NBSIR 75-693

Measurement Methodology for

Determining tlie Sound Output of

Model Airplanes and Noise Producing

Bicycle Attachments

Marilyn A. Cadoff and William A. Leasure, Jr.

Applied Acoustics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

April 1975

Final Report for Period 7/73-6/74

Prepared for Bureau of Engineering Sciences

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20014

NBSIR 75-693

MEASUREMENT METHODOLOGY FOR

DETERMINING THE SOUND OUTPUT OF

MODEL AIRPLANES AND NOISE PRODUCING

BICYCLE ATTACHMENTS

Marilyn A. Cadoff and William A. Leasure, Jr.

Applied Acoustics Section

Mechanics Division

Institute for Basic Standards

National Bureau of Standards

Washington, D. C, 20234

April 1975

Final Report for Period 7/73-6/74

Prepared for Bureau of Engineering Sciences

Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20014

U.S. DEPARTMENT OF COMRIIERCE. Rogers C.B. Morton. Secretary

NATIONAL BUREAU OF STANDARDS. Richard W. Roberts. Director

MEASUBEMENT METHODOLOGY FOR DETERMINING THE SOUND OUTPUT OF MODEL AIRPLANES AND NOISE PRODUCING BICYCLE ATTACHMENTS

1. Introduction

The Applied Acoustics Section of the National Bureau of Standards is conducting an ongoing program for the Consumer Product Safety Commission which was intended to: (l) identify noise

producing toys which are potentially hazardous to children's hearing ajid/or safety, (2) develop

generic test methods by which the noise exposure due to such toys can be determined, and (3) acquire data on selected toys as requested by the Consumer Product Safety Commission.

At present, there is no measurement methodology for determining the noise levels associated

with model airplanes or noise producing bicycle attachments (e.g. , horns and devices which

imitate motor sounds), and there is no known existing data base. This report presents a pro- posed measurement methodology for this group of toys, and data obtained on several of these toys

utilizing the proposed methodology.

2. Definitions

Intermittent noise: A noise whose sound pressure level [is less than or] equals the ambient

environmental level two or more times during the period of observation. The period of time

during which the level of the noise remains at an essentially constant value different from that

of the ambient is on the order of one second or more[l].—

Steady-state noise: Ongoing (continuous) noise whose sound pressure level remains essentially

constant (that is, fluctuations are negligibly small) during the period of observation [l ]

.

3. Technical Back-Up

3.1. Product Classification

3.1.1. Model Airplanes : Model airplanes are normally categorized according to their engine displacement. The engine size ranges from about 0.010 cu. in. to 0.800 cu. in. The engines

typically associated with children's model airplanes are usually no larger than 0.0^*9 cu.

in. displacement; however, the free-flight and radio-controlled airplanes used by model

airplane enthusiasts (typically teenagers and adiilts) can range as high as 0.800 cu. in. The engines are 2-cycle and turn at very high rotational rates — 12,000 to 23,000 rpm, resulting in a firing frequency of about 200-383 Hz. The noise produced by these engines can be characterized as steady-state.

3.1.2. Bicycle Horns : The horns used on bicycles generally can be separated into two groups. One group is comprised of the type of horn where the noise generating mechanism is a squeezable

rubber bulb on the end of the horn. The noise produced by this type of horn can be characterized as intermittent noise. The other type of horn is comprised of a cylinder of com- pressed gas on which a plastic horn-shaped actuator is mounted. When the actuator is depressed, the compressed gas is released through a pinhole in a metal diaphragm in the actuator. Initially — for approximately 5-10 seconds — the noise emitted is essentially

steady-state; however, the compressed gas in the canister tends to freeze unless a conscious

effort is made to keep the canister warm (e.g., holding it tightly with gloved hands). If the canister is not kept warm, the noise emitted by the device fades very rapidly, and

about 5 minutes is required before the device can be reused.

3.1.3- Bicycle Attachments Which Imitate Motor Sounds : The bicycle attachments which imitate motor sounds are characterized as steady-state noise producers. They are battery operated

and emit a continuous noise, the level of which is controlled by the operator.

The parties affected by the aforementioned noise producing toys and the effects of the noise must be identified. The operator(s) of the toy is affected and the nature of the effect can include communication interference as well as possible hearing damage. Although hearing loss is not a potential problem for neighbors and bystanders, they certainly can have their tasks interfered with or be annoyed. The measurement methodology presented in this report primarily considers the operator(s) of the toy.

— Figures in brackets refer to the literature references at the end of this report.
3.3- Methodology Development

There are no current measurement methodologies for detennining the noise levels associated with

this class of toys, and there is no known existing data base.

It is proposed for practical reasons to utilize the A-weighted sound level as the basic measure

for model airplane and bicycle attachment noise. The A-weighted sound level was selected because

it correlates reasonably well with the known effects of noise on the individual[2] and it can be

read directly on commercially available instrumentation which meets accepted performance standards.

The ideal test environment for the conduct of tests on toys in this class would be a free-field

environment. An acoustically free field is an environment without any sound reflecting obstacles.

When operated in such an environment, a device will radiate free progressive sound waves. Perfect

free-field conditions are difficult to obtain in practice; however, nearly ideal free-field con- ditions can be obtained in an anechoic chamber. It would be possible to test noise producing bicycle

attachments in such a chamber; however, it would not be a suitable test environment for model airplane engines due to the dangers associated with the build-up of exhaust fumes and the potential

damage to the absorbent wedges as a result of oil dripping from the engine or spilled fuel. This,

coupled with the fact that few, if any, toy manufacturers would have easy access to an anechoic

chamber, led to the investigation of an outdoor test site as a suitable alternative. It was felt

that if the toy to be tested was mounted high (3 metres) above a grass-covered surface with no , obstacles other than the ground surface within 5-nietres of the toy under test or the microphone— , and measurements were made close to the toy (l metre) , then essentially free field conditions

would exist. For these distances the shortest path for any reflected signal — source to ground

and back to the lowest microphone position — would be 5-nietres , and the level of the reflected

signal would be well below the source level. The data resulting from this study confirmed this

hypothesis

.

In order to select appropriate measurement positions — both number, and location — measurements were made at numerous positions surrounding the various noise sources. Although primary

emphasis was on the selection of measurement locations corresponding to operator ear locations —

to allow for assessment of the hazard presented to the operator of the toy — other measurement

locations utilized during this study also provided an indication of the noise levels impacting

bystanders.

For those toys for which there is a fairly well-defined operator location (bicycle attach- ments as compared to model airplanes) measurements were made at the approximate location of the

operator's ear. For this study the operator location is defined as 51 cm behind the device and

1*0.5 cm above it. This position was determined by measuring the arm-to-trunk and trunk-to-ear

distances of several children between the ages of 5 and 8 and choosing approximately the median

value. It was felt that this would represent worst case conditions for the device under test. Since bicycle attachments are normally positioned below the operator's ear, additional measurement locations were selected to sample the semicircular arc of 1 metre radius above the device.

In the case of model airplanes, the operator position cannot be accurately ascertained. With

the exception of the short time which the operator spends very close to the airplane during

engine startup, the operator is at a position below and at an indeterminate distance from the

airplane. This position is basically determined by the length of the control line, which is a matter of personal preference with regard to ease of operation. Therefore, in order to provide

the best indication of the hazard presented to the operator by the model airplane, the measure- ment locations for testing the airplanes were chosen to sample the two semicircular arcs (located 90° apart, see Figure 1) of 1 metre radius below the device.

With the exception of bicycle horns, the maximum A-weighted fast response sound level

should be utilized as the criteria for Judging compliance with the regulation and for assessing the hazard, if any, presented to the toy's operator or bystanders. In the case of the

horns, a hold feature — which stores the maximum rms value of the applied signal — must be

utilized to ensure that the maximum A-weighted sound level is measured. Appendices A and B contain data on toys tested according to the above procedures.

A few special notes are necessary to aid in the conduct of the tests:

Model airplane engines should be removed from the plastic fuselages for testing. It was found that the engine/propeller vibrations generated dxiring operation with the entire

model airplane mounted rigidly on the pole resulted in the engine breaking through the

plastic and destruction of the fuselage.

—It should be noted that the 5-nietre restriction cannot be met when testing bicycle horns due to the fact that a person must be present to actuate the devices — unless a mechanical actuator

system were designed. ., ..

2
The bicycle horn which utilizes compressed gas in a canister tends to freeze up, with a corresponding drop in the sound output. Unless a conscious effort is made to keep the

canister warm (e.g., holding it tightly in gloved hands, wrapping it in cloth), the

noise emitted hy the device fades rapidly, and about a 5-minute wait is required before

the device can be retested.

h. Regulation

l+.l. Meas\irements Made at Operator Location

Utilizing the measurement methodology outlined in Section 6:

U.1.1. Toys which exceed an A-weighted sound level of Y_ decibels re 20 micropascals are banned

from the market.

h.1.2. Toys which produce A-weighted sound levels in the range X-Y decibels must bear a visible

warning label, and the manufacturer must conduct or participate in a program to develop

toys that produce an A-weighted sound level of X decibels or less. Also, manufacturers

with products in this category must submit regular reports to the Consumer Product

Safety Commission on the status of this program.

h.1.3- Toys which produce A-weighted sound levels less thaji X decibels are allowable on the

market with no restrictions.

U.2. Measurements Made at Positions Other Than Those

at the Operator Location

Utilizing the measurement methodology outlined in Section 6:

h.2.1. Toys which exceed an A-weighted sound level of S_ decibels re 20 micropascals are banned

from the market.

h.2.2. Toys which produce A-weighted sound levels in the range R-S decibels must bear a visible

warning label, and the manufacturer must conduct or participate in a program to develop

toys that produce an A-weighted sound level of R_ decibels or less. Also, manufacturers

with products in this category must submit regular reports to the Consumer Product

Safety Commission on the status of this prograjn.

U.2.3. Toys which produce A-weighted sound levels less than R decibels are allowable on the

market with no restrictions.

5. Acoustic Environment

5-1. Measurement Location

5.1.1. The sound source shall be mounted on a pole no greater than 2.5^ cm +_ 0.2 cm in diameter and

3 metres +0.1 metre above a grassy surface in an environment where no other so\ind reflecting

obstacles, with the exception of the ground plajie, are present within 5 metres of either the

location of the toy or the microphone. Note that the microphone must be separated from the

sound level meter by an extension cable sufficiently long that the person reading the sound

level meter does not violate the 5-metre requirement. An exception to the 5-metre restriction is allowed in the case of the bicycle horns where an operator may be present within

the 5-metre zone to actuate the device. However, at no time shall the operator of the

device position himself directly between the device iinder test and the microphone.

5.1.2. During tests conducted on model airplanes, the microphone shall be located at ten different

positions (see Figure 1 for a sketch of the test configuration) — five measurement positions

are located in the same vertical plane as the model airplane's propeller (position 3 is located directly under the propeller) while the remaining five measurement positions are located

in the same vertical plane as the model airplane's longitudinal centerline (position 8 is located directly under the propeller). The microphone shall be located 1.0 +0.0h metre from

the model airplane engine at all measurement locations.

5.1.3. During tests conducted on noise producing bicycle attachments, the microphone shall be locaat five different positions (see Figure 2 for a sketch of the test configuration) in the

same vertical plane as the centerline of the device \inder test and 1.0 +^0.0U metre from

the attachments. At the sixth measurement location, corresponding to the operator's ear, the

microphone shall be located 51-0 jJL.5 cm behind and Uo.5 il'5 cm above the device under test

(see Figure 2).

3
3

90"

FRONT VIEW

180° 10 -r^VJ:-x>'i^i:i

RADIUS = 1 m.

Figure 1. Test configuration for determining the maximum sound

-. . level of model airplanes (engine only). All

measiirement positions are 1.0 + O.OI4 metre from the

sound source. Positions 1-5 are in the same vertical

plane as the model airplane's propeller and measurement

positions 6-10 are in the same vertical plane as the

model aij-plane's longitudinal center line.

0° 1

RADIUS = 1 m.

DIAPHRAGM OF AHACHMENT

SIDE VIEW

Figure 2. Test configuration for detemining the maximum sound

level of noise-making bicycle attachments. All

positions are oriented in relation to the center of the

diaphragm of the attachment. Positions 1-5 are 1.0

O.0I4 metre from the sound source. Position 6, corres- ponding to the operator's ear, is 51.0 cm +_ 1.5 cm behind the attachment and ^4 0.5 cm + 1.5 cm above it.

4
5.2. Environmental Conditions

5.2.1. If calibration devices are used which are not independent of ambient pressure (e.g., a pistonphone) , corrections must be made for barometric or altimetric changes according to the recommendation of the instrument manufacturer.

5.2.2. When measurements are made out-of-doors, the following conditions must be met.

a. Measurements shall not be made when the wind speed exceeds 5 metres/second.

b. Measurements shall not be made during precipitation.

5.3- Background Noise

The maximum A-weighted fast response sound level observed at the test site immediately before

and after the test shall be at least 10 dB below the regulated level.

6. Measurement Methodology

6.1. Instrumentation

6.1.1. Microphone: The microphone shall have the following characteristics. It shall be a one-half

inch microphone or smaller, and shall have a dynajnic range covering the interval 50 to n decibels relative to 20 micropascals , where n decibels is 10 dB greater than or Y decibels.

6.1.2. Windscreen: The windscreen shall not affect the measured A-weighted sound levels from the

noise source in excess of +^0.5 dB. This may be experimentally evaluated by comparing the

measured A-weighted sound level with and without the windscreen, at a position close enough

to the source that wind noise is not a factor.

6.1.3. Sound Level Meter: The sound level meter. Including the microphone, shall meet the specifications of a Type 1 meter as given in American National Standard Specification for Sound

Level Meters, SI. l*-19Tl[ 3] • The sound level meter shall be equipped with a hold feature

which indicates the maximum RMS level of the input signal. The integrating time constant for the hold circuitry shall be 35 msec. The microphone on the so\ind level meter shall be oriented

with respect to the source so that the sound strikes the diaphragm at the angle for which the

microphone was calibrated to have the flattest frequency response characteristic over the

frequency range 100 Hz to 20 kHz.

6.I.U. Additional Instrumentation Requirements:

a. An anemometer or other device for measurement of ambient wind speed accurate within +_ 10^

at 5 m/sec.

b. A barometer for measurement of ambient pressure accurate within +1%.

6.2. Calibration

The measurement system shall be calibrated both before and after the tests at each microphone

position. The calibration shall be accurate to within +0.5 decibel. If the calibration is of the pressure type or of the pistonphone plus electrostatic actuator type, it shall be corrected to free-field conditions in accordance with the manufacturer's instructions. The calibrator shall be

checked annually against a laboratory standard microphone whose calibration is directly traceable

to the National Bureau of Standards to verify that its output has not changed.

A complete calibration of the instrumentation over the frequency range of interest shall be

performed at least annually using methodology of sufficient precision and accuracy to determine that

the instrumentation is in compliance with the requirements of Section 6.1.

6.3. Measurements

6.3.1. The following procedure will be used to determine the sound level produced by model airplanes and bicycle attachments which imitate motor sounds.

a. The quantity to be measured is the A-weighted sound level for fast meter response as defined in American National Standard SI . I4-I9TI [ 3 ] . The model airplane engine under test shall be operated in accordance with the manufacturer's instructions. The bicycle attach- ments which imitate motor sounds shall be operated at the setting which produces the

maximum sound output.

5
b. One readinp. shall be obtained at each measurement location. Bun the toy for a period

, . , of ten seconds, and record the highest reading observed on the sound level meter.

c. The highest sound level recorded during these tests shall be utilized to determine com- pliance with the regulation.

d. The wind velocity and barometric pressure shall be measured at the toy height and within

one metre of the location of the toy when the toy is not being operated.

6.3.2. The following procedure shall be used to determine the sound level produced by bicycle horns.

i a. The quantity to be measured is the A-weighted sound level with the sound level meter in the hold (rms level of the signal) mode. The horns shall be operated in such a way as to produce the maximum sound output.

b. A minimum of five readings shall be obtained and recorded for each measurement location.

The average of the five readings for each measurement location shall also be recorded

. "• for that measurement location.

c. The highest average sound level recorded during these tests shall be utilized to determine compliance with the regulation.

d. The wind velocity and barometric pressure shall be measured at the toy height and within

one metre of the location of the toy when the toy is not being operated.

G.h. Data to be Contained in Test Report

1. Complete identification and description of the test equipment.

2. Complete identification of the sound source under test.

3. Mounting and operating conditions of the sound source.

k. Location of sound source in the test area.

5. Description of the test area.

6. Description of test conditions, including ambient wind speed during measurements (m/sec) and

atmospheric pressure (mm Hg).

Complete description of deviations, if any, from the prescribed test procedure.

Number of measurements made during tests.

Positions at which the measurements were made.

'

Date and time when the measurements were performed.

9

10

11 The maximum A-weighted sound level, using the fast response characteristic (for model airplanes and bicycle attachments which imitate motor sounds) or the maximum average A-weighted

sound level using the rms hold mode (for bicycle horns), for each measurement location during

the tests.

12. For bicycle horns, the range of the recorded A-weighted sound levels.

7. References

[l] American National Standard Methods for the Measurement of Sound Pressure Levels, SI. 13-1971

(American National Standards Institute, New York, New York, July ih , 1971)-

[2] Inform.ation on Levels of Environmental Noise Requisite to Protect Public Health and Welfare

with an Adequate Margin of Safety, Report No. EPA 550/9-7^-OOl4 (U. S. Environmental Pro- tection Agency, Washington, D. C, March 197*^).

[3] American National Standard Specification for Sound Level Meters, Sl.i4-1971 (American National

Standards Institute, New York, New York, April 27, 1971).

6
8. APPENDIX A

Sound Level Produced by Noise Producing Bicycle Attachments

The A-weighted sound levels emitted by three noise producing bicycle attachments were measured

at a nominal distance of one metre from the device. In addition, measurements were also made at a position approximating the operator's ear — 51 cm behind the device and hO.3 cm above (see Figure

A-l). The toys tested were as follows:

1. Toy A - bicycle horn: The noise producing mechanism was a squeezable rubber bulb.

2. Toy B - bicycle horn: The noise was generated by depressing a plastic, horn-shaped

actuator, thereby releasing bursts of compressed gas from a metal canister through

a pin hole in a thin metal diaphragm in the actuator.

3. Toy C - bicycle attachment to imitate motor sounds: This device is battery-operated

with a manual setting which controls the level of noise produced. All tests on

this device were conducted with the setting at "FULL". (it was determined that

the maximum sound level occurred at this setting.)

The tests were conducted in the NBS anechoic chamber with the toys rigidly mounted on the top

of a three-metre pole. A one-half-inch free-field condenser microphone positioned at normal incidence was used for the measurements. The microphone was connected (via a 3-metre cable) to a sound

level meter set at the hold (indicating the maximum rms value of the signal) mode for Toys A and

B, and at "FAST" response for Toy C. A pistonphone was used for calibration of the measuring system,

(microphone and sound level meter) at one frequency (250 Hz) before and after each test. In addition

to direct sound level meter readings, a limited amount of data were recorded for later analysis —

(l) 15 seconds of data for Toy B at measurement positions 1 and 6 and (2) 30 seconds of data for Toy C at measurement position 3. The tape recorded sound output was then processed utilizing a real-time analyzer which was linked to a mini-computer-based data analysis system. The data analysis

system sampled the recorded sound levels at 0.1 second intervals and printed out the A-weighted

sound level for each 0.1 second sample and the one-third octave band spectrum for the sample where

the maximum A-weighted sound level occurred. A complete list of the equipment used is given in Table A-l.

One averaging technique which is receiving acceptance in the standards community states that

the number of measurements to be made at each position shall equal or exceed the range in decibels

between the lowest and highest of the readings. For example, in Table A-2, position h, the highest

reading was 95-0 dB and the lowest 92.0 dB, and the range was 3 dB. Thus, a minimum of three

readings is required. For this reason only four and three readings for Toys A and B, respectively, were made, instead of the five required by the methodology. After examining the data, it was decided to keep the methodology as simple as possible; therefore, five readings at each position

were recommended as it was felt that this would more than adequately account for the range in readings that might be encountered for these toys.

The results of the measurements are given in Tables A-2 through A-^t and Figures A-2 through

A-7. The data in Figure A-2 illustrates the effect that the freezing of the compressed gas in the canister has on the sound level of Toy B. In a period of 15 seconds, the sound level has dropped 22 dB. This recording was taken when a conscious effort was being made to keep the device

warm. When an effort is not made to keep the canister warm, the sound output will only continue

for about 5 seconds (see Figure A-3 for an example). Figures A-h and A-5 are examples of

representative spectra for Toy B. As can be seen, the sound output of this toy is mainly composed

of high frequency components.

Figure A-6 is a plot of A-weighted sound level versus time for Toy C. This toy starts up

in a rather Jerky fashion, reaches a peak sound output (at approximately 5-6 seconds), and then

settles into an oscillating pattern in which the sound level varies about 2 dB every 2-h seconds.

Thus, the sound output of this toy can be described as only nominally steady state. Figure A-T

is an example of a representative spectrum for Toy C.

A short series of tests were run outdoors over a grass-covered ground surface for Toy B. In comparing the results of these measurements with those taken indoors, they were found to be

in close agreement with each other. For example, the average A-weighted sound level for position

1 in the anechoic chamber was 103.5 dB, while the average sound level at position 1 outdoors

was 102.8 dB.

7
3

45'

4 135'

3.

40.5

cin

RADIUS = 1 m.

51 cm DIAPHRAGM OF ATTACHMENT

SIDE VIEW

Figure A-1. Test configuration for determining the maximum

sound level of noise-making bicycle attachments.

All positions are oriented in relation to the center of the diaphragm of the attachment.

Positions 1-5 are 1.0 0.0^+ metre from the sound

source. Position 6, corresponding to the

operator's ear, is 51-0 cm +^ 1 . 5 cm "behind the

device and i+0.5 cm + 1.5 cm above it.

Table A-1. Equipment used for Tests of Toys A, B, and C. 3/

Manufacturer Instrument Model No. Serial No.

Brllel & Kjaer 1/2-inch microphone Ul33 310856

Brllel & Kjaer Sound level meter 220U 252772

Kagra Tape recorder IV-S 1081

Brliel & Kjaer Pistonphone 1+220 28i+737

Brliel & Kjaer Real-time analyzer 33^+7

Raytheon Mini-computer

—3/ Certain commercial equipment and instruments are identified in this

report in order to adequately specify the experimental procedure. In no case does such identification imply recommendation or endorsement

by the National Bureau of Standards , nor does it imply that the

equipment identified is the best available for the purpose.

8
Table A-2. A-weighted sound level (in dB re 20 yPa) produced

by Toy A. Position refers to those shown in Figure

A-1. The average value for each position is based on

four readings.

Position

1 2 3 It 5 6

100 0 96.0 9^.0 92 0 93 0 101 5

100 0 96.0 9^.0 95 0 9U 0 100 0

99 0 98.0 95.5 95 0 9h 0 100 0

100 0 98.0 95.0 9'^ 5 9h 0 100 0

Average 99-8 97.0 9!+. 6 9h 1 93.8 100 1*

Table A-3. A-weighted sound level (in dB re 20 laPa) produced

by Toy B. Position refers to those shown in Figure

A-1. The average value for each position is based on three readings.

Position

1 2 3 it 5 6

103 0 100.0 98.0 96 5 91 5 110.0

105 0 100.0 97.0 95 5 9^* 0 109.0

102 5 99-0 96.5 9h 5 91 0 109.5

Average 103 5 99.7 97.2 95 5 92 2 109.5

Table k-h . A-weighted sound level (in dB re 20 pPa) produced

by Toy C. Position refers to those shown in Figure

A-1. The value for each position represents a single

reading.

Position

1 60 0

2 6lt 5

3 67 0

it 6i4 0

5 61 0

6 66 5
no Tl—I

\—I—I—

r

ra . a.4.

oCM

CU ? 90

LU

I o

oCO

CO

LU

I <

70

50 J_-J \ \ L_l L J \ \ \

I I I 6 8

TIME, sec

10 12 14 16

Figure A- 2. A-weighted sound level (in dB re 20 pPa) versus time for Toy B. taken at position 1 as shown in Figure A-1. The reading was no

OCM

0»

QQ

90

oC/3

C9

I <

70 -

50

m m m *

1—I

\—\—I—I—

r

I i I i J L

0 6 10 12 14 16

TIME, sec

Figure A-3. A-weighted sound level (in dB re 20 yPa) versus time for Toy B. The reading was taken at position 6 (operator location) as shown in Figure A-1.

10
120

CO

CM

09

OQ

<CO<I—u

o

I LUo

100 -

80

60

M I I I

I M I M I

BASELINE

I I I I I I I I I M I I I I I I I [ I I I I I I I

0.1 1.0 BAND CENTER FREQUENCY, kHz

10.0

Figure A-k. One-third octave band levels for Toy B. The reading was taken at position 1 as

sho-wn in Figure A-1. [The computed A-veighted sound level (in dB re 20pPa) was

lOk.8]. Note that the one-third octave hand where the peak sound level occurs is 2000 Hz ; which is in the frequency range of maximum sensitivity of the ear

(1000-ltOOO Hz).

11
120

CO a.=1

o

03

k. . CO

m

o

o

100

80

I I I I

i

I I I I I I I I I I

I I I I I

I I I I

I

I

BASELINE

60 M M I i I I I I I I I

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

Figure A-5. One-third octave band levels for Toy B. The reading was taken at position 6 as (operator location) shown in Figure A-1. [The computed A-weighted sound level (in dB re 20 pPa) was IO9.O]. Note that the one-third octave band where the peak

sound level occurs is 3150 Hz, which is in the frequency range of maximum sensitivity

of the ear (lOOO-UoOO Hz).

12
I 1 I I I I i I I—I

\—\—rn—

r

I <

10 I I \ I I \ I \ \ \ I I \ I I \ I 0 2 4 6 8 10 12 14 16

TIME, sec

Figure A-6. A-weighted sound level (in dB re 20 pPa) versus time for Toy C. The reading

was taken at position 3 as shown in Figure A-1.

13
70

oCM

QQ

<

OQ

O

O

I

I

I I I I I I I I I

I

I I I I I I M I

I I

H 50

I ' I' I 'I I I I I I I I I i I I I I

0.1 1.0 BAND CENTER FREQUENCY, kHz10.0

Figure A-7. One-third octave band levels for Toy C. The reading was taken at position 3 as shown in Figure A-1. [The computed A-weighted sound level (in dB re 20 yPa) was 6h.6.

]

14
9. APPENDIX B

Results of Tests on Model Airplane Engines

The maximiijn A-weighted sound levels produced by four different model airplane engines were measured at sixteen positions, each of which was nominally one metre from the device under test

(see Figure B-l). Positions 1-8 were in the same vertical plane as the model airplane's propeller

and positions 9-l6 were in the same vertical plane as the model airplane's longitudinal centerline.

The test sample included:

1. Brand D: 0.020 cu. in. engine displacement, 3-blade propeller (engine not equipped

with a muffler)

.

2. Brand D: 0.0l+9 cu. in. engine displacement, 3-blade propeller (engine equipped with

a muffler)

.

3. Brand D: 0.0^9 cu. in. engine displacement, 3-blade propeller (engine not equipped

with a muffler)

.

1*. Brand E: 0.0^*9 cu. in. engine displacement, 2-blade propeller (engine not equipped

with a muffler).

At the onset of testing, the entire model airplane — engine/propeller plus plastic fuselage —

was mounted on the top of a 3-metre pole. However, the engine/propeller vibrations generated during operation with the entire model airplane rigidly mounted on the pole resulted in the destruction

of the plastic fuselage. For this reason, the engine/propeller only were tested in this study. The tests were conducted out-of-doors over grass with no sound reflecting obstacles, other than the

grass covered ground plane, within 5 metres of the toy under test or the measuring microphone. A one-half inch free-field condenser microphone positioned at normal incidence was utilized for these measurements. The microphone was connected, via a 10-metre extension cable, to a sound level meter set for fast response and the A-weighting network. A pistonphone was used for single point

(250 Hz) calibration in the field of the measurement system (microphone and sound level meter)

before and after each test. In addition, at a single microphone position for each engine — position number 5 > 1 metre below the propeller — the sound output was recorded on tape for further

analysis. The analog tape was processed utilizing a one-third octave band real-time analyzer

which was interfaced to a mini-computer-based data analysis system. The data analysis system then

printed out the noise spectrum for each particular engine at the time corresponding to the occur- rence of the maximum A-veighted sound level at measurement position number 5- A complete list of equipment utilized for data acquisition, reduction and analysis is given in Table B-l.

The data are given in Figures B-2 through B-5 and Tables B-2 through B-5. Since the noise

emitted by model airplane engines is essentially steady-state, the measurement results are based

on a single reading at each microphone location.

In addition, in order to assess the adequacy of the outdoor test site — source mounted on top of a 3-metre pole over a grass covered ground plane — as a "free-field" environment, supplementary measurements were made on three of the four model airplane engines at locations 2-, h-,

8-, and l6-metres from the side of the engine (see Figure B-l) along a line which was chosen as an estimate of the orientation of the model airplane's control line in actual practice. On the

basis of these data, it was observed that the noise radiated from the model airplane engines tested

under these conditions closely conformed to spherical spreading, i.e., there was approximately a

6 dB attenuation per doubling of distance in the direction tested.

In general, the spectra for engines without mufflers are dominated by mid to high frequency

(I-8 kHz) exhaust and/or engine radiated noise, which is also the frequency range of maximum

sensitivity of the ear. The noise associated with the firing frequency of the engine (200-315 Hz)

is present in all cases. It is interesting to look at the effectiveness of the muffler on engine

number 2. A significant reduction in the sound pressure levels in the 1-8 kHz range resulted in an overall reduction of 15 dB in the maximum A-weighted sound level at all microphone locations,

even though the noise level corresponding to the firing frequency of the engine was somewhat higher

for the muffled engine than for the unmuffled engine. The effect of the muffler on the performance

and fuel consumption of the engine was not determined.

15
0°

1

Figure B-1. Test configuration for determining the maximum sound level

of model airplanes. Positions I-I6 are 1.0 +_ 0.0^4 metre

from the sound source. Positions 1-8 are in the same vertical plane as the model airplane's propeller and

positions 9-l6 are in the same vertical plane as the model

airplane's longitudinal centerline. Positions 17-20 are

2, k, 8, and 16 metres, respectively, from the side of the

sovmd source along a line which is an estimate of the

orientation of the model airplane control line in actual

practice.

16
Table B-1. Equipment Used for Tests of Model Airplanes.—

Manufacturer Instrument Model No.

Brllel & KJaer 1/2-inch microphone i^l33

Brllel & KJaer Sound level meter 220U

Brliel & KJaer Pistonphone 1;220

Nagra 2-channel tape recorder IV-S

Brilel & KJaer Real-time analyzer 33)47

Raytheon Mini-computer 70lt

— Certain commercial equipment and instruments are identified in this report in order to adequately specify the experimental

procedure. In no case does such identification imply recommendation or endorsement by the National Bureau of Standards, nor does

it imply that the equipment identified is the best available for the piirpose.

17
Table B-2. The A-weighted sound levels (in dB re 20 pPa) produced by airplane engine number 1. Measurements were made at the positions shown in Figure B-1.

Position

A-weighted

Sound Level

dB

Position

A-weighted

Sound Level

dB

1 98 11 98

2 98 12 99

3 96 13 101

h 96 Ih 99

5 100 15 96

Q5y y l6 98

T 96 IT

8 97 18

9 98 19

10 98 20

110

oCN

a> CO

00

u

o

90

70

50

I I M I

I I M I I I I I

I

I I I I I I I I I

I

I

8 i I i I I ' I ' I I I I ' I ' i ' I I I I I I I I

0.1 ^ 1.0 BAND CENTER FREQUENCY, kHz

10.0

Figure B-2. Noise spectrum produced by airplane engine number 1. The location where the measurement was made is position 5 as shown in Figure B-1.
Table B-3. The A-weighted sound levels (in dB re 20 yPa) produced by airplane engine number 2. Measurements

were made at the positions shown in Figure B-1.

Position

A-weighted

Sound Level

dB Position

A-weighted

Sound Level

dB

1 85 11 P(

2 83 12 86

3 81 13 81+

k 82 lit 83

5 8U 15 81

6 8h 16 83

T 8h 17 71+

8 85 18 70

9 85 19 63

10 86 20 58

I I M I I I I I I

I I I I

I

I I I I I I I I I

I

I

i « I » i i ' I I I I I I I I I I I I I I I I I I I

0.1 1.0 10.0

BAND CENTER FREQUENCY, kHz

spectrum produced by airplane engine number 2. The location where the

•ement was made is position 5 as shown in Figure B-1.

IIU a.:t oCM

03 m

_i 90

<ea

LU<»—o

o

70

I LUo

50

Figure B-3. Noise

meast

19
Table B-U . The A-weighted sound levels (in dB re 20 yPa) pro- duced by airplane engine number 3- Measurements

were made at the positions shown in Figure B-1

.

Position

A-weighted

Sound Level

dB Position

A-weighted

Sound Level

dB

1 100 11 100

2 99 12 100

3 98 13 100

k 99 ' ll+ 100

5 100 15 97

6 99 l6 97

T 98 IT 92

8 97 18 86

9 101 19 80

10 101 20 75

0.1 1.0 BAND CENTER FREQUENCY, kHz

Figure B-U. Noise spectrum produced by airplane engine number 3- The location where the measurement was made is position 5 as shown in Figure B-1.

20
Table B-5. The A-weighted sound levels (in dB re 20 yPa) pro- duced by airplane engine number h. Measurements

were made at the positions shovm in Figure B-1.

Position

A-weighted

Sound Level

dB Position

A-weighted

Sound Level

dB

1 99 11 97

2 - 99 12 98

3 97 13 99

h 97 Ik 102

5 99 15 9^

6 98 16 98

7 96 17 90

8 96 18 &h

9 99 19 78

10 98 20 72

21
Acknowledgements

The authors wotild like to express appreciation to the following members of the Applied Acoustics

Section for the contributions they made to this program: Mr. Denzil E. Mathews for his assistance

in the conduct of the testing program; Mr. Jack M. Fath for assistance with the model airplane testing program; and Mr. Ronald L. Fisher for his assistance with data analysis.

USCOMMNHSOC

22
NBS-114A (REV. 7.7))

U.S. DEPT. OF COMM.

BIBLIOGRAPHIC DATA

SHEET

1. PUHl.K A riON OK Kl POK 1 NO. NBSIR 75-6932. Gov't Accession

No.

3. Recipient's Accession No.

4. Tl I LK AND SUm ITI.K Measurement Methodology for Determining the Sound Output

of ^k)del Airplanes and Noise Producing Bicycle Attachments

5. Publication Date April 1975

6. Performing Organization Code

7. AUTHOR(S)

Marilyn A. Cadoff and William A. Leasure, Jr.

8. Performing Organ. Report No. NBSIR 75-693

9. PERFORMING ORGANIZATION NAMF AND ADDRl Ss NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Proiect/Task/Work Unit No. 2130496

11. Contract /Grant No.

12. Spon.soring Organization Name and ( ompU ti- Address (Street, City, State, ZIP)

Bureau of Engineering Sciences ' Consumer Product Safety Commission

5401 Westbard Avenue

Bethesda, Maryland 20014

13. Type of Report & Period

< overcd Final 7/73-6/74

14. sponsoring Agency v. ode

15. SUPPI.FMKNTARY NO'l IS

16. ABSTRAC;T (A 200-word or less (actual summary of most signilicant information. II document includes a signilicant

bibliography or literature survey, mention it here.)

In recent years, a great concern has been expressed for consumer protection

and safety, especially for children. As an outgrowth of this concern, acoustical

testing of potentially-hazardous noise producing toys has been carried out at the

National Bureau of Standards for the Consumer Product Safety Commission under

the authority of the Toy Safety Act of 1969. This report outlines a methodology

which was developed to measure the noise levels of model airplanes and noise

producing bicycle attachments. The technical back-up and rationale for the

development of the methodology are discussed. In addition, data taken using

the proposed methodology are presented.

17. KEY WORDS (six to twelve entries; alphabetical order, capitalize only the lirst letter of the lirst key word unless a proper name; separated by semicolons

)

Bicycle attachments; children; consumer safety; model airplanes; noise; toys.

18. AVAILABILITY [X] Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

QJ For Official Distribution. Do Not Release to N'MS

UNCL ASSIFIED

24

Order From Sup. of Doc, U.S. Government Printing Office Washington. D.C. 20402. SD Cat. No. CI 3

20. SI-:( URITY ( LASS

(1 MIS PAGE)

22. Price

[y^ Order From National Technical Information Service fNTIS)

Springfield, Virginia 22151 Ij'NCLASSIMED $3.25

USCOMM.DC 29042-P74