550/9-74-011
un MOWERS:
NOISE UNO COST OF 101TEMENI
JUNE 1974
u.s. Environmental Protection Agency
Washington, D.c. 20460
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Document is available to the public through the National Technical
Information Service, Springfield, Virginia 22151
Document is available in limited quantities through the Environmental
Protection Agency, Office of Noise Abatement and Control, Arlington,
Virginia 20460
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WALL STREET JOURNAK
appreciate what you've done about the noise of
your power mower, Adams!"
Reproduced by Courtesy of the Wall Street Journal
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FOREWORD
The Environmental Protection Agency is publishing a
series of reports prepared by contractors describing the
technology, cost, and economic impact of controlling the
noise emissions from commercial products. It is hoped that
these reports will provide information that will be useful
to organizations or groups interested in developing or
implementing noise regulations. This report was prepared
by Bolt, Beranek, and Newman under EPA Contract 68-01-1539.
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TABLE OF CONTENTS
page
LIST OP FIGURES vli
LIST OP TABLES viii
1. INTRODUCTION 1
2. CURRENT LAWN MOWERS 2
2.1 Noise Ordinances 5
2.2 NIPCC Report 5
2.3 Lawn Mower Industry 6
3. BASELINE NOISE LEVELS 10
3.1 Reasons for Differences in Noise Levels 14
3.2 Measurement Standards 16
3.3 Measures of Performance 18
3.4 Statistical Variations in Noise Level 19
4. NOISE CONTROL 21
4.1 Noise Sources 21
4 . 2 Definition of Manufacturer' s Cost 24
4.3 Noise Reduction by Component Interchange 24
4.4 Noise Reduction by Noise control Engineering 27
5. CONCLUSIONS 34
Minimum Standard Best Curren Levels 24
Intermediate Standard 37
Strictest Standard 38
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page
REFERENCES 39
APPENDIX A: LIST OP MANUFACTURERS' ASSOCIATIONS AND
RETAILERS CONTACTED 40
APPENDIX B: EXTERIOR SOUND LEVEL MEASUREMENT PROCEDURE FOR
SMALL ENGINE POWERED EQUIPMENT - SAE RECOMMENDED
PRACTICE 48
APPENDIX C: NOISE LEVELS OF CURRENT LAWN MOWER MODELS 6l
vi
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LIST OF FIGURES
page
Reel Mower 2
Gasoline Powered Rotary Mower 3
Riding Mower 4
Lead Time Figure 8
Pig. 1. Noise Levels of Walk-Behind Mowers at 50 ft 11
2. Operator's Ear Noise Level of Walk-Behind Mowers . 12
3. Noise Levels of Riding Mowers at 50 ft 12
4. Noise Levels of Riding Mowers at Operator's Ear .. 13
5. SAE Test Geometry 17
6. Sources of Noise 22
Cut-Away View of Briggs & Stratton 3-1/2 hp Lawn
Mower Engine 23
7. Level 1: Best Mufflers Currently Available 25
8. Level 2: Slower Engine 26
9. Level 3: Muffler and Quiet Blade 29
10. Level 4: Slower Engine and Quiet Blade 29
11. Level 5: Partial Enclosure 30
12. Level 6: Partial Enclosure and Quiet Blade 31
13. Level 7: Pull Enclosure 32
14. Level 8: Pull Enclosure and Quiet Blade 32
15. Noise Reduction Costs of Walk-Behind Mowers 35
16. Noise Reduction Costs of Riding Mowers 36
Bl. Test Site .' 56
vii
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LIST OF TABLES
page
Table I. Size Ranges of Lawn Mowers '. 4
II. Sales Distribution of Lawn Mowers 4
III. Chicago City Ordinance Levels for Lawn Mowers . 5
IV. NIPCC Noise Goals and Abatement Costs 6
V. Noise Level Ranges of Rotary Lawn Mowers in
dB(A) 13
VI. Cost and Noise Levels of One Manufacturer's
Mower Line 14
VII 15
VIII. Variations in Noise Levels Observed at 50 ft .. 19
viii
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1. INTRODUCTION
The manufacture of lawn care equipment accounts for sales of
$700 million annually, of which $550 million goes to power lawn
mowers. There are 95 manufacturers listed in Thomas' Register
and probably well over 200 altogether in the United States. For
this study, we contacted by telephone or letter about 35 of the
larger manufacturers; six of the more helpful manufacturers were
then visited directly. A list of the manufacturers contacted is
given in Appendix A.
For the small manufacturer, lawn mower fabrication is pri-
marily an assembly operation involving the purchase of many of
the parts required. Ninety-five percent of all lawn mowers use
either Briggs and Stratton or Tecumseh engines. Only two manu-
facturers make some of their own engines. A number of large
manufacturers specialize in the "Private Label" market where
they do not market under their own names but sell to large chain
stores or distributorships.
Unconventional substitutes for power lawn mowers have not
been considered seriously in this report. Such unconventional
approaches include plastic lawns, sheep, horses, and chemical
growth retardants.
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2. CURRENT LAWN MOWERS
The oldest type of power lawn mower currently in use is the
gasoline reel or barrel mower. The reel consists of five or six
helical blades which bear upon a cutter bar. The mower relies
upon a scissors type of action to cut the grass. When the mower
is adjusted so that the reel and cutter bar do not quite touch,
the reel can be very quiet. In this case, the engine is the
major noise source.
About twenty years ago, the rotary type of gasoline-powered
mower started to become popular. The rotary mechanism consists
of a two-arm blade rotating about a vertical axis. The blade re-
lies on it speed to cut grass, requiring a tip speed of between
16,000 and 19,000 feet per minute (fpm) to give a good cut. The
sharpness of the blade has little to
do with the actual cutting process,
this being determined primarily by
the blade speed, but sharpness does
determine whether the ends of the
grass blades become bruised or
split. Because of their high speed,
the blades on rotary mowers are
noisier than those of reel mowers.
Several modifications of the
basic rotary mower are now on the
market. Designers found that cut-
ting quality was improved by put-
ting lift on the blade by.shaping
it like an airfoil, so that the
grass blades are sucked up before
they are cut. This lift can also
be used to pick up the grass
REEL MOWER
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clippings and throw them
into a catcher bag. Other
mowers retain grass clip-
pings within the housing
and chop them up into a
mulch. In addition, some
walk-behind mowers offer
a self-propelled feature.
In recent years, the
popularity of riding
mowers has increased.
They use the same cutting
principle as the walk-
behind rotary mowers, but
do not usually bag the
grass clippings. Riding
mowers tend to have more
powerful engines and
larger structures than do walk-behind mowers. These structures
act as sounding boards for engine-induced vibration. Hence, rid-
ing mowers tend to make more noise. Both walk-behind and riding
rotary mowers are available with electric power.
For very large mowing operations, lawn tractors are used
with mowing attachments, but these tractors are not considered to
be within the scope of this investigation.
Lawn mowers are sized according to both installed engine
horsepower and cutting width. The ranges are listed in Table I.
GASOLINE POWERED ROTARY MOWER
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TABLE I.
Type
Reel
Walk-Behind Rotary
Riding Rotary
RIDING MOWER
SIZE RANGES OF LAWN MOWERS
Installed hp Cutting Width
2 to 2-1/2 hp 18 to 21 in.
3 to 5 hp
5 to 8 hp
18 to 22 in.
22 to 36 in.
The number of lawn mowers sold in 1970, together with their
dollar value, is listed in Table II [2].
TABLE II. SALES DISTRIBUTION OF LAWN MOWERS (1970)
Type Number of Units Dollar Volume
Reel 130,383 $ 12,993,686
Walk-Behind Rotary
Riding Rotary
4,056,059
889,432
5,075,874
229,755,763
318,839,378
$561,588,827
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It may be seen that walk-behind rotary mowers are by far the most
numerous but that riding rotary represent the largest dollar vol-
ume. The volume of reel mowers is only a few percent of rotary
mowers.
2.1 Noise Ordinances
Many cities and states have ordinances governing noise from
lawn equipment. Most well-known is the Chicago City Ordinance,
which sets a sliding time scale for equipment to achieve a given
noise level. These levels are listed in Table III.
TABLE III. CHICAGO CITY ORDINANCE LEVELS FOR LAWN MOWERS
Date Level at 50 ft
Manufactured after 1 January 1973 74 dB(A)
Manufactured after 1 January 1975 70 dB(A)
Manufactured after 1 January 1978 65 dB(A)
A manufacturers' association, the Outdoor Power Equipment
Institute (OPEI), has laid down a voluntary noise level criterion
at the operator's ear of 92 dB(A) for walk-behind mowers and
95 dB(A) for riding mowers. The OPEI standard covers many other
safety aspects of lawn mowers and all equipment which complies is
entitled to carry the OPEI sticker- Compliance is verified by an
independent testing laboratory.
2.2 NIPCC Report
In 1971 the National Industrial Pollution Control Council
(NIPCC) of the U.S. Department of Commerce published estimates of
feasible noise control goals for leisure time products including
walk-behind and riding mowers [3j. The goals and costs of their
* # ^
implementation are listed in Table IV.
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TABLE IV. NIPCC NOISE GOALS AND ABATEMENT COSTS
Date 1970 1973 1978 1983
Cost Increase
(% 1970 price) 0 5% ±5% 30%
Walk-Behind Mowers
[Levels in dB(A)]
At user's ear 92 88 85 82
At 50 ft 68 68 64 62
Riding Mowers
[Levels in dB(A)]
At user's ear 95 90 85 82
At 50 ft 78 73 68 65
For walk-behind mowers between 1970 and 1973, a 4-dB(A) reduction
at the operator's ear is predicted, with no reduction in the level
at 50 ft. This estimate is hard to understand.
The levels being considered in this report are very similar
to those listed in Table IV. However, we have been able to get a
more exact idea of how the levels will be achieved and have ob-
tained more accurate cost estimates. If the full distributor's
mark-up is applied, then our cost estimates are comparable to
those above.
2.3 Lawn Mower Industry '
There are over 200 lawn mower manufacturers in the United
States. They range in size from the large multimillion dollar
corporations with full-size engineering departments to small job-
shop operations. Only two of the larger corporations manufacture J
their own 2-cycle engines, all other companies buying their 4-
cycle engines from either Briggs and Stratton or Tecumseh. The
small manufacturers also buy the lawn mower decks, cutting blades,
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wheels, and handles and assemble these into the final lawn mower.
Many of the larger manufacturers sell similar models under differ-
ent brand names (private labels).
There are about 15 large manufacturers with engineering de-
partments capable of developing an acoustically treated lawn
mower. The other manufacturers rely on their suppliers for design
information, usually Briggs and Stratton who supply the engines
and can also provide some information on mufflers and engine
acoustic treatment. However, Briggs and Stratton do not offer
any information on how to quiet the lawn mower blade since this
is not their business.
Mark-ups
Manufacturers' costs for rioise reduction are very different
from the cost to the consumer, the difference being comprised of
manufacturer's overhead and profit, distributor's mark-up, and
retailer's mark-up. Some chain stores are able to buy directly
from the manufacturer and eliminate the distributor's mark-up. A
typical breakdown for a nominal $1.00 item is as follows:
Manufacturer's Cost $1.00
Manufacturer's Selling Price $1.50
Distributor's Selling Price $2.10
Retailer's Selling Price $3.00
Price to -Consumer $2.00 $4.00
These ratios may be larger for some "prestige" models for which
the manufacturer conducts large-scale national advertising. Also,
the mark-up on spare parts can be Very large. For example, a
muffler can cost the consumer $2.20.
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Mark-up can also be considerably lower than the above figures,
A manufacturer may apply a much lower mark-up for a bought out
item, such as the engine. For example, the engine on a lawn mower
which retails for $52.00 costs the manufacturer $24.00. If a
consumer wished to purchase a spare engine it would cost about
$70.00.
Manufacturing Schedules and Lead Time
The model year for lawn mowers starts in August of the pre-
vious year, and the engineering design is frozen one year before
that. Thus, a 1975 mower appears in August of 197^, but its de-
sign is frozen on August 1, 1973. Typically, there will be a
year of development engineering on the initial design. Thus, it
takes a total of 2-1/2 years from initial design to 1 January of
the model year. If the design has to be deduced from known tech-
nology, the process may take three years. Hence, three years is~
the minimum lead time required for a significant change in noise
levels.
RSD
PRODUCTION TOOLING
INVENTORY RUNDOWN
1 2
LEAD TIME (YEARS)
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Differential Effect of Regulations on Companies
The effect of noise regulations will vary with the size of
the company. It is likely that the 15 large companies with engi-
neering departments will be able to redesign and develop their
products to meet the various levels of noise reduction in proposed
regulations. Smaller companies, who will have to rely upon others
to quiet their machines, will have to buy from suppliers such
noise-controlled items as engine enclosures or quiet blades.
In the survey, there was no evidence of any significant cost
differences to small or large manufacturers. For example, engines
and mufflers are priced by cases of 30 or 60 units. The price is
the same whether one purchases 1 or 10,000 cases. (There is a
6% discount for spreading delivery.) A small manufacturer will
have to purchase items from a larger manufacturer, who will pre-
sumably apply his mark-up. However the small manufacturer will
not have the development and tooling costs. The cost estimates
given in Sees. 4 and 5 are, in any case, very rough, since even
the large manufacturers have a very poor estimate of their costs
and the small manufacturers have not even considered the question.
Universally, the estimated cost of a major design change for
most large manufacturers was the same: $250,000. This cost is
attributable to retooling and is almost independent of the actual
change made.
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3. BASELINE NOISE LEVELS
As shown in Sec. 2.1, there are some noise control standards
for lawn mowers. These standards have resulted in some degree of
noise control. Just about all mowers currently manufactured com-
ply with the voluntary OPEI standards of 92 dB(A) at the operator's
ear for walk-behind mowers and 95 dB(A) for riding mowers. All
walk-behind mowers comply with the current Chicago ordinance of
74 dB(A) at 50 ft and many comply with the 1975 level of 70 dB(A)
at 50 ft. However, many riding mowers do not comply with the
current Chicago ordinance,.and none comply with the 1975 level.
Because noise control generally costs money and manufacturers
have not found quiet to be a very good selling point, there has
so far been little incentive to quiet lawn mowers. From 1958 to
I960, Lawnboy and Dille & McGuire both marketed very quiet lawn
mowers with noise levels of about 58 dB(A) at 50 ft [about 10 dB(A)
below current levels], but their cost was about 30% more than
comparable mowers. These mowers had the full noise control treat-
ment discussed in Sec. 4 (Level 8), but they were smaller and did
not bag grass so well as other machines. The mowers did not sell
and, since then, manufacturers have been apprehensive of being at
a competitive disadvantage if they- produce a machine which is
quieter than it has to be but consequently more costly. However,
sensing an emerging public awareness of noise pollution, one
leading manufacturer plans to market a quieter mower in the fall
of 1973-
The noise levels of current walk-behind rotary mowers at 50
ft and at the operator's ear are listed by model in Appendix C
and illustrated in Figs. 1 and 2. Corresponding noise levels of
riding mowers are shown in Figs. 3 and 4. The noise levels are
plotted as a function of price, although, as will be discussed
10
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60
£ 70
o
in
<
CD
60
1 1 1 1 1
MANUFACTURED
AFTER JAN. 1
~ 1973 CHICAGO
60 60- 16B «
1975 CHICAGO 50 2B~
29t Z9-Z9- 3
6O 6O- 7 1^ 1^1* IB
1978 CHICAGO ' 1* IB
1O
30 19I
B 21"
0 18"
D 21"
A 21"
A 18"
I i i i i
1 1 1
WALK-BEHIND MOWERS
*
2m- e^Zm- Zm-
gg 1 1 SB-
2 A 2A
WITH CATCHER
GAS ROTARY -
GAS ROTARY B-
ELECTRIC ROTARY Q-
WANKEL ROTARY
REEL- GAS
REEL- PUSH
i i i
50
50
100
RETAIL PRICE ($)
150
200
Code of Manufacturers
1. Lawnb oy
2. Toro
3. Sears, Roebuck
H. Simplicity
5. Polaron
6. Black & Decker
7. General Leisure Products
8. Jacobsen
9. Scott
10. International Harvester
11. Huffman Eng.
12. General Electric
13. John Deere
11. MTD
15. Murray Ohio
16. Hahn Eclipse
FIG. 1. NOISE LEVELS OF WALK-BEHIND MOWERS AT 50 FT.
11
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100
OPEI
I I I
WALK-BEHIND MOWERS
2 30
uj
o.
o
S
CD
o
80
«O 6O-
,1.1
6O 6O-
10
TD
WITH CATCHER
O ELECTRIC ROTARY O-
19"GAS ROTARY
D 21" GAS ROTARY
WANKEL ROTARY
1
1
I
I
I
50
100 150
RETAIL PRICE ( $ )
200
FIG. 2. OPERATOR'S EAR NOISE LEVEL OF WALK-BEHIND MOWERS
80
O
in
1 1 1
RIDING MOWERS
MANUFACTURED
AFTER JAN.l
1973 CHICAGO
10* 10*
O ELECTRIC-ROTARY
5 hp GAS ROTARY
8 hp GAS ROTARY
1975 CHICAGO
11
14
1978 CHICAGO
6O
12O 13O
ZOO
4OO 6OO
RETAIL PRICE ( $)
600
FIG. 3. NOISE LEVELS OF RIDING MOWERS AT 50 FT.
12
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100
OPEI
I I
RIDING MOWERS
oc.
0.
o
*>
BO
14*
11
I
11
1*
13 O
200
400 600
RETAIL PRICE ( $)
800
FIG. 4. NOISE LEVELS OF RIDING MOWERS AT OPERATOR'S EAR.
further in Sec. 3.1, there is no correlation. One pays the extra
money on a mower, not for quiet, but for die cast deck, self-
propulsion, electric starter, or grass bag. Most mowers use very
similar engines, by far the most popular being the Briggs and
Stratton 3.5 hp for walk-behind mowers. One often finds essen-
tially the same engine on a $70.00 or $200.00 machine. The range
of noise levels is summarized in Table V.
(
t
TABLE V. NOISE LEVEL RANGES OF ROTARY LAWN MOWERS IN dB(A)
Walk-Behind Mowers:
Gasoline
Electric
Riding Mowers:
Gasoline
Electric
At Operator's Ear
8? to 92
86 to 92
90 to 95
At 50 ft
65.5 to 72
62 to 68
72 to 83
63
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One interesting fact which emerges is that electric walk-
behind mowers are not much quieter than gasoline mowers. The
reasons are that the noise from the rotating blade is the dominant
source and that a high-speed electric motor is also extremely
noisy. A Wankel engine powered mower has also been measured, but
it was not significantly quieter than any other mowers.
Correlation between noise levels at the operator's ear and
at 50 ft is shown in Table 5. The correlation is quite good, indi-
cating that a noise regulation at, say, the 50-ft level will
benefit both the community and the operator by the same reduction
in level from present values.
Some measurements have been made on a manually propelled
lawn mower which produced 53 dB(A) at 50 ft. These measurements
are discussed in Appendix C.
3.1 Reasons for Differences in Noise Levels
To explore some reaons for differences in noise levels among
lawn mowers, consider the model line as given in Table VI.
TABLE VI. COST AND NOISE LEVELS OF
ONE MANUFACTURER'S MOWER LINE
Electric Self- Self- Electric Start
Start
Model
Price $
Noise Level
CdB(A) at 50 ft]
Table VI shows that one pays $30.00 for electric start and $40.00
for self-propulsion, with no noise abatement. (The engine and
19 In.
130
69.5
21 In.
150
70.5
19 In.
160
69.5
19 in.
170
69.5
21 In.
190
70.5
21 1n.
220
70.5
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blade are identical.) $20.00 more for the larger machine pur-
chases slightly higher noise levels because of the slightly larger
engine and blade. As another example, consider the mowers one
can buy for $120.00 as shown in Table VII.
TABLE VII
Model
Noise Level
[dB(A) at
50 ft]
Capacitor
Discharge With
Ignition Catcher
19 in. 19 in.
65.5
67,. 5
Good Muffler/
Slower Blade
19 in. 19 in. 21 in. 20 in
68
69.5 70.5
72
Different Manufacturers
Here the mower with the grass catcher is noisier because more of
the underside of the deck is exposed. However, this manufacturer's
catcher design is unique and, in general, the noise difference
owing to the catcher is not significant. Noise levels vary from
one manufacturer to another, possibly because of variations in
measuring conditions. These variations should disappear when the
proposed SAE code of measurement practice is adopted. Other
factors are
Different Blade Lift -
Different Blade Clearances
Different Engine Governor Speeds
More lift often means more
noise but better bagging.
Less clearance means more
noise.
Manufacturers set engines to
run at different speeds.
OPEI limits blade tip speed
to 19,000 fpm. Some mowers
are closer to this limit
than others.
15
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It has not generally been found that the type of deck, steel or
magnesium, makes much difference unless a very thin steel deck
is used.
An electric mower with twin 9 in. blades rotating at 7S200
rpm has very high motor noise. Single rotor mowers rotating at
3,600 rpm were much quieter.
For the case of riding mowers, there is a large difference
in the noise levels produced by 5-hp and 8-hp machines, the 8-hp
engine being about 5 dB(A) louder. Other differences arise
mainly from the use of different mufflers. There are usually no
significant differences in noise levels produced by similar horse-
power engines of different manufacturers. They are all aluminum
and air-cooled. Briggs and Stratton and Tecumseh engines carry
identical prices, but engines made by the lawn mower manufacturers
themselves cost a little more.
3.2 Measurement Standards
There are currently two relevant'standards for the measure-
ment of lawn mower noise: American National Standards Institute
(ANSI)B 71.1 (1972) - Operator's Ear Noise - and Society of Auto-
motive Engineers (SAE) J952b - Community Noise at 50 ft. Both
standards describe how to take the noise measurements as well as
all necessary precautions. The SAE, however, has not found its
standard to be sufficiently detailed and consistent and is in the
process of developing a new code of practice. A draft of this
standard is included as Appendix B.
The new SAE code of practice aims at simulating the noise
levels generated under operating conditions. For this reason, the
tests measure the highest sound levels of a mower as it is driven
or walked by the measuring point. The type of surface over which
16
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the noise measurements are made causes a significant difference
in the results. The hardness of the ground and state of the grass
both have an influence, thereby indicating that results are not
repeatable from summer to winter. Consequently, the SAE subcom-
mittee employs a synthetic grass surface to obtain even results.
"Tartan Turf" (made by the Minnesota Mining and Manufacturing
Corp.) is glued to 1/2 in. to 3/4 in. plywood. The area covered
is a right-angled isosceles triangle with a long side of 46 ft
(see Pig. 5). The walk-by or drive-by takes place on the long
side with the observer holding a sound level meter at the right
angle. The setup requires twenty-eight panels 8 ft x 4 ft.
4ft
-46ft-
Y/////////7/7////////777,
DRIVE PATH
TARTAN TURF
MICROPHONE
FIG. 5. SAE TEST GEOMETRY,
The SAE subcommittee has also found that the loading on the
mower affects its noise level. A walk-behind mower makes the
greatest noise when it is not cutting, because the blades, which
are the main source of noise, move faster when unloaded. However,
a riding mower, in which the engine is the dominant source, makes
the most noise cutting long grass, because the engine is working
hardest then. Thus, the SAE specifies that riding mowers tow a
17
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load when measurements are made. This condition can make as much
as 7 dB(A) difference in the noise. Consequently, walk-behind
and riding mowers must be measured with slightly different pro-
cedures .
The revised SAE noise measurement standards have been care-
fully developed and have received wide acceptance in the industry.
It therefore seems reasonable that they be used for lawn mower
noise performance standards.
Equipment costs for performing these noise measurements are
$1500 for the special surface and $1000 for a precision sound
level meter. Each mower can be tested in half an hour.
3.3 Measures of Performance
Lawn mower performance is judged on the basis of cutting and
possibly of bagging grass. There are no objective measures of
these quantities, but manufacturers are generally agreed on the
performance criteria. As mentioned above, a high blade-tip speed
(16,000 to 19,000 fpm) is required for a good cut. If the blade
is slowed, one way of reducing its noise, then its performance in
thick grass and weeds will degrade. Tufts of grass may be left
uncut and have to be gone over again. Roughly speaking, a 10$
reduction in blade speed will mean that it will take 10% longer
to mow a given lawn.
The bagging ability of a mower is primarily determined by the
lift on the blade. If a blade is slowed, then its lift will^be
reduced and it will not fill the bag as densely with lawn clip-
pings . Typically, a 10/6 reduction in speed will mean that the
bag will have to be emptied 10# more often.
18
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3.4 Statistical Variations in Noise Level
Because of manufacturing variations and differences in mea-
suring conditions, there will be statistical variations in the
noise levels of a given model.
Manufacturing Variations
It is generally agreed by manufacturers that changes of
±1.5 dB(A) are observed for different samples of the same model
of machine.
Observer Variations
Changes of ±1 dB(A) are found for different observers making
the same measurement on the same machine with similar, well-cali-
brated instruments. The SAE sub-committee did a study of this
variation and an example of the same measurement taken by seven
different observers is shown in Table VIII. It is assumed that
this variation occurs because the noise level is fluctuating and
different observers tend to estimate the average value of an un-
steady meter needle in different ways.
TABLE VIII. VARIATIONS IN NOISE LEVELS OBSERVED AT 50 FT
Observer
Level, dB(A)
1
70
2
71
3
71
4
71.5
5
71
6
72
7
71.5
Average
71.1
Surface Variations
Large variations in noise level, as much as ±3 dB(A), have
been found to arise from different surfaces used for the measure-
ment. A hard surface will give a higher level than a soft one.
19
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Fortunately, this variation has been removed in the proposed SAE
code of practice which specifies a Tartan Turf surface (Appendix
B).
Combining the variations due to sample and observer 9 we get a
total maximum variation of ±2.5 dB(A). Thus, on occasion a given
model of machine may be measured 2.5 dB(A) louder or quieter than
its average level.
20
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4. NOISE CONTROL
The most commonly used lawnmower is the rotary gasoline type.
It thus represents a "standard" mower in terms of performance,
cost, and noise. Other types of mowers may be quieter. For
example, a battery-powered riding mower is about 63 dB(A) at 50
ft, and a gasoline-powered walk-behind reel mower is about 64
dB(A) at 50 ft. Both comply with the 1978 Chicago ordinance
level. However, they both have significant cost and performance
penalties. Battery-powered riding mowers initially cost 35% more
than gasoline-powered riding mowers and they run for only 45
minutes on one charge. A gasoline-powered walk-behind reel mower
costs 50% more than an ordinary rotary and 10$ more than a self-
propelled rotary mower. (A reel mower is always self-propelled
to ensure the right 'bite' of the blade.) Further, a reel mower
does not cut long grass or uneven lawns well and is difficult
to manage in confined spaces.
The cost of quieting a mower is nearly independent of its
total cost, which is determined by luxuries like self-propulsion.
Thus, the cost of quieting a cheap mower is relatively much higher.
4.1 Noise Sources
The four main noise sources of gasoline-powered rotary mowers
A
are illustrated in Fig. 6.
Mechanical Vibrations
The engine causes the structure of the mower to vibrate and
the vibrating structure in turn radiates sound. Vibrations are
not generally important with walk-behind mowers, because the deck
is relatively stiff, but they do produce substantial noise on
21
-------
80
o
in
7O
65
6O
WALK-BEHIND MOWERS
O
I
i
X
III
o
z
u
_l
<
o
75 -
70 -
6O -
55 >-
-
RID
I
NC
MO
1
U
Z
<
bJ
O
4
I
i
CO
3
<
X
UJ
u
z
<9
Z
Ul
o
»-
FIG. 6.
SOURCES OF NOISE
riding mowers where there are more mechanical linkages to rattle
and a larger structure. No significant noise difference has been
found between pressed steel and cast magnesium decks.
Blade
The blade on a rotary mower serves three functions: (1) to
lift the grass in preparation for cutting, (2) to cut it, and (3)
to lift the cuttings into a bag or distribute them. The blade
moves air, thereby generating noise. On a walk-behind mower, the
blade is one of the most important noise sources. There are five
main mechanisms whereby the blade produces its noise. In the 100
to 500 Hz frequency range, these mechanisms are steady blade lift
22
-------
and drag, blade thickness, fluctuating blade lift and drag due to
housing, and fluctuating blade lift and drag due to vortex shed
from a preceding blade. In the 500 to 2000 Hz frequency range
edge noise due to turbulence shed from the trailing edge of the
blade is dominant.
Exhaust
Exhaust noise arises from the pulse of exhaust gas emitted
each time the engine fires. This source is important because at
the present time small engines are not very well muffled.
Engine
Engine noise, in addition to exhaust noise, includes intake
noise, casing noise, cooling fan noise, valve noise, piston slap,
and noise from play in the big-end of the connecting rod.
CUT-AWAY VIEW OF BRIGGS
AND STRATTON 3-1/2 hp
LAWN MOWER ENGINE
(REPRODUCED BY COURTESY
OF BRIGGS AND STRATTON)
23
-------
4.2 Definition of Manufacturer's Cost
The costs of quieting quoted here are the manufacturer's
costs of buying the item. Cost is not the same as f.o.b. price,
which includes the manufacturer's overhead and profit. The f.o.b.
price may be typically 50% more than the cost, but this percentage
will vary.
In estimating the cost, a reasonably large production is
assumed so that the manufacturer is not incurring the costs of
small-scale production. Thus, when we are including the tooling
costs for the design changes ($250,000), it is assumed that these
costs are spread over a fairly substantial number of units,
namely 250,000 units for 5 years, giving a cost of 20£ per unit.
If a manufacturer produces fewer units, then the costs will be
iiigher. All prices quoted are at the 1973 level.
4.3 Noise Reduction by Component Interchange
It is possible to reduce typical noise levels of mowers by
fitting currently available items to the machines. Two levels
of effort are possible with this approach. The sound levels
quoted here are the median levels for the machines.
Level 1 Muffler
Use best muffler available. Current engine exhaust mufflers
can reduce exhaust noise to a point where it is no longer a major
noise source. The effect on noise levels is shown in Fig. ,?. It
can be seen that there is about a 2.5 dB(A) reduction in total
noise level. The cost of fitting the best muffler is about 80
-------
o
in
80
75
70
65
60
55
WALK-BEHIND MOWERS
$0.80
I
ffl
-------
engine made. Even so, the larger engine can also be quieted and
the result is still a quieter mower. The results are shown in
Fig. 8.
Level 2 quieting reduces noise about 4.5 dB(A) on the walk-
behind mower and 4 dB(A) on the riding mower. The net cost is
about $4.40 on the walk-behind and $4.00 on the riding mower.
There is also a performance penalty of about 10% in grass cutting
ability. This noise reduction is the most that can be achieved
with currently available components. Any further noise reduction
requires special design and. noise control engineering.
so
75
S 70
^
O
ffl
65
6O
55
WALK-BEHIND MOWERS
$4.40
i,
ui
o
0
m
<
x
X
_J
<
80
75
7O
65
60
55
RIDING MOWERS
$4.00
<
o
<
o
<
_l
CD
I
X
(U
o
z
UI
<
O
FIG. 8. LEVEL 2: SLOWER ENGINE.
26
-------
4.4 Noise Reduction by Noise Control Engineering
Two areas of development are-clearly required if the noise
of mowers is to be reduced below that of Level 2: a "quiet blade"
and engine enclosures.
In 1959, W.C. Sperry and G.J. Sanders [2] of the Armour Re-
search Foundation undertook an examination of the blade noise
problem for Briggs and Stratton, a leading manufacturer of small
engines. They proposed a quiet blade which was "swept forward"
and had a sharpened trailing edge. A blade noise reduction of
about 7 dB(A) was produced, but whether this reduction could still
be achieved with the high lift blades currently being used to bag
grass is open to question. The Toro Company used a sickle blade,
which was swept forward, on their whirlwind mowers between 1963
and 1970 but have now discontinued it.
Further research is required to determine which of the five
blade-noise mechanisms mentioned in Sec. 4.1 is the most import-
ant and how it can be quieted. Some manufacturers have proprie-
tary ideas as to how blade noise can be reduced. A conservative
estimate is that redesign of the blade and housing can achieve
5 dB(A) of noise reduction at a cost of $2.00 for walk-behind
mowers and $4.00 for riding mowers.
Certain manufacturers are currently investigating various
engine enclosures. Fully enclosing the, engine prevents the noise
from escaping, but at the same time blocks cooling air from enter-
ing and leaving the enclosure. A partial enclosure surrounding
the cylinder head on a walk-behind mower solves the air problem
but does not provide as much quieting. It costs about $1.70. A
full engine enclosure with provisions for air flow costs about
27
-------
$3.70. On a riding mower, a partial enclosure consisting of a
simple box around the engine costs about $8.00. A full engine
enclosure complete with acoustic lining costs about $20.00.
Other noise control approaches include reducing the toler-
ances on manufacturing the engine so that there is less valve
noise, piston slap, and connecting rod noise as well as soft-
mounting the engine to reduce the vibrations transmitted to the
mower. This latter measure is very important on riding mowers.
In the following paragraphs, we describe the results of dif-
ferent levels of noise control effort based on the treatments
described above. The sound levels quoted in this section are the
median levels for the machines.
Level, S Muffler and Quiet Blade
We retain the muffler used to achieve Level 1 and add a quiet
blade. On walk-behind mowers, we achieve a reduction of 5.5 dB(A)
for a cost of $2.80. On riding mowers, the improvement over Level
1 is not significant, because blade noise is not a major source
(see Fig. 9).
Level 4 Muff lev, Slow Engine, and Quiet Blade
We now fit a quiet blade to a machine which already has a
good muffler and slower engine. The improvement is not very great,
since blade noise is already low because of the slow engine. We
get a reduction of 6.5 dB(A) for $6.40 on walk-behind mowers. The
blade noise on riding mowers is also very low. The levels are
shown in Fig. 10. A leading manufacturer expects to be marketing
a machine with this state of acoustic treatment in the fall of
1973.
28
-------
801
75 -
70 -
£
o
o
4
ffi
65 -
6O -
55 «
~ WALK-BEHIND MOWERS 80
$2.80
- 75
%mm
Hi
I
65
60
*.*.
- RIDING MOWERS
$8.00
-
0
\
p
1
I
O
_l
ffl
I-
co
X
UJ
O
z
<9
Z
hJ
t-
O
UJ
o
_l
ffi
I-
co
<
I
X
UJ
Itl
Z
<9
Z
UJ
FIG. 9. LEVEL 3: MUFFLER AND QUIET BLADE.
80
79
O
10
65
6O
55
WALK-BEHIND MOWERS
$6.40
6O
I
u
o
(O
3
X
X
m in in
<
o
70
65
6O
55
RIDING MOWERS
$8.OO
M
in S ^
o < ?
< X (9
-I X Z
ID UJ 111
<
O
FIG. 10. LEVEL 4: . SLOWER ENGINE AND .QUIET BLADE.
29
-------
Level 5 Muffler, Slow Engine, and Partial Enclosure
At this level, engine noise is reduced by a partial enclosure
and the engine tolerances on walk-behind mowers are lowered.
Blade noise now dominates on the walk-behind mower which means
that we get only a 5-5 dB(A) reduction for $7.90. With a riding
mower we get a 6.5 dB(A) reduction for $12.00 (see Pig. 11)-
75
70
£
O
<
m
60
95
50
WALK-BEHIND MOWERS
$790
I
111
O
I
I
O
z
III
<
O
75
7O
65
60
55
50
RIDING MOWERS
$ 12.OO
I
1
< X
-I X
m in
o t-
Z O
111 f-
FIG. 11. LEVEL 5: PARTIAL ENCLOSURE.
Level 6 Muffler, Slow Engine, Partial Enclosure, and Quiet Blade
The treatment is the same as Level 5 with the addition of a
quiet blade. We now have an 8.5 dB(A) reduction on walk-behind
mowers for $9-90, but on riding mowers the improvement over Level
5 is not significant. The levels are shown in Pig. 12.
30
-------
75
70
65
6O
55
nn
~ WALK-BEHIND MOWERS 75
$ 9.90
-8
I
I
\
70
65
60
55
*n
~ RIDING MOWERS
$ 16.00
;
I
!
xx
xx
//.
XX
XX
y/'
;xx
*/y
-------
751-
70 -
65 -
O
A
2 60
55 -
501-
~ WALK-BEHIND MOWERS n
$9.60
-
-
^
^
^
^
^
I
i-
at
bl =
o <
«₯ T
70
65
I
60
55
~ RIDING MOWERS
$ 28.00
-
-
1
~ -1
u
> J 1
- < T
n« 1- ^
1
1
1
ui is--
o < 5 <
-I
o
X
bl
Z
111
X
bl
FIG. 13. LEVEL 7: FULL ENCLOSURE.
75
70
O
m
I
55
50
WALK-BEHIND MOWERS
$ 11.60
w
o
-------
Level 8 represents the state of the art for the near future
until a new significant research contribution is made to the
problem. The costs are of the same magnitude as those of the
safety features required by OPEI, about $3.00 for walk-behind and
$7.00 for riding mowers.
Any further substantial reduction would require a fundamental
look at the lawn mower noise sources and considerable innovation.
The concept of the engine and rotary blade would have to be re-
assessed and a completely new design or means of cutting grass
devised. Just what could be done is not currently known.
33
-------
5. CONCLUSIONS
The results of the previous section, expressed in terms of
sound level at 50 ft vs cost to the manufacturer, are presented
in Pig.. 15 for walk-behind mowers and in Pig. 16 for riding mowers.
Note that slowing down the engine results in a performance
penalty of about 10$ in mowing speed. However, note also that
the costs and performance penalties of going to electric-powered
or reel mowers are still greater than those for quieting gasoline-
powered rotary mowers.
Riding mowers tend to 'be noisier because they are larger and
must meet more power demands than walk-behind mowers. Further,
riding motors tend to be used on large lawns where they are not
very close to other homes or buildings. Thus, in view of the
high cost involved in quieting them, there is a good case for
setting different levels for riding and walk-behind mowers.
Given below is a list of the costs and time scales to meet
three different levels of quieting: (1) the best levels currently
achieved by any manufacturer, (2) the best level which could
possibly be achieved with current technology, and (3) an inter-
mediate level. The sound levels quoted in this section are the
maximum "not to exceed" levels where an allowance for manufactur-
ing tolerances has been included.
MINIMUM STANDARD - BEST CURRENT LEVELS
Walk-Behind Mowers 68 dB(A)
This requires fitting the best available muffler and slowing
the engine 200 rpm.
Cost Per Unit = 80
-------
U)
ui
WALK-BEHIND
MOWERS
REGULAR BLADE
QUIET BLADE
BEST ON
MARKET
1975
CHICAGO
1978
CHICAGO
4 6 8 10
MANUFACTURERS COST (1)
FIG. 15. NOISE REDUCTION COSTS OF WALK-BEHIND MOWERS
-------
u>
a\
80
LU
UJ
U_
O
in
00 70
60
RIDING
MOWERS
(8hp)
REGULAR BLADE
QUIET BLADE
BEST ON
MARKET
^ 8
i
10 20
MANUFACTURERS COST {$)
30
1973
CHICAGO
1975
CHICAGO
1978
CHICAGO
FIG. 16. NOISE REDUCTION COSTS OF RIDING MOWERS.
-------
Riding Mowers 74 dB(A)
This requires fitting the best available muffler, slowing
engine to 3,400 rpm and fitting a cover around the engine, making
provision for cooling air.
Cost Per Unit = $12.00
Tooling = $250,000 (some manufacturers have
already incurred this cost)
Lead Time = 1 Jan 1975 (since most manufacturers
have already started)
INTERMEDIATE STANDARD
Walk-Behind Mowers 66dB(A)
This is achieved by the best muffler, slowing engine 500 rpm,
and fitting an acoustic enclosure around it. An alternate way of
achieving this standard would be to incorporate a quiet blade on
the mower instead of enclosing the engine. However, only certain
of the larger companies would have the capability to do this.
Cost Per Unit = $9-60 (Standard Manufacturer)
= $6.40 (High Technology Approach)
Tooling = $250,000
Lead Time = 2 1/2 years (One leading manufacturer
will achieve this level
in his 1974 model.)
Riding Mowers 70dB(A)
This essentially requires the best muffler., an engine slowed
to 3»000 rpm, and an acoustic enclosure around the engine.
Cost Per Unit = $28.00
Tooling = $250,000
Lead Time = 2 1/2 years
37
-------
STRICTEST STANDARD
Walk-Behind Mower 62dB(A)
This requires the best muffler available, slowing the engine
500 rpm, an acoustic engine enclosure, and a quiet blade.
Cost Per Unit = $11.80
Tooling = $250,000
Lead Time = 3 years (2 years for a leading
manufacturer who now has
capability)
Riding Mowers 68dB(A)
This requires the best muffler available, engine speed reduced
to 3»000 rpm, acoustic enclosure around engine, and a quiet blade.
Cost Per Unit = $32.00
Tooling = $250,000
Lead Time = 3 years
38
-------
REFERENCES
1. National Industrial Pollution Control Council Sub-Council
Report, "Leisure Time Product Noise", May 1971.
2. W.C. Sperry and G.J. Sanders, "Quiet Blades for l8-in. Rotary
Type Power Lawn Mowers", Noise Control, 26 May 1959-
39
-------
APPENDIX A
LIST OF MANUFACTURERS, ASSOCIATIONS AND RETAILERS CONTACTED
Company: AMP Inc.
Address: 695 Hope Street; Stanford, Conn. 06907
Telephone Number:
Person Contacted - Position: Mr. J.A. Cosh (Director)
Company: Ariens Company
Address: 655 W. Ryan Street;. Brillion Wisconsin 5^110
Telephone Number: (4l4)-756-2l4l
Person Contacted - Position: Michael Ariens (President)
Company: Atlas Tool & Mfg. Co.
Address: 5151 Natural Bridge; St. Louis, Mo. 63115
Telephone Number: (31*0-385-7800
Person Contacted - Position:
Company: Black and Decker Mfg. Co.
Address: 701 East Joppa Road; Towson, Maryland 21204
Telephone Number: (301)-828-3900
Person Contacted - Position: Ray Duran (Engr); Leonard Bloom (Director
Patents and Licenses) x3240
Company: Boise Cascade Corp.; Power Systems Division
Address: P.O. Box 809; Springfield, Ohio
Telephone Number: (513)-325-0494
Person Contacted - Position:
-------
Company: Briggs and Stratton Corp.
Address: 3300 North 124th Street; Wauwatosa, Wisconsin 53201
Telephone Number: (4l4)-46l-1212
Person Contacted - Position: Douglas Gordon; Joseph R. Harkness (VP
Research); Leo Lechtenburg (VP)
Company: Bolens Division (PMC Corp.)
Address: 275 Park Street; Port Washington, Wisconsin 53074
Telephone Number: (4l4)-284-5521
Person Contacted - Position: Mr. David Philips
Company: Cooper Mfg. Co.
Address: 4ll South First Avenue; Marshalltown, Iowa 50158
;Telephone Number: (5i5)_752-5409
Person Contacted - Position: Mr. C.H. Cooper (VP Mower Division)
Company: Deere & Co.
Address: John Deere Road; Moline, Illinois 61265
Telephone Number: (4l4)-485-44ll
Person Contacted - Position: Dick Mylie
Company: General Leisure Products Corp.; (Sub. of Arctic Enterprises)
Address: P.O. Box 635; Thief River Palls, Minnesota 56701
Telephone Number: (2l8)-68l-ll47
Person Contacted - Position: Mr. Dennis Brown
Company: Gibson Bros. Co.
Address: Plymouth, Wisconsin 53073
Telephone Number: (4l4)-893-1011
Person Contacted - Postion: E.W. Enters (VP Engineering)
-------
Company: Hahn Division (Kearney-National Inc.)
Address: 1625 North Garvin St., Evansville, Indiana 47717
Telephone Number: (8l2)-424-0931
Person Contacted - Position: Charles Sorenson (Director of Engi-
neering)
Company: Homelite (Subs Textron)
Address: 70 Riverdale Avenue, Port Chester, New York 10573
Telephone Number: (9l4)-939-3400
Person Contacted - Position: Mr. Burke
Company: Huffman Mfg. Co.
Address: Richmond, Indiana
Telephone Number: (317)-966-0555
Person Contacted - Position: Dan Hart (Product Engineer)
Company: International Harvester
Address: 401 North Michigan Avenue; Chicago, Illinois 60611
Telephone Number: (312)-527-0200
Person Contacted - Position: Roger Ringham (VP Environmental Quality)
Bennett (Hinsdale)-(312)-325-1700 x 496
Company: Jacobsen Mfg. Co.; (Subs. Allegheny Ludlum)
Address: 1721 Pachard Avenue; Racine, Wisconsin 53403
Telephone Number: (4l4)-637-6711
Person Contacted - Position: Paul Clymer
Company: King 0 Lawn Inc.
Address: 10127 Adella Avenue; South Gate, California 90280
Telephone Number: (213)-567-2107
Person Contacted - Position: Leonard A. Pass (VP)
43
-------
Company: Locke Mfg. Div. (Stellar Industries)
Address: 1085 Connecticut Avenue; Bridgeport, Conn. 0660?
Telephone Number: (203)-333-3157
Person Contacted - Position: George I. Wiese (VP/GM)
Company: M.T.D. Products Inc.
Address: 5389 West 130th Street; Cleveland, Ohio 44111
Telephone Number: (2l6)-225-7711
Person Contacted - Position: Don Thon
Company: McDonough Power Equipment Inc.; (Subs. Fuqua Industries Inc.)
Address: McDonough, Georgia 30253
Telephone Number: (4o4)-957-39l6
Person Contacted - Position: H. Jackson (Chief Engineer)
Company: Montgomery Wards
Address: 619 West. Chicago Avenue; Chicago, Illinois 60607
Telephone Number:
Person Contacted - Position: Mr. Gould (Chief Buyer, Lawn Equipment)
Company: Murray Ohio Mfg. Co.
Address; 635 Thompson Lane; Nashville, Tennessee 37204
Telephone Number: (6l5)-834-4500
Person Contacted - Position: D.L. Pitman (VP Engineer)
Company: Nelson Muffler Corp.
Address: Stoughton, Wisconsin 53589
Telephone Number: (6o8)-873-664l
Person Contacted - Position: S.L. Gjermo (Sales Engineer)
44
-------
Company: Outboard Marine; Evinrude Works
Address: Milwaukee, Wisconsin
Telephone Number: (4l4)-445-0643
Person Contacted - Position: Richard Lincoln (Manager, Environmental
Engineering) x2o4
Company: Outdoor Power Equipment Institute Inc.
Address: 734 15th N.W.; Washington, B.C.
Telephone Number: (202)-737-6510
Person Contacted - Position: Dennis Dicks (Executive Director)
Company: J.C. Penney
Address: 1301 Avenue of the Americas; New York, N.Y. 10019
Telephone Number:
Person Contacted - Position: Mr. Bunker (Chief Buyer Lawn Equipment)
Company: Roper Corp.
Address: Newark, Ohio
Telephone Number: (6l4)-345-988l
Person Contacted - Position: Don Gobin
Company: The O.M. Scott and Sons Co. (Subs. ITT)
Address: 333 West Maple Street; Marysville, Ohio 43040
Telephone Number: (513)-642-6015
Person Contacted - Position: Mr. Amerine
Company: Sears Roebuck
Address: 925 South Homan Avenue; Chicago, Illinois 60607
Telephone Number: (312)-265-5l65
Person Contacted - Position: Mr. Hillbrand (Senior Buyer for Lawn
Mowers) Dept. 609
-------
Company: Simplicity Mfg. Co. Inc.; (Subs. Allis-Chalmers)
Address: 500 West Spring St., Port Washington, Wisconsin 53074
Telephone Number: (4l4)-284-5535
Person Contacted - Position: Igor Kamlukin (VP Engineer)
Company: Sunbeam Corp.; Research, and Development Division
Address: South Carolina
Telephone Number: (803)-435-844l
Person Contacted - Position: John Robinson
Company: Tecuinseh Products Co.; Taylor Products Division
Address: Elkhart, Indiana 46512
Telephone Number: (219)-522-4l87
Person Contacted - Position: P. Melkus (Sales Director); B. Mann
(Sales Engineer)
Company: Tecumseh Products Co.; Lawson Emgines Division
Address: New Hollstein, Wisconsin
Telephone Number: (4l4)-989-57H
Person Contacted - Position: William Hermanson, Dr. Otto Reiger
(R&D Centre)
Company: Toro Company
Address: 8111 Lyndale Avenue, South; Minneapolis, Minnesota 55420
Telephone Number: (6l2)-888-8801
Person Contacted - Position: Robert Witt
Company: Wood Brothers Mfg. Co.; (Subs. Hesston Corp.)
Address: Rte. 2; Oregon, Illinois 61061
Telephone Number: (8l5)-732-6l56
Person Contacted - Position: Mr. McAmse
46
-------
Company: United States Testing Co., Inc.; Research Division
Address: 1415 Park Avenue, Hoboken, New Jersey
Telephone Number: (201)-792-2400
Person Contacted - Position: Mr. Yoder
Company: Yazoo Mfg. Co.
Address: P.O. Box 4207, Jackson, Mississippi
Telephone Number: (601)-368-6421
Person Contacted - Position:
-------
APPENDIX B
EXTERIOR SOUND LEVEL MEASUREMENT PROCEDURE FOR SMALL ENGINE
POWERED EQUIPMENT -
SAE Recommended Practice
Scope This SAE Recommended Practice establishes the instrumentation
and procedure to be used in measuring the maximum exterior sound
level for engine powered equipment under 20 rated brake horsepower.
It is not intended to include equipment designed primarily for opera-
tion on highways or within factories and buildings, or vehicles such
as motorcycles snowmobiles and pleasure motor boats that are covered
by other SAE Standards.
This SAE Recommended. Practice may also be used when measuring the
maximum exterior sound level on similar equipment powered by electricity
or other power sources.
Instrumentation The following instrumentation shall be used for the
measurement required:
2.1 A precision ccunc! level irsster which m«?^t-!? -Hir* Tvne I recmire-
ments of American National Standards Specification for Sound
Level Meters (ANS SI.4-1971).
2.2 As an alternative to making direct measurements using a sound
level meter, a microphone or sound level meter may be used
with a magnetic tape recorder and/or a graphic level recorder
or indicating meter providing the system meets the requirements
of SAE Recommended Practice J184.
2.3 A sound level calibrator (see Paragraph 4.2.4).
2.4 The microphone shall be used with an acceptable windscreen.
To be acceptable, the screen must; not affect the microphone
response more than - 1 dB for frequencies from 20 to 4000 HZ
or - 1% <3B for frequencies from 4000 to 10,000 HZ (see Para-
graph 4.3).
2.5 An anemometer or other device for measurement of ambient wind
speed and direction.
2.6 An engine speed indicator.
-------
2.7 A thermometer for measurement of ambient temperature.
Procedure
3.1 Test Site The test area shall consist of a flat-open space
free of any large reflecting surfaces such as a signboard,
building, or hillside located for a minimum distance of
100 feet (30.4 metres) of the measurement zone.
3.1.1 The minimum dimensions ,of the measurement zone are
defined as a path of travel 4 feet (1.2 metres) wide
by 46 feet (14 metres) long plus an adjacent triangu-
lar area having the base along the edge of the path
of travel and the apex 23 feet (7 metres) from the
midpoint of the base. (See figure 1).
3.1.2 The surface of the measurement zone shall be: Syn-
thetic turf surface mounted to 3/4"exterior plywood
or V minimum1 thickness marine plywood with suitable
adhesive. Turf to be. %" pile height, 60 denier nylon
6 fiber, approximately 32 oz/sq. yd. on polypropylene
backing approximately 5 oz/sq. yd.
properties after mounting or. ply.-.'ood chall
HZ
125
250
500
1000
2000
4000
Sound Absorption Coefficient
.04 -
.09 -
.20 -
.30 -
.40 -
.46 -
.06
.12
.28
.32
,46
.62
3.1.3 The observer with the meter shall be at least 10 feet
(3.0 metres) from the microphone. Not more than one
persor} other than the observer reading the meter,
shall be within 50 ft (15.2 m) of the vehicle path or
instrumentation, and that person shall be directly
behind the observer who is reading the meter, on a
line through the microphone and the observer.
3.1.4 The ambient sound, level (including wind effects) due
to sources other than the equipment being measured,
shall be at least 10 dB(A) lower than the level of
the equipment being measured.
-------
3.2 Equipment Operation
3.2.1 Operate the equipment at the combination of load and speed
which produces the maximum sound level without violating
the manufacturers operation specifications.
3.2.2 Recommended Loading Techniques:
3.2.2.1 Walk-behind Mowing Equipment;
Test as mobile equipment (3.3.5). Run engine
or motor at the mower manufacturer ' s maximum
specified speed. Set blade at closest avail-
able setting to 2" (50.8 mm) cutting height.
Engage blade and self propelling mechanism if
available. Additional loading mechanism not
deemed necessary.
3.2.2.2 Riding, Mowing Equipment;
Test as mobile equipment (3.3.5). Run engine
or motor at the mower manuf eicturer ' s speci-
fied maximum speed. Set blades at closest
ciVciiXciJ->j-c; :.>t_:L Lilly Lo 2 \SC.G ITuTi/ Cutting
lici'/ht cine! engage bladss, m-d-rjir* +-"hr» mr»vimnm
sound level with a brake load and/or towing a
load (see Paragraph 3.2.3),
3.2.2.3 Walk-behind Snow Blowers and ._Ti_llers :
Test as equipment which is not traveling (3.3.4).
Set no load speed of engine at manuf actxirer ' s
specified maximum setting, engage all mechanism
other than propelling, load equipment output
shaft with a brake to obtain maximum sound level
(see Paragraph 3.2.3).
3.3.3.4 Chain Saws
Test as equipment which is not traveling (3.3.4).
Position the equipment 2 feet (.6 metres) above
the test surface and operate to produce maximum
sound level. Loading by cutting a log may be
required.
51
-------
3.2.2.5 Garden Tractors with Attachments other than
Mowers;
Test as (3.3.6). Run engine(s) or motor(s)
at the manufacturer's specified maximum speed.
With attachments engaged, obtain the maximum
sound level with a brake load and/or tow load.
(see Paragraph 3.2.3).
3.2.2.6 Miscellaneous Equipment
Run engine(s) or motor(s) at the manufacturer's
specified maximum speed. With equipment engaged,
obtain the maximum sound level with a brake load,
tow load or other method of loading. (see Para-
graph 3.2.3).
3.2.3 Auxiliary Loading
The sound level of the auxiliary load shall be at least
10 dB(A) less than the equipment being measured. The
presence of the auxiliary load shall not affect the
sound radiated to the microphone.
3.3 Mensxirements
3.3.1 The microphone shall be located at the apex of the tri-
angular test area at a height of 4 feet (1.2 metres)
above the ground plane.
3.3.2 The sound level meter shall be set for "slow" response
and for the A-weighting network.
3.3.3 The ambient wind speed and direction relative to source
and microphone, ambient temperature , and ambient dB(A)
sound level shall be measured and recorded.
3.3.4 For equipment which is not traveling, test as follows:
With operator in normal position, orient equipment to
obtain maximum sound level. Record the highest repeat-
able sound level obtainable at 23 feet (7 metres) from
the nearest surface of the equipment. Operate the
equipment as specified in section 3.2.
52
-------
3.3.5 For mobile equipment, take measurements at 23 feet
(7 metres) normal to a major side surface along a
path of straight line travel. Operate the equipment
as specified in section 3.2. Rotary mower chute ex-
tensions are not to be considered a major side surface.
The applicable reading for this test condition will be
the highest repeatable sound level obtained from the
equipment as it moves along the line of travel. The
equipment shall run at least twice in1 each direction
or until the number of readings equals or exceeds the
range of decibels of the A-weighted sound level obtained.
The highest repeatable dB(A) reading shall be reported
as the sound level of the particular equipment for this
test condition.
3.3.6 For the equipment that can be operated mobile and not
traveling, test under both specifications 3.3.4 and
3.3.5. The highest sound level results shall be
recorded.
3.3.7 To convert the sound level readings obtained at 23 feet
(7 mei-ro.r;) to 50 feet (15.2 metres) readings, subtract
7 dii^A) irom the 23 feeL (7 m^Lrer} rc-Etc-ir--j =
4. General Comments
4.1 It is strongly recommended that technically trained personnel select
equipment and that tests be conducted only by experienced persons
trained in the current techniques of sound measurement.
4.2 Proper usage of all test instrumentation is essential to obtain
valid measurements. Operating manuals or other literature furnished
by the instrument manufacturer should be referred to for both recom-
mended operation of the instrument and precautions to be observed.
Specific items to be considered are:
4.2.1 The type of microphone, its directional response characteris-
tics, and its orientation relative to the ground plane and
source of noise.
4.2.2 The effects of ambient weather conditions on the performance
of all instruments (e.g. temperature, humidity, and baro-
metric pressure) . Instrumentation can be influenced by low
temperature and caution should be exercised.
53
-------
4.2.3 Proper signal levels, terminating impedances, and cable
lengths on multi-instrument measurement systems.
4.2.4 Proper acoustical calibration procedure, to include the
influence of extension cables, etc. Field calibration
shall be made immediately before and after each test
sequence. Internal calibration means is acceptable for
field use, provided that external calibration is accom-
plished immediately before or after field use.
4.3 It is recommended that measurements be made only when wind vel-
ocity is below 12 mph (19.3 kmA)
References
Suggested reference material is as follows:
1. ANS SI. I - 1960
2. ANS SI. 13 - 1971
Acoustical Terminology
Methods of Measurement of Sound
3. ANS SI. 4 - 1971
4. SAE J184
Specification for Sound Level -Meters
Qualifying a Sound Data Aquisition
System
(Applications for copies of documents
listed under 1, 2 and 3 should be
addressed to: American National
Standards Institute, Inc,
1430 Broadway
New York, N. Y. 10018)
DG:ht
-------
The following sound levels, when measured in accord with the test
procedure described above, represent current engineering practice
as of January, 1973, on the following types of equipment:
dB(A)
EQUIPMENT 23 Feet 50 Feet
1. Rotary Mowers, walk-behind 77 70
2. All Riding Mowers 82 75
3. Snow Blowers .and Tillers 85 78
4. Chain Saws 93 86
55
-------
VJl
46 FT
(14 METRES)
23 FT
(7 METRES)
»
MINIMUM
4 FT (1.2 METRES)
J
EQUIPMENT PATH-*
23 FT (7 METRES)
4
10 FT
(3.0 METRES)-
MICROPHONE
LOCATION
OBSERVERS
MEASUREMENT
ZONE
= 100FT (30.4 METRES)
RADIUS MINIMUM
FIG. B.I. TEST SITE.
-------
RATIONALE FOR SPECIFIC ITEMS IN THE PROPOSED
SAE RECOMMENDED PRACTICE
1. Scope
All terrain vehicles (ATV's) and Mini-bikes are not included in
this procedure.
2. Procedure
3.1 Open space has traditionally been the best test site for
measuring sound levels because there are not many indoor
test facilities for testing outdoor powered equipment.
3.1.1 The measurement zone has been established using a fixed
loczition for the microphone 23 feet away from the path of
the equipment being tested. In the past, SAE procedures
have used 50 foot distance as a standard measuring dis-
tance. This distance has been used for pass by sound level
tests on cars, trucks, and busses. The sound levels of
small engine powered equipment are normally 5 to 15 clB(A)
lower thaii {.ho IciirgciT equipment using the 50 feet mcasur-incj
distance. hen using a 50 fool" nn^fmvina distance with
small equipment, the effects of wind on the sound propoga-
tion can be a significant error in the test measurements.
On most small engine powered equipment, the source of the
sound is very close to an absorptive ground surface and
having a low grazing angle between the sound and this surface.
The further the distance is to the measuring meter, the
greater the possibility of variation in attenuation between
the source and the microphone, especially when measuring over
different grasses and different soils and soil conditions
(wet versus dry)
Also, a 23 foot measuring distance reduces the size of the
test area needed, and it effectively allows higher back-
ground sound levels on the test site. A distance of 25
feet was at first considered, but 23 feet (7 metres) was
decided upon as being a better distance to measure since
7 metres is used now in many European standards.
"*
The cost of the area of the artificial test surface was
also considered in the above decision.
-------
3.1.2 The majority of the equipment to be tested under this
recommended practice is in the lawn care equipment cate-
gory. Sound level tests were made by individual committee
members using one mower at many different grass sites.
This testing produced differences between sound levels
measured on the same equipment of up to 8 dB(A). The
three major variables that caused this large deviation are:
1. The variability of the test sites: The grass and sound
varies between test sites due to the quality of the
grass, the type of ground underneath and also the amount
of moisture.
2. Instrumentation variables which include the type of
microphones, sound level meters, the calibration, and
the actual reading of the instrumentation by the ob-
servers.
3. The speed of the equipment, the type of .loading, and
the number of measurements taken can also affect the
final level measurement.
To rorJncc the variciL.l<.>ji V>i~ tvr.cn measurements on different
Lus,L s-iLcc;, clue to the differences in the grass uiiu yju^and
surface, the committee decided to consider using an arti-
ficial surface to test the equipment on. The committee
thus sponsored the conducted three separate field tests:
The first test was to compare measurements over grass to
measurements over polyurethane foam sxirface 1%" thick.
This foam was donated by the Scott Company. It was their
best judgment as being the equivalent absorption of grass
surfaces. Because of troubles of running the equipment
over the foam surface, and also because electric mowers had
much higher readings on this foam surface, it was decided
to run a second test using a synthetic turf surface over the
vehicle path, but using the urethane foam on the area be-
tween the vehicle path and the microphone. This test re-
sulted in good vehicle operation, but we still continued
to have higher readings with electric mowers and we also
had a lower reading on this material with 2 cycle rotary
lawnmowers. A preliminary test was conducted by two members
of the committee using the synthetic turf surface*over the
vehicle path and the entire measuring area between the vehicle
and the microphone. This was done as a stationary test, but
58
-------
it showed the best correlation between grass and the synthetic
surface of all the tests that were made. In a third field
test by eight committee members testing only on synthetic turf,
the correlation to the readings made on grass in previous tests
was 1.1 dB(A). Not only does this material have good sound
level correlation to grass, but it is a very durable surface
to run and load the equipment upon.
The other two testing variables, instrumentation and equip-
ment operation have been considered in other parts of this
Recommenced Practice.
3.2 Equipment Operation
The committee used the same equipment operations wording as in
the J952b but we have added a section on "Recommended Loading
Techniques" to give guidance to people testing particular pieces
of equipment.
In many of the loading tcchniq'ues, we have recommended using
a Tow Load or an auxiliary Brake Load to obtain maximum .sound
levels. In our f i ol rl tests, this was found to be-a practical
wav to obtain maximum noise when resting on.a^Lificial cur
faces, as well as on grass.
3.3.2 Since the type of equipment tested in this Recommended Practice
is either stationary or slow moving, the committee feels "slow"
response on the sound level meter is a more satisfactory setting.
3.3.4 With a specific measurement zone, it was found that keeping the
microphone stationary and orienting the equipment was the most
practical way of obtaining maximum sound levels on stationary
equipment.
3.3.5 Our committee felt that the applicable reading should be the
highest repeatable sound level obtained. Our field test showed
that this reading was obtained very consistently and that any
averaging of the higher readings would not give the maximum
sound level.
3.3.7 Since this Recommended Practice specified a 23 foot or 7 metre
measuring distance, it was felt that we should put in a con-
version factor to convert to 50 foot readings which would give
\correlation to existing sound level measurements. The 7 dB(A)
59
-------
correlation factor is the calculated sound level reduction
that would occur under ideal conditions between 23 feet and
50 feet.
45 data points comparing 50' to 23' on tests made by our
committee members showed an average of 6.9 dB (A) difference
between 50' and 23'
16 data points in the third field test produced a 6.99 dB (A)
difference between 50' and 23 .
Douglas Gordon
Secretary
3-26-73
DG:ht
60
-------
APPENDIX C
DRAFT #11
NOISE LEVELS OF CURRENT LAWN MOWER MODELS
DRAFT - MARCH 26, 1973
61
-------
Lawn Mower
Make
1 . Lawnboy
(Outboard
Marine)
Model
No
3058
5239-B
5241
5269-B
5271
5501
7223
7260-B
7262
7262-E
6254
Price
$
100
110
120
120
130
90
130
130
140
175
150
Noise
Level
dB(A)
66
66.5
65.5
67.5
67
64
65.5
67.5
66.5
67.5
67
Cutting
Width
Inches
18
19
19
19
19
19
21
21
21
21
21
Engine
Speed
rpm
3200
3200
3200
3200
3200
3200
3200
3200
3200
3200
3200
Manu-
facturer
OM
OM
OM
OM
OM
Denso
OM
OM
OM
OM
OM
Engin
hp
3
3
3
3
3
1
3
3
3
3
3
e
No. of
Strokes
2
2
2
' 2
2
Electric
2
2
2
2
2
Treatment
Level
1 1/2
1 1/2
1 1/2
1 1/2
1 1/2
1 1/2
1 1/2
1 1/2
1 1/2
1 1/2
Extras
C/D
Catcher
C/D, Catcher
C/D
Catcher
C/D Catcher
C/D, ES, Catcher
Hevi-Duti
C/D - Capacitor Discharge Ignition
ES - Electric Start
DCD - Die Cast Deck
SP - Self Propelled
BS - Briggs 8 Stratton
T - Tecumseh
-------
Lawn Mower
Make
Lawnboy
(cont)
2. Toro
Model
No.
62?6
8231
8231-E
16073
16173
16273
19173
19273
19373
21173
21273
Price
$
170
180
220
100
120
160
130
170
160
150
190
Noise
Level
dB(A)
68
67.5
67.5
69.5
70.5
70.5
69.5
69.5
69.5
70.5
70.5
Cutting
Width
Inches
21
21
21
19
21
21
19
19
19
21
21
Engine
Speed
rpm
3200
3200
3200
3400
3400
3400
*
3400
3400
3400
3400
3400
Manu-
facturer
OM
OM
OM
T
T
T
T
T
T
T
T
Engine
hp
3
3
3
3
3.5
3.5
3
3
3
3.5
3.5
i
No. of
Strokes
2
2
2
4
_n
4
4
4
4
4
4
Treatment
Level
1 1/2
1 1/2
1 1/2
0
0
0
0
0
0
0
0
. Extras
Commercial
SP, Catcher } C/D
ES,SP, Catcher , C/D
SP
SP
ES
SP
C/D - Capacitor Discharge Ignition
ES - Electric Start
DCD - Die Cast Deck
SP - Self Propelled
BS - Briggs S Stratton
T - Tecumseh
-------
Lawn Mower
Make
Toro (cont)
3. Sears
Roebuck
4. Slmplicltj
Homelite
5. Poloron
Model
No.
21373
10018
10121
10221
See Sim]
Price
$
220
160
180
110
140
180
75
120
140
llcity
52
Noise
Level
dB(A)
70.5
65
65
68
68.5
68.5
63
68
72
Above
70
Cutting
Width
Inches
21
18
21
20
20
22
18
19
21
19
Engine
Speed
rpm
3400
Reel
Reel
3400
3400
3400
3500
3400
3500
f '
Manu-
facturer
T
T
T
T
T
T
Electric
BS
BS
BS
Engin
hp
3.5
4
5 '
5
1
3.5
3.5
3
B
No. of
Strokes
4
4
4
4
4
4
4
4
4
Treatment
Level
0
0
0
0
0
0
0
Extras
ES, SP
SP
SP
Stamped Steel Deck
C/D - Capacitor Discharge Ignition
ES - Electric Start
DCD - Die Cast Deck
SP - Self Propelled
BS - Briggs a Stratton
T - Tecumseh
-------
Lawn Mower
Make
6. Black and
Decker
7. General
Leisure
Products
8. Jacobsen
Model
No.
_
Lawn
Lion
Arctic
Cat
11801
11825
12104
31902
32108
Price
$
50
60
70
90
75
160
150
165
185
125
140
Noise
Level
dB(A)
66.5
66.5
72
72
68
68.5
70
65
65
70
Cutting
Width
Inches
18
18
18
18
20
22
18
18
21
19
21
Engine
Speed
rpm
4000
4000
7500
7500
3400
3300
Reel
Reel
Reel
3400
3400
Manu-
facturer
B&D
B&D
B&D
B&D
BS
Fichel
& Sachs
B&S
B&S
B&S
B&S
B&S
Engine
hp
.7
.7
1
1
3.5
4
2
2
2.5
3
3
i
No. of
Strokes
4
Wankel
4
4
4
4
4
Treatment
Level
0
i
0
1
1 -
0
0
Extras
Steel Deck
Steel Deck
2 Blade
2 Blade, Catcher
Stamped Steel Deck
C/D - Capacitor Discharge Ignition
ES - Electric Start
DCD - Die Cast Deck
SP - Self Propelled
BS - Briggs a Stratton
T - Tecumseh
-------
Lawn Mower
Make
9. Scott
10. Interna-
tional
Harvester
11. John
Deere
14. M T D
Model
No.
32109
4214?
42148
31901
32106
42143
42144
10M3
See Out
113-670
Price
$
175
180
215
135
150
190
225
61
board IV
See Tor
Noise
Level
dB(A)
70
70
70
70
70
70
53
arine a
o above
67
Cutting
Width
Inches
21
21
21
19
21
21
21
18
Dove
20
Engine
Speed
rpm
3400
3400
3400
3400
3400
3400
3400
Reel
3200
Manu-
facturer
B&S
B&S
B&S
Jacob
Jacob
Jacob
Jacob
BS
Engim
hp
3
3.5
,3.5
3
3
3
3
Push
3.5
B
No. of
Strokes
4
4
4
2
2
2
2
21
Treatment
Level
0
0
0
0
0
0
0
1 1/2
Extras
ES
SP
ES, SP
*
SP
ES, SP
C/D - Capacitor Discharge Ignition
ES - Electric Start
DCD - Die Cast Deck
SP - Self Propelled
BS - Briggs S Stratton
T - Tecumseh
-------
, ~~
Lawn Mower
Make
Riding
4. Simplicity
10. Interna-
tional
.Harvester
11. Huffman
12 . General
Electric
13. John
Deere
/
14. M T D
1 . Lawnboy
(Outboard
Marine)
Boise Cascade
Model
No.
728
Cadet
75
E8M
E90
133-445
9329
9329E
9329ES
See Ou1
Price
$
400
600
795
890
450
535
620
655
Aboard 1
Noise
Level
dB(A)
77
76
73
82
64
63
71.5
82
82
82
larine
Cutting
Width
Inches
36
32
30
38
36
34
34
32
32
32
Engine
Speed
rpm
4000
3500
3600
3600
3200
3400
3600
3600
3600
1
Manu-
facturer
B&S
-B&S
B&S
B&S
Electric
Electric
B&S
B&S
B&S
B&S
Engine
hp
8
7
5
8
8
8
8
8
i
No. of
Strokes
4
4
4
4
4
4
4
4
Treatment
Level
0
0
0
0
4
0
0
0
Extras
ES
ES jSynchrobalanced
C/D - Capacitor Discharge Ignition
ES - Electric Start
DCD - Die Cast Deck
SP - Self Propelled
BS - Briggs 8 Stratton
T - Tecumseh
-------
Lawn Mower
Make
Riding (cont)
13. John Deere
15. Murray
nv>i r\
unjio
Model
No.
JD55
N.
Price
$
Noise
Level
dB(A)
70
No load
68.5
Cutting
Width
Inches
28
Engine
Speed
rpm
3700
Manu-
facturer
T
B&S
Engin
hp
5
8
e
No. of
Strokes
4
H
i
Treatment E f
Level
0
0 Not Towing
i
i
C/D - Capacitor Discharge Ignition
ES - Electric Start
DCD - Die Cast Deck
SP - Self Propelled
BS - Briggs S Stratton
T - Tecumseh
-------
BIBLIOGRAPHIC DATA
SHEET
Report No.
550/9-74-011
2-
3. Recipient's Accession No.
4. Title and Subtitle
Lawn Mowers:
Noise and Cost of Abatement
5. Report Date
June 1974
6.
7. Authorfs)
M.J. Rudd and E.K. Bender
8. Performing Organization Kept.
No.
9. Performing Organization Name and Address
Bolt Beranek and Newman Inc.
10. Project/Task/Work Unit No.
11. Contract/Grant No.
68-01-1539
12. Sponsoring Organization Name and Address
Environmental Protection Agency
Office of Noise Abatement and Control
Crystal Mill #2, 1921 Jefferson Davis Highway
Arlington, Virginia 20460
13. Type of Report & Period
Covered
Final
14.
15. Supplementary Notes
16. Abstracts
This document contains information useful for the development of
noise emission standards for lawn mowers. Topics covered include
information on lawn mower construction, noijse characteristics of
models currently on the market, and noise reduction techniques and
costs necessary to achieve specified noise levels.
17. Key Words and Document Analysis. 17a. Descriptors
Lawn mower noise
Lawn mower noise control
Costs of Noise Reduction
17b. Identifiers/Open-Ended Terras
17e. COSATI Field/Group
18. Availability Statement
llimited supply available at ONAC, Arlington
Virginia 20460
Available at NTIS
FORM STIS-35 (10-70)
19.. Security Class (This
, Report) X
UNCLASSIFI1 1
20. Security Class (1 us
*1jNCLASSIFIT K_
21. No. of Pages
22. Price
EPA-RTPTIBKBRY
------- |