
Compressor Output: 150 cfm
Kiiglne/Conpr<-s3or Type: Reciprocating , Gas, Standard
Compressor Sii.r-: 1. 73x. 77x1.47m
*«* FA« FIELD DATA (7 METHE RAOIUS1
A WEIGHTED Lt VtL CM I
ANGULAR
MIC HEIGHT
(METRES)
.575
1. 725
2.H75
4.025
5. 175
6.375
7.000
UKIFNTATIONIDEG) 0
NUM ELEVATION
7
1
6
2
5
3
4
IDEGl
4.7
14.*
24.2
35.2
47.6
65.7
90.0
83.9
83.5
84.3
85.4
06.3
87.0
86.1
30
85.2
b',.o
d5.0
86.4
t>6.7
65.7
06.1
60
85.5
b5.2
85.2
85.9
85.9
85.8
65.9
90
04. 9
84. 5
84.4
85.6
85.8
85.3
35.2
120
87.0
85. B
85.6
H6. 1
86.3
65.7
86.3
150
A a. 5
37. 1
Ofa.b
87. 1
87.0
B6.U
86.6
IbO
88.3
d7. 7
67 .3
07. 7
87.1
B6. 5
86.2
210
87.5
06. 7
B6.1
86.V
86.6
8o.3
86. I
240
35.7
t)4. t.
d4.b
O.O
(4V(i. OF MIC4 ABOVE!
** A WMGHTED SOUND POWER Iff Vt'L-llU. B 03 RE I PICOkATl IbAShD ON 73 POINTS)
JULIAN DAY 155
*HEST SIDE*
MIC
HEIGHT 0.5 1.5
3M NORTH ***** *****
2H NuRTH ***** *****
1H NllKTH 95.8 93.6
•CENTERLINE 95.1 94.3
1M SOUTH 94.9 94.1
2M SOUTH ***** *****
3M SOUTH ***** *****
NEAR
TEST NUMBER 2
2M
W
MIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
2.5 3.5
«»**» *****
***** *****
93.7 *****
94.2 *****
94.4 *****
***** *****
***** *****
FIELD DATA PRESENTATION
*N
-------
T»ble 3.3
A-UDIOHTCD SOUND PRESSURE LEVEL DATA
Te«t Nuttber 3 Compreunor Output: 160 cfn
Engine/Conpreeuor Type: Rotary van*. Diesel, Quietmd
Compressor Gize: 2.07x1.14x1.77m
17 MCt«f-
T F »1 " f
A'I(,ULA*
»( T«t S)
.575
1 . 7?S
4. i>?5
5. 1 '!>
s« 175
7. 00 J
O^IENIATIUNUHGI 0
Mft ttLVATlUN
7
I
2
5
3
(lli-GI
4.7
14.4
?4.2
33.2
47.0
65.7
»0.0
82.7
81. 7
U1.4
du.B
83. 2
64. 2
30
82.2
82.3
01. V
7o.7
82.7
d3.1
,0
82.1
81.7
80.9
01 ,0
82.5
81.0
90
rtO. 7
80.2
80. 3
dO.9
«0.9
f. 1.5
42.4
A HEIGHT tO LfcVEl (OB)
120 150 180 210 240
82.3
81.2
bl.8
82.0
81.9
61. 0
82. U
M?.8
82.8
83.2
G2.2
82.7
H I. 5
82.3
83.4
d2« 5
83.7
80. 0
83.0
81.5
6i.lt
81. t>
82.2
82.6
B2.3
8J.1
H?.rt
82. 8
82. 4
60.7
02.3
U2.2
d3.2
6\. <»
J2.8
270
81.7
80.7
81.3
80.7
til. 7
81.4
82.8
3JO
•Jl. 3
79.5
30. d
BJ. 1
d2. 1
il. J
82.3
i )0
u).4
7 i.4
b 1 .0
aa. '»
u2.a
6 1 . b
o2.2
FAK Flllli MfcTMIIOOLOGY "ATA
«1C HH&MT POSITION LfVFL
(MFTfFS I (Oil)
0.8-1.6 F
0 . U- 1 . o S
J.li-1.6 W
7.0
1.0
OVftltAO
*AX
82.0
84.0
32.0
«2.H
84.0
(AVG. UP MIC4 AJOVF)
•* A KFlOHTtO SOUMO POKCR LtVet^U^.8 Jrt <.2 68.9 ***** *****
If, NuhTH 92.2 90.0 88.2 ***** 99.6
CtUTbRLlNE 92.2 90.8 '89.4 ***** 90.6
1M SOUTH 92.9 VI.e. 90.4 ***** 91.2
2M SOUTH 89.8 9J.O 63.6 ***** *****
3M SOUTH ***** **»«* ***** ***** *****
SIDt*
CCNTER IM 2M
1 i Nt F E
93.6 91.5 *****
90.6 91.1 *****
89.9 88.3 *****
***** ***** *****
*T(JP*
***** *****
***** *****
92'U 89.9
S3.6 90.5
91.8 89.5
***** *****
***** *****
EAST S106*
3.5 2.5 l.i O.b
***** 4**** ***** *****
*»*«* 68.4 87.J 9'J.l
***** bb.6 09.9 90.6
***** 40.0 91.1 91.5
***** 69.0 91.4 93.4
***** 87.8 39.* 89.8
*«*** ***«« ***** *****
).^ ***** ***** ***** ***** *****
2.5 ***** (id.7 89.3 38.6 *****
|.5 ***** <»1.4 91.0 9O.4 *****
,5 ***** tl.t
-------
Test Number 1<
Table 3.>i
A-VEICHTED SOUND PRESSURE LEVEL DATA
Compressor Output: 150 cfm
Enginc/CoC'preBcor Type: Rotary screw, Diesel, Standard
Compressor Size: 1.71x1.24x1.40m
***" FAR FIELD DATA (7 METRE RADIUS)
A ViF.lGHTEO LEVEL
ANG.UIAR
MIC HEIGHT
(METRES)
.575
1.725
2.875
4.025
i. 175
6.375
7.000
ORIENTATIONIOEG! 0 30
.MUM ELEVATION
(DEG)
7 4.7
I 14.4
6 24. 2
2 35.2
5 47.6
3 65.7
4 90. 0
87.
87.
87.
B9.
89.
89.
86.
FAR FIELD METHODOLOGY
MIC HEIGHT
(METRES)
0.8-1.6
0.6-1.6
0.8-1.6
0.8-1.6
7.0
1.0
POSITION
N
E
S
W
OVERHEAD
MAX
LEVEL
(OB)
89.5
89.0
90.5
K8.5
86.9
92.0
6 8G.6
6 D9.I.
9 68.1
3 89.7
3 69.7
I 89.5
<* dT.L
DATA
(AVG. UF
60
87.8
87.5
67. 4
87.5
aa.a
88.3
84.8
MIC4
90
87.0
87.2
85.9
67.7
87.5
87. 8
86.9
AUOVE)
120
88.3
87.5
87.1
03. 1
88.5
87.7
87.1
150
89.7
09. 8
38.7
69. 1
89.5
48.2
86.9
180
89.1
90.0
89.6
90.0
89.8
89. 7
87.1
210
88.5
86.8
83.9
BS. 4
89.7
66.5
8fa.5
240
30.4
87.4
87.1
B7. 6
U7.7
37.9
87. 1
270 300 330
66.2 36. B ud.3
86.2 8b.4 U3.7.
85.5 B7. 3 08.7
a 7. > 07.6 a9.<.
30.9 t>7. 2 33. <.
37.4 ' 37.7 33.9
«6.9 86. 7 tt&. 7
** * WEIGHTED SUUNO POWER LEVELM13.1 08 Rh 1 PICOWATT (BASED ON 72 POINTS)
JULIAN DAY 157
*WF.ST SIDE*
MIC
HEIGHT 0.5 1.5
3M NORTH ***** *****
2H NORTH ***** *****
1M NORTH 9B.2 98.7
CtNTtRLiNE 95.0 77.<>
1M SOUTH 96.8 97.0
2M SUUTH ***** *****
3M SOUTH ***** *****
NEAR
TEST NUMBER 4
2M
H
MIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
FIELD DATA PRESENTATION
*NORTH SIDE*
1M CENTER 1M 2M
W LINE E E
84.1 98.3 99.2 *****
98.4 99.4 100.1 *****
***** ***** ***** *****
***** ***** ***** *****
• TOP*
2.5
*****
*****
*****
*****
*****
*****
*****
3.5
*****
*****
*****
*****
*****
*****
*****
*****
*****
96.4
96. b
97.0
*****
*****
*****
*****
100.6
102.1
100.3
*****
*****
*****
*****
98.6
98.8
97.7
*****
*****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** ****t
***** ***** ***** *****
***** ***** 98.7 98.2
***** ***** V8.3 96.1
***** ***** 98.1 97.4
***** ***** ***** *****
***** ***** ***** *****
J.S ***** ***** **<.** ***** *****
2.5 ***** ***** ***** ***** *****
1.5 ***** 98.7 101.0 99.7 *****
.5 ***** 99.4 102.3 99.0 *****
SOUTH SIDE*
-------
Test Number 5
Table 3.5
A-WEIGHTED SOUND PRESSURE LEVEL DATA
Compressor Output: 200 cfm
Engine/Conpressor Type: Reciprocating, Diesel, Standard
Compressor Size: 1.83x.98x1.50m
*** FAR FIELD DATA (7 METRE RADIUS)
A WEIGHTED LEVEL (DB)
ANGULAR
MIC HEIGHT
(MFTKESI
.575
1.72S
2.875
4.025
5.175
6.375
7.000
MIC HEIGHT
(MFTK6S)
0.8-1.6
0.8-1.6
0.8-1.6
O.R-1.6
•7.0
1.0
URIENTATION(DEG) 0 30
NUM ELEVATION
(OEG)
7 4.7 85.3 85.7
1 14.4 63.4 64. b
6 24.2 83.0 84.1
2 35.2 32.7 85.7
5 47.6 82.2 b3.7
3 65.7 82.9 83.1
4 90.0 80.9 81.4
FAR FIELD METHODOLOGY DATA
POSITION LEVEL
(OB)
N 85.5
E 89.0
S 87.0
H 85.5
OVERHEAD 80.9 (AVG.
MAX S7.0
60
64.1
B2.9
63.0
64. 3
84.0
B2.4
81. 2
OF MIC4
90
<)4.b
33.5
83.4
83. 3
83.6
82. b
81.0
AttOVb)
120
05.8
64.7
83.8
84.2
83.7
82.3
81.3
150
86.7
83.7
84.2
85.3
64.0
83. 3
81.0
180
86. 0
84.9
85.0
85.4
83.6
83. 1
01.1
210
85.4
84.7
85.3
84.5
84.5
63.2
80.9
240
86.4
64. 1
03. I
84.3
83.5
82.3
80.6
270
84.2
83.6
32.7
82. A
62.3
82.3
8J.6
300
85.1
83.6
83.3
83. 7
33.o
31. -i
60.5
330
85.5
d3.7
64. 1
64. J
83.0
bl.5
60.9
** A WEIGHTED SOUND POWER LEvEL«ios.9 OB RE i PICOWATT (BASED UN 73 POINTS)
JULIAN DAY 162
TEST
*WEST SIDE*
MIC
HEIGHT 0.5 1.5
3M NORTH ***** *****
2M NORTH 95.0 93.8
1M NORTH 97.4 94.1
CENTERLINE 94.5 93.3
1H SOUTH 94.8 94.1
2M SOUTH 93.5 92.7
3M SOUTH ***** *****
2.5
*****
89.9
89.9
89.9
90.2
91.8
*****
NEAR
NUMBER 5
2M
M
MIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
1.5
*'••>**
*****
*****
*****
*****
*****
*****
FIELD DATA PRESENTATION
*NORTH SIDE*
IM CENTER 1M 2H
W LINE E E
95.0 96.1 96.6 *****
94.0 93.1 93.3 *****
89.5 89.8 90.0 *****
***** ***** ***** *****
*TOP*
***** ***** *****
***** ***** *****
90.5 88.3 90.5
90.4 89.3 90.4
90.1 87.7 90.7
***** ***** *****
***** ***** *****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** *****
***** 91.3 92.8 94.8
***** 91.0 95.3 96.7
***** 90.9 93.7 96.3
***** 90.7 93.9 96.8
***** 90.4 92.7 94.7
***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
2.5 ***** 90.8 89.2 90.3 *****
1.5 ***** 93.4 93.7 93.3 *****
.5 ***** 95.7 95.* 96.2 *****
SOUTH SIDE*
-------
Table 3.6
A-WEIOHTED SOUND PRESSURE LEVEL DATA
Test Number 6 Compressor Output: 100 cfrc
Englne/Cotf-preeoor Type: Reciprocating, Diesel, Standard
Conpressor Size: 1.52x.67x1.42m
*»* FAR FIELD DATA (7 METRE RADIUS)
A WEIGHTED LEVEL ( Ofi I
ANGULAR
MIC HEIGHT
(METRES)
.575
1.725
2.875
4.0?5
5. 175
6.375
7.000
OR1ENTAT10NIDEG) 0
NUM ElEVATIUN
(DEG)
7 4.7
1 14.4
6 24.2
2 35.2
5 47.6
3 65.7
4 90.0
84.
62.
81.
83.
62.
83.
62.
FAR FIELD METHOOOLUGY
MIC HEIGHT
(METRES)
0.8-1.6
0.8-1.6
0.8-1.6
0.8-1.6
7.0
1.0
POSITION
N
E
S
k
OVERHEAD
MAX
LfcVEL
-------
Teat Dumber 7
Table 3.7
A-WEIQHTED SOUND PRESSUKE LEVEL DATA
Compressor Output: 160 cfm
Engine/Compressor Type: Rotary vans, Gnu, Quieted
Compreaeor Sire: 2.10x1.28x1.78»
**• FAR FIELD DATA (7 METRE RAD1USI
A WEIGHTED LCVEL (DO)
ANGULAR
MIC HEIGHT
IMtTKES)
.575
1.725
2.875
<>.025
5. 175
6.375
7.000
H!C HEIGHT
J METRES!
0.8-1.6
0.8-1.6
0.8-1.6
0.8-1.6
7.0
1.0
ORlFNTATIONfOEGI 0 30
NUM ELEVATION
(DEGI
7 4.7 81.6 81.4
1 14.4 79.6 81. 2
6 24.2 81.2 82.0
? 35.2 80.2 81. 8
5 47. to S3. 5 82.6
3 65.7 84.3 84.1
4 90.0 85.6 85.5
FAR FIELD METHODOLOGY UATA
POSITION LEVEL
(DB)
N 80.5
E 80.0
S 81.0
W 81.0
OVERHEAD 85.6 IAVG. OF
MAX 82.5
60
8l.il
79.6
81.3
81. 4
83.6
83.3
84.9
MIC4
90
dl.2
79.6
80.6
79.8
83.1
-------
Test Number 6
Tatle 3.8
A-WEIGHTED SOUND PRKSSURE LEVEL DATA
Compressor Output: 125 cfm
Engine/Compressor Type: Rotary vane, Gas, Quieted
Compressor Size: 1.78x1.30x1.85m
*»» FAR FIELD DATA 17 METRE RADIUS)
A WEIGHTED LEVEL (UDI
ANGULAR
MIC HEIGHT
{METRES )
.575
1.725
2.875
4. 025
5.175
6.375
7.000
MIC HEIGHT
(METRES)
0.8-1.6
0.8-1.6
o.a-1.6
0.8-1.6
7.0
1.0
ORIENTATIUN(DEG) 0 30
MUM ELEVATION
(DEC)
7 4.7 74.5 75.3
1 14.4 75,1 75.6
6 24.2 77.7 77.6
2 35.2 75.4 76.6
5 47.6 79.8 79.6
3 65.7 79.5 79.8
4 99.0 81.9 81.5
FAR FIELD METHODOLOGY DATA
POSITION LEVEL
(OB)
N 76.0
E 79.0
S 79.5
W 77.5
OVERHEAD 81.9 (AVG. OF
MAX 60.5
60
76.5
76.3
77.0
76 ,9
79.2
80.2
81.6
MIC4
90
76.6
75.4
76.7
76.9
78. 1
BO. 6
dl.8
ABOVE)
120
79.3
76.1
77.0
77.9
78.0
80.5
82.0
150
7B.8
77.5
7B.O
79.0
79.2
79.6
82. 1
180
77. V
76.3
77.3
77.6
79.1
78.7
82.0
210
77.1
76.2
76. 5
77.4
79.3
79.2
82.3
240
78. 1
76.4
77. 1
77.9
79.0
80.2
82.0
270
77. 7
76.0
77. 3
78. J
79.6
ao.r
82.0
300
78.2
76.6
77.1
77.0
80.1
81.0
82.2
330
76. B
76.1
77.7
77.1
79.8
80.2
81.6
** A WEIGHTED SOUND POWER LFVEL*103.1 08 RE 1 PICOWATT (BASED ON 73 POINTS)
JULIAN DAY 165
*WEST SIDE*
MIC
HEIGHT 0.5 1.5
3M NORTH ***»* *****
2M NORTH ***** *****
1M NORTH 86.5 66.2
CENTERLINE 86.0 86.5
1M SOUTH 86.3 85.9
2M SOUTH ***** *****
3M SOUTH ***** *****
NEAR
TEST NUMBER 8
2H
H
MIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
3.5
*****
*****
*****
*****
*****
*****
*****
2.5
*****
*****
87.9
88.2
86.1
*****
*****
FIELD DATA PRESENTATION
*NORTH SIDE*
1M CEH1ER SH 2M
M LINE E E
85.2 86.1 85.7 *****
85.8 86.2 85.4 *****
87.8 88.1 87.3 *****
***** ***** ***** *****
*TOP*
***** ***** *****
***** ***** *****
89.8 90.8 88.2
89.4 91.8 89.4
85.7 66.9 86.3
***** ***** *****
***** ***** *****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** *****
***«* ***** ***** *****
***** 86.9 65,9 85.4
***** 07.1 85.6 85.2
***** 85.2 86.0 86.5
***** ***** ***** *****
***** ***** ***** *****
3.5 **»*» ***** ***** ***** *****
2.5 ***** 86.1 86.2 85.4 *****
1.5 ***** 84.8 84.8 66.6 *****
.5 ***** 86.5 89.6 87.3 *****
SOUTH SIDE*
-------
Table 3-9
A-VE1GHTED 80UHD PRESSURE LEVEL PATA
Teat Nuiaber 9 Compressor Output: 365 cfm
Engine/Compressor Type: Rotary vano , Dieael, Quitted
Compressor Size: 3.66x1.82x2.14m
»*« FAR FIELD OATA (7 METRE HAOIUSI
A WFKiHTED LEVEL (DB)
ANGULAR
MIC HEIGHT
(METRESJ
.575
1.725
2.875
4.025
5.175
6.175
7.000
MIC HEIGHT
(MCTkES)
0.8-1.6
0.8-1.6
0.8-1.6
0.8-1.6
7.0
1.0
ORIENTATIQN(UEG) 0 30
MUM ELfVATtON
(QEGI
7 4.7 74.0 73.3
1 14.4 72.0 73.0
6 24.2 72.1 73.3
2 35.2 71.7 73.8
5 47.6 71.1 71.3
3 65.7 70.1 70.9
4 90.0 66.4 69.4
FAR FIEtO METHODOLOGY OATA
POSITION LEVEL
(06)
N 75.0
f. 75.5
S 77.0
W 75.0
OVERHEAD 68. 4 ( AVG. OF
MAX 75.5
60
73.3
74.3
72.6
73,6
72.0
71.3
69.5
HIC4
90
73.7
74.4
74.0
63.5
72.3
74.4
68.0
120
72.
74.
73.
73.
72.
71.
68.
5
1
5
7
3
9
4
150
73.1
73.0
72.8
72.9
71.7
70.5
67.4
180
74.4
73.9
73.7
73.7
72.6
69.7
68.2
210
76. 3
73.0
77.2
73.4
75.4
70.5
67.7
240
82.4
72.3
80.9
73.0
80. 1
70.5
68.5
270
73.5
73.4
73.2
73.5
72.2
70.8
68.9
too
72.7
72.7
73. J
73.9
72.4
70.5
67.9
330
72.3
72.0
72.9
72.6
71.0
70.4
67. <«
ABOVE 1
** A UFIGHTEO SOUND POrfER LEVEL' 98.7 OB RE 1 PICOHATT (BASED ON 73 POINTS!
JULIAN DAY 168
*WEST SIDE*
MIC
HEIGHT 0.5 1.5
3H NORTH ***** *»***
2M NORTH 81.8 82.1
IN NORTH 82.2 81.7
CENTERLINE 82.2 80.1
IN SOUTH 81.6 79.9
2M SOUTH 80.1 79.3
3M SOUTH ***** *****
NEAR
TEST NUMBER 9
2M
H
MIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
2.5 3.5
***** *****
78.5 *****
80.2 *****
78.6 *****
78.2 *****
78.0 *****
***** *****
FIELD OATA PRESENTATION
*NORTH SIDE*
1M CENTER 1M 2M
W LINE E E
81.5 ul.6 82.1 *****
78.2 78.4 78,4 *****
75.8 76.7 76.1 *****
***** ***** ***** *****
*TOP*
***** ***** *****
74.8 75.9 75.7
76.6 77.0 77.7
79.1 80.6 78.8
79.5 81.B 79.6
76.3 76.9 76.1
***** ***** *****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** *****
***** 79.0 81.9 81.9
***** 79.0 82.1 82.9
***** 78.5 79.5 83.0
***** 78.6 80.1 81.0
***** 77.2 79.2 79.9
***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
2.5 ***** 77.8 79.3 77.5 *****
1.5 ***** 78.3 79.2 78.8 *****
.$ ***** so.9 83.6 81.4 *****
SOUTH SIDE*
-------
Table J.10
A-WEIGHTED SOUND Pr.ESSIIHE LEVEL DATA
Tect Dumber 10 Compressor Output: 900 cfm
Engine/Compressor Type: Rotary vane, Diesel, Quieted
Compressor Size: 4.29x2.19x2.51m
*** FAB FICLD DATA (7 METRE RADIUS)
A WEI&HTfcD LFVEL (06)
ANGULAR
MIC HEIGHT
ORItNTAT [CIN(OEG) 0
NUM ELEVATION
(MCTRFS)
•
1.
2.
4.
5.
6.
7.
575
725
875
025
175
375
000
7
1
b
2
5
3
4
UJEGl
4.7
14.4
24.2
35.2
47.6
65. 7
90.0
72.
74.
76.
80.
79.
81.
77.
7
2
2
4
9
7
4
30
74.9
77.2
77.2
79.5
78. d
81.0
77.5
60
76.0
77.0
75.9
79.1
78.0
81 .1
77.3
90
74.
77.
76.
79.
78.
79.
77.
8
0
1
6
2
3
1
120
76.8
77.2
79.6
til. 2
82. 1
79.5
77.4
150
77.3
79.1
81.7
B3.8
H *> 7
81.5
77. 7
I 60
210 240
77.9 76.2
79.5 77.7
83.0 80.t>
85.3 82.7
85.8 Bi.
73.3
FAR FIELD METHODOLOGY DATA
MIC HFIGHT POSITION LEVEL
(METRFSI (OB)
0.8-1.6 N 75.0
0.8-1.6 E TB.O
0.8-1.6 S 81.0
0.8-1.6 W 79.5
7.0 OVERHEAD 77.4
1.0 MAX 61.0
(AVG. OF MIC4 ABOVE]
•* A WEIGHTED SOUND POrftft LEVEL=104.8 08 KE 1 PICOWATT (BASED ON 73 POINTS)
JULIAN DAY 169
NEAR
TEST NUMBER 10
ZM
W
FIELD DATA PRESENTATION
*NORTH SIDE*
IH CENTER 1M 2M
M , LINE E E
MIC
HEIGHT
*WEST SIDE*
HIC
HEIGHT 0.5 1.5
3M NORTH 79.9 79.1
2M NORTH 81.6 80.2
IH NORTH 83.1 62.9
CENTERLINE 82.7 61.9
IH SOUTH 82.3 62.0
2M SOUTH 82.2 80.8
3M SOUTH 79.6 61.4
.5 ***** 81.0 81.3 77.0 *****
1.5 ***** 73.4 78.4 77.6 *****
2.5 ***** 78.0 78.6 80.2 *****
3.5 ***** 82.1 79.9 82.3 *****
*TOP*
2.5 3.5
80.0 81.2 ***** ***** *****
81.5 82.0 83.3 84.1 62.8
83.0 83.8 86.6 86.9 85.3
84.7 86.8 90.5 89.5 91.0
86.d 86.4 90.2 87.2 90.6
86.1 88.7 90.4 91.8 92.5
85.0 86.4 ***** ***** *****
EAST SIDE*
3.5 2.5 1.5 0.5
80.9 80.7 79.5 79.8
81.9 82.3 80.4 81.4
64.0 63.4 81.9 82.5
87.7 65.4 81.6 82.1
87.7 87.4 81.6 82.0
86.6 85.0 SI.4 81.7
67.3 83.2 80.3 80.7
3.5 ***** 90.3 90.1 90.5 *****
2.5 ***** 85.8 87.5 85-9 ***»*
1.5 ***** 80.6 81.0 81.1 *****
.5 ***** 80.7 81.9 81.2 *****
SOUTH SIDE*
-------
Table 3-11
A-VEIOHTED 80UJTD PRE38OTE LEVEL DATA
T««t NunSor 11 Compressor Output! 100 eta
Engine/Compressor Type: Rot«ty «cr«w, C«», Standard
Compreaaor Size: 1.78xl.27.xl.37a
»*« FAR FIELD DATA (1 METRE RADIUS)
A MEIGHTEO LEVEL (OBI
ANGULAR
HIC HEIGHT
(METRES)
.575
U7?5
2.875
4.025
5. 175
6.375
7.000
ORIENTATION(OEG) 0
NUH ELEVATION
7
I
6
2
5
3
4
(DEC)
4.7
14.4
24.2
35.2
47.6
65.7
90.0
80.6
80.5
81.6
82.6
83.4
84.9
83.7
30
80.9
81. 3
82.3
82.7
83.0
84.7
84.0
60
81.1
80.4
81.3
82.3
82.5
84.0
63.9
90
82.1
81.4
81.2
82.5
82.4
84.1
84.0
120
82.3
83.0
82.7
82.9
24.0
B4.0
83.5
150
83.2
83. U
83.2
83.1
B4.3
84.6
83.8
180
84.0
84.5
83.8
83.4
84. a
84.7
83.6
210
83.1
83.2
83.1
83.6
83.3
84.6
83.9
240
82.0
82.0
81.0
62.3
83.7
B3. 0
63.7
270
82.6
BO. 5
81.1
81. S
82.2
BJ. 9
83.4
300 330
81.3 80.4
80.5 79.7
31.7 81.7
82.1 82.2
83.1 83.1
84.6 83.9
83.5 8J.7
FAR FIFLD METHODOLOGY DATA
HIC HEIGHT POSITION LEVEL
(HtTRESt <08I
0.8-1.6 N 82.5
0.8-1.6 t 82.5
0.8-1.6 S 86.0
0.8-1.6 W 83.5
7.0 OVERHEAD 83.7 IAVG. OF MIC4 ABOVE)
1.0 MAX 86.0
** A WEIGHTED SOUND POWER LEVEL*107.7 06 RE 1 PICQWATT (BASED ON 73 POINTS)
JULIAN DAY 176
• WEST SIDE*
MIC
HEIGHT 0.5 1.5
3H NORTH »**** »*»**
2N NORTH ***** *****
1M NORTH 90.3 90.5
CENTERLINE 90.6 90.6
IN SOUTH 91.8 91.6
2H SOUTH **•** *****
3M SOUTH ***** *****
NEAR
TEST NUMBER 11
2M
U
HIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3,5 *****
3.5
*****
*****
*****
*****
*****
*****
*****
2.5
*****
*****
*****
*****
*****
*****
*****
FIELD DATA PRCSENIATION
•NORTH SIDE*
IN CENTER 1M 2M
U LINE E E
89.4 90.2 89.9 ****»
89.2 90.4 90.2 *****
***** ***** ***** *****
***** ***** ***** *****
• TOP*
***** ***** *****
91.0 91.8 90.9
92.7 93.5 92.6
94.1 98.9 94.8
94.4 97.8 94.B
91.8 94.0 91.8
***** ***** *****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** *****
***** ***** ***** *****
***** ***** 90.4 90.4
***** ***** 90.2 91.2
***** ***** 90.8 91.1
***** ***** ***** *****
***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
2.5 ***** ***** ***** ***** *****
.1.5 »**** 92.1 94.5 91.9*****
.5 ***** 91.9 94.0 91.2 *****
SOUTH SIDE*
-------
Table 3.12
A-WEIGHTED SOUND PRESSURE LEVKI, DATA
Teat NuEber 12 Compressor Output: 175 cfm
Engine/Compressor Type: Rotary screw. Gas, Quieted
Compressor Size: 2.70x1.29x1.43m
»»» FAR FIELD DATA <7 METRE RADIUS)
A WEIGHTED LtVEL I DB I
ANGULAR
MIC HEIGHT
(METRES)
.575
1.725
2.875
4.025
5.175
6.375
7. 000
MIC HEIGHT
JMETRFS)
0.8-1.6
0.8-1.6
0.8-1.6
0.8-1.6
7.0
1.0
ORIENTATIONIDEG) 0 30
MUM ELEVATION
(DEG)
7 4.7 74. B 77.2
1 14.4 74.9 75.6
6 24.2 74.5 76.3
2 35.2 75.8 76.9
5 47.6 76.3 76.8
3 65.7 75.8 75.1
4 90.0 74.4 74.3
FAR FIELD METHODOLOGY DATA
POSITION LEVEL
(D8I
N 78.0
€ 80.0
S 79.0
W 7V. 0
OVERHEAD 74.4 UVG.
MAX 80.5
60
77.5
76.4
78.2
77.5
75.7
76.5
73.9
OF HIC4
90
76.7
77.2
75. 3
75.4
75.7
74.8
74.1
ABOVE)
120
76.4
75.2
75.4
75.7
76.1
74.6
73.9
150
78.5
78.2
77.9
76.7
76.3
74.2
74.1
180
78. 3
77.5
76.9
76.0
75.9
75.2
74.0
210
76.8
76.3
75.7
77.0
76.2
75.2
74.5
240
76.3
76.3
74.8
76.0
75.0
74.2
74.4
270
76.3
75.4
75.7
75. B
74.6
74.9
75.1
30J
76.7
7S.3
75. d
7 b. 6
7t>. 0
7S.2
75.3
330
70.5
76.9
77. i
77. 3
76.2
75. <,
75.1
** A WEIGHTED SOUND POKER LEVEL=101.1 D8 RE 1 PICOWATT (BASED UN 73 PUINTS)
JULIAN DAY 178
*WEST SIDE*
MIC
HEIGHT 0.5 1.5
3M NORTH ***** *****
2M NORTH 85.6 83.4
1M NORTH 86.4 84.2
CENTERLINE 65.8 84.2
1M SOUTH 85.5 84.2
2M SOUTH 85.5 82.3
3M SOUTH ***** *****
NEAR
TEST NUMBER 12
2M
W
MIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
3.5
*****
*****
*****
*****
*****
*****
*****
2.5
*****
*****
*****
*****
*****
*****
*****
FIELD DATA PRESENTATION
*NORTH SIDE*
IM CENTER 1M 2M
W LINE E E
85.4 86.4 85.5 *****
84.2 85.1 83.9 *****
***** ***** ***** *****
***** ***** ***** *****
*TOP*
***** ***** *****
84.0 83.2 83.6
83.9 84.5 84.3
83.4 64.7 84.1
S3.2 82.4 82.8
82.2 82.4 82.5
***** ***** *****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** *«**#
***** ***** 84.3 84.2
***** ***** d5.6 87.0
***** ***** 86.9 36.9
***** ***** B5.2 Bo.O
***** ***** 82.6 84.8
***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
2.5 ***** ***** ***** ***** *****
1.5 ***** 83.7 83.4 84.6 *****
.5 ***** 84.3 85.9 85.2 *****
SOUTH SIDE*
-------
Table 3.13
A-VEIOHTED SOUND PRESSURE LEVEL DATA
Test Number 13 Compressor Output: 175 cfra
Engine/Compressor Type: Rotary screw, Diesel, Quieted
CoBpreosor Biie: 2.70x1.29x1.43m
*** FAR FIELD DATA (7 METRE RADIUS)
A WEIGHTED LFVEL (08)
ANGULAR
MIC HEIGHT
(METRES)
.575
1.725
2.875
4.025
5.175
6.375
7.000
MIC HEIGHT
(METRES)
0.8-1.6
0.8-1.6
0.8-1.6
0.8-1.6
7.0.
1.0
ORIENTATION(DEG) 0 10
HUM ELEVATION
(DEC)
7 4.7 77.2 78.}
1 14.4 77.4 76.8
6 24.2 76.7 76.5
2 35.2 77.5 77.2
5 47.6 77.1 75.9
3 65.7 74.8 74.6
4 90.0 72.9 73.0
FAR FIELD METHODOLOGY DATA
POSITION LEVEL
(08)
N 77.0
E 77.5
S 81.5
W 76.5
OVERHEAD 72.9 IAVG. OF
MAX 81.0
60
77.3
76.4
76.9
75.7
74. a
74.6
73.1
MIC4
90
75.0
74.2
76.0
75.0
75.2
75.7
73.1
ABOVE)
120
76.
77.
78.
77.
7t>.
76.
73.
5
7
0
3
8
9
0
150
00. I
7B.9
BO. 6
75.9
76. 1
75.4
72.8
180
79.4
78.4
77.1
75.5
75.2
75. 1
73.1
210
79.9
75.4
75.0
75.7
75.7
74.1
73.1
240
78.0
75.0
76.0
76.2
75.4
74.4
73.1
270
75.4
73. S
75.5
73.9
73.6
74.1
73.1
300
7S.8
76. 7
75.6
75.6
74.9
73.0
72.6
330
80. S
77.2
77.3
77.3
76.9
74.5
73.0
** A WEIGHTED SOUND POWER LEVEL-101.4 OB RE 1 PICOWATT (BASED ON 73 POINTS)
JULIAN DAY 183
TEST
• WEST SIDE*
HIC
HEIGHT o.s 1.5
3H NORTH ***** *****
2M NORTH 86.6 84.6
1H NORTH 67.9 83.9
CENTERLINE 86.2 83.2
1M SOUTH 87.2 84.1
2M SOUTH 84.3 65.1
3M SOUTH ***** *****
2.5
*****
*****
*****
*****
*****
*****
*****
NEAR
NUMBER 13
>M
W
MIC
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
3.5
*****
*****
*****
*****
*****
*****
*****
FIELD DATA PRESENTATION
*NURTH S10C*
1M CENTER 1M , 2H
W LINE E E
86.8 86.6 85.9 *****
84.9 85.0 83.9 *****
***** ***** ***** *****
***** ***** ***** *****
• TOP*
***** ***** *****
84.0 83.3 82.3
82.6 84.3 62.5
81.9 81.3 80.9
82.5 79.9 81.3
81.9 79.1 81.6
***** ***** *****
EAST SIDE*
3.5 2.5 1.5 0.5
***** ***** ***** *****
***** ***** 8*.2 84.7
***** ***** 83.8 88.0
***** ***** 83.4 87.4
***** ***** 84.6 88.0
***** ***** 83.6 85.6
***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
2.5 ***** ***** ***** ***** *****
1.5 ***** 83.8 82.2 83.1 *****
.5 ***** 85.1 86.1 06.2 *****
SOUTH SIDE*
-------
Table 3.ill
A-WE1GHTEC SOUND PRESSURE LEVEL DATA
Test Number lit Compressor Output: 135 cfffi
Engine/Compressor Type: Rotary screw, Diesel. Standard
Compressor Size: 2.70x1.29x1.43n
*** FAR FIELD DATA (7 METRE RADIUS)
ANGULAR ORIENTATION(DEG) 0 30
MIC HEIGHT NUM ELEVATION
• METRES) (DEC)
.575 7 4.7
1.725 1 14.4
2.875 6 24.2
4.025 2 35.2
5.175 5 47.6
6.375 3 65.7
7.000 4 90.0
A WEIGHTED LfcVEL ( DB )
60
90
120
150
ISO
210 2*0
270
300
33J
73.2 76.2 73.8 73.1 73.9 75.6 77.d
73.5 75.7 74.4 73.3 74.4 75.5 75.9
74.1 75.8
75.8 76.8
75.6 76.2
75.1 73.4
71.5 72.3
74.8
75.6
74.2
74. 4
71.7
73.1 73.6 74.6 76.4
74.2 75.5 75.4 76.3
73.3 73.8
74.0
71.8
74.5
71.4
74.6 75.3
74.1 72.9
71.6 71.3
75.0
74.1
74.1
75.5
74.0
74.0
71.4
74.0
73.4
73.2
73.2
72.8
73.0
71.6
72.7
72.2
72.
-------
Table 3.15
A-WEIGHTED SOUND PKE3SUHE LEVEL DATA
Test Number 15 Compressor Output: 175 cfm
Engine/Compressor Type: Rotary screw, Gas, Standard
Compressor Size: 1.99x1.27x1.45m
• *• FAR FIELII DATA (7 METRE RADIUS)
A WEIGHTED LEVEL (DB)
ANGUL AR
MIC HEIGHT
(MFTRES)
.575
1.725
2. 875
4.025
5.175
6.375
7.000
MIC HEIGHT
JHFTRES)
0.8-1.6
0.8-1.6
0.8-1.6
0.6-1.6
7.0
1.0
CmiENTATlONIOtG) 0 30
NUM ELCVATIUN
(OEGJ
7 4.7 82.2 82.0
1 14.4 61.1 82.3
6 24.2 81.1 82.1
2 15.2 83.6 83. 5
5 47.6 82.9 83.6
3 65.7 84.4 84.6
4 90.0 83.0 B2.9
FAR FIELD METHODOLOGY DATA
POSITION LEVEL
(DB)
N 82.0
E 83.0
S 89.5
M 83.5
OVERHEAD 83.0 (AVG. OF
MAX 88.5
60
82.7
82.9
82.4
83.3
62.8
&4.1
83.1
MIC4
90
82.5
82.4
82.6
83.2
83.6
63.3
83.1
ABOVE!
120
84.1
83.6
83.5
83.3
83.4
04.2
B3. 4
150
86.0
86.2
84.6
84.7
84.9
B3.9
82.8
180
87.3
a&. a
85.4
85.9
86.0
83.5
63.2
210
86.
07.
U4.
84.
85.
tt4.
32.
3
5
2
7
1
0
6
240
85.2
63.1
B2.2
62.8
03. 6
B4.6
83. 1
2 To
83.)
bl. 7
81.8
32.2
63. i
34. 1
d3.2
»00
43.7
61.0
dl.5
32.4
82. a
84.3
di. J
33J
tt2.4
81.5
81. u
02.5
63.1
44.1
62.6
** Jk WEIGHTED SOUND POWER LEVEL-108.7 DB RE 1 PICOHATT JBASED ON 73 POINTS)
JULIAN DAY 169
TEST
NEAR
NUMBER 15
•WEST SIDE*
MIC
HEIGHT 0.5 i.s
3M NORTH ***** *****
2M NORTH ***** *****
1M NORTH 92.0 91.7
CENTERLINE 92.0 92.9
1M SOUTH 92.5 93.8
2M SOUTH ***** *****
3M SOUTH ***** *****
2.5
*****
*****
*****
*****
*****
*****
*****
2M
U
M:C
HEIGHT
.5 *****
1.5 *****
2.5 *****
3.5 *****
3.5
*****
*****
***. *
*****
*****
*****
*****
FIELD DATA PRESENTATION
*NORTH SIDE*
IM CENTER 1M 2M
V. LINE E E
91.6 93.8 91.6 *****
92.0 92.2 91.6 *****
***** ***** ***** *****
***** ***** ***** *****
• TOP*
***** ***** *****
90.3 90.4 90.7
92.2 94.0 92.3
94.7 97.0 93.9
95.2 96.3 94.2
93.0 94.3 93.2
***** ***** *****
EAST SIDE*
3.5 2.5 1.5 .0.5
***** ***** ***** *****
***** ***** ***** *****
***** ***** 93.1 93.1
***** ***** 93.8 92.4
***** ***** 93.2 92.1
***** ***** ***** ****«
**•*» ***** ***** *****
3.5 ***** ***** ***** ***** «**»•
2.5 ***** ***** ***** ***** *****
1.5 ***** 95.0 98.4 95.2 *•*••
.5 ***** 95.5 9603 95>J *****
SOUTH SIDE*
-------
Table 3.16
A-WF.ICHTED SOUND PRESDURE LEVEL DATA
Test Number 16 Compressor Output: 85 cfm
Englne/Coir.preoiior Type: Rotary screw. Gas, Standard
Compressor Size: 1.96x1.10x1.34m
*** FAR FIELD DATA (7 MET»E RADIUS)
ANGULAK UR1ENTAT [OMOLG) 0
MIC HklGHT MUM tLhVATIUN
30
60
90
A WEI&HTfO LCVL'L
120 150 18J .
(l)rt)
240
JJJ
.Ucl
IMtTPf S)
.575
1.725
2.875
4.0?5
5. 175
6. J75
7.000
IDEGI
7 4.7
1 14.4
6 24.2
? 35.2
5 47.6
3 e>5.7
4 90.0
76.
74.
74.
74.
75.
75.
74.
FAR HELD METHODOLOGY
MIC HEIGHT
tMEiatS)
0 . B- 1 . 6
0.8-1.6
O.fl-1.6
0.8-1 .6
7.0
1.0
POSIT ION
H
E
S
W
OVERHEAD
MAX
LEVEL
IDUV
76.5
76.0
eo.o
75.5
74.1
80.0
5 76.4
1 74.5
0 74.0
b 72.0
9 76.2
3 74.6
1 74.1
DATA
(AVG.
76.0
74. t
74.6
74.6
75.9
T>.i
Tt.t
OF M1C4
76.1
73. 8
73.7
74.2
75.7
74.5
74.0
ABOVE
n.o
75.6
76.3
76.2
76.9
Jy.B
73.6
1 8.6
>B. 1
7b.O
7d. 4
7d.4
7t.. o
74.5
79.4
7->. I
77.9
79. 3
76.9
77.2
74.0
7U.2
7 i).2
77.0
78.0
7d.5
76.7
74.5
76.1 75.3
7 5. f> 74.
-------
T»bl« 3.IT
A-WEIOHTED SOUND PRESSURE LEVEL DATA
Teat Number 17 Compressor Output: 150 cfm
Engino/Comproasor Type: Rotary screw, Oae, StttuUxd
Compressor Size: 1.93x1.24x1.36m
• ** FAR FIELD DATA (7 METRE RADIUS)
A WEIGHTED LEVEL (DBI
ANGULAR
MIC HEIGHT
(METRES)
.575
1.725
2. 875
4.025
5.175
6.375
7.000
MIC HEIGHT
•METRES)
0.8-1.6
0. 8-1.6
0.8-1.6
0.8-1.6
7.0
1.0
ORIENTATIONIOEGI 0 30
NUN ELEVATION
(DEC)
7 4.7 76.8 77.7
1 14.4 76.5 76.8
6 24.2 76.9 76.6
2 35.2 78.2 77.4
5 47.6 78.6 7B.O
3 65.7 77.9 77.0
4 90.0 75.5 75.0
FAR FIELD METHODOLOGY DATA
POSITION LfcVEL
(DB)
N 77.5
E 7B.O
S 80.0
W 77.5
OVERHEAD 75.5 (AVG. OF
MAX 83.0
60
77.7
76.8
76.8
77.5
77.4
70.7
75.5
MIC4
90
77.5
76.1
77.4
77.7
77.8
76.4
75.1
ABOVE!
120
79.4
77.6
78.2
78.0
78.9
77.1
75.3
150
Bl.l
79.3
79.2
80.0
80.6
77.4
75.8
180
79.4
79.7
78.5
79.6
79.8
78.1
75. «
210
80.3
79.6
79.2
80. 0
BO. 7
7li.ll
75.7
440
79.6
78.2
77.9
79.0
78.6
77.5
75.8
270
77.1
76.5
76. (.
77.9
77.7
77.3
75.9
300
77.5
75. 7
77.2
77. 7
7b. 6
7S. I
330
77.8
76.3
76. 5
77.1
7B.I
77.9
75.d
** A WEIGHTED SOUND POWER LEVEL»103.0 DB RE 1 PICOWATT (BASED UN 73 POINTS)
JULIAN DAY 191
• WEST SIDE*
MIC
HEIGHT 0.5 1.5
3M NORTH *»»»* *****
2M NORTH S6.5 84.3
1M NORTH 67.6 86.3
CENTERLINE 87.9 86.9
1M SOUTH 89.4 87.6
2M SOUTH 88.8 86.5
3M SOUTH *«*** *****
NEAR
TEST NUMBER 17
2M
W
MIC
HEIGHT
.5 *****
t.5 *****
2.5 *****
3.5 *****
FIELD DATA PRESENTATION
•NORTH SIDE*
1M CENTER 1M 2M
W LINE E E
87.6 91.3 87.5 *****
85.8 86.3 87.0 *****
***** ***** ***** *****
***** ***** ***** *****
*TOP*
,5
<*
3
3
9
6
5
i*
2.5
*****
*****
*****
*****
*****
*****
*****
3.5
*****
*****
*****
*****
*****
*****
*****
*****
84.
ST.
89.
88.
88.
2
4
3
6
1
*****
*****
86.
8S.
90.
90.
88.
1
7
6
4
8
*****
*****
86.2
87.3
89.1
39.3
88.1
*****
EAST SlOE*
3.5 2.5 1.5 0.5
*t*** ***** ***** *****
***** ***** 85.5 85.4
***** ***** 87.7 87.9
***** ***** 88.0 88.1
•**** ***** 87.3 88.7
***** ***** 88.4 88.0
***** ***** ***** *****
3.5 ***** ***** ***** ***** *****
2.9 ***** ***** ***** «*»*# *****
1.5 ***** 90.2 90.1 90.3 *****
.5 ***** 90.3 92.5 90.1 *****
SOUTH SIDE*
-------
Table 3.18
A-WEIGHTED SOUND PRESSURE LEVEL DATA
Teat Number 18 Broad Band Reference Sound Source
»** FAR FIELD DATA 17 METRE RADIUS)
A WEIGHTED LEVEL IDB)
ANGULAR ORIENTATIONIDEG) 0 30 60 90 120 150 180 210 240 270 300 3 JO
MIC HEIGHT MUM ELEVATION
•METRES) (DEG)
.575 7 4.7 71.* 71.0 71.to 72.0 72.1 71.7 71.3 7Z.1 71.9 72.0 /2.1 71. J
1.725 I I*.* 70.8 71.5 70.5 70.* 70.2 70.7 71.2 71.0 71.3 71.5 71.'. 71.2
2.875 6 24.2 70.2 69.9 70.3 70.3 70.5 70.0 69.6 69.7 69.6 70.1 70.'. 70.1
4.025 2 35.2 69.8 69.9 70.1 70.3 70.6 71.1 70.7 70.fc 70.7 70.3 70.7 70.6
5.175 5 *7.6 69.6 69.6 69.8 70.1 70.0 70.1 68.7 69.7 69.3 69.2 69.J i9.7
6.375 3 65.7 69.5 70.0 69.8 69.6 69.3 69.* 69.7 69.8 70.7 70.2 70.2 70.1
7.000 * 90.0 69.4 69.* 69.2 69.5 69.2 69.3 69.5 69.9 69.6 69. t) 69.6 09.6
FAR FIELD METHODOLOGY DATA
MIC HEIGHT POSITION LEVEL
(METRES) (D8)
0.8-1.6 N 72.0
0.8-1.6 E 73.0
0.8-1.6 S 73.0
0.8-1.6 W 73.0
7.0 OVERHEAD 69.4 (AVG. OF MIC* ABOVE)
1.0 MAX 72.5
** A WEIGHTED SOUND POWER LEVEL= 95.3 D8 RE 1 PICOHATT (BASED ON 73 POINTS)
NEAR FIELD DATA PRESENTATION
JULIAN DAY 1*1 TEST NUMBER 18
*NORTH SIDE*
2M 1H CENTER IH 2M
W W LINE E f.
KIC
HEIGHT
.5 ***** ***** ***** ***** *****
1.5 ***** ***** 80.5 ***** *****
2.5 ***** > (2M FROM SOURCE) *****
*WEST SIDE* 3.5 ***** ***** ***** ***** ***** EAST SIDE*
MIC *TOP*
HEIGHT 0.5 1.5 2.5 3.5 3.5 2.5 1.5 0.5
3H NORTH ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****
2M NORTH ***** **»** ***** ***** ***** ***** ***** ***** ***** ***** *****
1M NORTH ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****
CENTERLINE ***** 79.7 ***** ***** ***** Bl.* ***** ***** ***** 81.3 *****
1M SOUTH *** <2M FROM SOURCE),*,, **,*(2M HIGH)**** *** (2M FROM SOURCE)***
2M SOUTH ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****
3H SOUTH ***** ***** ***** ***** ***** ***** ***** ***** ***** ***** *****
3,5 ***** ***** ***** ***** *****
2.5 ***** (2M FROM SOURCE) *****
1.5 ***** ***** 79.9 ***** *****
.5 ***** ***** ***** »»*»* *****
SOUTH SIDE*
-------
Table 3.19
A-VKJQilTOT BOUND PNBKNIIW I.KVM. DATA
1U
«•» f»» f>lflD DATA I? HEIDI HAOiui)
ANGULAR naUNTATIONIOtGI C JO
MIC NFICHT NUN HEVATIUN
* WCIGHTtO LIVCL (OS)
40 120 140 110 210
!40 no 300 DO
(KtW SI
.M*
I.T2»
2.675
*.02S
S. 175
6.J75
T.OOO
IBEGI
T 4.7
1 14.4
6 24.2
2 35.2
5 47.6
1 65.7
4 90.0
61. J 64.6
47.7 69.)
49.6 6J.O
56.8 61.}
62. 5 64.4
58.5 54.8
68.0 68.4
60.2
01.0
19.9
60. )
6J.3
55.3
68.0
65.5
62.1
66.8
52.6
66.7
57.4
67.9
66.4
65.6
68.1
59.0
69.7
56.0
68.1
69.)
67.8
69.7
62.2
71.9
57.2
67.9
72.2
72.6
73. S
67.0
73.8
55. S
68.6
T».9
74.2
75.4
69.0
75.5
55.)
68.1
73.0
72.8
75.1
68.5
74.3
50.7
67.7
70.1
60.5
70.9
63.9
72.7
56.6
68.1
67.6
65.7
6U.2
58.6
70.3
58.5
67.4
65.)
63.5
67.0
56.9
67.4
56.4
67.9
FAR FIELD METHODOLOGY DATA
NIC HEIGHT
(METRES 1
0.1-1.6
0.8-1.6
O.a-1.6
O.D-1.6
T.O
1.0
POSITION
N
t
S
K
OVERHEAD
MAX
LEVEL
(081
74.0
68.0
66.0
65.0
68. 0 (AVG. OF
64.5
MIC4
ABOVE)
•• A WEIGHTED SOUND POWER LEVEL- 9).5 08 RE 1 PICOWA'T (BASED ON 7) POINTS!
- Table 3.20
A-WEIOKTED BOUHD PRESSURE LEVEL DATA
Test Sunber 20 Pure-Tone Loudspeaker Source, 1000 Hz
• •* FA* FIELD DATA (7 METRE RADIUS)
ANGULAR ORIENT ATIONIDEG)
MIC HEIGHT NUM ELEVATlUN
A WEIGHTED LEVEL (OB)
120 150
180
210 240 270 300 330
(METRES)
.575
1.725
2.875
4.025
5. 175
6.375
7.000
7
6
2
5
3
4
(OEGI
4.7 57.4 bl.2
14.4 67.5 65.9
24.2 67.9 (.6.6
35.2 fee. 9 68.9
47.6 61.. 3 ' 68.7
65.7 66.5 68. 5
9}.0 64.7 60.1
60.3
65.4
68.9
69.0
67.4
68.0
64.7
61.6
68.0
68.5
70.0
70.5
71.4
64.9
59.2
66.1'
7i.7
71.9
73.6
73.4
66.8
65.9
71.8
76.3
77.8
64.6
75.6
65.7
67.2
73. J
78.0
79. T
79.1
78.6
66.5
73.2
75.8
79.3
81.4
80.4
80.0
65.4
68.0
72.4
75.9
78.Z
78.1
78.8
65.3
68.3
67. d
73. S
74.5
75.5
76.0
64.0
62. t
64.6
6V.4
70. d
70.3
72.3
66.9
61.5
65.3
D7.0
<>7.l
70.0
71.5
50.2
FAR FIELD METHODOLOGY DATA
MIC HEIGHT
IMETfclSI
0.8-1.6
0.8-1.6
0.6-1.6
0.8-1.6
7.0
1.0
POSITION LEVEL
N
E
S
N
I OB)
80.0
74.0
70.0
74.0
CVE'HEAO 64.7 (AVG.
MAX
77.0
OF MIC4
ABOVE)
•* A WEIGHTED SOUND POWER LEVEL- 98.6 08 RE I PICOWATT (BASED ON 73 POINTS)
Tdble 3.21
A-WEIGHTED SOUND PRESSURE LEVEL DATA
Test Kuaber 21 Pure-Tone Loudspeaker Source, £000 Hz
••* FAR FIELD DATA 17 NETKE RADIUS)
A WEIGHTED LEVEL (OBI
ANGULAR
MIC HEIGHT
(METRES 1
.575
1.725
2.875
4.025
».VT5
6.375
T.OOO
MtC HFICMT
(METRES)
0.8-1.6
0.8-1.6
0.8-1.6
0.8-1.6
T.O
1.0
ORIF.NTATIONIDEG) 0 30
NUM ELEVATION
(DEC)
7 4.7 65.7 55.0
I 14.4 53.5 64.9
6 24.2 64.0 54.0
2 35.2 66.3 64.8
J 47.6 67.9 5H.3
3 65.7 66.8 56.8
4 90.0 60. 8 70.1
FAR FIFLO METHODOLOGY DATA
POSITION LEVEL
(Ob)
N 89.0
E 71.0
S 69.0
W 76.0
OVERHEAD 68.8 (AVG.
MAX 83.0
60
69.
56.
65.
69.
64.
68.
70.
UF Mi
8
5
4
8
1
8
2
C4
90
72.2
68.6
63.9
70.6
68.6
69.7
08.1
ABOVt 1
120
77.4
71.9
67.4
73.2
71.5
74.5
69.3
150
85.6
80.5
70.5
77.4
79.3
7B.O
69.4
180
88.5
85.9
77.8
82.6
79.7
78.8
68.8
210
89.4
86.1
71.5
79.5
81.5
77.1
68.0
240
83.9
81.7
72.2
79.5
79.5
77.3
66.9
270
79. »
75.7
66.5
70.2
73.6
77. 1
69.1
300
71.0
6V. 2
64.3
68.5
66.4
73.4
69.0
330
62.2
64.2
65.1
63.8
65.7
72.0
68.8
• * A WEIGHTED SOUND POWER i.EVEL-lOJ.2 08 RE 1 PICOWATT (BASED ON 73 POINTS)
-------
3. SOUND POWER LEVEL CALCULATIONS
3.1. Far Field Sound Pover Calculation Procedures
The estimate of sound power (W(f)) from samples of mean square pressure or. a measurement surface
is of the form:
W(f) =2l^pi U) VPC (3.1)
where W(f) is the estimate ofisound power (watts) at the frequency f
p2 (f) is the time-average squared pressure at position i on the
measurement surface at the frequency f (pascals ).
[p2 (f) = 10SPL(i'f}/10 where SPL(i,f) is the time average sound
pressure level at position i and frequency f.]
S. is the area associated with the ith measurement position
(square metres).
pc is the characteristic impedance of the medium (p is the density
kg/m , c is the velocity of sound m/sec).
In the event that the microphone positions are chosen to represent equal areas of the measurement
surface, then equation 3.1 reduces to:
— . (3.2)
where: S is the total area of the measurement surface (square metres).
The far-field measurement art-ay was designed with this latter equation in r.ind. At each location of
the array, each microphone, except the top one, samples a sector of the hemisphere Troni $ — i$ to $ +
Ait and from z =z - Az to z =z + Az [where A = 15°, Az = 1.15m.].
2 ° 2
The area of a segment of a spherical surface between z and z,. is 2itrAz; thus the area represented by
each microphone position is: ^
&BI = 2ir(7.0) (1.15) (30/360)
= U.2 m
The area sampled by the top microphone is:
r2
= 1».3
S_ = 2itr2 - m(ASi)
For the purpose of sound power calculations in this report, these areas were treated as equal;
however, it should be noted that the areas involved are not identical in shape. This is a conceptual
disadvantage, since it is not entirely clear -f-.hat the sample from the center of a long narrow
rectangular shaped area will be as representative of the average level as a point which is at the
center of a circle of the same area. Such considerations are, however, beyond the scope of this
study.
3.1.1. Systematic Error in the Far Field Array
The array chosen presents another difficulty for the measurement of sound power level, which has
been previously noted by Baadefj]. This has to do with the fact that a compact (ka«l, k=wave number,
a= source radius) omnidirectional source at a height above the ground plane produces an interference
pattern on a hemisphere above the plane which in the far field approximation is of -the form [7].
(3.3)
" \ Ri R2 '1' 2 '
where:
o
p (r,z) is the mean square pressure at height z on a hemifphere
centered over the sources, of radius r;
37
-------
p "" io the mean oquuro proonure from the source in free apace
0 at tho radlun rj
R, is equal to tho ratio of path length for direct sound
to radiuo r;
R? - (r2- z2) -t- (h - z)2 = r2-2hz + h2
1 2 2
r r
R2 is equal to the ratio of path length for reflected sound
to radius rj
H? - (r2- z2) + (h + z)2 - r2 + 2hz + h2
«; g 2
r r
h is the height of the source center above the ground plane;
R(T) is the auto correlation function of the source radiation.
For random noise;
. . ,„ .. > Sin (2irAfT)
R(T) - cos (2i.fot) —%-fc
•
f is the center frequency of the band, Hz;
Af is the narrower bandwidth of the signal or the analyzing filter;
T is the time delay between direct and reflected sound [T=r(R1-R2)/e]
c = speed of sound in the propagation medium;
For pure tor.es, 6f = 0 and sin x = 1 when x = 0
x 2
so, R(T) = cos 2-nfT = cos (a-nfrd^-R^/c). For r /hz»l,
R1/R2 1, and fr(R.,-R2)/c 2fhz/rc.
For tones or bands of noise this expression predicts minim in the sound field at heights which
are odd multiples of fhz/rc when r »hz.
Thus for a small fixed height source, superimposed on its inherent directivity, interference
minima will occur at microphone heights z which are multiples of odd integers due to the n ground
plane reflection. Fortunately, our microphone array is sufficiently closely spaced so that minima
will not occur at all microphones rimultaneously. for a one metre source height, unless the conditions
f> 1000 Hz and source radius much xess then 0.053 m are met. At lower frequencies, the fact that
maxima will occur at some microphone positions which will compensate, to some degree, for minima at
other locations, presumably will tend to minimize this systematic error. Furthermore, for this
description to apply to a minimum at the top microphone only, the frequency must be greater than about
300 Hz with a source radius much less than O.l6 m. Tius, the fact that the typical component source
size of a compressor is considerably larger than these dimensions, except possibly for engine exhaust,
suggests that the existence of interference minima should not create a serious measurement problem for
this array.
An estimate of the possible error in the far field measurement for an omnidirectional source can
be obtained from Eq. 3.3 as follows.
We note.that an estimate of sound power output without sampling error, for a fixed source height
is given by'*'
We note that while the true power is analytically available by simpler means, at this Juncture
our purpose is to evaluate only the sampling error, uncluttered by other error sources.
36
-------
<»5T£HATIC f.HHOH IN ESTIMATION OF bOUNU POKE" FROM A CUHPACt SOURCE
OSINS SPL VALUES FRO*1 A /I POINT AKrfAT ON A 7 HETEK HEMISPHERE
SOURCE ' PU«f TONE A1 1/3 UU ClNttR FRtWutNCT
1(1 LOG MEST IMA1EDI/*
SOURCE HllGHfltM
f »EQUENC»
as.
12.
in.
so.
63.
79.
100.
126.
ise.
2UD.
7SI.
316.
}9fl.
601.
ill.
791.
1000.
I2S9.
ISBS.
I99S.
1412.
Hi?.
3*81.
SOU.
»3IO.
7913.
IOOJO.
AVG EHXOt
SO OF ERROR
.32
.UO
• 00
.00
.00
.00
.00
.00
.00
.111
.01
• 41
-.ul
-.03
-.Ul
.03
.01
-.J5
.07
-.01
-.20
-.Ml
-10.39
-.27
-.37
2.31
-.28
.81
-.32
2.J6
.10
.00
.00
.ou
.ou
• OU
.00
.00
.01
.01
.01
-.01
-.03
-.01
.03
.01
-.OS
.07
-.01
-.20
-.Ml
-IU.22
-.77
-.37
2.2V
-.78
.80
-. 17
-.33
7.91
.SJ
.O1)
.00
.00
.30
.DO
.90
.01
.01
.JO
-.31
-.03
-.01
.03
.01
-.OS
.97
-.01
-.20
-.11
-10.73
-.?7
-.17
7.2S
-.?•
.75
-.79
-.37
-.31
2.00
.43
.00
.00
.00
.00
.00
.01
.01
.00
-.01
-.03
-.01
.03
.01
-.OS
.or
-.01
-.21
-.12
-9.73
-.77
-.37
7.20
-.28
.67
-.19
-.OS
.SO
-.31
1.91
.79
.00
.00
.00
.00
.01
.01
.00
-.01
-.03
-.02
.03
.01
-.OS
.07
-.01
-.21
-.12
-9.2B
-.27
-.S«
2.10
-.29
.S3
-.11
.33
.17
.71
-.28
1.17
1.00
.00
.00
.01)
.01
.01
.00
-.01
-.03
-.02
.03
.01
-.05
.07
-.01
-.21
-.11
-»,62
-.27
-.39
1 .91
-.11
.78
-1.3.1
.as
.1*
.91
.97
-.23
1 .77
1.2*
.1)0
.00
.01
.01
.00
-.01
-.03
-.02
.03
.01
-.04
.07
-.01
-.22
-.IS
-7.*8
-.27
-.10
I.i6
-.30
-.1*
-2.02
1.12
.S9
1.08
1.11
.11
-.18
I.4S
I.Stt
.00
.01
.01
.00
-.01
-.03
-.02
.03
.01
-.06
.07
-.OS
-.23
-.17
-».1|
-.27
-.13
l.li
-.33
-.96
-2.61
1.12
1 .07
.S9
.91
.18
-1 .06
-.21
1.18
2.00
.00
.01
.00
-.01
-.01
-.02
.01
.01
-.07
.08
-.06
-.26
-.19
-1.79
-.28
-.19
.21
-.38
-2.27
- .87
.31
.16
- .61
- .61
.97
.19
-1.2S
-.10
1.26
2. SI
.UO
.00
-.02
-.01
-.03
.02
.0!
-.08
.08
-.08
-.29
-.17
-2.89
-.31
-.60
-1 .13
-.18
-2.93
.S3
-1 . IS
1 .07
-.31
.17
-.90
.86
-1 .23
.97
-.31
.96
A* EKH
.00
.00
.00
-.00
-.00
-.00
-.00
-.01
.00
-.01
-.03
-.08
-.36
-.58
-.79
- .OS
- .02
- .27
- .11
- .36
-.99
-.75
. 19
.10
.69
.28
.16
SO
.00
.00
• 01
.02
.02
.02
.02
.03
.01
.01
. 10
. 16
.90
1 .19
1 .98
2.37
2.68
2.99
3. 17
3.20
3.19
3.62
1.20
1.12
.78
.78
.82
SOURCE
fKE6UENCT
2S.
32.
in.
SP.
63.
T9.
133.
12*.
IS8.
2UO.
2SI.
316.
19S,
SOI.
431.
791.
IOOJ.
I7S9.
IS«S,
2SI7.
3I67.
3»ai.
SOI 2.
63IO.
>«13.
IOOJJ.
AVf CHKOR
so or e«Ku*
k.2
.32
.00
.uo
.uo
.JO
• uo
.00
.01
.ul
.uo
-•ul
-.01
.U7
-.UO
-.Ul
.ul
.01
-.U9
-.89
-.61
-.06
.37
.06
-.25
.23
SYSTEMATIC ERROR IN ESTIMATION OF SUUNU PO«ER F»e« « CUnPACT SOuRCt
USING SPL VALUES FRO" A 73 POINT AHKAT ON A 7 KtTEK HEKISPHERE
SOURCE-PINK NUISt I/J 0.8. "IDE AI 1/3 O.S. CENTER FHEUUENCT
• 10 LOG •(EST imrtoi/«
.Id .Sj .63 .79 1.00 1.26 I.S8 2.00 2.SI Av EKR SO OF ERR
ou
OL
03
UO
OU
OL
00
Ol
Ul
00
01
02
01
02
OU
00
01
01
03
08
««
61
06
37
16
2S
12
OS
23
.UO
.UD
.00
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-------
-7
r_
(2itr) pa(r.z) dz
pc
o
Tlie approximation obtained from the far-field array is
since p (r,z.t6.) is independent of 6 for an omnidirectional source, eq., 3.5 reduces to
"""•^Z aip2Zi) (3-6)
where: i=1
(12/73. i « 1 to 6
al *1
1 I 1/73, 1=7
The error in sound power level due to earaplint, (ALv(s)) is given by
10 Log10 ~- (3,7)
2
The results of this calculation, using eq. 3.3 for p (r,z) considering ten different source
heights for the far field array with the sources radiating ' either a pure tone or one-third octave
bands of noise, are shown in Tables l*.l and lt.2.
3.1.2. Far Field _ Sound Power Calculations
In performing the sound pover calculations, the significance of the ambient correction was
retained in terras of a signal quality code. As noted in Section 2.3.5, the average sound pressure
level value at a measurement position in each frequency band was coded to indicate one of the
following types of data quality:
a) normal data (greater than 3 dB above ambient);
b) upper bound data (data within 0 to 3 d3 above ambient, and corrected
for ambient);
c) no useful data (data at or below ambient, or at or below instrument
base line) , Data value replaced by higher of ambient level minus 3 dB
or baseline level.
In using these data in a sound power level calculation, the first step is the computation of an
average sound pressure. The data were summed in three components of the average with a breakdown
similar to the above, i.e.
a) sum of normal data, and number of points
b) sum of upper bound data, and number of points
c) sum of no-useful-data values, and number of points of no useful data.
The average sound pressure was determined by adding these sums together and dividing by the total
number of points . The power level computed using this average sound pressure was assigned a quality
code according to the relative magnitude of these sums and the number of points involved as described
below:
feo
-------
power level quality of data
quality code
1 all data type-a
2 • some type-a, no type-c, some type-b data which contributes less
than one-twentieth (0.2 dB) to the total power in the band,
3 some type-a, some type-b and -c data which contributes less
than one-twentieth to the total power.
k some type-a, no type-c, some type-b data which contributes
between one-twentieth and one-half of the computed power
(-0.2 dB to -3 dB).
5 some type-a, some type-b and -c data which contribute
between one—twentieth and one-half of the computed power.
6 some type-a, no type-c, type-b data which contribute more
than half of the computed power.
7 some type-a, type-b and -c data which contribute more
than half of the computed power.
Investigation of the data indicated that in the frequency range 25 Hz to 10 kHz, there was always
some type-a data so the above classification is complete. The data of code k through 7 are upper
bound sound power levels, since the estimate of true power level will be less than calculated.
Data of code 1, 2, and 3 was further classified according to the magnitude of the pooled value of
temporal variance according to the following scheme:
a. If the variance of the signal is less than that of electrical noise at the 99% level of
confidence, then the signal is called tone-like.
b. If the variance of the signal is within the 99% confidence interval of electrical pink noise,
the signal is called noise-like.
c. If the variance of the signal is significantly greater than that of electrical pink noise at
the °9% level of confidence, the signal is called fluctuating.
The data in each band where the quality code is less than or equal to 3 is given a letter code T,
H or F corresponding to the above classification — tone-like, noise-like and fluctuating,
respectively.
3.2. Hear Field Sound Power Calculation Procedures
The same general and specific forms of the far-field sound power calculations (eq. 3-1 and 3-2)
also apply to the near-field calculations. The same order of magnitude sound power value will result
since the value for mean square sound pressure will increase nominally inversely in proportion to the
change in S (as a consequence of the inverse square law of sound lield spreading).
The calculations reported here were performed for two different measurement surfaces and three
different subsets of the measured data as follows:
Near-Field Calculations
Label Calculation Procedure
NF 1 Conformal surface— (defined by Fig. B) - all appropriate measurement positions (see below).
KF 2 Conformal surface - engineering method, 8 measurement positions.
HF 3 Conformal surface - survey method, 5 measurement positions
KF 6 Rectangular surface - all measurement positions.
The conformal surface of radius r is that surface which is defined by being everywhere a distance
r from the nearest point on the envelope of the principal radiating surfaces of the source. (See
Figure 8).
Ill
-------
w
SECTION BB
W
PLAN
VNWMW^WroS^^
SECTION AA
Figure 8 Conformal surface at a distance r from a rectangular box
BF 7 Rectangular surface - engineering method, 9 measurement positions.
NF 8 Rectangular surface - survey method, 5 measurement positions.
The label above refers to the label of the calculation procedure as it appears in Tables 5-1-5-17
and Table 6. The references to engineering and survey methods refer to ISO Draft International
Standards [2] For Sound Power I. ./el Determination (DIS 37 l& and DIS 37>*6, respectively). The data
vere taken on a rectangular measurement surface (e.g., with square corners) rather than a conformal
surface, therefore some modification of the /data set was required for the conformal surface calcula-
tions. The modifications were as follows:—'
NF-1 -
Data points near edges and corners were included if the data points were with the surface's
corresponding distance from the source surface r such that:.
Sc(l) £S
1.125 Sc(l)
(S_(r) = 2hU + w + nr) T S.v + TIT (i + w) + 2irr )
c
This results in retaining some measurement positions (near edges and corners) which would be
••"Since all of the compressors in this study were contained within rectangular shaped enclosures, the
envelope taken for the source was also rectangular in shape, and of dimensions I, w, h where 8. and
w are the length and width of the enclosure respectively, and h is the height of the top of the
enclosure above the reflecting plane.
1.2
-------
NF-2 -
as much as 0.5 dB below the the expected value if inverse square si dding applies on the
measurement surface. The actual number of measurement positions ui * in each HF-1 calcula-
tion are identified in the data tables. It should be noted that most of the measurement
positions do lie on the measurement surface. An estimate of the maximum downward bias
(AL(P)) introduced by including those points not on the measurement surface is -0.2 dB £AL
(P)<0, vith the maximum error decreasing as source size increases.
The ISO draft standard engineering method prescribes an eight point measurement array for
use with a conformal surface. These eight points have position corrdinates as follows (for
a source of dimension £, w, h):
Pos. No.
1
2
3
h
5
6
7
8
X
a
0
—a
0
a/2
-a/2
-a/2
a/2
Y
0
b
0
-b
*!
D!
~bl
~bT
z«
hl
1
h
1
hn
1
h
1
h2
h2
h.2
ho
Where: a = 1/2 fc + r
b = 1/2 w + r
c = h + r
b^ = lA (b + c - r)
h2 = 3A (t> + c - r) <_ c
bx = 1/2 (b + c - r) <_ b
» The origin of the coordinate system is on the reflecting plane under the
center of the compressor.
The approximation of these positions used in the calculation in this study are:
positions 1-U (x, y dimensions as indicated, h^ nearest half integral value
in metres to calculated value)
positions 5-8 (x, y dimensions, nearest integral v-lues to calculated value.
h2 = c).
NF-3 6 -8 The five positions used for both calculations are the positions 1.5 m high, at the center
of each side, and the position on the center of the top array. The only difference in the
calculation is the difference in the area S used for the measurement surface.
NP-6 All points and rectangular surface used.
NF-7 The nine points required for this calculation include the five positions used in NF-3 and
-8 plus four additional points at the corners of the measurement surfaces. These four
points were approximated by the nearest measurement points.
The effect of these approximations may be treated as equivalent to a positioning error. The actual
error introduced is a function of the directivity of the sound source — most of the positioning error
is a lateral displacement on the measurement surface, as opposed to a "radial" displacement off the
measurement surface. Therefore, the approximations, in general, represent non-biasing errors which
may or may not contribute to the imprecision of the measurement, but will not tend to produce
systematic bias.
-------
3.3. Sound Power Level Data
The results of the sound pover level calculations for the 17 compressors are presented in Tables
5-1 to 5.17. Each table consists of five parts including: a plot of far-field power level, a table
of signal quality for far-field and near-field data, a table of far- and near-field power levels and
differences between near- and far-field power levels, and a table of far-field methodology power
levels and the difference from far-field power level.
The top of the table is a plot of the 1/3 octave band, far-field sound power level vs frequency.
Underneath the frequency scale is the signal quality code for both far-field and near-field (HF type
6) sound power level data using the same frequency scale as the plot. The next entry in the table is
the sound power level data for far-field and six different near- field calculations as described in
Sections b.l and U.2. The data are presented in a two line format with the first line containing
A-weighted and linear values plus the one-third octave band sound power level for band center
frequencies from 25 Hz to ^00 }iz. The second line of each entry is the one-third octave band sound
power level for band center frequencies from 500 Hz to 10,000 Hz.
The second group of entries in the data table give the deviations of the various near-field
calculation procedures from the far-field sound power level. The sign convention is such that
positive values imply that the near-field power level is higher than the far-field power level. The
significance of large individual deviations at low frequencies should be evaluated in the context of
the magnitude of the signal quality factor, and the fact that large values of this factor (greater
than 3) indicates a serious ambient noise problem (which typically caused an over estimate of the far
field power level).
The far-field methodology data is presented in octave bands, and A— and C- weighted levels since
the data were recorded in this format. For comparison purposes, the octave band and C-weighted
far-field power level were computed from the one-third octave band data.
-------
Test Umber 1
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106.0
94.8
105.0
106.1
95.8
106.6
95.8
105.6
95.8
107.5
97.0
315
SK
103.6
92.6
103. B
91.4
102.4
91.5
103.9
92.7
104.5
92.4
103.1
91.9
105.3
93.9
400
10K
103.1
90.1
103.2
87.8
102.4
104.2
89.7
103.9
89.1
103.4
89.2
105.7
90.9
NF PM. I
NF PWl 2
NF PM. >
NF PML 6
W PWL T
NF PHI 8
tUt FIELD rut
f»« FIELD HtTHODOLOCr PWi.
OiVUIIONS OF FF MCTH FROM FF
DEVIATIONS FOOM FF PWKDBI
.3
.0
l.S
I.I
.1
1.0
1.2
.6
1.8
l.S
1.)
1.2
-.3
. 7
-l.S
.1
1.4
2.B
1.0
1.1
.2
1.7
2.7
4.3
.7
.4
-1.)
.5
1.4
2.4
U>
.9
.2
1.6
2.T
3.9
.1
.5
-.9
.1
l.a
I.T
1.4
1.3
.7
1.0
1.1
>.l
1.0
. 1
.4
-.1
1.6
.6
l.B
1.0
1.4
.4
2.9
2.1
-.2
.2
-1.2
.1
-.5
1.9
.4
1.2
'1.4
l.t
.»
3.5
1.0
.2
-.0
.2
1.4
I.*
S.S
1.2
.1
.a
2.6
3.0
2.0
1.0
.7
2.3
1.)
2.5
1.5
1.9
.6
3.8
2.8
1.0
-.2
-.9
.9
-.4
l.S
.5
.6
-.1
2.2
.9
.0
-.1
-.3
.6
.2
.9
1.1
.0
.2
1.9
l.S
.2
.9
.3
1.4
.»
1.3
l.t
1.3
.(
2.7
2.2
.3
-.6
-.3
.6
.1
.9
.5
-.1
-.$
1.9
l.S
.6
-.»
-.8
.7
.5
1.2
.5
.2
.5
2.1
1.7
.2
-1.2
-I.I
.3
.1
.9
-.2
-.5
-.7
1.7
1.1
.1
-2.3
-.7
-1.5
1.1
-.4
.8
-1.0
.}
-.9
2.6
.»
TABLE OF OCTAVE SANO POUEK LEVELS
A C 11. S 63 125 2SO SOO IK 2K 4K *K
110.8 1)9.7 19.7 117.6 113.6 108.4 107.S 105.4 IDS.2 102.6 97.9
113.0 |20.( .0 118.S 115.3 108.1 109.9 10S.6 104.8 104.8 102.1
2.2 I.I .0 .« 1.7 -.3 2.4 .2 -.4 2.2 4.2
-------
120
d no
- »-
97.4 97.3 95.9 14.2 92.2 90.0
107.7 IIJ.3 78.0 76.0 77.6 J4.5 88.7 91.7 109.2 92.2 94.2 102.2
97.1 98.2 95.7 99.2 99.8 98.5 97.4 95.7 93.3 90.7
107.9 HJ.I 81.1 79.5 80.3 85.5 88.9 92.0 109.8 93.6 94.7 101.3
V7.7 97.3 96.1 59.8 100.3 99.9 97.5 95.1 93.2 91.1
107.8 112.4 77.6 76.1 77.8 84.5 88.1 91.1 108.5 91.6 9i.2 101.4
95.8 97.6 95.3 9V. 2 9V. 7 99.0 97.2 95.3 92.5 90.4
108.9 114.7 79.2 77.3 78.9 85.7 89.9 93.0 110.7 93.5 95.4 103.5
98.5 99.3 96.9 100.2 101. 1 99.7 98.6 96.9 94.5 91.9
DEVIATIONS FROM ff P r.lOBI
.1 .1 .5 .2 I.I 1.1 -4 .» --J .0
-.» -.4 6.7 1.8 .i -l.J 2.7 -.5 -2.J -1.6 -.7 .4
-l.l .0 -»4 -.8 -1.2 -.8 -.4 .5 -.5 -.4
.1 .9 .i -».S -».9 -1-1 *.« -9 .6 -.4 .2 1.8
.8 l.S .7 .1 1.2 .4 1.1 2.0 .6 .3
I.I .9 J.6 .2 -.2 -.1 J-0 1.2 1-2 1.0 .7 .9
1.4 .9 I.I .7 1.1 l.S 1.2 1.4 .5 .7
-.5 1.2 .9 .1 1.1 -9 -9 1.6 -.2 -.0
2.1 2.J l.J -2.0 -1.6 .1 4.0 2.2 2.1 .9 1.4 3.1
1.2 2.9 1.9 I.I 2.5 1.6 J.3 3.2 1.8 1.5
TASIE OF OCTAVE (AND POWER LEVELS
* C 11.5 / 63 125 250 500 IK 2K 4H
106.8 US.O »7.5 108.1 101. t 108.0 IO2.1 102. T 101.2 95.4
FM f-l(lf) HETHODOtOGr Put 107.1 111.4 .0 110.4 103.0 107.5 102. B 101. « 101.6 91.*
DEVIATIONS OF
FF MTH FROM FF l.O .4 .O I.T 1.2 -.5 .7 -.9 .4 2.O
47
200 25
9K.2 101
87.3 87
0 315
K 8K
.3 106.3
.5 83.3
9B.4 101.6 106.0
86.3 86.2 82.3
99.0 102.8 106.5
35.4 85.9 81.6
99.6 102.8 106.9
86.3 86.6 82.8
98.7 102.0 106.5
87.0 87.1 83.0
99.1 101. 1 105.6
85.9 86.1 82.0
100.9 104.2 108.3
87.5 87.8 84.0
-l.O -l.J -1.0
.8 l.S .2
1.4
-1.0
.5
-.3
.9
-1.4 -
.5 .6
-.9 -.5
.7 .2
-.4 -.3
.6 -.7
.4 -1.3
2.7 2.9 2.0
.2 .3 .7
8K
89.4
92.7
3.1
400
10K
98.9
79.5
96.1
77.8
98.1
77.0
99.5
78.0
96.5
78.4
98.1
76.0
100.9
79.3
-1.7
-.8
.6
-1.5
-.4
-l.l
-.8
-1.5
2.0
-.2
-------
t»«t Nuttwr
Tablet .k
SlKINI) FlWKH I.KVEL DATA
Co*pre««Jr Output: ISO et»
Engino/Covpreaaor Tyi>«: Rotary »cr«
Caaprciur El»: l.nil.2*«l.40«
• b 100
"£
o
80
SI. S
SIGNAL QUALITY
TAR FIELD 7 F
NEAR FIELD F F
TTTTTTTN
TTTTTTTH
zSO 500 1000 20
ONE-THIRD OCTAVE BAND CENTEX FREQUENCIES IN HZ
NNHNFFFFFFFrF
F F
F F
If 41 NUH8E*. 4
COMPRESSOR SURFACE »«E»»ld.l8 SO. «ET*ES
CONFORHAL SURFACE AREA-14.7} SO. BEIMS
KMtHT ING-LOM f«fOUENC»
HIGH
fto f inn P»l
Kf PXL I
Nf PWL 2
»4F P* 1
NF Pxl 6
M M M
31 NEAR flELO NIC COS 11 IONS.Of tfHICH
F F
F F
11 USEO IN NF1
ueiGMrto SOUND POUEK LEVEL IDS RS l PI COMA in
A
111. 1
114. 3
til. 8
115.4
115.4
114.4
116.8
LIN
Iftt 2
121.2
120.9
121.0
122.1
122.1
124.6
20
so o
99.5
84.0
1-31.0
83.6
99.7
89.5
101.2
85.1
U2.2
87.7
102.2
91.2
104.*
25
610
80.4
101. 0
81.5
102.8
81.1
102.1
88.6
106.4
84.7
104.0
86.9
105.1
90.1
108.0
11.5
800
100.9
85.2
102.5
84.4
101.8
89.4
102.5
86.3
103.7
87.7
102.0
91.1
101.7
40
IK
85.2
102.2
86.0
102.2
84.7
102.5
87.7
101.2
87.2
101.4
•ft.4
102.5
89.1
104.5
50
1.2K
103.1
94.8
103.«
94.9
101.7
97.2
105.1
97.9
105.0
96.4
1O4. 3
98.7
106.4
61 80 100
1.6K 2K 2.5*
116.0 ICO. 4 1O5.2
101.8 106.1 105.1
1S7.1 100.4 10&.7
104.7 107.9 107.2
114.7 99.3 l'.6.1
104.1 107.0 106.1
119.0 103.3 109.1.
107.1 109.1 105.9
118.1 101. » IOJ. !
105.9 109.0 108.4
117.5 102.0 107.7
105.9 109.0 106.3
120.7 105.0 111.0
108.6 110.5 107.1
125
S.IK
115.5
101.4
116.2
102.2
117.6
101.1
118.6
102.8
117.4
101.4
118.0
102.1
120.1
104.0
160
4K
10*.*
96.1
105.1
97.2
105.8
98.0
108.0
98.6
106.5
98.4
107.1
98.7
109.6
99.9
200
SX
109.7
95.7
110.8
96.6
111.7
97.2
111.8
97. S
111.9
97.7
111.2
9t.Q
111.2
98.7
250
6.3K
101.6
96.1
101.9
9&.8
101.6
97.9
107.0
98.7
105.0
98.0
1C5.6
98.7
108.6
99.9
315
8K
103.3
94.0
1C2.9
94.2
102.9
95.0
103.1
95.9
104.1
95.4
102.4
94.9
104.6
97.2
4CO
10K
104.3
90.7
103.3
90.9
102.6
91.8
106.1
92.8
104.5
92.1
104.7
92.0
107.8
94.1
Nf PML I
Nf Ptt. 2
NF PM. J
Nf PKL 6
Nf PM. 7
NF PHI 8
f« FIEIO fVL
H* FIELD NETHOOOLOCr FHL
OF ff ttflH FKON Ff
1.2
.7
2.3
2.3
1.1
1.7
IAM.E
4
113.1
114.6
1.5
1.0 4.1
US
.7 1.9
.2
2.1 9.8
l.T
2.1 5.6
2.7
1.9 1.0
2.7
4.4 l!.5
5.4
OP OCTAVE
X 31
3.1
l.e
2.7
1.1
8.2
5.4
4.1
1.0
6.5
4.1
9.9
T.O
MHO
.5
120.4 87.9
12C.4 .0
-.0
.0
2.8
1.6
2.0
.9
7.0
1.6
1.9
2.8
5.)
1.1
8.T
2.8
POME It
61
116.2
nr.»
1.4
.8
.0
-.S
.3
2.5
1.0
2.0
1.2
1.2
.1
4.1
2.1
LEVELS
111
11*. 2
114.7
-I.I
1.6
.8
-.1
.6
2.0
2.0
2.7
1.9
1.2
1.2
3.5
3.3
250
111.4
HO. 1
-1.1
1.1
.9
.0
1.6
-1.1 -2.1
.3 .7
1.0
1.1
2.1
2.1
1.5
2.1
4.7
*. 8
500
106J
10*. 1
1.1
2.9
2.8
1.2
2.7
1.6
2.7
4.6
4.2
IK
106.
107.
•
1.5
1.9
1.1
.«
4.2
.6
2.6
1.1
2.5
l.O
5.»
1.8
.7
.8
2.1
1.7
3.1
1.4
1.9
2.0
2.5
.7
4.6
2.6
2K
9 110
5 110
t
.0
.0
.0
.9
.9
1.4
1.7
1.6
2.1
2.1
2.1
2.7
2.4
5.2
1.6
4K
101.4
105.5
2.1
1.1
.9
2.0
1.5
2.1
1.1
2.2
2.0
1.5
2.3
3.5
3.0
*K
98.9
102.9
4.0
.1
.7
.0
1.8
1.4
2.6
1.4
1.9
2.0
2.6
5.0
3.8
-.4
.2
-.4
1.0
-.2
1.9
.a
1.4
-.9
.9
1.)
1.2
-l.O
.2
-1.7
1.1
1.8
2.1
.2
1.4
.4
1.3
1.5
3.4
48
-------
Te>t Huiaber 5
Table 5.5
SUUND POtfKK t.KVM. DATA
Conpressor Output: 700 dm
Knglne/ComjirMcor Typ«: Reciprocallog. Dl«B«i, Stand* d
Co»pr«»sor Kile: 1.83x.98xl.50»
120
110
zb 100
90
<*>
I.IH
TEST
"Boa"1 — ' 1600 '
' 4flba '
BKE-TH1RO OCTAVE BRNO CENTER FREQUENCIES IN HZ
SIGNAL QUALITY
FAR FIELD NTT
NEAR FIELD K F T
T T T T T T
N T T T T T
N T
T T
N N N N
N N
N N
F F
N N
F F F F F F F
F F F F F F F
ttSl NUH8ER 5
COMPRESSOR SURFACE AREA*10.22 SO. MITRES
CONFORHAL SURFACE AREA(R-1MI.34.76 SO. MfclHES
Hf iOH ING-inX FREQUENCY
HIGH FREQUENCY
FAR FIELD PUL
Hf PML 1
KF PML 2
IF PHL 3
IF PHL 6
NF PUL »
NF PKl 8
57 NEAR FIELD KIC POSITIONS.OF WHICH 33 USED IN NFl
WEIGHTED SOUND POKER LEVELIDB RE 1 PlCUXAItl
A
108.4
S09.6
JOT. 5
109. 1
109.9
lot.*.
109.}
LIN
119.1
119.8
117.6
118.5
119.9
113.7
119.7
20
500
BS.l
97.7
99.6
98. «
81.1
97.5
82.2
93.1
98. *
99.1
81. b
98. *
83.4
99.5
25
630
8T.9
97.7
100. 1
96.8
90.8
97.7
90.9
98.7
99.1
99.1
90.7
9H.8
92.1
99.9
31.5
800
97.4
99.0
101. *
99. 1
96.0
98. 4
97.4
98.6
100.8
100.4
97.5
98.8
98.7
99.8
40
IK
106.8
99.0
i 10,1
100.4
107.1
98.5
107.8
99.0
1 10.1
100.6
107.7
99.1
108.9
100.2
50
1.2K
102.5
101.3
101.5
103.0
9T.5
100.2
98.9
100. 3
101.2
103.6
98.8
100. I
10O.2
101.5
63
1.6K
106.2
99.6
110.9
100.6
109.6
98.5
109.4
98.6
111.3
101. 1
109.7
98.8
110.8
99.7
eo
2K
1)6.4
100.3
116.1
100.3
114.3
48.6
115.4
98.7
116.3
100. 7
115.7
98.8
116.7
99.8
100
2.5K
106.4
95.6
107.1
95.6
103.2
94.3
104.7
94.7
107.1
95.9
103.9
95.8
106.0
95.9
125
3.1K
111.7
94.3
111. I
93.8
104.3
92.1
106.6
92.7
110.7
94.2
105.5
92.1
107.9
93.9
160
4K
107.1
92.2
109.2
92.1
106.6
90.5
106.5
91.0
109.0
92.4
107.6
90.6
109.6
92.2
200
5K
105.9
89.7
105.7
69.5
103.1
67.8
105.1
68. 5
105.7
89.7
105.4
8t>.6
106.4
89.7
250
6.3K
106.5
90.3
106.5
90.0
105.5
83.1
107.0
68. a
lOt. 8
90.3
107.4
86.7
10S. 1
69.8
315
6K
100.6
89.5
100.5
86.6
98. 0
87.1
98.8
87.5
101.0
88.6
98.8
86.0
99.9
88.7
400
10K
100.6
87.9
96.8
84.2
97.5
82.3
98.5
82.4
9V. 1
84.4
99.5
81.8
99.7
83.6
NF PWL I
NF PM. 2
NF PUl 1
NF PM. 6
NF rm. T
NF PHL I
fHH FIELD P"l
FAR FltLD NETHOOOLOCY Pirt.
OEVUUONS OF ff HETH HoH FF
DEVIATIONS FROM FF f UK OB I
.7
.4
.8
.O
.5
.4
.7
-1.5
-.6
.a
-.*
.6
14.5
1.1
-4.0
-.2
-1.9
.6
13.3
1.4
-J.S
.7
-1.7
I. 8
12.2
1.1
2.9
.0
3.0
1.0
11.2
1.4
2.6
l.l
*.2
2.2
4.0
.9
-1.4
-.6
-.0
-.4
3.4
1 .4
.1
-.2
1.3
.8
3.3
1.4
.>
-.5
1.0
.0
3.3
1.6
.9
.1
2.1
1.2
-1.0
1.7
-5.0
-I.I
-3.6
-1.0
-1.3
2.3
-3.7
-l.Z
-2.J
.2
4.7
1.0
3.4
-1.1
3.4
-1.0
5.1
1.5
3.S
-.»
4.6
.1
- J
.0
-2.1
-1.7
-1.0
-1.6
-.1
.4
-.7
-1.5
.3
-.5
.7
.0
-3.2
-1.3
-1.7
-.9
.7
.3
-2.5
.2
-.«
.3
-.6
-.5
-T.4
-2.2
-5. 1
-1.6
-1.0
-.1
-6.2
-2.2
-}.«
-.4
2.1
--1
-.5
-1.7
1.4
-1.2
1.9
.2
.5
-1.6
2.5
-.0
-.2
-.2
-2.8
-1.9
-.8
-1.2
-.2
-.0
-.5
-1.1
.5
-.0
.0
-.3
-1.0
-2.2
.5
-1.7
.3
.0
.9
-1.6
1.6
-.5
-.1
-.9
-2.6
-2.4
-1-8
-2.0
.4
-.7
-i.e
-1.5
-.7
-.8
-1.8
-3.7
-3.1
-5.6
-2.1
-5.5
-1.5
-3.5
-2.1
-6.1
-.9
-4.3
TABLE OF OCTAVE BAND POWER LEVELS
A C 11. S 63 125 2JO 500 IK 2K
101.« 119.3 107.I 117.0 113.9 109.8 103.7 104.7 103.7
111.3 119.1 .0 116.8 115.9 111.6 106.1 104.1 105.2
z'* -6 .0 -.2 2.0 1.8 2.4 -.6 1.5
4K
97.2
101.6
4.4
IK
94.1
99.3
5.2
-------
TMt
T.ble 5.6
SOUKD FOWEa LCVei. DATA
Corrector Output: 100 cfm
iBflat/Coxpmsor Type: leciprocattot, Dl«««l. St«nd«id
CM«>ret>or Else: 1.52*.67»1.«2«
120
uc
b 100
90
80
TEST e
tJS
'iflofl '—'4800 '—' *6ofl '
6ME-THIRO
SIGNAL QUALITY
FAR FIELD TTTTTTTTTTT
HEAR FIELD TTTTTTTTTTT
TfSI l»UH*t« 6
CiKPSf SS'* SUSFiCS »••[»' 7.24 SO. HETJES
CONFORHAL SURFACE AREA(R-1M)"29.32 SO. METKES
eCTAVE BRNO CENTER FREQUENCIES IN HZ
TTH. NFFFFFFFFFPFF
TMFFFFFF'FFrrFF
29 USED IN
T T
33 HE IB FIELU *IC PUS II IONS.OF .MICrt
vlIGHTIXG-IU» FtFOUfNCT
Hir,n FKEOUENCY
F4P FIELD P*L
NF Pkl 1
M PWL 2
NF P.HI 1
Nf HI 6
NF Put 7
NF PdL 8
A LIN 20
500
1O9.U 120.6 83.0
101.*
109.3 121.0 83.7
102.7
1U8.4 119.5 82.7
101.9
101.0 121.2 Bo.»
102.2
110.* 122.0 84.9
103.B
104.9 120.6 85.6
101. 5
110.3 122.6 6li.4
103.4
25
630
111.3
tD.6
111.1
98.7
111.1
98.3
113.2
VB.5
112.*
99.9
112.3
98.*
EtGHieu SOUND PUWEK LEVELIDB »t
31. 5 »0 bJ 6t 60 100
dUO IK 1.2K 1.6K 2K 2.%
10%. I 89.1 113.6 IOT.O 111.7 I 1 «.. 5
46.3
105.8
9o.l 90.0
VS. 3
107.9 111.
97.0 95.6 96.0 V5.6
105.* 89.0 lU.4 107.5 110.
96.6 95.4 95.6 95.2 96.
107.7 90.4 115.5 109.9 113.
98.* 97.1 96.9 96.5 96.
95.8
1IU.2
96.3
112.1
95.9
107.0 90.5 114.8 109.1 113.1 115.6
98.2 96.8 97.2 96.8 97.1 97.2
107.2 89.9 114.4 109.5 112.5 112.4
98.3 96.5 97.1 96.4 96.t 96.3
109.3 91.9 117.0 111.5 116.2 113.3
99.9 <-8.7 Se.5 98.0 96.0 97.2
U J. *
93.U
111.*
9%.u
108.4
-.5.7
110.1
9>.v
112.2
96.8
109. d
96.7
111.4
97.2
160 200
4* 5K
109.1 106.)
93.0 92.0
109.3 106.9
92.2 91.J
106.6 105.4
92.2 91.4
107.3 107.0
92.1 91.1
110.4 107.9
93.4 92.4
106.6 106.4
91.4 93.5
10?.7 108.4
93.4 92.3
250 315
6.1K. bi".
105.8 106.6
96.1 94.4
106.9 107.0
93.2 91.9
105.0 105. e
94.3 92.5
105.8 106.8
92.8 91.5
107.9 108.0
94.7 93.3
106.0 106.7
92.1 90.8
107.1 107.u
94.1 92.8
4CO
10K
106.8
92.4
106.7
8S.5
105.9
90.1
1U7.8
50.8
106.4
69.2
iat.6
90.8
M PKL 1
NF PriL 2
NF PHI 3
NF PML 6
NF PML T
NF PML a
F»« MUD PML
f»« FIELD METHODOLOGY PML
DEVIATIONS OF fF BETH FROM FF
OEV1ATIUMS FkOK FF 6wL(Q&t
.3
•-.6
-.1)
1.4
-.1
1.3
.*
-1.1
.6
1.*
-.0
2.0
.1
1.3
-.9
. 5
3.2
.8
1.3
2.*
2.0
.1
4.8
2.0
-.2
.1
-.2
1.9
-.1
1.1
1.3
1.0
-.2
3.*
1.3
.7
.7
.3
2.6
2.1
1.9
1.9
2.1
2.0
4.2
3.6
.0
.3
-.1
1.3
l.B
1.4
1.5
.3
1.2
2.8
3.*
-.1
-.1
-.2
1.9
.8
1.2
1.1
.8
1.0
3.4
2.*
.9
-.4
.5
2.9
.5
2.1
.8
2.5
.*
4.5
2.0
.2
-.4
-1.4
l.B
.2
1.4
.8
.8
.3
3.6
1.5
.2
.5
-4.3
-2.*
.6
1.0
1.9
-2.1
1.0
-1.2
1.9
l.J
-.2
-2.0
-.3
.1
1.8
1.0
-.6
.9
1.3
1.*
.2
-.8
-2.5
-l.B
-.9
1.3
.4
-2.5
-1.6
-.4
.4
.6
-1.0
-.9
.7
-.9
1.6
.*
.1
-1.5
2.1
.3
1.1
-2.9
-.8
— 1.8
-.0
-3.3
2.1
-1.4
.2
-4.0
1.3
-2.0
.4
-2.5
-.8
- 1.9
-2.9
1.4
-1.1
.1
-3.6
.4
-1.6
-.1
-2.9
-.9
-2. 3
-1.2
-2.8
1.0
-1.6
-.4
-3.2
.0
-1.6
TA1LE Of OCTAVE BAND POKER LEVELS
A C JUS 6» »2* 2*0 SOO IK I*. ** •»
109.0 120.0 112.3 116.1 116.7 111.0 10B.* tOO.7 100.T 9«.7 99.J
110.1 122.2 112.3 11T.I 120.1 U3.S 110.* 99.6 »«.* 99.5 100.8
l.a 2.* .0 .8 J.* l.» i-0 -l.l -2-1 •• 1-*
50
-------
Toil Humbar 7
T«bl« S.J
SOUND COWER LKVU. DATA
Coepre&sor Output: 160 dm
Enelno/Ccmprettcr Tyj*: Rotary *»
Conpre»sor Sl»«: 2.10x1.28xl.78a
eo
SIGNAL QUALITY
FAR FIELD
WEAK FIELD
•«-THIRD BCVRVE BAND CENTER FREQUENCIES is HZ
1NHNTTTN
FFNNTTHN
T N
T N
T T
T T
N H H N F F
N N H F F F
F F F F F P F
F F F F F F T
F F
F F
TEST NIXICR 7
COMPRESSOR SURFACE AftEA-14.72 SO. METRES
CONFOBMAL SURFACE AREA(R-lH)-42.ai SU. METRES
S7 HEAR FIELD HIC PUS II IONS.OF HHICH 45 USED IN Hfl
«( IbHrlNS-lOM FREQUENCY A LIN 20
HIGH FREQUENCY 500
FA» FIELD PHI 106-9 115.2 82.3
97.0
NF PWL 1
NF PHI 2
NF PM. 3
NF PHL 6
•IF PW. 7
NF PHI 8
107.3 115.6 84.7
98.2
1O7.0 115.6 80.1
97.2
109.0 116.8 82.6
100.2
108.0 116.2 85.0
98.8
108.7 115.5 81.8
99.8
110.4 118.3 84.0
101.6
WEIGHTED SOUND POWER LEVELIOB RE i PICOViTII
25 31.5 40 50 6} 89 100 125 160
630 COO IK 1.2K 1.6K 2K 2.5H 3. IK 4K
79.4 81.5 ,66.8 87.4 97.6 113.3 94.2 94.2 99.8
101.5 95.3 95.6 94.3 93.3 ?3.4 90.5 VI. 3 86.3
82.7
102.2
79.2
100.6
79.5
103.8
Bi.l
102.8
79.5
102.6
80.6
105.2
34.9
96.1
87.5
95.0
82.0
96.1
85.3
97.0
tt.t
96. e
83.2
97.3
90.5
95.9
90.6
95.4
90.7
96.8
91.2
9T.O
90.5
96.8
92.0
97,9
83.7
94.7
83.5
93.5
89.1
95.1
89.4
95.6
88. a
94.1
90.2
96.3
98.5
94.1
98.5
92. S
97.5
93.7
99.1
94.9
96.7
92.9
99.0
94.9
113.9
93.8
113.6
92.9
114.0
93.5
114.4
94.8
112.6
92.7
1 15.5
94.7
94.8
90.9
94.7
90.6
94.7
91.3
95.4
91.7
93.6
90.8
96.1
92.5
94.7
91.5
93.7
90.4
94.4
91.3
95.5
92.4
93.4
90.8
9S.6
92.5
100.5
88.4
99.9
87.3
101.3
87.7
101.3
89.3
100. B
88.3
102.6
88.9
200
5K.
95.5
85.8
96.4
85.5
96.3
84.3
97.3
84.6
97.1
86.4
96.6
83.7
98.6
85.8
250
6.3K
99.6
84. 0
99.9
86.5
100.8
85.3
102.0
85.8
100.4
87.3
101.1
86.2
IOJ.5
87.0
315
an
110.2
82.6
110.2
82.8
110.9
81.3
112.5
82.0
110.8
83.4
111.5
81.5
114.0
C3.2
400
I OK
101.1
76.4
102.0
IS. 8
102.1
76.8
105.5
77.4
102.4
79.5
104. 1
77. J
107.0
78. 5
NF PM. 1
Hf nn. 2
NF PHI 3
NF PM. 6
NF PUL 7
NF Ptt. 8
*»• FIELD PHI
FAR FIELD NF. THOOOLOGtr *M-
DtVIATIONS OF FF KEIM FRON FF
DEVIATIONS FROM FF PUKOBI
.4
.!
wl
.1
%i
.»
.4 2.«
1.2
.* -2.2
.2
t't
1.0 2.7
1.8
.3 -.S
2.8
l.l 1.7
4.6
3.3
.7
-.2
-.9
2.3
J.7
1.3
.1
1.3
1.2
3.7
3.4
.8
6.0
-.3
,5
3.8
1.7
.1
1.5
1.7 3
2.0 ;
.7
.1
.9
-.4
.0
,4
.2
.7
.0
.2
.1
1.3
.4
1.1
-.8
.8
2.0
1.3
1.4
-.2
2.8
2.0
.9
.8
.9
-.5
.4
1.5
1.6
-.9
-.4
1.4
1.6
.6
.4
.3
-.5
.1
1.1
1.4
-.7
-.7
2.2
.6
.4
.5
.1
.8
1.2
1.2
-.6
.J
1.9
2.0
.5
.2
-.S
-.9
-.0
1.3
l.t
-.«
-.5
1.4
.7
.1
.1
-1.0
-.6
1.5
1.0
1.0
-.0
2. a
.9
-.3
.8
-1.5
-1.2
1.6
.6
I.I
-2.1
3.1
.3
•s
1.2
-.7
-.2
.8
1.3
1.3
.2
3.9
1.0
.0
.2
.7
-1.3
2.3
-.6
.6
1.0
1.3
-l.l
3.8
.6
.9
.4
1.0
-1.6
4.4
-1.0
1.3
l.l
3.2
-.7
5.9
.1
I ABIE Or OCTAVE BAND POME* LEVELS
* C 11.5 63 125 250 500 IK 2* 4K IK
1O6.9 115.7 89.9 IU.4 101.7 110.7 105.1 99.9 97.4 93.8 88.1
107.1 116.J «9.5 115.2 104.2 110.4 105^3 99.8 «6.4 94.2 90.9
.2 1.0 -.4 I.I 2.5 -.3 .2 -.1 -1.0 .4 2.8
51
-------
c no
i-
i-
a
> at
fM
"b 100
tM
IK
- O9
b-
J 90
CO
SIGNAL QUALITY
FAR FIELD
NEAR FIELD
TEST Nl
CONPRt '
CONFOR*
IrE ICHTINC-l
H
FAR FIEID P.'l
NF PMt I
M Put 2
NF PUl 1
NF PHI 6
Nf Put 7
NF Pill 8
NF Put 1
NF Put 2
NF PUt 1
NF PUt 6
NF PWt T
NF Put (
FM FlftD PU
M» FIftO Nt
DEVIATIONS Ol
T.Me 'i.e
SHIWD I-OWE* UVtl. DATA
Tect Kiuber 6 CoapreBsor Output: 125 cf«
Enxlne/Conpre»*or lype: Rotary vane, I'-att, (Jul«t«t
CcupreiiBor Size: 1. 78x1. 30*1.85.
• i * • i • • T •- • i • • • i • • i • • i - • i • • i •
TEST •
fi
I.IK
I \ / \ *~WI
'ai'-s' ' eb"' ' iis ' ' iit ' ' sdff ' ' lobo ' 'zobo' '.oba eoas
6NE-THIRO OCTOVE BPNO CENTER FREQUENCIES IN HZ
*BE« s *•> Htm FIELO MIC PQSHION5.0F WHICH 41 USED IN NF
SDR SURFACE ««f»«13.71 SO. WtRES
1AL SURFACE AREA(K-lK)»*l.i9 SO. HEIR6S
UEIGHUD iOUNU POtiFD LEV El (08 RE 1 PICOUATII
OK FREOUENCV A LIN 10 25 il.> *0 50 65 80 100 US 160 ^00 i
103.1 IU.? 82. J 83.0 8S.6 85.5 90.2 10«.2 91. •> 91. « JjO.6 93.'. 93.2 1(
9S.S 92.2 "»i.T 92.1 89.9 -52.7 90.2 86.8 »8.1 8*. 9 82.9
101. 3 112.8 77.1 7V. B 86.9 84.6 91.3 110.2 93.3 91,9 IOI.J 90.9 V3. 7 1
96.9 93.5 9*.l 92.4 90.4 93.4 90.6 86.8 88.1 85.0 82.3
103.0 112.2 77.9 79.3 85.5 82. B 90.1 109.0 92.3 91.1 101.5 fc9.O 92.8 1
96.5 92.7 93.9 90.5 89.8 94.0 69.5 J5.9 87.2 84.2 81.0
103.9 113.5 76.7 80.2 86.6 83.9 91.2 110.6 93.3 91.1 102.5 90.4 94.4 1
97.5 93.3 94.6 93.0 89.3 90.7 90.1 86.5 88.0 84.4 81.8
104.* 113.8 78.5 81.2 66.8 85.5 92.2 110.9 94.2 92.8 102.2 91.8 94.6 1
97.8 94.4 94.1 91.3 91.1 94.5 91.5 8T.8 89.1 B5.9 81. 1
101.1 112.7 76.2 80.0 86.2 83.1 90. S 109.8 92.5 90.9 101.8 50.2 93.5 1
96.9 92.6 93.7 92.3 89.4 90.4 90.0 87.1 68.4 63.5 81.3
105.4 115.1 77.8 »1.4 07.9 85.2 92.7 112.2 94.8 92.6 103. » 91.6 95.8 1
98.8 94.5 95.7 94.5 90.5 92.1 91.* 87.8 89.3 65.6 83.0
DEVIATIONS FROM FF PMLIDB)
1
50 315 400
3K 8K IOK
'6.9 96. J 97.7
15.4 81.6 76.4
)7.1 96.4 90.0
!5.5 81.0 76.3
X..9 96.6 98.3
14.6 79.6 75.4
>8.6 98.1 99.3
35.2 80.2 75.0
J9.4 97.3 99-0
B6.5 81.9 77.4
37.8 96.8 98.7
34.2 80.0 74.1
10.2 99.5 100.8
B6.3 81.4 76.2
-.1 -.0 -4.1 -3.7 -.» -Z.7 -.1 -.2 .4 -.3 .9 -1-4 -.4 .0 .6 .6
1.0 .5 .2 -1.6 -.1 UJ -.' — » -•» -•» -»•» — " -*-° -»-°
.1 l.l -S.J -Z.B 1.0 -1.6 1.0 1.4 1.4 -.1 1.9 -.0 1.2 1.7 U9 1-6
2.0 1.1 .9 .9 -.6 -2.0 -.1 -.1 -.1 -.5 -1-1 --Z ->•* ->•*
l.J 1.6 -».» -1.8 1.2 .0 2.0 l.T 2.J 1.4 1.6 1.4 1.4 1.5 1.1 1.1
.2.3 Z.2 1.* 1-2 1.4 1.8 1.1 1.0 1.0 1.0 .4 l.l -3 1.0
-.0 -S -*.B -1.0 .6 -i.* .* .6 .* -.5 1.2 -.2 .3 .9 .6 1.0
1.4 .4 -.0 .2 -.5 -2.1 -.2 .3 .3 -1.4 -1.6 -1.2 -1.6 -2.1
«.! Z.I 2.C 2.4 .6 -.6 1.2 1.0 l.Z .T .1
IA84.E OF UCTAVC BAND POUER LEVELS
A C 11. S 61 125 250 500 IK 2* 4K 8K
L 101.1 112.0 (9.6 109.1 101.4 107.4 100. i 96.9 «5.1 90.6 (7.1
rHoootocr put 104.4 111.4 .0 112.1 103.3 106.6 101.9 97.: 95.4 94.1 90.6
: ff ME1H FROM fF 1.1 1.4 .0 2.8 1.9 -.( 1.1 .4 .1 1.5 1.1
52
-------
SOUHU POWER I.CTKL DMA
T»«t «u«b«r 9 Cocpreiiior Output: 365 ct«
toglne/Coapre.Bor Type: »ot«ry ..„«, Olexl, (JuIK.d
Co«sr«««or 81u: 3.«*1.»J»2.U.
w "0
w
•e »-
o %
|^ too
W kJ
o*
rfg
h, *""
1 80
•0
SIGNAL QUALITY
PAR FIELD
NEAR FIELD
TESt NUMB
CONPRE SSOf
CONFCRMAL
MCICHI ING-LOU
HIGH
FAR FIFLO PML
NF PML 1
NF PML 2
NF PwL 3
NF PUl 6
NF PML 7
NF PML 1
NF PML 1
NF PML 2
NF PUL 3
NF PWl 6
NF PML T
NF PML «
*AR FIELD PML
FAR flFlO METHOD!
DEVIATIONS Of M
TEST •
0
UIN
' ins1"" "~ BS iis ' ' jiu ' ' sdfl ' ''iflbo ' ' zcbo *"™'~4'3o'o~' — "Tofor1 — -1 ' — '
ME-TMIRO eCTBVE BRNO CENTER FREQUENCIES IN HI
•* * 63 NEAR FIELD MIC POSITIONS. OF HM1CH 63 USED IN NF1
SURFACE AREA>30.U SO. KETRfS
SURFACE AREA(R-1M).67.06 SO. METRES
WEIGH! to SOUND POWER LE'/tLlDB RE 1 PICOKAfTI
FBEOUfNCY A LIN 20 25 31.5 40 50 63 80 100 125 160 200 250 315 400
FREOUtHCV SOO 63O 800 1* 1.2K 1.6K 2K :.5K 3 . IK 4K Sit 6.3K 6* I OK
98.7 104.5 81.6 83.7 93.8 89.2 88.9 94,0 91.7 91.9 97.0 89.6 92.3 95.1 91.1 92.6
89.4 8S.3 86.0 88.6 89.3 90.2 89.2 89.3 88.0 84.1 83.3 83.9 79.9 78.6
<8.l 10S.1 82.0 84. D 95.3 89. B 89. B 95.2 92.6 92.5 98.1 92.0 92.5 97.0 U9.7 91.1
90. S 81.7 87.5 88.2 88.4 99.3 88. S 87.3 85. B 82.4 80.5 80.5 77.7 75.1
97.1 104.3 81.6 84.0 95.6 88.8 89.1 96.1 92.0 91.4 97.7 92.5 91.8 94.5 86.4 89.4
H9.6 86.3 85.8 87.5 87. « 88.5 88.4 85.7 84.7 81.2 79.3 79.5 76.9 75.3
97.9 106.2 82.4 85.5 99.2 90.1 90.0 96,0 92.3 93.0 101.1 93.3 93.0 95.9 87.9 91.0
91. i 87.6 86.4 87.1 88.3 89.5 88.4 86.1 86.0 82.4 80.7 80.9 18.1 76.3
»».0 105.9 83.4 85.6 96.1 90.7 90.6 96.0 93.4 93.3 9S.9 92.8 93.4 97.8 90.5 91.9
91.3 88.6 88.4 89.1 89.2 90.1 69.3 88.1 86.6 83.3 81.3 81.4 78.5 76.0
»».* IO4.9 82.0 84.5 97.2 88.7 88.6 94.6 91.9 92.1 100.0 92.6 92.2 94.5 86.4 B9.4
89.9 86.1 85.1 85.8 86.7 «7.9 86.9 85.0 84.9 81.4 79.3 79.7 77.3 75.6
»».9 1O7.2 83. J 86.4 IOC. 2 91. 0 VI, 0 97.2 93. J 9*.0 1O2.2 9».2 93.8 96.7 S8.7 91.9
9.2.4, BB. 5 87.3 SS.O 89.3 90.6 89.4 87.0 86.9 83.3 81.7 81.8 79.0 77.2
DEVIATIONS FROM FF PULIDBI
I.I -.6 1.5 -.4 -.9 -.9 -.7 -2.0 -2.2 -1.7 -2.8 -3.4
-».» -.2 .0 .3 1.8 -.4 .2 2.1 .t -.5 .7 2.9 -.S -.6
-2.2 -3.5
-4.7 -3.2
.2 -1.0 -.2 -l.l -1.5 -1.7 -.8 -3.6 -3.3 -2.9 -4.0 -4.* -3.0 -3.3
1*9 »3 2.* .5 -.1 -.1 .1 -l.Z -U* -.8 -2.0 -2,5
• S -2.2 -.9 -2.8 -2.6 -2.3 -2.3 -4.3 -3.1 -2.7 -4.0 -4.2
.t l.T 1.7 2.7 6.4 1.1 2.1 3.2 1.6 2.1 5.2 4.6 1.5 1.6
TABLE OF OCTAVE BAND fOiied LEVELS
* C 11.5 63 12$ 250 500 IK 2K 4K 8K
98. T 104.6 «5.4 96.* 98.1 97.* 15.3 93. 0 94.4 90.4 B6.2
310GV Put 99.9 10*.* 95,3 98. « 100. 0 99. J 96.9 «2.l VI. • 91.0 B8.4
MtIN FROM M U2 .« -.1 2.0 1.3 1.4 1.6 -. » -2.6 .6 2.2
53
-1.8 -2.3
-.6 -.7
-1.4 -2.6
-4.7 -3.2
-2.6 -3.0
-2.4 -.7
-.9 -1.4
-------
SOUND POWER U:VEI. DATA
Tc*t N tuber 10 Compressor Output: 900 cfm
En«tne/C41.92 SO. METRES
CONFORMAL SURFACE AREA (R-1HJ-S4.3* SO. METRES
95 NEAR FIELD MIC PUS 11 IONS.OF MMICH 13 USED IN NF1
Wt-IGHTlNG-LOW FREO'JtNCT
HIGH FREQUENCY
FAR FICLO PWL
HF PHI 6
MF PM. 7
NF PM. I
WEIGHTED SOU1D POWER LEYELID8 RE 1 PICOMATTI
A
1O4.B
104,6
105.8
10*. 2
IDS. I
102.8
101.?
LIN
109.0
109.5
1 10.2
109.1
110. 0
ioe.8
110.0
20
500
•55.7
95.5
98.7
95.7
101.6
46.0
99.0
91.4
»9.1
96.4
99.1
92.*
99.9
«4.2
25
630
90.2
91.6
94.4
91.9
97.7
94. U
91. 8
91.2
94.7
94.5
90.8
V2.4
92.6
93.9
31.5
600
97.4
»5.1
99.3
95.6
99.8
96. U
99.9
93.6
99.7
St.. 2
96.2
92.6
100.6
94.5
4C
IK
94.3
96.9
95.6
95.8
96.1
97.4
95.5
94.1
95.9
96.4
94.4
92.7
96.3
95.2
50
1.2K
93.4
95.1
94.9
94.9
94.9
97.1
94.3
94.6
95.3
95.6
93.7
93.?
95.2
95.7
63
1.6K
9S. 7
95.0
97. O
95.0
96.1
95.9
96.8
95.1
97.4
95.6
95.2
93.5
97.7
96.2
80
2K
-------
Tral number 11
T.Me 5.11
SOUND I'llWrK LEVEL BATA
Co«pr««0or Output! 100 cf«
Enilne/CoKpreuor Type: Rotary •crew.
CoapreKor 81i«: 1.78*1.22*1.37.
10
SIGNAL QUALITY
FAR FIELD
HEAR FIELD
50 500 tOOD ZO
ONE-THIRD eCTflVE BAND CENTER FREQUENCIES IN HZ
tl H
r N
TTT1TTTTT
TTTTTTTTT
TEST NUKBER II
COMPRf SSOR SURFACE AREA.10.39 iO. HtlRfS
CONfORMAL SURFACE AREA(R-IH)-3*.71 SO. KEIRES
NFICHTING-LOW FREQUENCY
HIGH FREQUENCY
Fift FIELD PHI
IF PWL I
NF PWL 2
NF PM. 3
NF PWt 6
NF PWL 7
NNHNFFFFFFFFFF
NHNKFFFFFFFFFF
39 NEAR FIELD MIC POSITIONS,OF WHICH 33 USED IN NFl
4
107. T
108. Z
108.2
110.0
109.2
109.5
m. 6
LIN
119.0
119.9
119.9
122.)
120.9
III. I
12). 9
20
500
10.2
98. 1
eo.9
99.0
75.*
91.0
81.7
100.1
81. S
99.9
SO. 5
99.7
83.4
101.5
WEIGHTED SOUND POKER LEV EH Ob RE 1 PICOWATT)
25 11.5 40 50 tl 60 100 125 160
6)0 600 IK 1.2K 1.6K 2K 2.5K ). IK *K
11.2 H3.0 88.2 9U.2 111.0 117.0 9«.8 101. 1 109.1
96.9 96.6 96.5 96.) 97.6 100.5 91.8 93.0 92.3
eo.4
97.9
76.3
97.2
81. 6
98. »
»l.l
99.0
SO. &
96.)
03.5
too. i
«2.6
97.9
•0.0
97.7
83.1
98.8
I).)
98.5
82.0
98.5
»».6
100.}
88.3
96.5
86.4
96.4
88.)
97.7
89.0
97.6
87.7
97.)
89.7
99.2
90,*
96.9
89.6
97.0
92.0
97.2
91.3
97.9
91.1
97.8
93.6
98.6
110.7
98.3
110.7
98.9
11). 2
100.1
lil. 6
99.)
112.0
99.7
11*. 9
101.7
lie. e
101. 0
118.8
101.3
121.*
103.5
119.7
102.0
120.5
102.*
123.1
105.1
100.1
9?. 0
100.0
91.6
102.2
92.*
101.1
92.9
101.1
91.9
103.9
9). 7
10). 3
93.2
103.8
92.9
105.8
9). 9
10*.*
9«.l
10S.1
9). 2
107.*
9S.3
109.7
92.2
110.1
92.5
112.5
9*.)
110.8
93.2
111.*
93.2
11*. 1
95.8
200
5X
105.*
92.5
106.7
92.0
106.5
92.*
107.2
9*.*
107.8
92.9
106.6
9).)
108.8
95.9
250
6.3X
10*. 2
94.0
104.6
9*. 3
10*. 6
93.9
106.2
96.*
105.8
95.)
1O6.*
95.7
107,7
98.0
115
9K
10*. 7
92.8
10*. 6
93.6
104.9
9). 2
106.1
95.7
106.*
9*. 6
105.9
95.0
107.7
97.3
400
10K
97.1
88.1
97.9
85.3
97.1
85.8
100.7
87.5
98.8
86.3
99.9
87.2
102.)
89.0
DEVIATIONS FRON FF PMLIOBI
NF P* 1
NF PM. 2
MF PM. )
NF PM. 6
NF PM. T
NF PM. B
fAR FIE1D PHI.
FAR FIELD H
-------
tut Inker IS
T«ble > .u
SOUHIl IIIWKIt I.EVKt DATA
Coapr«BBor Output: 175 cf»
Englno/CoDgireaBor Type: Rotary ftcrev. G««. Quieted
Coupre.sor SU«: 2.70»1.29«1.«3«
120
110
fa 100
SIGNAL QUALITY
FAR FIELD
NEAR FIELD
ONE-THIRD 8CTSVE BfiKO CENTER FREQUENCIES IN HZ
7 N
F P
T T
T T
NNTNNNHF
MNTNUNNN
NFFNPFFFFF. FFF
HNFNNFFFFFFFF
lESF NUMBER It
COMPRESSOR SUKHCt A«CA«14.B5 SO. METRES
CONFOHMAL SURFACE AREA(R-1M).42.61 $0. MEIRES
47 NEAR FIELD NIC POSIT IONS.OF ml CM 41 USED IN NFl
KfICHTINC-lOW FREQUENCY
HIGH FREQUENCY
F" FIELD PWL
Hf PM. I
NF PM. f
liF PW. I
Kf PM. 6
NF PM. 7
NF PM. a
» LIN
101.1 III.4
101.1 112.B
100.6 112.6
101.1 111.5
102.0 111.*
100.8 112.1
102.4 114.9
20
500
>2. a
91.6
89.4
91.7
82.6
91.5
(2.9
91.3
90.1
94.6
82.6
92.1
84.0
94.4
WEIGHTED SOUND POWER LEVELIDg Rt I PICOVATI)
25
610
01.0
92.5
88.4
»2.9
82.4
92.5
Bl.O
92.6
B9.1
91.8
82.6
92.0
B4. 1
91.7
11.5
800
84.8
91.9
88.7
92.0
85.8
92.1
66.2
92.1
89.5
92.9
86.5
91.6
87.1
91.2
40
IK
90.8
90. «
92.1
90.8
90.6
90.1
91.1
90.6
93.1
91.7
90.7
90.4
92.2
91.8
50
1.2K
8V. 1
88.1
90.5
B8.9
89.5
88.0
90.1
88. 5
91.1
89. B
89.9
as. a
91.1
B9.6
61
I.6K
100.2
88. J
102.4
• 8.3
101.8
88.2
102.2
88.5
101.1
89.8
100.7
88. a
101.7
89.6
80
2K
111.2
90.0
112 .9
89. B
111.0
88.5
114.0
89.6
113.9
90.7
112.2
89.5
115.5
90.7
too
2.5K
92.7
89.1
91.6
88.8
"2.1
88.6
92.5
89. a
94.5
89.7
91.9
89.7
91.7
90.9
125
3. IK
12.8
94.9
91.5
94.1
91.8
94.5
92.2
96.4
94.1
95.0
91.7
95.7
93.3
97.4
160
4K
*•}.!
85.0
98.4
84.8
96.7
81.9
97.0
84.4
99.2
85.7
97.4
84.1
96.1
85.5
200
5K
92.4
84.9
94.7
82.4
92.1
62.1
91.4
81.8
95.4
81.4
92.9
81.2
94.6
82.9
250
6. IK
94.9
86. 2
96.1
83.7
93. i
84.2
94.0
85.2
96.9
84.7
94.3
84.0
95.2
86.1
115
6K
92.3
81.8
92.7
80.6
92.2
81.5
92.4
81.0
93.6
81.8
91.5
60.4
91.6
82.2
400
I OK
93.8
79.1
93.6
76.6
93.2
77.8
91. 1
75.6
94. 7
77.8
91.3
74.2
94.2
76. a
NF PH. |
MF PM. 2
NF PM. 1
NF PM. 6
NF PW. T
NF PM. I
F»« FIELD PML
F«R FlflO MEIHOOOLOCv Pill
DEVIATIONS OF FP MEIM FROM FF
DEVIATIONS FROM FF
.0
-.5
.2
.9
-.3
1.3
1.4 6.6
.1
1.2 -.2
-.1
2.1 .1
-.3
2.4 7.3
1.0
.» -.2
-.«
3.5 1.2
.6
5.4
.4
-.6
.0
-.0
.1
4.1
1.1
-.4
-.»
t.l
1.2
3.9
.1
.2
1.4
.2
4.7
1.0
I.T
-.1
2.5
1.1
1.5
-.1
-.8
.1
-.3
2.1
.8
-.1
"•*
1.4
.9
1.4
.8
-.1
1.0
.4
2.2
1.7
.B
.T
2.2
1.5
2.2
.5
-.1
2.0
.2
1.1
1.5
.5
.5
1.5
1.3
PULIOB1
1.7
-.2
-1.5
2.B
-.4
2.7
.7
1.0
-.5
4.1
.7
.9
-.5
-.7
-.2
.5
t.B
.4
-.*
.4
1.0
1.4
.7
-.8
-.4
-.6
1.5
1.5
.1
•rl.l
.B
.5
2.5
-.7
-.2
-1.1
-2.1
-.6
.1
.7
-1.7
-.7
-1.0
.5
2.3
-2.5
-2.6
1.0
-3.1
3.0
-1.5
.5
-1.7
2.2
-2.0
1.2
-2.5
-2.0
-.9
-1.0
2.0
-1.5
-.6
-2.2
.1
.1
-.1
-1.2
— .6
-2.1
-.4
-2.8
.8
-2.0
-1.3
-1.4
.8
-1.6
-.2
-2.5
-.6
-1.1
-.7
-1.5
.9
-I.I
-.5
-4.9
.4
-2.1
!«BIE OF OCTAVE BAND POWER LEVHS
• C 11.5 63 125 250 500 IK 2K
101.1 III.* 92.1 111.6 lOO.B 98.3 96.1 95.1 94.0
10J. 7 115.0 «2.2 115.0 102.2 9*. 7 9S.7 94.6 95.4
2.6 1.1 -.1 3.4 1.4 .4 1.6 -,9 1.4
56
4K
95.7
9)7. B
2.1
•K
88.7
92.4
1.7
-------
tzo
d n°
hJ
_J
•C 1-
IS
••N
|"b 100
V) W
s:
u a
8 -
•0
SIGNAL QUALITY
FAR FIELD
NEAR FIELD
TFST NUMB
CQWRE'.SO
CONFORMAL
HE IGHTING-lOW
HIGH
(1C FIELD P«L
M PM. 1
Nf PWL J
MF PM. 1
NF Put 6
Nt- PHI T
NF F«. 6
•IF PW. 1
NF PM. 2
NF PM. 1
NF PM. 4
NF PM. T
Hf PM. I
F»« FIELD rut
FA* FIFIO HETMO!
DEV 1*1 IONS or F
T.*l« 5.13
SOUND POKKK LKVtl. DATA
Test Kuaber 13 Conpreasor Output: 175 cf»
Engine/Compressor Type: Rotary screw. Diesel. (Juleted
Compressor Stie: 2. 70»1 . 29.1 . t )»
TEST 19
0
LIN
/ \ A-WT
'si'.S'" ' fci ' ' ifa ' ' jiu ' ' Swfl ' '" iobo ' 'zobo ' • 4t-bo sobs
ONE-THIKO OCTRYE BUND CENTER FREQUENCIES IN HZ
(ft 1} *7 WFAR FI€LO MIC POSITIONS. OF rfHlCH 43 USED IN NF1
« SURFACE »«t»-l<,.«'i SU. HETRFS
SURFACE AREA(R=1M)«*2.6J SO. MF.TPES
«ICHTtD SOUND POWER LfVELIOS «E I PICOi<»Trl
FRf&UE-iCV » LIN JO Z» Jli> *0 io 6J 80 100 125 160 200 250
IOU* lOft.B »0.» 80.* 81. 7 ST. 7 68.2 9J.S 10*. 2 87.7 B8. J It,.
9J.U 90.6 93.5 9*. 3 91.0 VO.O 90.6 VO.l 92.9 88.3 66.1 85.
JOl.l 107.2 83.0 80.5 82.5 89.0 88.7 9*. 1 10^.7 88.* 89.1 92.9 9*. 2 97.
93.* 90.7 93.7 9*.l 91.1 90.* 9O.B 38.6 90.3 87. O 63.0 82.
V9.1 105.5 77.9 77.0 81.* 08.8 88.7 93.1 103.5 i5.6 86.6 93.1 89.5 93.
90.5 88.9 93.* 92. C 89.2 88.7 88.* 85.9 88.5 85.2 80.9 81.
99.2 105.6 79. J 79.2 83.0 9O.O 89.7 92.7 103.0 66.8 86.1 9*. 1 91.8 95.
90.1 89.1 93.1 92.0 89.3 38.9 68.* 86.2 88.* 85.0 80.6 81.
10*. 0 108.1 81.0 81.3 63.5 89.9 89.6 95.1 1 05. 7 89.2 89.9 93.7 9*. 9 98.
9*.* 91.6 9*. 6 9*. 9 92.0 91.3 91.7 89.7 91.3 88.0 8*.0 83.
99.* 105.6 19.1 78.9 81.9 89.6 89.* 92.5 102.7 87.3 88.2 93.1 91.1 93.
90.* 89.3 93.5 92.8 89.5 89.* 68.9 87.* 88.4 86. 0 80.9 80.
100.3 106.8 60.5 «0.5 8*. 3 91.2 90.9 93.9 10*. 2 88.0 89.2 95.1 93.0 96.
91.2 90.2 9*. 2 93.0 90.* 90.1 89.6 87.3 89.6 86.2 62.0 82.
DEVIATIONS FRON ff PWLIDB)
.» .1 .1 -.2 .1 .* .0 -1.3 -2.6 -1.3 -3.1 -2.
-2.> -l.l -2.S -3.* -.5 I.I .5 -.* -.7 -2.1 -1.5 1.2 -3.* -2.
-2.S -1.7 -.1 -2.3 -1. 8 -1.3 -2.* -*.2 -*.* -3.1 -5.2 -*.
-2.2 -1.2 -1.2 -1.2 I.) 2-3 .5 -.8 -1.2 -.9 -.2 2.2 -l.l -I.
-2.9 -I.S -.» -2.3 - .7 -l.l -2.* -3.9 -*.S -3.3 -5.3 -*.
315 *00
6K iOK
S 8"». 8 8B.O
* 83.2 77.9
* 90.3 88.3
7 60.0 7*.*
8 67. 1 87.0
2 78.* 72.9
0 66.6 88.0
1 78.0 72.5
Z 91.1 69.2
7 81.0 75.*
9 86.5 88.1
9 76.6 72.0
1 S9.6 89.1
2 79.1 73.7
9 .5 .3
7 -3.2 -3.5
7 -1.9 -1.0
2 -4.8 -5.0
5 -1.2 .0
3 -5.2 -5.*
I.* 1.0 l.l .6 .0 1.3 .9 -.* -»-* -.3 -2.1 -1.7 -?-2 -2.5
-2.0 -1.2 -l.l -I.S .2 1.9 .2 -1.0 -I.S -.* -.1 1.2 -1.8 -2.6 -1.3 .1
-2.6 -1-3 -.0 -1.5 - .5 -.6 -1.9 -2.7 -4.0 -2.3 -5.2 -4.5 -*.6 -5.9
-l.l -.0 .1 .1 2.6 3.S 2.7 .* -.0 .3 .9 3.2 .1 -.* --O l.l
-l.« -.* .T -l.l -.6 .1 -1.2 -2.8 -3.3 -2.1 -*.l -3.2 -*.l -*.2
T»»IF OF OCTAVE CMiD POHEP. LEVELS
A C 31.5 6) 125 250 500 IK 2K *K •"
101.* 107.J §9.1 IO*.T 9*.S 9».7 »S.« 97.9 95.1 94.8 »7.9
XllDGY PUL 103.5 101.2 .0 10*.l V6.0 98.* 96.9 97.4 94.6 96.0 42.1
f NHH FRO" FF J.I -.1 .0 -.» l.» -••> l.l -.» -.* ••* *-*
-------
T.ble VU
SUUND FOVfK LKVKL DATA
ll« CoBprrv&ur Output: 185 cfa
Englne/Conpresaor Typet Rot.ry screw. Ore.el. sr.nd.rd
Compressor Slie: 2.70«1.29xl.«)«
KU
•£ *-
M *-
Ot IT
S"fa 100
5«
« 80
•0
SIGNAL QUALITY
FAR FIELD
TEST 14
, A
A *~WT
/ ^AV"~V^V
jl.S 63 125 250 500 1000 2000 4000 8000
ONE-THIRD OCTAVE BRNO CENTER FREQUENCIES IN HZ
UM hU«»E« 14 47 NEAR FIELD NIC POSITIONS. OF HHICH 43 USED IN
COMPRESSOR SURFACE ARfA«14.»5 SO. METRES
CONFORMAL SURFACE ARtA ( R=1M) •<• 2.6 > SO. METRES
HEIGHT ING- LOU
HIGH
FAR FIELD PHL
Xf PUL 1
NF PUL 2
NF PHI )
NF PHI 6
NF PUL 7
NF Put 8
NF PUL 1
NF PUL I
NF PUL 3
NF PUL 6
Mf f«L T
NF PHL 1
FAS FIELD PUL
HEIGHT tO SOUND POWER LEVELIDB RE 1 PI'.OKtTTI
FREOUEHCY A LIN 20 25 >1.5 40 50 63 60 100 125 16C 200
FREQUENCY 500 630 800 IK 1.2K 1 .6K 2K 2.SK 3. IK 4K 5K
99.) 104.5 85.6 79.0 81.4 88.4 91.9 90.5 S9. 3 89.1 88.7 92.8 90.8
88.9 90.2 90.6 91.3 91.6 88.7 6C.8 86.) 88.4 84.0 82.4
•»9.4 IDS. 2 89.3 65.6 85.4 89.8 93.8 91.5 100.1 90.0 90.1 94.7 91.9
89.3 90.4 41.0 90.9 91.6 89.5 88.9 86.) 88.5 84.6 82.2
98.7 104.2 86.7 79.5 82.1 88.8 94.1 91.4 99.7 87.9 87.0 91.8 89.2
90.0 90.1 90.7 90.3 91.3 89.0 87.8 85.) 87.7 83.2 79.7
99.0 104.4 86.9 80.2 81.1 89.7 94.0 91.3 100.0 88.7 87.1 90.6 90.3
89.6 90.2 91.1 90.5 91.4 89.6 88.4 86.2 87.7 83.3 80.2
100.4 106.2 90.1 86.3 86.2 90.6 94.7 92.7 101.3 90.8 90.9 95.5 92.7
90.* 91.* 92.0 92.0 92.6 90.5 89.8 87.2 89.4 85.5 83.2
49.2 103.7 87.1 80.2 82.3 89.5 94.9 91.2 99.6 89.0 88.1 90.4 90.0
90.0 90.2 90.7 90.4 90.9 89.6 88.5 85.9 88.0 83.7 80.1
100.2 105.6 88.1 81.* 84.2 90.8 95.0 92.5 101.3 89. : 88.3 91.8 91.5
90.7 91.3 92.2 91.6 92.5 90.8 89.5 87.4 88.8 84.4 81.3
DEVIATIONS FROM FF PHI (OBI
-.6 -.3 1.1 .5 .7 .* 2.2 .9 .4 -1.2 -1.7 -1.0 -1.6
I.I -.1 .1 -1.0 -.3 .3 -1.0 -1.0 -.7 -.8 -2.7
-.3 -.1 1.3 1.2 1.7 1.3 2.1 .a .7 -.* -1.6 -2.2 -.5
.7 -.0 .5 -.8 -.2 .9 -.* -.1 -.7 -.7 -2.2
I.I 1.7 4.5 7.3 4.8 2.2 2.8 2.2 2.0 1.7 2.2 2.7 1.9
l.S 1.2 1.4 .7 1.0 1.8 1.0 .9 1.0 1.5 .8
1. 1 .0 .1 -.9 -.7 .9 -.3 -.4 -.4 -.3 -2.3
.9 1.1 2.5 2.4 2.8 2.4 3.1 2.0 2.0 .7 -.4 -1.0 .7
1.8 1.1 1.6 .3 .9 2.1 . .7 1.1 .4 .4 -1.1
TABLE OF OCrAVE (AND POME* LEVELS
* t 31.5 63 125 250 500 IK 2K *K IK
99. 3 104.7 119.6 100. S 95.* 97.6 94.0 96.0 42.* 90.5 (5.6
e
UK
HH
250
6.3K
93.9
83.4
94.3
83.2
91.6
81.3
92.1
82.2
95.0
84.1
91.8
81.8
93.2
8). 3
-2.3
-2.1
-1.8
-1.2
l.l
.7
-1.6
-.7
-.1
315
8K
93.1
80.4
93.5
82.1
90.5
76.8
91.0
77.2
94.)
82.9
90.8
76.7
92.1
78.4
1.7
-2.6
-3.6
-2.1
-3.2
1.2
2.5
-3.7
-1.0
-2.0
400
10K
88.4
75.1
91.2
77.6
67.7
69.9
88.)
70.6
92-0
78.4
88.6
70.4
89.4
71.8
2.5
-.7
-5.2
-.1
-4.5
3.6
3.)
.2
-4.7
1.0
-3.3
FAR FIELD KETHDOOLOCr rui IO0.9 105.1 .0 101. 0 97.3 96,8 96.1 94. T 93.3 92.2 92.3
DEVIATIONS OF FF
METH FROM FF 1.6 .4 .0 .5 1.9 '.* 2.1 -1.3 .5 1.7 6.7
58
-------
Te.t »u»b«r 15
Table 5.15
SIIUKI) riWER LKVtL DATA
Cofl^>re*£ur Output.: 175 cf»
Knglnc/Compressor Type: Rotary cere*. C*«, Standard
Co«j,r. 0 86.4 IDS.) 117.8 9*. 9 105.1 113.4 106.4 105.1 103.1 101.3
102.5 98.9 19.2 97.9 'vi.l 98.5 99.0 93.6 95.5 92.1 89.4 39.8 61.7 84.3
NF PWl I
NF P«l 2
NF PHI i
NF P* 6
NF PUL 7
NF PHI 8
109.8 120.0 78.9 79.0 82.0 68.4 87.5 107.1 118.7
101.9 100.4 100.6 100.2 98.1 99.4 99.3
110.1 119.8 78.S 78.5 81.9 87.9 86.5 1O5.8 117.)
105.1 100.2 V9.9 99.6 98.1 100.0 100.1
111.2 121.3 79.4 78.9 82.1 88.7 87.7 107.5 119.1
106.6 101.6 100.5 100.4 98.6 100.3 100.2
110.7 120.8 79.7 79.9 82.8 C9.2 88.} 107.8 119.3
104.? 1O1.2 101.5 101.1 98.9 100.3 100.2
110.7 120.6 79.3 79.0 81.4 88.7 88.0 107.1 118.7
105.8 101.1 100.2 100.2 98.9 100.1 100.0
95.4 104.3 113.9 106.7 106.4 103.6 102.9
95.1 97.5 93.7 91.2 90.9 88.2 81.0
95.3 105.5 115.1 106.0 107.4 104.2 102.4
95.1 97.2 93.9 91.3 91.4 88.9 85.7
96.1 106.7 116.4 109.3 109.0 105.7 105.6
95.7 97.9 94.3 91.3 91.9 89.0 85.2
96.3 105.5 115.1 107.7 107.3 104.5 103.8
95.9 98.3 94.5 92.0 91.9 89.1 U4.9
94.7 106.0 115.7 108.5 108.6 104.5 104.2
95.0 98.1 9;.7 91.1 91.6 89.3 84.6
112*5 122.7 80.7 80.0 83.3 90.0 89.0 108.9 120.5 97.5 108.0 117.7 110.7 110.3 107.1 107.2
107.6 102.9 101.7 101.6 99.8 101.7 101.5 96.9 99.1 95.5 92.5 93.1 90.2 86.4
DEVIATIONS FROM FF PULIDBI
NF PWl 1
NF PM. 2
Nf PM. 3
NF PWl 6
NF PHI 7
NF Pill I
FA« FIELD PKL
FA« Finn METHODOLOGY PKL
DEVIATIONS OF Fp KflH F«(IK FF
I.I
1.4
2.5
2.0
2.0
1.1
.6
.4
1.9
1.4
1.2
1.1
-US
1.4
-1.9
2.6
-1.0
4.1
-.7
2.2
-l.l
».»
.3
S.I
-.1
1.*
-.6
1.3
-.2
2.7
.6
2.3
-.1
2.2
.9
4.0
2.6
1.4
1.9
.7
2.7
1.3
3.4
2.3
2.0
1.0
J.9
2.5
2.4
2.3
1.9
1.7
2.7
2.S
3.2
3.2
2.7
2.3
4.0
J.7
.6
1.0
-.4
1.0
.8
l.S
1.4
1.8
1.1
1.8
2.1
2.7
-1.2
.9
-2.5
1.5
-.8
1.8
-.5
1.8
-1.2
1.6
.6
3.2
.9
.3
-.5
1.1
1.3
1.2
l.S
1.2
.9
1.0
2.7
2.S
.5
l.S
.4
1.5
1.2
2.1
1.4
2.3
-.2
1.4
2.6
3.3
-.8
2.0
.4
1.7
1.6
2.4
.4
2,6
.9
2.6
2.9
3.6
.5
1.6
1.7
1.8
5.0
2.2
1.7
2.4
2.3
1.6
4.3
3.4
.3
1.8
1.6
1.9
2.9
1.9
1.3
2.6
2.1
1.7
4.3
3.1
1.3
l.l
2.3
1.6
3.9
2.1
2.2
2.1
3.5
1.6
5.2
3.3
.5
.5
1.1
1.2
2.6
1.3
1.4
1.4
1.4
1.6
4.0
?-5
1.6
-.3
1.1
1.4
4.3
.9
2.5
.6
2.9
.3
5.9
?-l
TABLE OF OCTAVE IANO POWER LEVELS
A C 11.S 61 125 2SO
10«. 7 120.0 IT.S 1U.3 114.1 109.8
110.9 120.5 .O 119.0 111.4 109.1
2.2 .S .0 .7 -.7 -.7
SOO IK 2K 4K 8K
10S.9 102.9 102.4 97.8 92.6
101.2 104.6 102.6 100.6 98.1
2.1 1.9 .2 2.8 5.5
59
-------
Table i .16
SUUNII IVUCk l.tVtL DATA
16 CoMpreieor Output: 85 cl»
Englne/Cumprrasor Type: Rotary ecrev.
Conprnsor Size: 1.96,1. JO«1.K«
lev
u »0
It*
•C t-
Ul 1-
Is
|b 100
O
0*
w o
It- "
£ 90
•0
SIGNAL QUALITY
FAR FIELD
. 1 • • \ • ' 1 • • 1 • —
TEST 16
-*— 1 —
fl
UK
A A
\ \A & •
N \x
i . /. i . . i . . i
31.5 63 I2S ZSO
^
. 1
sdo
V
^\-
. . i
1000
~^-\
• L • • !
2000 «oi
\^.
)0
cv
8000
eNE-THl«0 ACTftVE BRNO CENTER FREQUENCIES IN HI
TEST NUMBER 16
COMPRESSOR SURFACE ADEAM0.36 SO. METRES
CONFOWAL SURFACE AREA (R»1M)»J4.67 SO. MEtRSS
N r
39
NEAR FIELD
MIC POSITIONS
WEIGHTED SOUND POKES LEVEL (09 RE
UF IGHT1NG-LOH FREQUENCY A LIN 20 25 31.5 40 50 63 80
HIGH fRECUENCY 500 630 800 IK l.iK i.6K 2P
FAR FIELD PWL 101.1 111.1 78.7 77.4 79.0 79.5 81.5 103.7 93.2
95.1 93.0 91.7 90.9 89.3 89.4 89.4
NF PKl 1
NF PM. 2
NF PM. 3
NF PM. 6
NF PBL 7
NF PM. 8
NF PM. 1
NF PM. 2
NF PWL »
NF PM 6
NF PUl 7
NF PM. 6
FAR FIELD PWL
101.6 tit. 9 74.8 75.2
96.2 93.8
101.8 112.9 68.7 72.6
96.2 92.9
102.4 111.7 75.4 75.6
97.0 91.3
102.8 113.0 75.4 75.8
97.2 94.7
lOt. 9 112.7 73.8 74.4
96.2 92.8
103.7 115.0 77.1 T7.0
98.1 94.6
.7 .* -1.9 -2.2
1.1 .8
1.1 -.1
1.7 1.9 -1.3 -1.6
2.1 1.7
.1 1.6 -4.9 -1.0
l.l -.2
2.6 1.9 -1.6 -.4
*~2 1.6
TA«IE Of OCTAVE SANO
A C 31.5
101.1 III.* 83.5
FAR FIELD METHODOLOGY PHL 102.5 III.) .0
DEVIATIONS OF
FF MfTH FBOH ff l.« -.1 •*
80.)
92.4
76.0
91.0
78.2
91.6
81.0
93.)
78.4
91.4
79.6
92.6
1.3
.7
-.1
2.0
1.6
-.6
-.3
.6
POWER
6)
104.. 1
I OS.*
1.5
79.8 82.5
91.2 90.2
78.0 80.8
90.7 88.8
79.1 82.5
91.3 89.5
80.6 81.)
92.2 91.1
79.1 81.«
91.2 89.0
80.4 8). 9
92.5 90.7
104.5 94.)
9Q.3 89.7
103.9 93.7
81, V 89.2
105.7 95.1
90.6 89.9
105.3 95.1
91.2 90.6
104.2 93.8
90.6 89.9
107.2 96.6
91.9 91.1
.OF WHICH
33 USED IN
1 PICOUAITI
100 125 160
2.5K 3. IK 4K
90.7 109.2 99.9
86. « 87.1 84.6
92.0
87.4
92.1
87.2
91.6
87.6
92.9
88.)
92.)
87.6
95.1
88.9
DEVIATIONS FROM FF PWLCOBI
.) 1.0 .8 1.1 1.)
.3 .1 .9 .) .»
-1.5 -.7 .2 .5 1.4
1.1 1.8
1.) 1.8
-.4 .1
.1 .5
.9 2.4
1.6 1.4
I f VFl S
125 250
109.7 101.
109.0 101.
-.7
.5 -.2
1.6 1.9
1.8 1.2
.5 .6
1.2 .5
3.5 1.4
2.5 1.7
2.2
1.5
1.6
-e
4.4
2.1
500 I*
5 98.7 95
4 100.0 96
1 1-3 1
.5
.5
.0
110.0
87.5
111.8
86.9
112.6
87.7
111.2
88.5
lll.b
88.2
113.9
89.0
.8
.4
-.2
2.0
1.4
2.4
.1.1
4.7
1.9
2K
93.S
93.6
.1
100.9
85.2
102.4
85.0
103.2
85.8
102.0
86.1
102.2
84.9
104.5
87.1
1.0
2.5
2.1
t.5
2.3
.3
4.6
2.5
4K
90.0
91.4
1.4
200
96.5
83.2
97.9
83.1
98.2
99.5
83.8
98.8
84.1
99.4
83.1
100.8
85.2
1.4
1.7
2.)
.9
2.9
-.1
4.)
2.0
8K
86.4
89.8
3.4
NFl
250
6.3K
99.4
83.7
100.3
83.9
99.9
83.7
99.9
83.7
101.3
84.8
99.9
83.7
101.3
85.1
.9
.5
1.9
l.t
.5
.0
1.9
1.4
315
Ht,
89.7
81.4
89.5
81. I
89.9
81.1
90.3
81.4
90.5
82.1
90.)
80.7
91.5
82.8
-.2
.6
.8
.7
.6
-.7
1.8
1.4
400
10K
93.5
78.3
93.5
77.4
92.9
70.3
93.8
78.6
94.5
78.3
93.3
78.6
95.1
80.0
.0
1.0
-.0
-.2
.3
1.6
1.7
60
-------
Tut Number 17
T.Uo 5 .17
BOUND IIIWtK LEVBL DAT*
Conprtaior Output: 150 elf
Engine/Compressor Type: Rot«ry tcrcw, G»t, st«nd«rd
Conprciaor BUe: 1.93xl.24>l.]6e
120
d no
5
St
£ix
at
*"2
"b 100
•0
SIGNAL
FAR FIELD
NEAR FIELD
TEST IT
o
UN
"snr
~BT"
-rir
' sic '—' iob'6'—' iobo'—' 46154' ' sobs'
ONE-THIRD eCTRVE BBND CENTER FREQUENCIES IN HZ
TFTTNTTT
TNTNNTTT
T T T
T T T
H N
N N
FFFFFFFFFFFFF
FFFFFFFFFFFFF
TEST NUMBER 17
CDHPRFSSUR JURFlCt AREA»11-02 SO. METRES
CONFORMAL SURFACE AREA IK-IK)- 55 .DO S3. METRES
47 NEAR FIELD MIC PUS HUMS.OF WHICH 3! USED IN NF 1
WEIGHTING-LOW FUEOUENCr
HIGH FREOUENCY
FAP FIELD PWL
NF PWl I
NF Pill ?
NF PHI 3
NF PUt 6
NF PUL 7
NF PWt 8
WEIGHTED SOUND POWER LEV6LID8 RE I PICOWATT)
A
103.0
104.4
1D3.6
104.2
105.1
103.3
105.6
LIN
111.6
112.4
111.7
112.6
112.9
111.7
114.0
20
83.9
93.3
90.0
95.0
92.2
94.0
93.0
94.9
90.5
95.7
92.5
91.9
94.2
96.1
25
> 610
9J.1
93.8
B9.6
94.8
90. 8
93.7
92.5
94.1
90.1
95.7
91.9
94. 8
93.9
95.4
31.5
600
39.6
93.4
B9.2
95. 6
90.0
94.5
91.5
94.4
89.6
96.6
90.7
95.7
92.8
95.6
40
It.
99.3
93.1
99.7
94.1
99.0
93.1
99.2
93.0
100.4
94. B
98.6
92.3
100.4
94.2
50
1.2K
99.7
92.6
97.6
94.6
96.8
92.4
98.1
93.3
98.1
95.3
97.9
92.7
99.4
94.6
63
1.6K
100.6
93.1
101.6
94.6
100.1
93.2
100. 1
9J. 7
102.4
95.3
99.4
92.9
101.4
95.1
eo
105.4
91.3
104.7
91.3
101.6
9i. a
102. B
92.3
105.4
94.1
101.7
91.8
104.0
93.6
100
2.5K.
105.3
69.7
105. 0
91.6
103.4
91.1
103.0
91.8
105.4
92.?
102.3
91.1
104.3
93.2
125
3. IK
97.4
92.0
100.8
93.9
101.0
93.5
100.4
94.7
101.2
94.6
99.7
93.6
101.8
96.1
160
104.8
89.5
106.6
91.2
101.0
91.1
109.2
91.1
106.8
91.8
108.5
90.3
ilO. 7
92.5
200
9^-2
BV.5
99.8
88. ft
100.5
68.5
101.4
88.7
100.5
89.2
100.5
87.7
102.9
90.2
250
6.3K
95.0
87.0
97.2
88.1
97.9
68.2
98.4
88.5
97.8
88.6
97. 2
99.9
£9.9
315
6*
95.4
85.4
93.0
85.7
96.7
85.5
96.5
85. 9
99.0
86.1
96.9
84.8
47.9
87.3
400
•.or.
96.9
83.3
96.1
84.-
95.3
85.2
96.3
85.5
96.9
84.7
95.5
84.5
97.6
86.9
DEVIATIONS FROM FF CWLIDBI
NF PWL 1
NF PWt 2
NF PWl 3
NF PWL 6
NF Ptrt. 7
NF PWt 8
F*R FIFLO MfTHODOlOG* PWL
DEVIATIONS OF FF "ETH FROM FF
>4
.6
-2
'. 1
.3
1.6
.a
.1
1.0
1.1
.1
2.4
1.1
1.7
3.3
.7
4.1
1.6
1.6
2.4
3.6
.6
5.3
2.8
-.5
1.0
.7
-.1
2.4
.3
-.0
1.9
1.8
1.0
3.8
1.6
-.6
2.4
.2
l.t
l.l
1.0
-.2
3.2
.9
2.3
3.0
2.2
.4
1.0
-.3
-.0
-.1
-.1
l.l
1.7
-.7
-.8
1.1
1.1
-2.1
2,0
-2.9
-.2
-l.fc
.7
-1.6
2.7
-1.8
.1
-.3
2.0
1.0
1.5
-.5
.1
-.5
.6
1.8
2.2
-1.2
-.2
.8
2.0
-.7
2.0
-1.8
.5
-2.6
1.0
-.0
2.8
-3.7
.5
-1.4
2.3
-. 1
1.9
-1.9
1.4
-Z. 3
2.1
.1
2.6
-3.0
1.4
-1.0
3.5
3.4
1.9
3.6
1.5
3.0
2.7
3.8
2.6
2.3
1.6
4.4
4.1
1.8
1.7
2.2
1.6
4.4
1.6
2.0
2.3
3.7
.1
5.9
3.0
.6
1.1
1.3
1.0
2.2
1.2
1.3
1.7
1.1
.2
3.7
2.7
2.2
1.1
2.9
1.2
3.4
1.5
2.8
1.6
2.2
.6
4.9
2.9
2.6
.3
1.3
.1
l.l
.5
3.6
.7
1.5
-.6
2.5
1.9
-.8
.9
-1.6
1.9
-.«.
2.2
-.0
1.4
-1.4
1.2
.7
3.6
IA8Lf OF OCTAVE BAND POWER LEVELS
A C 11.5 63 125 250
101.0 111.9 100.2 107.4 108.4 101.7
104.2 112.2
1.2 .3
500 IK 2K 4K an
99.7 97.8 96.4 94.6 90.}
99.0 1UT.6 109.3 100.6 100.9 97.1 95.4 96.6 93.9
-l.Z .2 .» -l.l 1.2 -.7 -1.0 1.8 1.6
61
-------
It. DISCUSSION OF EXPERIMENTAL RESULTS
14.1. Sound Pressure Level Data
There are two aspects of the sound pressure level data which are worthy of note with respect to
compressor noise measurement — a) directivity of compressor noise, and b) systematic variation of
noise with elevation above the reflecting plane.
U.I.I. Directivity of compressor noise
A directivity index for a source may be defined as[8]
DI(0) = Lp(0) - Lp
where DI(0) is the directivity index at the angle 8
L (e) is the sound pressure level at the angle 6
L is the average sound pressure level over the hemisphere
(L »
-2!*.9 dB for the data in Table 3)
The range of maximum values of directivity index for A-weighted sound level for all tests was 1.8
dB to 7-6 dB. As might be expected, the larger values of directivity index were those associated with
the larger machines. For comparison, the maximum directivity index of A-weighted level for the
reference source was 1.5 dB while that for the tone source ranged from 6.9 to 11.1 d3. The average
value for the maximum directivity index of A- weighted level was 3.k dB, indicating that compressors
as a group are not substantially directive sources. Furthermore, because of the relatively small
directivity of compressors in comparison with tonal sources, we are led to suspect that the A-weighted
level of compressor noise is not strongly dominated by tones. As a result, it is expected that the
average of a small number of measurements is likely to give reasonably good estimates of the true
average level over the measurement surface. For 12 of the 17 samples the side exhibiting maximum
noise level in near-field data was in the same direction as the direction of maximum level ^n the
far-field. For two compressors, the direction of the far field maxiKum vas-within +1+5° of the
direction of the side with maximum level. For three of the compressors — those with lev directivity
index — the maxima of sound pressure level in the near and far field data occurred on different
sides. This may be reasonably attributed to second order effects due to the size of the different
sides as well as the typical interference patterns'in the near-field for these sources. In all three
cases, the maximum directivity index occurs close to the ground in the region of the first
interference maximum, so that small elevation positioning errors may contribute to a false
identification of the side with the maximum noise. Furthermore, for compressors, the near-field
maximum typically occurs on a short side and the increased area associated with a long side may in
fact lead to larger intensities in the far-field for the side with the highest value of average sound
level times area. It is for these reasons that directivity patterns are only defined in the far field
of the source where the directivity pattern is independent of measurement radius [8].
1» . 1 . 2 Systematic variation of noise with position
It should be noted that both the far-field and near-field sound pressure level data exhibit
stronger variation with height above the reflecting plane than with change of lateral position on the
measurement surface. The effect is larger in the far-field data than in the near-field data. This is
a direct consequence of two facts: a) interference patterns are a result of the radiation from two or
more coherent sources spaced some distance apart and b) the principal coherent sources arc- any
position on the compressor and its mirror image on the other side of the reflecting plane. This may
be predicted if one assumes that all the principal radiators of sound are small and not strongly
correlated to all other radiators.
This factor is important for a measurement methodology since it implies that averaging in the
vertical direction in the far-field will be much more important than averaging in the horizontal
direction, and also more important in the far field than in the near-field.
It.2. Sound Power Level Data
Several noteworthy conclusions can be drawn from the sound power level data [Tables 5.1-5.17].
The first is that for each individual test, for the frequency range above which the signal quality
indicates no background noise problems, to an upper frequency limit of about 2.0 kHz, the deviations
of the near field calculations are predominantly positive and small. One means for summarizing this
result is shown in Table 6 where the averages of these deviations for 17 compressors are shown. (Note:
points corresponding to signal quality greater than 3 are excluded from the average). Also shown are
62
-------
the computed standard deviations of these deviations. The average deviation may be interpreted us an
estimate of the average bias of the measurement methodology, while the standard deviation can be
interpreted aa a measure of the precision of the methodology. These results will be more fully
discussed in the next section.
Second, the signal quality code, which classifies the variance of the signal as tone-like,
noise-like or fluctuating, generally agrees with an estimate of the presence of a tone from
qualitative examination of the spectrum (i.e., peaks in the spectrum correspond to T"s in the signal
quality) except at frequencies above about 500 Hz- Also the classification of variance in the
near-field data typically indicates the same or lover variance than in the far-field data. These.
observations are interpreted as indicating that the propagation medium is not uniform during the
period cf observation at a single position (30 seconds) causing the interference pattern and thus the
variance of the signal to change significantly during the observation period. The cause of uniformly
high variances at high frequencies is probably due to the fact that tones, when they are present, are
not steady, but rather, shift due to changes in source rotating speed. This change in frequency leads
to significant changes in the interference pattern at high frequencies, which can produce large
fluctuations in mean square pressure at the observation point. Alternately, unsteady propagation
conditions over a region of a few wavelengths in dimension, caused by changing thermal and temperature
conditions or changes in their gradients, can lead to the same effect.
Table 6.
Average deviation and standard deviation of average deviation -f
"*« fieid sound power level from f*r field sound power level
for seventeen portable air compressors, six nearfield calculation
procedures (see text section 3.2) are shown plus slnllsr statistics
lor far flela nethodology.
LOW FREQUENCY
MICH
S'AtlSUCS fQJ DEVIATIONS
NEAR FIELD-FAR FIELD
Nf 1 AV DEV
SIGN* DEV
NF 2 IV OEV
SIGMA OEV
NF 3 AV DEV
SIGH* DEV
NF 6 AV DEV
SIGMA OEV
Hf 7 AV f>f.V
SICK* DEV
t>f 6 AV DEV
iU.KA DEV
A LIN
.4 .7
.5 .3
-.2 .1
1.0 1.0
.5 1.1
1.4 1.2
1.3 1.5
.5 .4
.0 .4
1.4 1.0
1.8 2.5
1.1 1.4
20
i>00
1.6
.9
4.4
.5
-1.0
.2
4.1
1.1
.5
1.2
3.5.
1.9
2.2
1.8
4.0
.5
-. 1
.6
3. 3
l.B
2.4
3.6
2.0
25
630
1.5
.6
4.0
,b
-.5
-.2
3.2
.9
.4
.8
l.l
1.7
2.1
1.5
3.6
.6
-.2
.4
2.9
1.5
1.6
2.1
3.1
1.9
31.5
BOO
1.4
.8
1.8 :
.0
.1
.2
2.4
.7
1.2
.6
Z.S
1.0
2.0
1.7
1.8
.6
.6
2.1
1.2
2.5
1.8
2.6
1.2
40
IK
.8
.2
! 1.1
.7
-.2
-.5
1.4
1.0
.6
-.0
1.5
1.4
1.5
1.1
1.1
.7
.1
-.4
1.6
1.6
1.9
1.2
1.5
1.6
50
1.2H
.6
.5
1.1
.7
-.3
-.4
1-8
l.l
.7
.2
1.7
l.t
1.3
1.4
1.3
.6.
.2
-.1
1.7
1.4
1.9
1.4
1.7
1.3
63
1.6K
1.0
.5
1.2
.b
.2
-.1
1.4
l.l
1.1
.4
1.4
1.4
1.8
1.4
1.1
.6
.4
-.0
1.3
1.5
2.5
1.6
1.5
1.5
80
2K
.7
• *
.a
.1
-.5
-.5
1.6
I. 1
.9
.1
1.8
1.6
1.4
1.2
.9
.7
.1
-.3
1.7
l.fc
2.3
1.3
2.0
1.7
100
2.5H
.8
.2
.6
1.0
-.T
-.5
1.5
i.a
.4
-.2
1.8
i.a
1.5
1.0
.7
1.0
-.3
-.3
1.5
1.8
1.7
l.U
1.-)
1.8
125
3. IK
.7
-.1
.9
1.1
-.2
-.8.
2.4
1.7
. .6
*-.!
2.2
1.9
1.5
.7
1.0
1.1
-.0
-.4
2.2
l.B
1.9
l.l
2.3
1.9
160
4K
.9
.0
.tl
.9
.3
-.6
1.7
1.6
1.4
-.1
V
2.1
1.7
1.7
.9
.7
.9
.7
-.4
2.0
1.5
2.6
l.l
2.2
l.B
2JO
5K
.8
-.7
.6
1.3
-.1
-1.4
1.6
2.1
.,
- .9
1.4
2.2
1.5
.2
.7
1.3
.5
-1.4
1.3
2.2
2. I
.3
1.5
2.3
250
6.3K.
.6
-.9
.6
2.0
.1
-1.5
1.5
2.5
1.0
-1.0
1 . t>
2.9
1.6
-.0
.7
1.9
.4
-1.5
1.6
3.0
2.3
.2
i.a
2.9
315
8K
.?
-.8
.6
1.4
-.6'
-l.i.
1.6
i.a
.1
-1.3
1.5
2.3
1.1
.1
.8
1.3
-.4
-1.8
1.0
2.1
1.4
-.1
1.7
2.4
4CO
10K
-.0
-1.5
1.1
1.9
-.9
-2.2
1.2
2.5
.t
-2.3
2.0
3.1
.6
-.«.
1.2
1.9
.1
-2.7
1.7
2.V
1.9
-1.1
2.2
3.1
ft MFTH AV DFV
SI&MA DEV
SMTISTICi FOR DEVIATIONS
FAR FIELD HHHUUUl OGV-f AR FIELD
A c
US . .7
.9 1.0
31.5
-.1
.5
63
1.2
1.1
125
.9
25l)
-.2
1.0
500
1.3
.8
IK
-.3
l.l
2K
-•i
1.2
4K BK
2.0 3.3
l.S 2.7
-------
5. ANALYH10 OF MEAOUHKMKNT KHHOB
5.1. Introduction
The errors associated with a measurement procedure moy be broken into three major components as
follows:
1. Error associated with the test methodology;
2. Error associated with the measurement instrumentation;
3. Instrument operator error.
In this section we will discuss estimates of error for various sound power test methodologies on
the basis of this experiment and attempt to put some bounds on the first two components of error,
within the field test environment. We anticipate that the field test environment will include a'test
site and instrumentation meeting minimum requirements of the proposed ISO Draft engineering
standard[2). This implies a flat, hard-surfaced test site, and a commercially available, portable,
precision sound level meter, operated under the supervision of a trained test engineer.
5.2. Error in Sound Power Measurement Methodologies
The deviation of sound power level estimates using near-field pressure levels from estimates
using far-field pressure levels as presented in Table 6 and plotted in Figure 9 are surprisingly
small. Further, they are consistent in suggesting that the estimate of sound power from near-field
pressure measurements is higher than that of estimates from far field measurements, within the limits
of sampling error. This consistent behavior of the data leads us to question whether or not an
underlying physical principle in fact forces this behavior. A cursory review of the literature
[3,9»10] indicates that the topic of analytically relating near-field pressure to sound power has
• With Microphone Directional Response Correction
I—I I I_J
I I I » I I I » I I I I t i "I I I I i I I
31.5
1000
2000 , 4000
8000
A.WT LIN
ONE-THIRD OCTAVE CENTER FREQUENCY, Hz.
Figure 9 Plot of average deviation of near field from far field
sound power level
-------
received little or no attention. While a detailed analytic description is beyond the scope of this
work, ve are compelled, baaed on the strength of the data, to advance some hypotheses' In this area
both to aid in the interpretation of these data, and to suggeot directions for further research.
We begin by introducing the true sound pover, defined as [1»]
I.(r).«i(r.) dS (5.1)
~
f
where W is the acoustic power radiated by all sources within ZQ.
!_(£) is the time average intensity vector at a position r_.
fi(r_) is the unit vector normal to the surface SQ at the point r..
An idealization of our measurement is given by
W" = f
pg(r)_dS (5-2)
PC
where p is the time-average squared pressure at the position r_.
Since the squared pressure is a scalar field, ve introduce a third estimate of power for comparison,
i.e.
W = f l!(r)| dS (5.3)
s
o
where |lj is the scalar magnitude of intensity.
Since |l(r)l i!(r)-n(rj,
It is clear that
W' >_ V (5.k)
Now, by analogy with the case of geometrical optics, we have^in the geometric aco-astic limit
(i.e., vanishingly short wavelengths for incoherent noise sources— ) we have that [11]
P (?)
|l(r)| — (5.5)
kr*-°° pc
vhere k=2Tj_ is the acoustic wave number (A is the wavelength of sound)
T
r is the distance to the nearest source
Thus we may write
W" = W >_ W (5-6)
Where - indicates asymtotically equal to. Thus at least in the geometric acoustic (high frequency)
limit the near-field and far-field es-cimates of power for incoherent noise sources are asyir.totic to
an upper bound estimate of the true power. The degree of over-estimation is determined by the degree
to which the shape of the measurement surface So conforms to the surface .of wave fronts from the
source.
Our concern of course is how this description holds as wavelength increases. A cursory review of
the data suggests the hypothesis for free field over reflecting plane determinations that
W" > W ' (5.7)
By incoherent we mean (in analogy with an incoherent or white light source) that the radiation
from any point on the source has vanishingly small temporal correlation with that from any other
source point, and its temporal auto correlation approaches a delta function in time, such limiting
processes being taken in a manner which yields a finite power output.
-------
throughout the frequency rnnp.e of meauurcment , but we wunt emphanixe that t.hio hypotheoin io vltliout
on analytic banio, for reounurcmcnto in Uio aoouotic netir-field. It in tempting to ucck an analytic
Justification for thin hypotheoic boned on a compuritjon of moan squared preouure with the acalur
magnitude of intensity, but we muat add that such attempts arc met vith considerable analytic
difficulty for all but the simplest oourcea. For example, consideration of the simple monopole and
dipole sources in free opo.ce. yield
o
P (£) 2L ll(r)| (5.8)
pc
for all frequencies, but a similar relationship for more complex sources has not been identified.
Thus, though our data are very encouraging, ve must emphasize at this point that there is no firm
analytic basis for near-field sound pover determinations.
With this preamble, let us now turn to the question of differences between an estimate of power
and true power. Equations 5-1* through 5.6 suggest the following partitioning of the error (as
distinct from that proposed by Hubner [3] 5
W
vhere 6 = rr
s w
(5'9)
The term 6 is associated principally with the shape of the measurement surface relative to the
time-average wavefront shape. Based on Huygens principle, we expect this term to be nominally
independent of the "radius" of a measurement surface, at least for nearly conformal measurement
surfaces. The term S (kr) is a frequency dependent term which is a measure of how the change in mean
square pressure due to spreading differs from inverse square law. Thus, if the source does produce an
acoustic near field, its contributions will occur principally in this term.
From equation 5.k, the term S is seen to be always greater than or equal to unity. An estimate
of the magnitude of the tern 6 (kr? is unavailable at this time except at high frequencies where eq.
5.5 indicates that it assymtotically approaches unity.
Until this point, this discussion has ignored the effect of spatial sampling on the measurement
result. To consider its effect we introduce a third estimate of sound power defined as
£.. W. I* -,M
1=1
where S. is the element of measurement surface area associated with the ith measurement of mean square
pressure. If the measurement is designed so that the areas S^ are equal, then
S = N S.
and M
Wit. = -2.
pc
In this form it is clear that the intent of the spatial sampling should be to produce an unbiased
estimate of the average mean squared pressure over the measurement surface. Thus the expected value
of W" which results from an unbiased sampling plan will equal W". Thus we are led to expect that
the effect of point sampling will be to introduce an imprecision in the measurement rather than a true
bias. Further, the magnitude of this imprecision should be directly proportional to a function of the
variance over the measurement surface and inversly proportional to a function cf the number of
uncorrelated measurement points used.
Returning to the data in Table 6, we note that all of the above comments are supported in detail.
First consider the comparison between HF 1 compared with KF 6 which represents the most sensitive test
of the difference between a conformal versus a rectangular surface. Above 250 Hz, NF6 is a, very
consistent 0.9 dB high with a standard deviation of 0.8 dB or less through most of this range. A
t-test indicates that this difference is. significant at or above the 99% level. Thus ve conclude that
the difference between the procedures is statistically significant with the non-conforml surface
producing the higher estimate, and thus that the term 6 is greater than unity as expected. In Figure
10, the data for NP1 is plotted versus frequency including the microphone directional response
correction suggested in Section 2.3. Here"we see a trend for the near field sound power estimate on
the conformal surface to asymtotically approach the far field power with increasing frequency as
suggested by eq. 5.6, but further, moving toward lower frequencies, the upward bias becomes
statistically significant.
66
-------
Thus we are led to a corollary of the hypothesis of eq. 5,7, that
E (W ") > W
(5.11)
i.e., the expected value of a sound power estimate based on Bound pressure measurements is greutor
than or equal to the true sound power within the limits of sampling error for free field over
reflecting plane measurements.
We also note from the data in Table 6, that decreasing the number of measurement positions
generally does not alter the mean upward bias, but does significantly increase the measurement
imprecision as suggested by the error model. This effect is emphasized in Figure 10, where the
average deviation and standard deviation data of Table 6 are plotted vs number of measurement
positions for the A-weighted data. One notable exception to these trends is the result for NF-7
calculation procedure (nine measurement points, one on each of five sides, one at each of four
corners, rectangular measurement surface). Here, the selection of measurement positions has been
optimized to minimize bias on the average for the rectangular surface, but with the result that the
increased number of measurement points does not significantly improve the precision of the measurement
over that for five measurement positions (for this sample of data). From this we must conclude that
the sound pressure level at the corner positions is correlated with the center points in an average
sense.
"
cr 5 "-
> 5. uj
LU Ul __l
O £UJ
a: cc "Y
ujet.cc
> UJ <
a
LU O
a
§S
CO
0
i i
I
8 9
NUMBER OF MEASUREMENT POSITIONS
ALL
Figure 10 "Bias" and "precision of A-weighted sound power level vs
number of measurement positions (17 compressors)
67
-------
Ul
§1
ec j
UJ UJ
o oc
-J UJ
p
Is
Ss
u.'V
o ts.
OHUYOENS SURF ACE INF
H RECTANGULAR SURFACE (NF 6)
8 (metres)
1 1.25 1.6 2.0
Figure 11 A-weighted sound power level deviation vs source size •
2.5
3.2
Another possible type of bias in the measurement methodology is systematic variation as a
function of machine size. Figure 11 shows a plot of deviation as a function of Eachine size for the
HF-1 and NF-6 A-weighted sound power data. This plot indicates that both measurement methodologies
have a significant tendency to overestimate sound power for smaller machines. This is indicative of
the dependence of the deviation from true sound power on measurement radius. However, it is probable
that the microphone angular response problem is a factor in these data as well. Unfortunately, the
data for larger machines is too sparse to provide accurate estimates of trends of deviation for very
large machines, but eq. 5-6 suggests that both curves will have horizontal asymtotes at or above 0 dB
deviation.
5-3. Instrumentation Accuracy
The analysis of measurement procedure error based on experimental data, discussed above, in
effect eliminates instrumentation error except for microphone angular response, since we deal only
with differences in levels measured with the same equipment. Errors due to bias from measurement
system drift are minimized with frequent calibration, while bias from detection of signals is
eliminated by using the same system in both measurements, etc. For measurement in the field
environment however, these cancelations of error do not occur and must be considered in the estimate
of total measurement error.
Table 7 provides a listing of pertinent sources of instrument error, their specified values for
precision sound level meter and the range of expected error for presently available equipment.
The largest single source of error is tolerances on the A-weighting response, when that is used,
since vith proper microphone size, the error due to angular response can be minimized. Combining
these errors leads to a total instrument imprecision (two standard deviations) on the order of 1.2 to
1,1» dB for tests made over a small temperature range from the temperature at calibration. (For
calculations of total error we will use a value of 0.7 <3B for one standard deviation (90? confidence)
for the instrument error component).
68
-------
Table 7- Instrument Imprecision (two Standard Deviations) Associated with
Commercially Available Precision (Type I) Sound Level Meters
Property
Standard* Limits
Typical Limits
Level Calibration
Frequency Response
(at each one-third
octave center
frequency
A-weighted
Linear
Attenuator Accuracy
Temperature Stability
10°C to 60°C
-10°C to 60°C
Detector Linearity
Crest factor: 10
Crest Factor: -v 1.7
Angular Response**
(+90°, 50 Hz - 10 kHz)
One inch microphone
One-half inch microphone
0.2 dB
+ 1 dB
i 0.5 dB
i 0.5 as
+. 1 dB
+ 1 dB to -5 dB
. 5
+ 2.1 to -It
same
+ 1 dB t
i 0.5 dB
+ 0.5 dB
same
same
+_ .5 dB to + 1 dB
+ .5 dB t
+ '1 to -9 dB
+ 0.5 to -4.5 dB
* IEC 179, MSI Sl.U - 1971 [12]
t Assuming Spectra Similar to those measured
** For spectra similar to those measured and allowable standard tolerances vs.
Frequency.
5.4. Total Measurement Error
The total imprecision in the measurement procedure is equal to the rms total of the error
components when they are uncorrelated.
,2 + e2 + e2 ,1/2
total ~ Meth Instr e Operator
The methodology imprecision may be estimated from the standard Aviation, of the difference
between the two procedures. (Ignoring the contribution of variance of the far field measurements, if
it is not in fact negligible, contributes to make the estimate more conservative.) The standard
deviation of the deviation from the far field procedure (Sigma Dev. , Table 6) is a nearly unbiased
estimate of the standard deviation (o) of the methodology, assuming that the errors are normally
distributed. Examination of the cumulative distributions of the data indicate that this normality
assumption is a reasonable approximation. However, because of the small number of tests involved,
there is uncertainty associated with this estimate. To be conservative, we choose to estimate the
methodology imprecision as the upper end of the 95$ confidence interval for a.
Neglecting operator error, and using a value of .7 dB for one standard deviation of instrument
error, the range in achievable procedure error for the measurement of A-weighted sound power level is
estimated to be in the range 1.1 to 2.4 dB depending on the number of measurement positions used, as
shown in Table 8.
The fact that the achieved precision of 1.5 dB for the NBS Far-field Methodology (see Table 6)
(using a hand held sound level meter, and six measurement points) agrees reasonably well with the
computed total precision of the survey methods, represents some confirmation of the precision
analysis.
69
-------
Table 8. Estimated achievable measurement error (95? confidence) for measurement of
A-weighted Bound power Ieve3 of portable air compressors in a field test
environment using a measurement surface 1 metre from the source surface
excluding operator error[13].
Measurement Methodology
Conformal Surface
Laboratory grade
(l measurement per
square metre of
measurement surface)
Engineering grade
(eight positions)
Survey grade
(five positions)
Rectangular Surface
Laboratory grade
(1 measurement per
square metre of
measurement surface)
*
Engineering grade
(nine positions)
Survey grade
(five positions)
Methodologyt
Precision, dB
(l standard
deviation)
.8
1.5
2.3
.8
2.1
2.3
Instrument*
Precision, dB
(1 standard
deviation)
.7
.7
.7
.7
.7
.7
Total
Precision
(l standard
deviation)
1.1
1.7
2.1*
1.1
2.2
2.1*
Probable Inter-
val of Bias**
(90* Confidence)
-.3 to 1.1
-1.6 to +1.2
-1.5 to +2.5
+ .6 to 2.0
-2.0 to +2.0
-2.0 to +3.8
t Estimated frota data of Table 6 using the expression (see toxt section 5)
a = 1.52 S(Table 6)
where 1.52 is the upper limit of the 95% confidence interval for a/S based on S
vith 16 degrees of.freedom (lU).
* Assumes Type 1 sound level aeter (see text, Section 6).
** See reference 13, paragraph 3.
70
-------
6. CONCLUSIONS
The experimental data and analysis provided in this report support the following conclusions:
(]) An estimate of the "far field" sound power level output of a machine of a. type similar to
the compressors studied can be accurately inferred from sound pressure level measurements taken
on a measurement surface close to the source if:
(a) the measurement surface conforms to the source shape;
(b) a sufficient number of measurement positions are used consistent with the precision
requirements of the measurement;
(c) a microphone is utilized which has uniform response to sound, incident over any
directions in front of the microphone over the frequency range of interest.
(2) Generally, the more measurement points that are used in a sound power level measurement the
more precise the value of estimated sound power.
(3) Considering total invested measurement cost, imprecision of the results, and ease of
microphone placecer.t, the ISO Draft International Standard (DIS 371*1*) engineering method for
sources using a conformal surface represents a most reasonable balance of these factors for
making noise eirassion measurements for regulatory purposes.
(U) For the sample of compressors tested, the overall measurement precision (one standard
deviation), in the field environment using the methodology of conclusion (3), is estimated to be
+1.7 dB (95£ confidence limits 3.1* dB) ignoring instrument operator error.
71
-------
Y. AOKNOWl.raXJlWIN't'U
In any program of this olsse and acopo, a lurp.a nwilier of indivldualn contribute to il.n tiuocpno,
Tlie author in particularly indebted to the following indi.vidua.lu and organizations for thoir
coritri\)Utionn to thin proRrtt.T..
Appreciution is expressed to the U. S. Army, Mobile Equipment Research and Development Command,
Fort Belvoir, Virginia, for providing the use of a suitable teat site and assistance in the receipt
and shipment of test specimens.
The author also expresses appreciation to Mr. D. E. Mathevs for design and to the NBS Plant
Division, for construction of the far-field array; and to the following members of the Mechanics
Division, NBS: D, E. Mathevs, B. R. Fuller, C. 0. Shoemaker, and N. Rekos for their assistance during
the data acquisition phase of the project; G. Hruska for calibration of the microphone cartridges; R.
L. Fisher for prograiriming and systems analysis of the data acquisition system; D. S. Blomquist for
instrumentation design and guidance; J. S. Forrer, J. M. Keinen, C. 0. Shoemaker, and M. Tarica for
instrumentation construction; C. T. Molloy (EPA/OKAC), D. R. Flynn, R. K. Cook ar.d E. B. Magrab for
suggestions to improve the theoretical analysis; D. M. Corley for assistance with data analysis and
reduction; K. A. Cadoff and W. A. Leasure for editorial review of the manuscript; and J. Russell, Y.
Morosko, and M. Hildebrand for typing and assembling the manuscript.
-------
8. REFERENCES
[l] American National Standard for the Physical Measurement of Sound, SI.2-1962, (American
National Standards Institute, New York, Nev York, 1971).
[2] International Organization for Standardization Draft Standard for Acoustics — Determination
of Sound Power Levels of Noise Sources. Part k: Engineering Methods for Free-Field
Conditions Over a Reflecting Plane, DIS-37'*'* (American National Standards Institute, New York,
New York); International Organization for Standardization Draft Standard for Acoustics —
Determination of Sound Power Levels of Noise Sources. Part 6: Survey Method for In Situ
Measurements, DIS-ST^S (American National Standards Institute New York, Hew York).
[3] For example: Synrcosium on sound power measurement of machines "in situ", J. Acous. Soc. Am.
5i C*) (1973) p. 960-98*1.
[It] Patterson, W. K., Ely, R., and Muggins, G., Portable air compressor noise measurement, Report. 279i>£i
(Bolt Beranek and Newman, Inc., Cambridge, Massaclnisetts , March 197*0.
[5] Kearney, A. T., Inc., A study to determine the economic impact of noise emission standards in
the construction equipment industry — Draft portable air compressor report (U. S.
Environmental Protection Agency, Washington, D. C., December 1973).
[6] American National Standard Test Code for the Measurement of Sound from Pneumatic Equipment,
?5.1-1971 (American National Standards Institute, Hew York, Hew York, 1971).
[7] Baade, P. K. , Standardization of machinery sound measurement, ASME Paper 69-WA/FE-30 (American Society
for Mechanical Engineers, Mew York, New York, November 1969).
[8] Beranek, L. L. , (ed.), Noise and Vibration Control, Chapter 6, Section 6.10 (McGraw-Hill, New
York, New York, 1971, 158-163).
[9] Morse, P., and Ingaard, K. U., Theoretical Acoustics, Chapters 6 and 7 (McGraw-Hill, Kew York, Sew
York, 1968).
[10] Skudrzyk, E., Four.iatior.s of Acoustics (Springer-Verlag, New York, New York, 1971).
[ll] Felsen, L. B. and Marc-avitz, N. , Radiation and Scattering of Waves, Chapter 1, (Prentice Hall, Englewood
Cliffs, H. J., 1973).
[12] IEC 179 - International Electrotechnical Commission Recommendation Publication 179 (1965)
Precision Sound Level Meters. AKS Sl.l»-1971 - American National Standard Sl.lt (1971)
Specification for Sound Level Meters.
[13] Proschan, F., Confidence and "-olerance intervals for the normal distribution, KBS Special
Publication 300 (National Bureau of Standards, Washington, D.C.).
[lit] Pearson, E. S., ar.A Hartley, H. 0., ed. Biometricka, Tables for Statisticians, Vol. 1.
(Cambridge University Press, 1958) Table 35, p. 18't, Moments of S/o.
73
-------
HbS 1UA ".»
i'.'j. O';P r. OF COMM.
iiiiUGGRAPHic DATA
SHEET
1. ITSU.H A'! ION OK HI-.POKT \O.
2. (,iov'l Accession
No.
3. Recipient's Acce-.sum No.
4. i! 11 i .\\!i • rn 11 n.i
PROCEDURES FOR ESTIMATING SOUND POWER FROM MEASUREMENTS OF
SOUND PRESSURE
An Lxperiinc-nt.nl Investigation with Application to Noise From
Portable Air Compressors
?. AU'lliORtS!
Curtis I. Holmer
5. 1'uhlicaiion Pair
Jan. 1975
6. Performing O[f;.ini?:ii ion I oilr
?. I'l.HI (>|V>._3_97& •- Dftr . 1Q7/J
14. Sponsoring Agency Code
IS. SUIMM.KMKNTAKY NOTKS
16. AKSTHAC "I' (A 200-word or less factual summary of moat significant information. If document inc/urft-s a significant
bibl,oGraphy or literature survey, men lion it /irrf.)
This report describes investigations of the accuracy and precision of various
measurement methodologies for determining the estimated sound power output of "large"
machines in the free field over a reflecting plane. Ona purpose of this investigation
is to place empirical error bounds on many of the free field measurement procedures
currently proposed or in use; and in particular, compare the results of "near-field" and
"far-field" measurements. The sources used for the investigation included 17 portable
air compressors of various types (powered by internal combustion engines), a "reference"
sound source, and a loudspeaker driven by a pure tone source. The data recorded include
sound pressure level (A-weighted, linear, and 1/3-octave band) on an 84 point hetnispheri
cal array of seven metre'radius, and "near-field" measurements, sampled every square
metre, on a rectangular surface one metre from the machine surface. These data were
reduced to provide information on the deviation of "near field" sound power determina-
tions from "far-field" power level (using subsets of the data as appropriate to various
methodologies). The measured data for seventeen sources suggests that the value of a
sound power estimate based or "near-field" sound pressure level measurements may be an
upper bound to the sound power level estimated from far field measurements, subject to
the limitations of sampling error. Estimates of total achievable measurement error of
A-weighted sound power level of near field determinations relative to far field determin
tions are made for several measurement methodologies, based on the experimental data.
17. KEY «'ORDS (nix to twelve entries; alphabetical order; capitalize only tiic firnl /elisr of the drat key word unless a proper
name; separated by semicolons) Air compressors; error of sound power measurement; noise;
noise measurement; sound power level; standard test procedures for sound power
measurement.
18. AVAILABILITY Qjl Unlimited
f^~2 For Official Distribution. Ho Not Release to NT1S
[~~] Order From Sup. of Doc., U.S. Government Printing Office
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[•Jl Order From National Technical information Service (NT15)
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21. NO. OF PACKS
78
22. Price
$4.75
USCOMW-DC 29042-P74
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