NBSIR 73-417
EPA-550/9-73-007
Evaluation of
Commercial Integrating-Type
Noise Exposure Meters
William A. Leasure, Jr.
Ronald L. Fisher
Marilyn A, Cadoff
NATIONAL BUREAU OF STANDARDS
December 1973
Joint EPA/NBS Study
Approved for public release; distribution unlimited
Applied Acoustics Section
Mechanics Division
Institute for Basic Standards
National Bureau of Standards
Washington, D. C. 20234
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NBSIR 73-417
EPA-550/9-73-007
EVALUATION OF COMMERCIAL INTEGRATING-
TYPE NOISE EXPOSURE METERS
William A. Leasure, Jr., Ronald L. Fisher, and Marilyn A. Cadoff
Applied Acoustics Section
Mechanics Division
Institute for Basic Standards
National Bureau of Standards
Washington, D. C. 20234
December 1973
Final Report
Prepared for
Office of Noise Abatement and Control
U. S. Environmental Protection Agency
Washington, D. C. 20460
U. S. DEPARTMENT OF COMMERCE. Frederick B. Dent. Secretary
NATIONAL BUREAU OF STANDARDS, R.chard W. Roberts. Director
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ABSTRACT
As a result of the promulgation of occupational noise exposure regulations by the Federal government,
there are a number of commercial noise exposure meters on the market today that provide a measure of
noise Integrated (with appropriate weighting) over a time Interval. This report presents Che results of
an evaluation of such Instruments by the National Bureau of Standards (under the sponsorship of the U. S.
Environmental Protection Agency) as to their usefulness in monitoring compliance with occupational
noise regulations as well as their applicability as instruments for use in achieving the broader goals
of the EPA. Tests were designed and conducted to evaluate microphone and system response to sound of
random incidence, frequency response, crest factor capability, accuracy of the exchange rate circuitry,
performance of the noise exposure meter as a function of temperature, and the dependence of the device on
battery voltage. The rationale of the test procedures utilized to evaluate overall system as well as
specific performance attributes, details of the measurement techniques, and results obtained are discussed.
Key words: Acoustics, (sound); dosimeter; environmental acoustics; instrumentation; noise exposure;
noise exposure meters.
ii
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TABLE OF CONTENTS
1. Introduction 1
2. Functional Operation of Noise Exposure Meters 1
3. Description of Tests 3
3.1. Acoustical Tests 5
a. Microphone Calibration 6
b. System Response 6
3.2. Electrical Tests 6
a. Frequency Response 6
b. Crest Factor Capability 7
c. Exchange Rate 8
d. Temperature Response 8
e. Battery Voltage 8
3.3. General Observations 8
4. Results of Test 8
4.1. Model A 8
4.1.1. Acoustical Tests 8
a. Microphone Calibration 8
b. System Response 8
4.1.2. Electrical Tests 9
a. Frequency Response 9
b. Crest Factor Capability 10
c. Exchange Rate LO
d. Temperature Range 10
e. Battery Voltage 10
4.1.3. General Observations 11
4.2. Model B 12
4.2.1. Acoustical Tests 12
a. Microphone Calibration 12
b. System Response 12
4.2.2. Electrical Tests 12
a. Frequency Response 12
b. Crest Factor Capability 12
c. Exchange Rate 14
d. Temperature Range 15
e. Battery Voltage 15
4.2.3. General Observations . i. 15
4.3. Madel C 15
4.3.1. Acoustical Tests 15
a. Microphone Calibration 15
b. System Response 15
4.3.2. Electrical Tests 16
a. Frequency Response 16
b. Crest Factor Capability 16
ill
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c. Exchange Rate 16
d. Temperature Range 16
e. Battery Voltage 16
4.3.3. General Observations .... 16
4.4. Model D 18
4.4.1. Acoustical Tests 18
a. Microphone Calibration 18
b. System Response 18
4.4.2. Electrical Tests 18
a. Frequency Response 18
b. Crest Factor Capability 18
c. Exchange Rate 21
d. Temperature Range 21
e. Battery Voltage 21
4.4.3. General Observations 21
4.5. Model E 21
4.5.1. Acoustical Tests 21
a. Microphone Calibration 21
b. System Response 22
4.5.2. Electrical Tests 23
a. Frequency Response 23
b. Crest Factor Capability 23
c. Exchange Rate 23
d. Temperature Range 23
e. Battery Voltage 24
4.5.3. General Observations 25
4.6. Model F 25
4.6.1. Acoustical Tests 25
4.6.2. Electrical Tests 25
4.6.3. General Observations 25
4.7. Model G 26
4.7.1. Acoustical Tests 26
4.7.2. Electrical Tests 26
4.7.3. General Observations 26
4.8. Model H 26
4.8.1. Acoustical Tests 26
4.8.2. Electrical Tests 27
4.8.3. General Observations 27
5. Summary and Conclusions 28
6. Bibliography 29
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EVALUATION OF COMMERCIAL INTEGRATING-TYPE NOISE EXPOSURE METERS
by
William A. Leasure, Jr., Ronald L. Fisher, and Marilyn A. Cadoff
1. INTRODUCTION
As part of its present and anticipated responsibility for monitoring and controlling noise, the
Environmental Protection Agency, Office of Noise Abatement and Control, has a need to develop and dis-
seminate technical information on the levels and durations of noise to which individuals are directly
exposed.
Present Federal regulations, promulgated under the authority of the Occupational Safety and Health
Act and the Coal Mine Safety Act, set definite limits on the noise exposure of workers during their 8-
hour working day. The intent of these regulations is to reduce the risk of permanent noise-induced
hearing damage.
In order to comply with these regulations, it is necessary to determine an individual's noise
exposure for work environments that have A-weighted-noise levels of 90 dB or higher. The conventional
method of determining an individual's noise exposure is to use a sound level meter in conjunction with
a detailed time-and-motion study and then calculate the cumulative noise exposure.
Whether an observer armed with a stop watch and a sound level meter can accurately characterize
the noise "dose" to which a worker has been exposed is a debatable question. For constant noise sources
and fixed operator locations, no problem exists. For the roving worker, however, and the worker who
functions in a fluctuating noise environment, it is difficult to observe their noise exposure and to
compute an accurate daily noise exposure. This measurement approach is expensive and time-consuming and
is generally inaccurate due to the approximations in the time-and-motion study that practicality dictates.
The promulgation of occupational noise exposure regulations by the Federal government has resulted
in a proliferation on the market of new sound level meters and, to a lesser extent, noise exposure meters,
or dosimeters, which provide a measure of noise level integrated, with appropriate weighting, over a time
interval. Because of the motivation for production of these devices, most of them now being manufactured
cover only the range from 90 to 115 dB.
At present there are no standard performance specifications for such integrating noise exposure
meters. For this reason, the National Bureau of Standards, under the sponsorship of the Environmental
Protection Agency, conducted a research program to evaluate some available existing noise exposure
meters -- both acoustically and electrically -- as to their usefulness in monitoring compliance with the
OSHA noise exposure regulations and/or carrying out the broader goals of EPA, including determination of
the average individual daily noise exposure of persons in different living patterns.
2. FUNCTIONAL OPERATION OF NOISE EXPOSURE METERS
Section 1910.95, Occupational Noise Exposure, of the U. S. Department of Labor Occupational Safety
and Health Standards (Federal Register, Part II, Vol. 37, No. 202, October 18, 1972) includes the
following:
"(a) Protection against the effects of noise exposure shall be provided when, the sound
levels exceed those shown in Table G-16 when measured on the A scale of a standard
sound level meter at slow response
(b) (1) When employees are subjected to sound exceeding those listed in Table G-16,
feasible administrative or engineering controls shall be utilized. If such controls
fail to reduce sound levels within the levels of Table G-16, personal protective
equipment shall be provided and used to reduce sound levels within the levels of
the table.
(2) If the variations in noise level involve maxima at intervals of 1 second or less,
it is to be considered continuous.
(3) In all cases where the sound levels exceed the values shown herein, a continuing,
effective hearing conservation program shall be administered.
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TABLE G-16 PERMISSIBLE NOISE EXPOSURES1
Sound level dBA slow
Duration per day, hours response
8 90
6 92
4 95
3 97
2 100
1 1/2 102
1 105
1/2 110
1/4 or less 115
When Che daily noise exposure is composed of two or more periods of noise exposure of
different levels, their combined effect should be considered, rather than the individual
effect of each. If the sum of the following fractions: C1/T1 + C2/T2 + Cn/Tn exceeds
unity, then, the mixed exposure should be considered to exceed the limit value. Cn
indicates the total time of exposure at a specified noise level, and Tn indicates the
total time of exposure permitted at that level.
Exposure to impulsive or impact noise should not exceed 140 dB peak sound pressure
level."
The permitted durations, T, shown in the above table can be described by the formula
2/5
where t is expressed in hours and L is the equivalent noise level, expressed in decibels re 20u-PA.
In general, the equivalent noise level of a time-varying signal of duration T is
r fT 1n/3
111 3/n
Leq = 10 Iog10b/ (10L/1°) dtj , (2)
where L is the time-varying sound level and n defines an exchange rate between noise level and time. For
instruments using energy equivalence, n = 3, corresponding to a rate of 3.01 decibels per doubling of
time. Present U, S. hearing conservation regulations (Table G-16 and eq. (1)) use an exchange rate of
n = 4.98, corresponding to a rate of 5 decibels per doubling of time-
The equivalent duration of time-varying signal of actual duration T is
,3/n
, f
J o
fceq - / I10 r I dc-
where L is the rating sound level. For OSHA regulations, Lr = 90 dB.
The percent of allowable noise exposure is
,T
i l
PE = 100
c,-;
o
,T ,. -> 3/n
1 f f (L-Lr)/10|
-J J ,..
~~ The relation between eqs. (2) and (5) is seen by observing that (10L^10) " = (10L/L0)3
relation between
.301^75 2L/5 t
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where tr is the rating duration. Substituting the OSHA rating duration of 8 hr, the rating sound level
of 90 dB, and n = 4.98, this becomes
.602
PE = 12.5 / |10V~ '-""I dt
(L-90)/5
2 dt
(5)
Thus if L equals 90 dB, one will acquire 12. 5* of the allowable noise exposure during each hour exposed
and the total allowable exposure in 8 hours. If L equals 95 dB, 25% is acquired each hour so that only
four hours of exposure are permitted.
All of the U. S.-made personal Integra ting- type noise exposure meters investigated purported to
measure the quantity defined in eq. (5). Because of the wording of present Federal regulations the
devices intentionally do not include levels below 90 dB in the integration. In addition to measuring
percentage of allowable noise exposure, some of the devices provide a means of indicating whether or not
the sound level exceeded 115 dB during the measurement interval.
There has been some ambiguity as to the interpretation of Table G-16 in the OSHA regulations. One
stationary (non-wearable) integrating noise exposure meter did not follow eq. (5) but, rather, followed
the steps in Table G-16. That is, the percent of allowable exposure was computed from
PE = i nn
where Cn indicates the total time of exposure in a specified range of noise level and Tn indicates the
total time of exposure permitted at that level. Thus Tl = 8 hr corresponds to levels in the range 90-
92 dB, T2 = 6 hr corresponds to 92-95 dB, etc.
Some devices did not measure noise exposure. The simplest of these caused a warning light to be
turned on when the noise level exceeded a particular value. One device measured the total time that
a particular noise level was exceeded. One device, of European manufacture, did not provide Information
compatible with OSHA regulations. Such devices are not included in this report.
Basically, a noise exposure meter consists of two parts- a sound level metering section and an
integrating section. A block diagram showing the principal of operation for a typical dosimeter is
shown in Figure 1. A microphone (most devices utilize an omnidirectional ceramic microphone) senses the
sound pressure and the output is fed into an A-weighting filter which appropriately attenuates the
signal. The signal is then detected and averaged to provide an output hopefully equivalent to therms
A-weighted slow response value that would be read on a sound level meter.
The output of the sound level metering section is then fed into an integrator section which performs
the integration indicated in eq. (5). The output of the exponent circuit (a voltage) is typically
converted to a frequency (pulses), or in the case of the devices that utilize an electrochemical
memory cell, to a current. The pulse count is accumulated, then monitored and when a given percent of
the allowable exposure is reached -- for example, one-tenth of one percent -- a signal is sent to the
counter and the readout display registers one-tenth percent.
In addition, most devices have a detector which monitors the signal for A-weighted noise In excess
of 115 dB. If such a noise is detected, an electronic latch Is tripped. The latch is attached to an
indicating light and by closing the circuit with a test button, its status can be checked.
3. DESCRIPTION OF TESTS
The primary goal of this program was the evaluation of commercial noise exposure meters as to their
applicability as instruments for use in achieving the broader goals of EPA rather than their usefulness
in monitoring compliance with occupational noise regulations. Therefore, the study included testing
of specific performance attributes in addition to overall systems tests. Well-defined electrical and
acoustical signals were provided to each device and Che response of the instrument was compared with the
known input. It was felt that the following factors required attention:
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-i OVER 115 dB
J COMPARATOR
OVER IISdB
LIGHT
MICROPHONE
A-WEIGHTING NETWORK
SQUARING CIRCUIT
AVERAGING CIRCUIT
-] OVER 90 dB
J COMPARATOR
EXPONENT CIRCUIT
(EXCHANGE RATE)
INTEGRATION /DISPLAY
T2(L-90)/6dt
Figure 1. Block diagram showing the principle of operation for a typical noise exposure meter.
Acoustical Evaluation
- microphone response to sound of random incidence
- errors or uncertainties due to reflection, diffraction, and absorption effects arising from use
conditions
- overall system response to sound of random incidence
Electrical Evaluation
- frequency response
- detector characteristics (i.e., how true is rms response?)
- dynamic response for time varying signals
- dynamic range (including internal noise and distortion)
- nature and accuracy of time integration
Overall Evaluation
- appropriateness of quantity measured
- convenience of use
- ease and accuracy of calibration
- sensitivity to environment
- durability
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It would have been prohibitively expensive and time consuming to conduct detailed calibrations and
physical tests to evaluate all of the quantities listed above. Therefore, the manufacturer's instruc-
tion manual and wiring diagrams were carefully studied to ensure that the operation of the device was
fully understood and that test signals were applied and sampled at appropriate locations. On this
basis, carefully selected'tests were carried out to yield the most important information regarding the
performance of each noise exposure meter. The following sections contain detailed descriptions of the
various tests -- both acoustical and electrical -- which were performed.
3.1. Acoustical Tests
Acoustical tests were performed in a 425 m reverberation chamber. For A-weighted-sound levels at
and below 100 dB, the input signal was broad-band noise shaped to be "pink".!/ from 50 kHz to 10 kHz.
Above 100 dB an octave band of pink noise centered at 1 kHz was utilized.
Microphone and speaker placement as well as the signal generation and data retrieval system utilized
for acoustical tests are sho«m in Figure 2.
NOISE SPECTRUM THREE
GENERATOR SHARER AMPLIFIERS
TO THREE
SPEAKERS
1
REVERBERATION
CHAMBER
©
MICROPHONE
PLACEMENT
DETAIL
FROM
MICROPHONE
TELETYPE COMPUTER REAL-TIME
ANALYZER
Figure 2. Block diagram of equipment used for acoustic tests in a reverberation chamber.
2f "pink" noise is white noise passed through a network which weights at -3 dB per octave.
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Sound pressure Levels were measured using a one-inch condenser microphone.
For all tests the vanes in the chamber were rotated at 5 r.p.m. to promote diffuseness of the sound
field.
a. Microphone Calibration
During microphone calibration the reference microphone was located at position 1 (see Figure 2)
and noise exposure meter microphones (test microphones) occupied the remaining six positions on the
circumference of a two-foot diameter circle surrounding the standard microphone. All microphones were
located five feet above the floor.
The noise exposure meter microphones had been removed from the devices. Care was taken to main-
tain microphone cable length. The signal from each test microphone was fed into a preamplifier and
then into a one-third octave band real-tine analyzer.
The sound level of the pink noise was adjusted to read 100 dB on the A scale of the real-time
analyzer. Other sound levels were utilized to check the linearity of the microphones over the range
of interest (90-115 dB) .
Once the response of the measuring system -- reference microphone, preamplifiers and real-time
analyzer -- had been set utilizing a pistonphone and the sound field established, the calibration was
placed under computer control. The one-third octave band correction values based on electrostatic
actuator calibration of the reference microphone were stored in the computer. The computer was pro-
grammed such that signals from the reference microphone were interrogated 120 seconds (approximately
6 time constants in the slow-random mode of the real-time analyzer) after the onset of the sound
fields. Addition of the correction values and the response of the reference microphone to the sound
field resulted in the establishment of the desired one-third octave band sound pressure levels in the
room. In sequence each of the test microphones were interrogated in a similar manner. Using these
data, the computer calculated the response of each test microphone.
b. System Response
For system response testing, the microphone of each noise exposure meter was positioned on the
circumference of a two-foot diameter circle which surrounded the reference microphone. All microphones
were located five feet above the floor. The response of the measuring system was set with a pistonphone
(124 dB at 250 Hz), the desired sound field was established, and the sound field was turned off. Once
all of the noise exposure meters were turned on and zeroed, the sound field was turned on, at the
established level, for a time equivalent to 75% of the permissible noise exposure under OSHA regulations.
This was chosen rather than 100% since one device would not indicate overranging above 100%. Upon
completion of the appropriate time period, as monitored by a stop watch, the sound field was turned off
and the noise exposure meter readings were recorded. This procedure was utilized for sound fields of
92, 95, 100, 105, 110 and 115 dB.
3.2. Electrical Tests
In this section, descriptions are given of the various tests which were carried out to determine
specific attributes of device performance.
For these tests an electrical signal was inserted in series with the microphone. A signal
generator with a low output impedance, compared to the impedance of the microphone, was used to ensure
that the total input impedance to the electronics was essentially the same as in normal usage.
In principle, all of these tests could be performed using the readout device provided with the noise
exposure meter. However, because of the large quantity of data being acquired this would have been
prohibitively time-consuming. Accordingly, for one of the tests (see 3.2.a.) .voltage measurements were
made at an internal point in the instrument. For other tests, direct measurements were made of the
period of the pulse train which advanced the counter (mechanical or electronic) in the noise exposure
meter. In many cases, a fairly high frequency pulse train was available (with a dividing circuit to
produce a lower frequency signal to actuate the counter) so that the time to obtain a datum point was
reduced from possibly hours to the few seconds needed for the system to stabilize after changing the
input signal.
a. Frequency Response
The frequency response was measured by injecting a sine wave voltage in series with the microphone
and then measuring the voltage at the output of the A-weighting network while the frequency of the test
signal was swept over the frequency range from 20 Hz to 20 kHz. The frequency response was recorded
directly on a graphic level recorder which had its paper speed synchronized with the oscillator sweep
speed.
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The frequency response of the electronics was combined with that oE the microphone (see 3.1.a.),
to obtain the overall frequency response curves shown in Section 4.
b. Crest Factor Capability
A pulsed sine wave was presented to the noise exposure meter via the voltage insertion technique to
obtain a measurement of the crest factor handling capability. The crest factor of a signal is defined
as the ratio of peak signal value to rms (root-mean-square) value. It is important to consider because
many industrial noises have a high crest factor.
The pulsed sine wave consisted of a 1 kHz sine wave gated by a pulse train with a frequency of 100
Hz (period = 10.0 ms) and an adjustable pulse duration. By changing the pulse duration from full-on
to a very short pulse (12.5 ms), the crest factor was increased from 1.414 (sine wave) to 4.0. As the
pulse duration was decreased, the pulse amplitude was increased in order to maintain a constant rms
voltage. The rms voltage levels applied were those corresponding to the 114 dB and 95 dB levels for the
individual noise exposure meters.
The equipment setup is shown in Figure 3. The gating of the sine wave was accomplished using an
analog multiplier. A precision ac voltmeter (accurate for signals having a crest factor up to 10)
was used to measure the rms value of the pulsed sine wave. An oscilloscope was used to msasure peak
values. The response of the noise exposure meter was determined either by measuring the period of the
pulse train which actuated the counter or by using the actual readout from the noise exposure meter.
SINE WAVE
OSCILLATOR
TRUE RMS
VOLTMETER
I
*
PULSE
GENERATOR
ANALOG
MULTIPLIER
o
OSCILLOSCOPE
STEPPED
ATTENUATOR
MICROPHONE
IN
OUT
DIGITAL
COUNTER
NOISE EXPOSURE
METER
Figure 3. Block diagram of the equipment used for crest factor measurements.
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c. Exchange Race
Using the voltage Insertion technique, a 1 kHz sine wave was injected in series with the microphone
and the response of the noise exposure meter observed (either directly or by observing the internal pulse
train) as the voltage was varied over a range corresponding approximately to a sound level of 90 to 115
dB.
The data hours for 100Z exposure vs. the input voltage level (i.e., vs. the logarithm of voltage)
were plotted and a straight line was drawn through the central portion (main trend) of the data. The
voltage corresponding to an allowable exposure time of 0.25 hr was then read from this curve. Using
this voltage in an expression analogous to eqs. (4) and (5) in Section 2, calculations were made of the
percent of allowable noise exposure which the device would be expected to read for each test voltage
provided it were functioning perfectly. The observed readings (actual data points) were then ratioed to
the calculated expected readings. In effect, this procedure compares the response of the device at any
test voltage to the response which would be expected if the device (1) were functioning perfectly at a
voltage corresponding to a noise level of 115 dB and (2) had exactly the correct exchange rate of 5
decibels for a doubling of exposure time.
d. Temperature Response
Since personal noise exposure meters may be used in occupations where temperature extremes occur,
limited measurements were made of performance as a function of temperature.
A 1 kHz signal was injected in series with the microphone and the output of the noise exposure
meter measured with the device at room temperature (24°C), in a small oven at 45+l°C, and in a refrigera-
tor at 5+l°C. The instruments were allowed to reach thermal equilibrium before data were taken.
e. Battery Voltage
Personal integrating noise exposure meters are battery operated and during normal usage the battery
voltage will decrease. To determine the dependence of the dosimeter on battery voltage, an adjustable
dc power supply was substituted for the Internal battery. The voltage was adjusted over a wide range
appropriate for the battery type (in a specific voltage range given by the manufacturer) while injecting
a 1 kHz signal in series with the microphone, Thus the performance of the instrument was determined as
a function of supply voltage. Most of the devices had a voltage regulator and a battery check feature
to indicate when the battery voltage was too low for proper operation. When these features were function-
ing properly, the tests indicated that low battery voltage would not result in erroneous measurements
unless the battery was sufficiently discharged to deactivate the battery check indicator. For one
instrument, however, readings of noise exposure were found to be significantly in error before the
battery check indicator revealed a problem. For this instrument the performance is reported at the
voltage which deactivated the battery check indicator.
3.3. General Observations
In addition to the specific acoustical and electrical tests described above, observations were made
relative to the convenience of use and to factors which could lead to maintenance or operational difficul-
ties. These observations are listed in Section 4 for each Instrument evaluated.
4. RESULTS OF TEST
In this Section, results are given for the tests descrioed in Section 3. The test samples included
the following commercial noise exposure meters: Columbia models 101 and 104, Dupont, General Radio models
1934 and 1944, 3M, Quest M-6, and Tracoustics. Unless otherwise Indicated, two samples of each model
were tested. All of the models tested were purchased between March and May, 1972; therefore, present
models may not be identical to those teste due to possible modifications by the manufacturer.
Personal (Wearable) Instruments
4.X. Model A
4.1.1- Acoustical Tests
a. Microphone Calibration
The relative response of the microphone based on 0 dB response at 1 kHz, is shown as a function of
frequency in Figure 4.1-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated
no problems with linearity.
b. System Response
The overall performance of the noise exposure meter, when placed in a random, diffuse sound field
as described in Section 3.1.b.,is shown in Figure 4.1-2. The response was measured relative to a
8
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calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated
uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure
meter was tested.
20
10
O
o
uT
CO
Q.
CO
Ul
<
d -'o
K
-20
I
1 I
- MODEL A
o SAMPLE I
A SAMPLE 2
I
I
I
0.1
1.0
FREQUENCY, KHz
Figure 4.1-1. Relative Frequency response of microphone.
10.0
RELATIVE RESPONSE, PERCENT
g g 1 § I
1 1
MODEL A
o
0
1
O
1
t
1
\\X\\\\\\\\\\\\\\\\\\\\\\
\\\\v\\v\\\\\\\\\\\\\\\\\
~ 0 SAMPLE 1
A SAMPLE 2
I |
1
0
A
1
o
A
1
8
A
i
90 95 100 105 110 115
A-WEIGHTED SOUND LEVEL,dB reZOftPo
Figure 4.1-2. Response of noise exposure meter, relative to expected response
when placed in a field of pink noise (see text) at A-weighted-
sound levels from 92 to 115 dB.
4.1.2. Electrical Tests
a. Frequency Response
The combined frequency response of the microphone, the input amplifier, and the A-weighting network,
as measured at the output of the A-weighting network, is shown in Figure 4.1-3.
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20
10
ffi
o
uf
tn
- IO
> 20
<
UJ
-30
-40
-5O
MOD
INSERT
o SAMPLE I
A SAMPLE 2
\
I _
I -
O.I
1.0
FREQUENCY, kHz
10.0
Figure 4.1-3.
Relative combined frequency response of microphone plus
electronics. The dashed curves indicate the allowable response
level limits for a Type 2 sound level meter as specified in
American National Standard Specifications for Sound Level Meters
SI.4-1971.
b. Crest Factor Capability
The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine wave),
is shown in Figure 4.1-4. as a function of the crest factor (ratio of peak voltage to rms voltage) of the'
test signal.
c. Exchange Rate
The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative
to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time Is
shown In Figure 4.1-5. The important thing to consider here is whether or not the data points define a
flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range shown
could be compensated for, by gain adjustments, if the curve is flat over a total of at least 25 dB.
d. Temperature Range
The response of the noise exposure meter, at high and low temperatures, relative to 100% response at
24°C, was found to be:
5°C
45°C
Sample 1
106%
106%
e. Battery Voltage
Sample
94%
113%
The response of the noise exposure meter, relative to 100% response for a full-charged battery, was
75% for Sample 1 and 91% for Sample 2 at the voltage at which the battery check indicator showed battery
failure.
10
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ERRATUM*
NBSIR 73-417, EPA-550/9-73-007
Replace Figure 4.1-3, page 10, with figure below:
+20
+10
-10
20
-30
40
-50
MODEL A
I I
I
e SAMPLE 1
A SAMPLE 2
0.1
1.0
FREQUENCY. kHz
10.0
Replace Figure 4.2-3, page 13, with figure below:
20
10
8
uT
-10
-30
-40
-50
I
MODEL B
I I I
I I
- /r/
I I I
I I I
0.1 1.0
FREQUENCY. kHz
10-0
-------
120
t-
8 100
tf
*
Ul
z 8O
2
CO
Ul
tc
u, 60
p
-i
c 40
2O
1 1 1 1 1
~~ MODEL A ~~
A
u
_ OIISdB
A A 95dB
~ O ~~
A
A
_ 0 _
'
0
1 1 1 1 1
12345
CREST FACTOR
Figure 4.1-4. Response of noise exposure meter, normalized to 100% for
a sine wave input, as a function of crest factor.
140
Ul
u
tc
CO
o
CO
Ul
IE
Ul
Ul
tc
120
100
60
1
~ 1
_
MODEL A
io
A 0^0o.0rt00o
° v fft> o° A O A
A
A
^
A ^ ^^^^dD
0 SAMPLE 1
A SAMPLE 2
oA A
A ~~
o «
o
o
Figure 4.1-5. Relative response of noise exposure meter to an electrical signal
covering a range of approximately 25 dB. See text for method of
normalization.
4.1.3- General Observations
a. This instrument did not appear to have a voltage regulator.
b. The microphone shield lead was soldered to the case hinge and relied on electrical conduction
from one side of the hinge to the other.
11
-------
Personal (Wearable) Instruments
4.2. Model B
Two samples were purchased but tests are reported for only one since the other was found to be
defective.
4.2.1. Acoustical Tests
a. Microphone Calibration
The relative response of the microphone,based on 0 dB response at 1 kHz, is shown as a function of
frequency in Figure 4.2-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated
no problems with linearity.
b. System Response
The overall performance of the noise exposure meter, when placed In a random, diffuse sound field
as described in Section 3.1.b.,is shown in Figure 4.2-2. The response was measured relative to a cali-
brated condenser microphone and measurement system. The cross-hatched region indicates the estimated
uncertainty (95 percent confidence limits) In the level of the sound field in which the noise exposure
meter was tested.
ul
CO
o.
CO
UJ
QL
UJ
20
10
UJ
tc
- 10
-ZO
i i r
h- MODEL B
I I
I I
0.1
10.0
1.0
FREQUENCY, kHz
Figure 4.2-1. Relative frequency response of microphone.
4.2.2. Electrical Tests
a. Frequency Response
The combined frequency response of the microphone, the Input amplifier, and the A-welghting network,
as measured at the output of the A-weigb.ti.ng network, is shown in Figure 4.2-3, The manufacturer of
this instrument has notified MBS that they have'modified the design to improve the high frequency perfor-
mance.
b. Crest Factor Capability
The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine wave),
Is shown in Figure 4.2-4 .as a function of the crest factor (ratio of peak voltage to rms voltage) of the
test signal.
12
-------
140
UJ
oe 120
o 100
a.
V)
UJ
o:
UJ
> 80
§
UJ
(T
60
MODEL B
I
I
I
I
I
I
90 95 100 105 110 115
A-WEIGHTED SOUND LEVEL, dB re 20 ftPo
Figure 4.2-2. Response of noise exposure meter, relative to expected response,
when placed in a field of pink noise (see text) at A-weighted-sound
levels from 92 to 115 dB.
20
IO
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^
uf
O -10
Q.
W
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K
-20
E
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-30
-40
-5O
MODEL B
i i i i r i i
INCORRECT
Y SEE INSERT
O.I
i.o
10-0
FREQUENCY, kHz
Figure 4.2-3. Relative combined frequency response of microphone plus electronics.
The dashed curves indicate the allowable response level limits for a
Type 2 sound level meter as specified in American National Standard
Specifications for Sound Level Meters, SI.4-1971.
13
-------
120
gioo
ui
0.
RESPONSE,
OD
O
UJ 60
£
i
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K 40
20
1 1 1 1 1
_ MODEL B _
~~ 0 ~
A
° A °
_ A
a
~~ "
~ 0 1 1 5 dB ~~
_ A 95 dB _
1 1 1 1 1
12345
CREST FACTOR
Figure 4.2-4. Response of noise exposure meter normalized
to 100% for a sine wave input, as a function
of crest factor.
c. Exchange Rate
The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative
to the response of an instrument with an exchange rate of exactly 5 decibels par doubling of time is
shown in Figure 4.2-5. The important thing to consider here is whether or not the data points define
a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range
shown could be compensated for, by gain adjustments, if the curve is flat over a total of at least 25 dB.
I4O
PERCENT
N
O
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U)
° inn
O. IOO
tr
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P 8°
<
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60
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^
i
MODEL B
». A & A
, . . - -.
:
~^
r
Figure 4.2-5. Relative response at noise exposure meter to an electrical
signal covering a range of approximately 25 dB. See text
for method of normalization.
14
-------
d. Temperature Range
The response of the noise exposure meter, at high and low temperatures, relative to 100% response
at 24°C, was found to be:
5°C 102%
45°C 99%
e. Battery Voltage
Operation of the battery check indicator appeared satisfactory -- as long as the light would go on,
the response of the noise exposure meter did not change.
4.2.3. General Observations
a. Turning the switch from "on" to "battery check" and back to "on" was observed to advance the
counter by one count (.1%).
Personal (Wearable) Instruments
4.3. Model C
Only one sample was tested.
4.3.1. Acoustical Tests
a. Microphone Calibration
The relative response of the microphone,based on 0 dB response at 1 kHz, is shown as a function
of frequency in Figure 4.3-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB
indicated no problems with linearity.
CD
bl
o
Q.
v>
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or
u
20
10
-10
uJ
-20
I I
MODEL C
T
T
T
I I
O.I
1.0
10.0
FREQUENCY, kHz
Figure 4.3-1. Relative frequency response of microphone.
b. System Response
The overall performance of the noise exposure meter, when placed in a random, diffuse sound field
as described in Section 3.1.b.,is shown in Figure 4.3-2. The response was measured relative to a
calibrated condenser microphone and measurement system. The cross-hatched region indicates the estimated
uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure
meter was tested.
15
-------
140
UJ
u
id 120
UJ
CO
OL 100
UJ
tr.
UJ
I 80
UJ
Q£
60
I I
MODEL C
I
I
90 95 100 105 110 115
A-WEIGHTEO SOUND LEVEL, dB re 20/j.Pa
Figure 4.3-2. Response of noise exposure mecer, relative Co expected response,
when placed in a field of pink noise (see text) at A-weighted-
sound level from 92 to 115 dB.
4.3.2. Electrical Tests
a. Frequency response
The combined frequency response of the microphone, the input amplifier, and the A-weighting network,
as measured at the output of the A-weighting network, is shown in Figure 4.3-3.
b. Crest Factor Capability
The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine wave),
is shown in Figure 4.3-4. as a function of the crest factor (ratio of peak voltage to rms voltage) of the
test signal.
c. Exchange Rate
The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative
to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is
shown in Figure 4.3-5. The important thing to consider here is whether or not the data points define
a flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range
shown could be compensated for, by gain adjustments, if the curve is flat over a total of at least
25 dB.
d. Temperature Range
The response of the noise exposure meter, at high and low temperatures, relative to 100% response
at 24°C, was found to be:
5°C
45"C
e. Battery Voltage
This instrument did not have a battery voltage indicator.
4.3.3- General Observations
(none)
100%
101%
16
-------
20
IO
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Q
u
M
I -.0
J3
oe
> -20
u
-30
-40
-50
T 1
MODEL C
T T
I _
I L
O.I I.O
FREQUENCY, kHz
10X3
Figure 4.3-3. Relative combined frequency response of microphone plus
electronics. The dashed curves Indicate the allowable
response level limits for a Type 2 sound level meter as
specified in American National Standard Specifications for
Sound Level Meters, SI.4-1971.
I2O
8 ioo
(T
HI
Q.
ISPONSE,
0»
O
ud
(T
u 60
u
o: 40
ZO
1 1 1 1 1
MODEL C
_ 0 1 1 5 dB _
A 95 dB
_ 0 _
~~ A ~~
0 _
_ A _
o
1 1 1 1 1
12345
CREST FACTOR
Figure 4.3-4. Response of noise exposure meter, normalized
to 100% for a sine wave input as a function
of crest factor.
17
-------
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o
£.20
Q. IOO
en
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tr.
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C 80
r~
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60
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'
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~
1
1 MODEL C
1
1
\ '
<13 Oo 9
_
. -
^^
^^^
Figure it.3-5. Relative response of noise exposure meter to an electrical signal
covering a range of approximately 25 dB. See text for method of
normalization.
Personal (Wearable) Instruments
4.4. Model D
Two pilot-production samples, designated 1 and 2, were tested. The overall (acoustical) system
performance of two production samples, designated 3 and 4, was determined.
4.4.1. Acoustical Tests
a. Microphone Calibration
The relative response of the microphone, based on 0 dB response at 1 kHz, is shown as a function of
frequency in Figure 4.4-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated
no problems with linearity.
b. System Response
The overall performance of the noise exposure meter, when placed in a random, diffuse sound field
as described in Section 3.1.b.,is shown in Figure 4.4-2. The response was measured relative to a cali-
brated condenser microphone and measurement system. The cross-hatched region indicates the estimated
uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure
meter was tested.
4.4.2. Electrical Tests
a. Frequency Response
The combined frequency response of the microphone, the input amplifier, and the A-weighting network,
as measured at the output of the A-weighting network, is shown in Figure 4.4-3.
b. Crest Factor Capability
The response of the noise exposure meter, normalized to 100% for a crest factor of 1.414 (sine wave),
is shown in Figure 4.4-4.as a function of the crest factor (ratio of peak voltage to rms voltage) of the
test signal.
18
-------
20
ME RESPONSE,
0 0
£
u-IO
ac
-20
"1 T
MODEL D
frte*^
o SAMPLE 1 S^
A SAMPLE 2
III III II
O.I 1.0
FREQUENCY, kHz
Figure 4.4-1. Relative frequency response of microphone.
10-0
RELATIVE RESPONSE, PERCENT
n 0» Q ro £
o o o o o
-T- n~ -i i i" ~r
MODEL D
l_ A
* A 4 t
\\\\\\^\\\\\\\
\\ V\»\ V\ V\ V\ \9\ \
A
" o SAMPLE 1
- A SAMPLE 2
SAMPLE 3
~ A SAMPLE 4
I 1 1 1 1 1
90 95 100 105 110 115
A-WEIGHTED SOUND LEVEL, dB re 20
Figure 4.4-2. Response of noise exposure meter, relative to expected response,
when placed in field of pink noi«e (see text) at A-weighted-sound
levels from 92 to 115 dB.
19
-------
2O
10
-10
-30
-40
-50
MODEL 0
o SAMPLE I
A SAMPLE 2
O.I I.O
FREQUENCY, kHz
10-0
Figure 4.4-3. Relative combined frequency response of microphone plus
electronics. The dashed curves indicate the allowable response
level limits for a Type 2 sound level meter as specified
in American National Standard Specifications for Sound Level
Meters, SI.4-1971.
120
:, PERCENT
0
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|ao
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ui 60
\
£ 40
20
1
MODEL D
A a a a a
u
0 1 15 dB
_ A 95 dB
1
1 1 1 1 1
Figure 4.4-4.
12345
CREST FACTOR
Response of noise exposure meter, normalized to 100% for a
sine wave input, as a function of crest factor.
20
-------
c. Exchange Rate
The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative
to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is
shown in Figure 4.4-5. The important thing to consider here is whether or not the data points define a
flat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range shown
could be compensated for, by gain adjustments, if the curve is flat over a total of at least 25 dB.
d. Temperature Range
The response of the noise exposure meter, at high and low temperatures, relative to 100% response
at 24°C, was found to be
5«C
45°C
Sample 1
101%
Sample 2
96%
102%
140
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120
O
(L
id
IT
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3
UI
80
60
_ A
MODEL D
" ° nCwO & A O O O
O A A ** " A Mi A A A /
o^
o SAMPLE 1
A SAMPLE 2
& _
Figure 4.4-5. Relative response of noise exposure meter to an electrical signal
covering a range of approximately 25 dB. See text for method of
normalization.
e. Battery Voltage
Operation of the Battery check indicator appeared satisfactory.
4.4.3, General Observations
a. It was observed that the unit can be permanently damaged during battery installation if the
battery terminals are touched with reversed polarity to the connector.
b. Difficulty was experienced in connecting the production noise exposure meters to the calibrator
due to mechanical misalignment.
c. The normal calibration check was not sufficiently precise (+ 10% of permissible noise exposure).
Personal (Wearable) Instruments
4.5. Model E
4.5.1 Acoustical Tests
a. Microphone Calibration
The relative response of the microphone, based on 0 dB response at 1 kHz, is shown as a function of
frequency in Figure 4.5-1. Tests over the range of A-weighted-sound levels from 90 to 115 dB indicated
no problems with linearity.
21
-------
m
o
UJ*
en
Q.
80
UJ
o:
60
1 T
MODEL E
O SAMPLE I
A SAMPLE 2
_L
_L
_L
_L
Figure 4.5-2.
90 95 100 105 110 115
A-WEIGHTED SOUND LEVEL, dB re 20/iPd
Response of noise exposure meter, relative to expected response,
when placed in a field of pink noise (see text) at A-weighted-
sound levels from 92 to 115 dB.
22
-------
4.5.2. Electrical Tests
a. Frequency Response
The combined frequency response of Che microphone, the input amplifier, and the A-weighting network,
as measured at the output of the A-welghtlng network, is shown in Figure 4.5-3. It should be noted that
this unit has a potted electronics module; therefore, measurements had to be made at the output of the
exchange rate circuit rather than at the output of the A-weighting network. For this reason one could
only check the frequency response over a 25 dB range.
20
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CD
TJ
uf
CO
£ -10
a
cr
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-------
at 24°C, was found to be:
u uv .
5°C
45°C
I4O
Ul
o 120
Ul
Q.
RESPONSE,
O
O
uj 80
<
Ul
«r 6O
4O
Sample 1 Sample 2
100% 99%
101% 102%
1 1 1 1 1
~~ MODEL E ~~
_ A _
a
A
G o
^
_ o
~~ o I 15 dB ~
_ A 95 dB
1 1 1 1 1
234
CREST FACTOR
Figure 4.5-4. Response of noise exposure meter, normalized
to 100% for a sine wave input, as a function
of crest factor.
ONSE, PERCENT
> ro Z
> o O
Q. IUU
tr
S 80
UJ
a 6O
]
o
MODEL E
A /V» n o
o o
«""*^ rlrt hi
0 SAMPLE 1
A SAMPLE 2
~
_
O.
Figure 4.5-5. Relative response of noise exposure meter to an electrical signal
covering a range of approximately 25 dB. See text for method of
normalization.
e. Battery Voltage
The response of the noise exposure meter, on both samples, relative to 100% for a fully-
24
-------
charged battery, was 94% at the voltage at which the battery check indicator showed battery failure.
4.5.3. General Observations
a. The clip for attaching the microphone to the user's clothing easily became detached from the
microphone.
Personal (Wearable) Instruments
4.6. Model F
These devices were received very late in the program. Only the overall acoustical performance and
the exchange rate were evaluated.
4.6.1. Acoustical Tests
The overall performance of the noise exposure meter, when placed in a random diffuse sound field
as described in Section 3.1.b.,is shown in Figure 4.6-1. The response was measured relative to a cali-
brated condenser microphone and measurement system. The cross-hatched region indicates the estimated
uncertainty (95 percent confidence limits) in the level of the sound field in which the noise exposure
meter was tested.
RELATIVE RESPONSE, PERCENT
0> o> O w *
O O O O O
1 1 1
- MODEL F
1 1 1
\\\\\\ \\\\\\\\\\\\\\\\
\\\\\\X\\^\>
o
A
0 SAMPLE 1
A SAMPLE 2
1 1 1
\
6
i i i
^
\
s
^
;
90 95 100 105 110 115
A-WEIGHTED SOUND LEVEL,dB re 20 /APa
Figure 4.6-1. Response of noise exposure meter, relative to expected response when
placed in a field of pink noise (see text) at A-weighted-sound levels
from 92 to 115 dB.
4.6.2. Electrical Tests
The response of the noise exposure meter, normalized to 100% at a duration of 0.25 hours, relative
to the response of an instrument with an exchange rate of exactly 5 decibels per doubling of time is
shown in Figure 5.6-2. The important thing to consider here is whether or not the data points define
a £lat curve over a range of at least 25 dB. Deviations from flatness at one end of the 25 dB range
shown could be compensated for, by gain adjustments, if the curve is flat over a total of at least
25 dB. It should be noted that sample 2 is a first generation design while sample 1 is a later model.
The manufacturer of this instrument notified NBS that they had modified the design to cover the necessary
25 dB dynamic range.
4.6.3. General Observations
(none)
25
-------
140
i
2JI20
uf
CO
0
^k I^X^X
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140
120
5
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(/>
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Q.
(rt
UJ
ac
UJ
80
100
UJ
(K
60
1 T
!- MODEL G
044
O SAMPLE I
A SAMPLE 2
I
Figure
90 95 100 105 110 115
A-WEIGHTED SOUND LEVEL, dB re 20 ft Pa
.7-1. Response of noise exposure meter, relative to expected response, when
from 921?oamedt°f Plnk n°1Se (S6e teX° " A-»"8"ted-sound ieve?"
140
u
o
o:
120
V)
glOO
UJ
tc
80
UJ
-------
5. SUMMARY AND CONCLUSIONS
In general, the following conclusions can be drawn as a result of this test program:
Microphone response Most noise exposure meters utilize well-proven ceramic microphones
with characteristic response being relatively flat from 50 Hz to 5-8 kHz.
None of the microphones tested showed any evidence of nonlinearities over
the dynamic range of Interest (90-115 dB).
System response Since no performance standard exists against which these devices can
be built and tested, the system responses are widely varying depending on the
particular design.
Frequency response Most noise exposure meters meet the allowable tolerances for a Type
2 sound level meter (relative combined frequency response of microphone plus elec-
tronics) as specified in American National Standard Specifications for Sound Level
Meters, SI.4-1971.
Crest factor capability Most devices can handle only small crest factors. Whether or not
this presents a problem depends on the use situation. The response for all models,
with the exception of model D, falls below a 90% reading or exceeds a 110%
reading at a crest factor of 2-4. Model D's response remains nearly perfect
at a crest factor of 4.
Exchange rate The exchange rate circuitry appears to be a troublesome design problem for
some manufacturers. One reason for this may be that they have no experience with
such circuitry from other instruments; however, it is a crucial part of a noise
exposure meter.
Temperature range Most noise exposure meters suffer only a few percent error due to temp-
erature effects over the range 5°C-45°C.
Battery voltage Those devices with voltage regulation showed no effect in dosimeter reading
due to battery drain effect for voltages above the battery check indicator minimum.
The obvious exception to the above general conclusions are models A and G, both of which performed
poorly in each of the above tests.
It is quite evident that a comprehensive performance standard for these devices is an absolute
necessity. American National Standards Institute Working Group S1-W45 is presently working on such
a standard and its efforts should be encouraged and accelerated. In addition, a usage standard might be
necessary to provide guidance on such items as microphone placement on the body, minimum recommended
checks prior to usage, and guideline handling procedures Important considerations which the per-
formance standard may not provide.
The test program has shown that there exists a wide variation in performance among the various
noise exposure meters tested. Some might serve as instruments for monitoring compliance with the
occupational noise exposure regulation; however, the user should be cautioned to carry out enough
evaluation tests to ascertain that the devices are performing adequately for his purpose.
28
-------
6. BIBLIOGRAPHY
1. American Standard Method for the Calibration of Microphones, SI.10-1966,American National Standards
Institute, New York, New York (March 1966).
2. American National Standard Specifications for Sound Level Meters, SI.4-1971, American National
Standards Institute, New York, New York (April 1971).
3. International Electrotechnical Commission Recommendation on Precision Sound Level Meters, Publication
179-1965, International Electrotechnical Commission, Geneva, Switzerland (1965).
4. American National Draft Standard for Integrating Sound-Level Meters, American National Standards
Institute, New York, New York.
5. Magrab, Edward B. and Blomquist, Donald S., The Measurement of Time-Varying Phenomena-Fundamentals
and Applications. Wiley Intersclence, New York, New York (1971).
29
-------
NBS.114A (REV 7-731
U.S DEPT. OF COMM.
BIBLIOGRAPHIC DATA
SHEET
1. PUBLICATION OR RKPORT NO
NBSIR 73-417
EPA-550/9-73-007
2. Gov't Accession
No.
3. Recipient's Accession No.
4. TITLE AND SUBTITLE
Evaluation of Commercial Integrating-Type Noise Exposure
Meters
5. Publication Dace
6. Performing Organization Code
7.
am A. Leasure, Jr., Ronald L. Fisher, Marilyn A. Cadoff
i. Report No.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
NATIONAL BUREAU OF STANDARDS
DEPARTMENT OF COMMERCE
WASHINGTON, D.C. 20234
10. Pro|eci/Task/W0rk Unu No.
2130491
11. Contract/Grant No.
12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)
Office Noise Abatement and Control
U. S. Environmental Protection Agency
Washington, D. C. 20460
13. Type of Report & Period
Covered
Final
14. Sponsoring Agency Code
15. SUPPLEMENTARY NOTES
16. ABSTRACT (A 200-word or less factual summary ol most significant information If document includes a significant
bibliography or literature survey, mention it here )
As a result of the promulgation of occupational noise exposure regulations by the
Federal government, there are a number of commercial noise exposure meters on the
market today that provide a measure of noise integrated (with appropriate weighting)
over a time interval. This report presents the results of an evaluation of such
instruments by the National Bureau of Standards (under the sponsorship of the U.S.
Environmental Protection Agency) as to their usefulness in monitoring compliance
with occupational noise regulations as well as their applicability as instruments
for use in achieving the broader goals of the EPA. Tests were designed and conducted
to evaluate microphone and system response to sound of random incidence, frequency
response, crest factor capability, accuracy of the exchange rate circuitry, perform-
ance of the noise exposure meter as a function of temperature, and the dependence of
the device on battery voltage. The rationale of the test procedures utilized to
evaluate overall system as well as specific performance attributes, details of the
measurement techniques, and results obtained are discussed.
17. KEY WORDS (six to twelve entries, alphabetical order, capitalize only the first letter of the first key word unless a proper
name, separated by semicolons)
Acoustics (sound); dosimeter; environmental acoustics; instrumentation; noise
exposure; noise exposure meters.
18. AVAILABILITY fX1 Unlimited
I ! For Official Distribution. Do Not Release to NTIS
I I Order From Sup. of Doc., U.S. Government Printing Office
Washington, D.C. 20402, SD Cat. No. C13
I | Order From National Technical Information Service (NTIS)
Springfield, Virginia 22151
19. SECURITY CLASS
(THIS REPORT)
UNCLASSIFIED
20. SECURITY CLASS
(THIS PAGE)
UNCLASSIFIED
21. NO. OF PAGES
34-
22. Price
USCOMM.DC 20042-P74
------- |