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A Measurement of Sound Levels Associated

With the Operation of a Portable Pneumatic

Pavement Breaker Equipped with a Muffler/Cas

Enclosure and Dampened Moils

by

Robert N. Hosier

National Bureau of Standards

Washington, D.C. 20234

Final Report

February 1979
r/
CONTENTS

1. INTRODUCTION 1

2. TEST APPARATUS AND PROCEDURE . 2

2.1 Test Apparatus 2

2.2 Procedure 5

3. DATA P^DUCTION 7

4. RESULTS 8

4.1 Mean and Maximum A-V7eighted Levels 8

4.2 Constant Bandwidth Spectra 10

4.3 Importance of Crest Factor Capability . . 12

5. CONCLUDING REMARKS 15

REFERENCES 17

TABLES 18

FIGURES 21

APPENDIX A 35
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A MEASURmENT OF SOUND LEVELS ASSOCIATED

WITH THE OPERATION OF A PORTABLE PNEUMATIC

PAVEMENT BREAKER EOUIPPED WITH A MUFFLER/ CASE

ENCLOSURE AND DAMPENED MOILS

by

Robert N. Hosier

National Bureau of Standards

Washington, D.C. 20234

1. INTRODUCTION

In carrying out the mandate given it in the Noise Control Act of 1972

[1]^ the United States Environmental Protection Agency (EPA) has

identified pavement breakers as a major noise source [2]. As a result of

this identification process, EPA has the dual tasks of specifying suitable

acoustic measurement methods and of studying source noise emission levels

which are achievable with known or projected technology. These tasks have

previously been systematically addressed in studies by Dames and Moore [3]

and NBS [4].

^ Numbers in brackets refer to references at the end of the test.

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The present study was intended to determine the effectiveness of certain

commercially available and experimental noise control devices in reducing

the noise levels emitted by the Swiss Industrial Gas (SIG)^ portable pneumatic

pavement breaker shown in Figure 1. The noise control devices consisted of

a muffler/case enclosure (shown in Figure 2) and elastomeric moil silencing

sleeves (shown in Figures 3 and 4) . The muffler/case enclosure was designed

to fit snugly over the pavement breaker case, totally covering the entire

tool except for the back head (see Figure 5) . Moll installation and removal

were easily accomplished by opening an access door on the side of the

muffler and releasing the moil retaining latch (see Figure 6) , The moils

were inserted through an opening which was contoured to match the shape of

the moil shank (see Figure 7)

NBS measured the noise emission levels of the SIG pavement breaker

both with and without each of the noise control devices installed. This

report presents the results of those measurements. Section 2 presents a

description of the test apparatus and procedure and the data reduction

procedure is described in Section 3. The measurement results are presented

in Section 4.

2. TEST APPARATUS AND PROCEDURE

The specifications for the test apparatus and procedures used in this

study are presented in detail in Appendix A.^ The purpose of this section

1 Certain commercial equipment and materials are identified in this paper

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

the product by NBS nor does it imply that the equipment or materials

are necessarily the best available for the purpose.

The methodology in Appendix A was provided by EPA.

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is to describe how those specifications were implemented and to identify

any differences between the specifications contained in Appendix A and the

actual tests performed.

2.1 Test Apparatus

The SIG portable pneumatic pavement breaker shown in Figure 1 was used

in this study. It weighed approximately 33.5 kg (74 Ibm) without any noise

control devices added and was loaded with an additional mass of 31.8 kg (70

Ibm) by using molded lead weights as specified in Appendix A (see Figure Al)

.

The muffler/case enclosure shown in Figure 2 was used in some of the testing

and could be easily removed to allow testing in an unmuffled configuration.

Five 3.2 cm (1 1/4 in.) diameter moils were used in these tests. Four

of these moils were equipped with different types of silencing sleeves. As

shown in Figures 3 and 4, three 17.8 cm (7 in.) long experimental sleeves

were molded onto the moils with their metal protective cover either a) unsplit,

b) split lengthwise into two equal sections, or c) split lengthwise into

three equal sections. A fourth sleeve (Figure 4) was of a commercially

available unsplit design and was shorter, 11.1 cm (4.38 in.), than those shown

in Figure 3. This sleeve mployed a pressure-fit design and was installed

by using a hydraulic press requiring no epoxy to secure it because of the

tight fit.

Figure 8 is a block diagram of the acoustic data acquisition system

used for these tests. Each of the nine channels of the system included a

commercially available 1.27 cm (1/2 in.) condenser microphone with a

windscreen, protecting grid, dehumidifier, preamplifier, and

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selectable in 10 dB increments. The gain settings for the amplifier were

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the pavement breaker noise emission and other ambient noise sources when

the data were recorded on magnetic tape. In addition to this system, a

Type I sound level meter was also used to monitor the levels measured

during the test by Microphone 6 (arbitrarily chosen)

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each microphone channel (voltage injection at the preamplifier through the

tape recorder) was made in the laboratory, A sample result of these sweeps

is shown in Figure 9. It can be seen that the system response was flat to

within less than 2 dB over the frequency range of 20 Hz to 20 kHz.

One track of the tape recorder was configured for digital recording.

The input to this track came from a control module with output coding to

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indicator, pavement breaker configuration, and start of data. This digital

information was used to allow automated computation of the A-weighted,

linear, and one-third octave band levels during data reduction.

A block diagram of the data reduction system used for this study is

shown in Figure 10. The analog signal served as input to a real time

spectrum analyzer which provided (slow-response) A-weighted, flat, and

one-third octave band levels. These levels were read every second by the

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2.2 Procedure

The eight acoustic tests shown in Table I were conducted at Ft. Belvoir,

Virginia, during the week of September 3, 1978, in accordance with the

specification in the Appendix A. (The specification in Appendix A was not

developed by NBS) . Figure 11 is a plan view of the test arrangement. The

concrete test blocks were placed in a hole cut- in an existing concrete pad

and were made flush with the pad surface.

Nine microphone positions were utilized. Positions 1-4 v;ere 1 m .Ira

from the pavement breaker case at a height of 1.5 m - .01 m above the

concrete test surface. Microphone positions 5-8 were 7 m - .1 m from the

pavement breaker case and were also at a height of 1.5 m + .01 m. Position

9 was 0.25 m + .1 m from the breaker casing at a height of 1.5 m + .01 m.

This last position was used to measure the noise levels at the operator’s

position.

Initially Position 9 was along the line through Positions 3 and 7;

however, during the course of the first two tests, it was observed that this

location was so close to the operator that he bumped into the microphone while

operating the pavement breaker. Therefore, for subsequent tests, Position 9

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was moved in front of the operator. In both cases. It was difficult to

place the operator’s microphone so that the microphone stand was not resting

on one of the test blocks. This is a problem since structural vibrations can easily be introduced into the acoustic signal. Budgetary and time constraints

did not allow a more suitable microphone support to be constructed. In

future testing, however, specially designed microphone supports may be

necessary in order to make acoustic measurements in such close proximity to

the operator. Because of this potential problem, caution should be used in

drawing conclusions from the Position 9 data shown in Table II.

The noise measurements were made after positioning the pavement

breaker (moil embedded to the taper as shown in Figure 12) on the concrete

block and positioning the microphones at the appropriate locations. The

tape recorder was started ten seconds prior to the commencement of the tool

operation. When the breaker began operation, a data ready switch was activated,

the digital track was encoded to indicate that the breaker was in operation.

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and the sound pressure at all nine microphone positions was measured

simultaneously. The operator continued breaking concrete for approximately

thirty seconds at which time the digital track was encoded to indicate that

the pavement breaker operation had ceased. The pavement breaker was then

moved to a different location on the test block and the 1-meter and operator

microphones were repositioned for a new set of noise measurements. Because

all the pavement breaker operations were within 0.3 m of the center of the

test block, the 7-meter microphones were not repositioned. This change in

pavement breaker position was calculated to affect the direct radiation to

the 7-meter microphones by less than 0.5 dB. The same procedure was used

for all the tests shown in Table I. Time and budget constraints only permitted

one test of each condition.

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During the testing it was observed that the moll release access door on

the muffler/case enclosure was acting as the exhaust outlet and tended to

flap with the exhaust pulses. To determine whether this action made a

significant contribution to the measured noise levels, the access door was

taped closed and tests numbered seven and eight were performed. The

results of these tests are given in Section A.

3. DATA REDUCTION

The system described in Section 2.1 was used to determine the mean

A-weighted and one-third octave band levels and the maximum A-weighted

level measured at each microphone position for each test sho^TO in Table I.

Initially these values were computed from the data acquired during the

entire thirty seconds of pavement operation. This procedure resulted in

differences of up to 9 dB between the mean and maximum A-weighted levels.

By listening to the data tapes, reviewing test notes, and examining the

I A-weighted time history, it became apparent (see Figure 13) that unusually

high sound levels were sometimes measured at the beginning of the test runs.

These high levels were attributed to initially high line pressure and pavement

breaker-operator instability when the breaker was first turned on. Although

both of these effects may be typical of pavement breaker operation, they are

very difficult to control. It was also noted that the levels had usually

stabilized to within -1 dB of a constant value about ten seconds into the test

run. Thus, it was decided to compute the mean and maximum A-weighted levels

from the second ten seconds of data for each run. These values are recorded

in Table II and will be discussed more fully in Section A.

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Mean one-third octave band spectra were obtained by sampling the

output of each digital one-third octave band filter once every second and

computing a linear average over the entire thirty second run. In order to

simulate a slow meter response, the filter output was exponentially averaged

with a one-half second time constant, prior to sampling every second. (These

spectra have been submitted to EPA with, but are not included in, this report.)

Constant bandwidth (12.5 Hz) analyses were also performed over the

range 0-5 kHz on selected data (Tests 1-4, 7, 8) measured at Position 6.

The resultant spectra (Figures 14 through 19) were obtained by averaging 32

spectra from the middle portion of the record. These spectra are discussed

more fully in Section 4.

4. RESULTS

4.1 Mean and Maximum A-weighted Levels

The mean and maximum slow response, A-weighted sound pressure levels

measured at each microphone position are shoT>m in Table II for each test

configuration listed in Table I. These data show that the mean and maximum

levels measured at each position differ by no more than 2 dB in all (99

percent) but one case, vrhere a 3 dB difference was observed. Moreover,

in 43 percent of the measurements the maximum and mean levels were found to

be equal (when rounded to the nearest decibel) and in 44 percent of the

measurements the difference was only 1 dB. Table III shows the mean and

standard deviation of the 1-meter and 7-meter levels for each test as

computed from the data in Table II.

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Important to recognize that caution must be used to reach generalized

conclusions from the data in Tables II and III» Test "variables such as

mounting of the test block, ground vibrations, initial moil depth, and moil

penetration rate may vary enough to cause significant variability in the

measured sound levels if a number of replications of each condition are

evaluated. Although there are very little data in the literature, one

study [3] found the .standard deviation of the sound levels measured from

repeated tests of six identical Csame model) pneumatic pavement breakers to be

i" 1.8 dB at a distance of seven meters. With this limitation in mind, the data

in Tables II and III seem to imply that the muffler/case enclosure provides

about an 8 dB reduction in the measured sound levels Ccompare the levels from

Tests 1 and 3 in Table III). The muffler/case enclosure also reduced the

directionality of the pavement breaker noise. This can be seen by again

> looking at the levels measured for Tests 1 and 3 shown in Table II, The

Test 1 data (no case muffler or silencing sleeve) show up to 7 dB variation

from position-to—position for the IOmeter levels (9 dB for the 7-meter

levels). By comparison, the Test 3 data Cease muffler used but no silencing

sleeve) show only a 2dB variation among the measurement positions for both

the 1-meter and 7-meter measurements.

Each of Tests 2 and 4 was conducted using the moil with the three-section

silencing sleeve and, in the case of Test 4, the muffler/case enclosure was

also installed. A comparison of the mean sound levels (Table III) for Tests

1 and 2 shows no change in the 1-meter and 7-meter A-weighted levels when the

silencing sleeve is used. Also, when the Test 3 and 8 (muffler and no sleeve)

data are compared with the data from Tests 4-7 (muffler and each of four sleeves)

| a maximum difference of only 1 dB is observed at 1-meter and 2 dB at 7-meters. |

I Considering the 7-meter standard deviation of + 1,8 dB reported by Dames and

9
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Moore [3] when repeatability measurements were made, the levels measured both

with and without the silencing sleeves in this study seem about the same.

The data in Table III can be used to evaluate the difference in sound

levels measured at 1-meter and 7-meters from the pavement breaker. By

using small sample statistical analysis (t-statistics) it is possible to

show with 99 percent certainty that, on the average, the 1-meter levels are

11 dB greater than the 7-meter levels. Previous testing [4] had shown a 15 dB

difference between the A-weighted levels at 1-meter and 7-meters.

4.2 Constant Bandwidth Spectra

In order to gain a better understanding of the effectiveness of the

noise control devices, constant bandwidth spectrum analyses were performed

on selected test measurements made at one position (Position 6) seven meters

from the pavement breaker. Two such spectra, shown in Figure 14, illustrate

the levels measured with and without the muffler/case enclosure in use (Tests

2 and 1, respectively). These spectra show that the muffler/case enclosure has

little effect on the sound levels below 500 Hz but becomes increasingly more

effective at higher frequencies. Two distinct spectrum peaks are observable

at about 3,550 Hz and 4,350 Hz under both conditions. It may also be observed

that the spectrum shapes above about 2000 Hz are nearly alike, but the levels

are reduced by 6 dB to 11 dB, depending on the frequency. Some variation in

these level differences should be expected from position to position since the

data in Table II show much more source directionality when the case muffler

was not used then when it was used.

10
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Constant bandwidth spectra were obtained for tests with and without the

three-section moil silencing sleeve. Figure 15 displays the results obtained

from Tests 3 and 4. The two curves clearly show an elimination of the spectrum

peaks at 3,550 Hz and 4,350 Hz; however, the spectrum levels have increased

at nearly all frequencies above 1 kHz. This same phenomenon was observed in

an earlier study by Hosier and Blomquist [4] but the mechanism causing it is

not understood.

It would appear from the spectra in Figure 15 that use of the threesection moil sleeve eliminated the high-frequency peaks that were

observed without the sleeve. However, the data in Figure 16 make it

impossible to conclude that the peaks are eliminated solely by using the

three-section moil sleeve. That figure shows spectra measured at seven meters

(Position 6) with no case muffler and with and without the three-section moil

sleeve (Tests 2 and 1, respectively) . Both of these spectra clearly show the

spectrum peak at 4,350 Hz, The peak at 3,550 Hz is also visible in both

spectra, although it is reduced in amplitude when the moil sleeve is used. Thus,

it is not conclusive that the tv;o high-frequency spectrum peaks can be associated

with the pavement breaker moil, or their elimination with the three-section

moil sleeve.

During the course of the testing it was observed that the moil latch

access door on the case muffler (see Figure 6) was flapping with the exhaust

pulses. This flapping was eliminated by tightly taping the access door shut.

Additional noise measurements were then made with and without the two-section

moil sleeve (Tests 7 and 8, respectively). Figure 17 presents a comparison of

the spectra from Tests 7 and 8 with those of Test 4 (access door untaped and

the three-section moil sleeve in use) . The spectra show a clear but small

11
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reduction in the noise levels in the mid-frequency range (1,500 Hz to 3,500

Hz). The two high-frequency peaks are again observable in both the Test 7

and Test 8 spectra. In the Test 7 spectrum, however, the 3,550 Hz peak has

shifted to a slightly lower frequency (about 3,A50 Hz) and has been broadened.

The peak remained at 4,350 Hz in both spectra, although the amplitude was

reduced about 4 dB for Test 7. There is also evidence of the same trend noted

in conjunction with Figure 15: that is, an increase in levels over much of the

spectrum when the moil sleeve is used.

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One further observation can be made about Tests 7 and 8, When the ^

moil access door was taped shut, a large amount of dust was blown from the test

pad by the breaker exhausting mainly through the moil opening in the case muffler

(see Figure 7). This was not observed when the access door was untaped.

. ^

4.3 Importance of Crest Factor Capability

As was mentioned in Section 2.1, a Type I sound level meter was used to

measure the levels at Position 6 during the day of testing. When compared with

the values shown in Table II, the sound level meter readings were generally

found to be lower by 2 dB or more. It was reasoned that the differences between

the two sets of data were either due to differences in the averaging period (the

entire test run for the on-site measurements versus ten seconds from the middle

9

of the run for the computer output shown in Table II) or to the crest factor^

handling capabilities of the two systems.

^ The crest factor of a signal F is defined by the relationship F = peak

^ ^ A , where A , and A are the peak and root-mean-square amplitudes rms

* peak rms 'i r of the signal. The largest value of F for which a device such as a sound level

meter can accurately measure the signa5 defines the crest factor handling

capability.

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To resolve this issue, a controlled experiment was conducted in which

two Type I sound level meters without microphones and with different crest

factor handling capabilities were used to measure the average (by "eye")

sound level recorded at Position 6 over the central ten seconds of each

test run as the data were played back. One sound level meter (Meter A) was

the same kind that was used to make the on-site measurements. It has the

capability to accurately measure the rms value of signals with crest

factors less than 5 to within + 1 dB. The second sound level meter (meter B)

could accurately measure the rms value of signals with crest factors less

than 10 to within + 0.5 dB. The rms detector in the real time analyzer,

used to obtain the computer values, could measure the rms value of signals

with crest factors less than 21 in the signal 'range used in this test

(accuracy is unspecified by the manufacturer)

The data from this experiment are shown in Table IV. A two-way

analysis of variance (ADV) was performed on these data to test the

following hypothesis:

At the 0.05 level of significance there is no statistically

significant difference among the three methods (Meter A,

Meter B, and the Computer Average) of measuring the sound

levels in these tests.

The two-way AOV was used in order to remove the test-to-test variability

due to the different tool configurations found in each test. For the

hypothesis to be accepted requires the F-statistic must be less than

F = 3.74. After carrying out the necessary computations, it was found

that the meter-to-meter variation yielded F = 16.78, a value well beyond

the region of acceptance. Thus, the hypothesis was rejected; that is, at

13
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the 0.05 level there Is a statistically significant difference among the

three methods.

In order to identify the magnitude of the differences, post hoc

contrasts were made among each of the methods. These contrasts consisted

of comparing the 95 percent confidence intervals about the difference

of the mean values of each set (column in Table IV) of meter readings.

The results of the post hoc testing were:

Comparison

1. Meter A - Computer

2. Meter B - Computer

3. Meter A - Meter B

95 Percent Confidence

Interval, dB

-0.94 + 0.35

-0.31 + 0.35

-0.63 + 0.35

From these contrasts it is clear that the confidence interval includes

zero only for Comparison 2. Thus, there is no statistically significant

difference between the Meter B and Computer Average Levels. There is,

however, a statistically significant difference between the Meter A

and Computer Average Levels. Thus, if the Computer Average is assumed

to yield the "correct” levels, then Meter B (crest factor <10) could be

expected to provide equivalent results, but Meter A (crest factor <5)

could be expected to provide a significantly different level (in this

case about 0.9 dB + 0.3 dB lower).

14
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A word of caution is necessary here. The +0*3 dB confidence interval applies only to the variability associated with a comparison

of the different meter types. It should not be interpreted to be

a repeatability interval associated with pavement breaker sound measurement

replications.

5. CONCLUDING REMARKS

Measurements have been made of the sound emission from a portable

pneumatic pavement breaker equipped both with and without noise control

devices such as a muffler/case enclosure and a variety of elastomeric moil

silencing sleeves. The test results, in the form of mean and maximum

A-weighted sound pressure levels and constant bandwidth spectra, have shown

that:

® The muffler /case enclosure reduces the directionality of the

noise emission and provides an 8 dB reduction in the measured

A-weighted levels.

15
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® The results of tests to assess the benefit of the moll silencing

sleeves were inconclusive.

® The 1-meter and 7-meter A-weighted measurements differed from one

another by about 11 dB. This is 4 dB less than had been observed

in previous measurements.

In addition, two important conclusions were reached concerning the test

procedure and instrumentation:

® By allowing ten seconds for the pavement breaker operation to

stabilize, the difference between the maximum and mean A-weighted •

levels measured at each position was found to be no greater than

2 dB in 99 percent of rhe measurements.

o There is a statistically significant difference between the

levels measured with a sound level meter with a crest factor

handling capability of 10 or greater (Meter A) versus one with

a crest factor handling capability of no more than 5 (Meter B)

At the 95 percent confidence level, the Meter B levels were

foui\d to be 0.63 dB + 0.35 dB lower than the Meter A levels.

Thus, in order to improve the test accuracy, the use of sound

level meters with a crest factor handling capability of 10 or greater scums to be necessary when measuring pavement breaker

noise.

16
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5. REFERENCES

1 . Public Law 92-574, Noise Control Act.

2. 42 Federal Register 6722 (3 February 1977).

3. Anon.: Technology Analysis - Noise Pavement Breaker and Rock Drill.

(Vol. 1), Draft final report to EPA under contract no. 68-01-3288-

phase I, Dames and Moore, Cranford, NJ, October 1977.

4. Hosier, Robert N. , and Blomquist, Donald S.; A Test of Portable

Pavement Breaker Sound Level Measurement Methodology. NBS Final

Letter Report submitted to EPA under Interagency Agreement

EPA-IAG-D7-H1087, March 1978.

5. American National Standards Institute, Inc., Specification for Sound

Level Meters. ANSI SI. 4-1971, April 1971.

17
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TEST

CONDITIONS

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TABLE III. - MEAN A-WEIGHTED LEVELS ATO STANDARD DEVIATIONS

Test Number

Location 1 2 3 4 5 6 7 8

1-meter 104^3 104^2 96^1 96^1 95±2 95^2 96tl 95±1

7-meters 93±4 93±4 85+2 86±2 84+2 84+2 83±1 84+1

Difference 11 11 11 10 11 11 13 11

TABLE IV. - COMPARISON OF A-WEIGHTED LEVELS, dB (re 20lJPa) FROM

SYSTEMS WITH DIFFERENT CREST FACTOR HANDLING CAPABILITIES

(Measured at Position 6)

Test Number

Sound Level Meter

Computer

Average

From Table II

A

Crest factor

Capability

<5

B

Crest factor

Capability

<10

1 92 93 93

2 91 91.5 92

3 84.5 84.5 85

4 86 87.5 88

5 84.5 84.5 85

6 84.5 84,5 85

7 83 84 84

8 83 84 84

Figure I. - Photograph of test arrangement and

portable pneumatic pavement breaker

without noise control devices.

E

I

Figure 2. - Photograph of a test pavement breaker with SIG

case muffler.

21
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t Figure 3. - End-view photograph of the three specially-made,

} molded, elastomeric moil silencing sleeves used

/ in Tests 2, 4, 5, 7, and 8 (see Table I).

f

4

Figure 4. hotograph of unsilenced moil used in Tests 1

, and 8 (see Table I) and the commercially

vailable moll silencing sleeve used in Test 6 .

i

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Figure 5. - Photograph of pavement breaker with

case muffler lowered to reveal the

exhaust ports.

/

Figure 6. - Photograph of the case muffler with the

moil latch access door opened.

23

Figure 7. - Photograph of contoured opening in the base

of the case muffler for inserting the moil

shank.

24
«.»Lvd r,X baii/dirtoa Vo rfqoisoJcxiH .\ ai»a^

ijtoa »4ti inli'"T5^ixl id1 o»»o
25

Figure

8,

-

Block

diagram

of

acoustic

data

acquisition

system.

CD

SP '13A31 indino IM31SAS

IT5 CM

Ln

CSI

CD

CO

CO

CD

CM

CO

fsl CD

CO

CD o

CD

CD LU

• ::d a

CD LU

CD CC

u..

CD

CD

CM

«

CD

CD

CD

UD

CD

26

Figure

9.

-

Sample

acoustic,

system

response

curve.

ANALOG

TAPE

recorder

real

time

analyzer

Figure

10.-

Block

diagram

of

the

nconstlc

data

reduction

system.

^ — Microphone positions

(^) - Position 9 for Tests

1 and 2 only

Figure 11. - Plan view of test arrangement

28

i

I

k

Figure 12 . - Photograph of pavement breaker, x^7ith

moil imbedded to the taper, prior to

test run (weights net in place)

i

29

30

Figure

13.

-

A-weighted

sound

level

time

history

measured

at 7

meters

(Position

6)

for

Test

Figure

14.

—

Comparison

of

spectra

measured

at 7

meters

(Position

6)

for

Test

1

(no

case

muffler

and

no

moil

sleeve)

and

Test

3

(case

muffler

but

no

moil

sleeve).

Figure

15.

-

Comparison

of

spectra

measured

at

7

meters

(Position

6)

for

Test

(case

muffler

but

no

moil

sleeve)

and

Test

4

(case

muffler

and

3-section

moil

sleeve)



Figure

17

-

Comparison

of

spectra

measured

at 7

meters

for

Test

4

(case

mtiffler

and

3-section

moil

sleeve)

,

Test

7

(case

muffler

with

latch

access

door

taped

shut

and

2-section

moil

sleeve)

,

and

Test

8

(case

muffler

with

moil

access

door

taped

shut

and

no

moil

sleeve)

PAVEMENT BREAKER SOUND LEVEL

MEASUREMENT METHODOLOGY ^ 1.0

INTRODUCTION

The purpose of this measurement methodology is to provide a test

procedure for the accurate measurement and reporting of pavement breaker

sound levels. The reported sound levels result from the A-weighted network

filtering of the emitted acoustic pressure.

2.0

SCOPE

2.1

Tools

The procedures described herein apply to the acquisition and

reporting of sound level data of portable pavement breakers

2.2 Sound Level Reported

The sound level reported is the A-weighted network filtering of

acoustic pressure in decibels (dB) referenced to 20 micropascals.

2 . 3 Accuracy

The limiting elements of this test procedure are assumed to be the

component sum of the inherent instrumentation error, the inherent error in

observing and transcribing the sound level meter readings, and others which

limit the accuracy of this test procedure to + 2 dB. (This tolerance is the

target which may be corrected after further study.)

3.0 SPECIFICATIONS, STANDARDS, AND TERMINOLOGY

3.1 Specifications and Standards

The following specifications and standards are referenced;

American National Standards Institute (ANSI)

51.

1-

1960 (R1971)

SI. 4-1971

SI. 8-1969

SI. 13-1971

55.

1-

1971

"Acoustical Terminology"

"Specifications for Sound Level Meters"

"Preferred Reference Quantities for

Acoustical Levels"

"Methods for the Measurement of

Sound Pressure Levels"

"Test Code for the Measurement of

Sound from Pneumatic Equipment"

American Society for Testing and Materials (ASTM)

C39 "Method of Test of Compressive Strength

of Molded Concrete Cylinders"

C94 "Standards Specifications for Ready

Mix Concrete"

1 This methodology was not developed by NBS

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International Electrotechnical Commission (lEC)

179-1965 "Precision Sound Level Meters"

Society of Automotive Engineers (SAE)

J-184 . "Qualifying a Sound Data Acquisition

System"

3. 2 Terminology

Definitions and terminology used shall be consistent with ANSI

SI. 1-1960 (111971).

4.0 INSTRUMENTATION

The sound level meter and microphone system shall meet the requirements

of ANSI SI. 4-1971 for Type 1 sound level meters. Units meeting the

requirements of lEC 179-1965 for precision sound level meters are also

acceptable.

4.1 Permanent Record

All data is to be tape recorded on a magnetic tape recorder for

post-test analyses.

4.2 Personnel and Measurement Practice

Persons technically trained and experienced in the current

techniques of sound measurements shall select the equipment and conduct the

tests. Proper usage of all test instrumentation is essential to obtain

valid measurements. Operating manuals or other literature furnished by the

Instrument manufacturer and ANSI SI. 13-1971 should be referred to for both

the recommended operation of the instrument and precautions to be observed.

Specific items to be considered are:

1, The type of microphone, its directional response

characteristics, and its orientation relative to the ground

plane and source of noise.

2, The effects of ambient weather conditions (for example,

temperature, humidity, and barometric pressure) on the

performance of all instruments. Instrumentation can be

influenced by low temperature and caution should be

exercised

3, Proper signal levels, terminating impedances, and cable

lengths for multi- instrument measurement systems.

36
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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 using

an acoustical calibrator (or pistonphone) with an accuracy of

+ 0.5 decibels or better.

4.3 Windscreen

A microphone windscreen shall be used which does not degrade the

system below the requirements of ANSI Si. 4-1971, for Type 1 sound level

meters.

4.4 Power Source Instrumentation

All measurements of input power to the units under test shall be

made at a point 10 meters (30 feet) + 1 meter from the tool. The following

instruments shall be used.

1. For pneumatically powered tools, a pneumatic flow meter, a pressure gage and temperature gage.

2. For hydraulic powered tools, a hydraulic flow meter, pressure

gage and temperature gage.

5.0 TEST ENVIRONMENT

The following conditions have been standardized to achieve the desired

degree of accuracy for this test procedure. Specific deviation from these

conditions to simulate the actual working environment of the tool can be

made, provided the modified test procedure is noted and can be shown to

provide comparable results.

5. 1 Meteorological Conditions

Sound level data shall not be taken when:

1. The wind is in excess of 5 meters per second (12 mph)

2. The relative humidity exceeds 90%.

3. If the air temperature is outside the operating temperature

range of the instrumentation or tools.

Meeting the proposed test schedule is thus contingent on having

suitable weather conditions.

3.

Acoustical Conditions

The following acoustical conditions shall be met:

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1 , Sound level shall not be recorded If the background ambient

sound level including wind is less than 10 dBA below the

sound level generated by the test unit (tool) at the

-microphone location. Background ambient sound levels should

be recorded prior to each test run for each tool tested. •

2, If an external power source (compressor, pump, generator) is

required, it shall be located or sound attenuated such that

its sound levels are more than 10 dBA below the sound levels

of the tool at each microphone location.

3, There shall be no large reflecting surfaces, other than the

ground plane, in the immediate area of the test pad. Free

field conditions shall be maintained in the test area within

10 meters of each microphone location.

5.3 Ground Plane

A hard surface equivalent to finished concrete or sealed asphalt

shall cover a minimum of 90 degress of arc (with the pavement breaker at the

vertex) and extend at least one meter beyond a microphone location.

5,4 Test Pad

The test pad shall conform to the following:

For portable pavement breakers, the material in which the pick

point (moil) is impacting shall be concrete slabs obtained from

Ft . Belvoir

,

6.0 OPERATING PROCEDURES

6.1 Set Up

The equipment set up and the operating conditions shall duplicate

the design output of the tools being tested. The power source, e.g.

,

compressor, pump, generator, etc., shall be of sufficient capacity for

design operation, including the starting requirements. The equipment shall

be operated by a person experienced with the tool's operation. In all

cases, the tools shall be operated in a vertical position impacting down

upon the work surface. The tool shall be operated at the power setting

specified by the manufacturer as typical of normal operation.

6.2 Molls

The moils shall be a standard moil (size 1-1/4 inches in diameter)

and with a muffler sleeve attachment. Definitive notes shall be kept to

Indicate whether muffling sleeves are employed.

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The moll shall conform to the following:

For pavement breakers, a pick point (moll) of standard commercial

quality and availability shall be used. The length of the moils

and rods shall be sufficient to allow the operating procedure

described in Section 6.3.

6.3 Equipment Operation

-Equipment operation shall be:

For portable pavement breakers, the pick point (moil) shall

penetrate into the concrete until the taper portion of the bit is

embedded. A weight equal to the designed down force shall be fitted

over the center of gravity of the tool. (See Figure Al) . The

operator shall then operate the tool, but not apply any down force

to the tool, at its design power setting until the sound level data

has been observed.

4 7.0 MEASUREMENT PROCEDURE

7.1 Microphone Locations

The microphone locations shall be as follows:

For portable pavement breakers, four locations shall be positioned

7+0*^ meter from the moil point of the tool at a height of 1.5

0.01 meter above the ground plane. Four locations shall be positioned

1 +0.1 meter from the moil point of the tool, at a height of 1.5 +

0.01 meter. The centerline of the exhaust of the tool, if any,

shall be equidistant between two measurement locations at both the

1 and 7 meter distances. The measurement positions shall therefore

be located 45°, 135°, 225°, and 315° from this line. In addition,

a fifth location shall be positioned 0.25 + 0.10 meter from the moil

point of the tool, at a height of 1.5+0.01 meter above the ground

plane. This position shall be located at a point which will detect

the noise levels of the tool typical to the operator.

Note: l-There the ground plane does not extend 8 meters out from the

center of the test block in all directions, the tool may be

rotated. The first half set of readings should be taken with

the tool oriented in one direction and the second half set

taken with the tool and operator rotated 180 degrees.

39
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7L.2 Personnel

The operator(s) shall be at the normal operating position(s) . The

person transcribing the sound levels from the sound level meter shall be

positioned at least 10 meters from any microphone position. There shall be

no other personnel within 10 meters of a microphone position.

7.3 Measurement Techniques

The microphone shall be oriented in positions, which minimize angle of

incidence effects. All measurements shall be tape recorded for post-test

analyses. The period of time during which the measurements are made, shall

be long enough to allow an average reading to be taken with the slow

response setting of the meter and long enough to facilitate frequency

analyses.

7.4 Data Required for Presentation

The following data shall be acquired/computed/presented;

1. Background ambient A-weighted sound pressure level at one

microphone position.

2. Sound levels - One-third, linear, and A-weighted sound pressure

levels at each microphone position for each test performed; and,

for a selected position and test, narrow (constant bandv/idth)

sound pressure spectra.

3. Average sound levels - The average A-vreighted sound pressure level

must be calculated from measurements performed by using the

following procedure:

L = 10 log

10

n

1 V -1

where L = average sound level

= sound level at i microphone

n = number of microphone locations

4.

Meteorological Data - the wind speed and direction, the

relative humidity measured using a dry and wet bulb.

40
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psychrometer , the temperature and the barometric pressure

shall be recorded at least once each hour.

Tool Identification - the tool being tested shall be

identified by the manufacturer's name and address, the tool's

generic name, the model identification (s) and brand name, the

tool serial number (s) and the tool bit and/or rod used.

Location - the test facilities shall be described by address,

date, time of testing and operating personnel present.

Operating Conditions - the operating condition and power

consumed determined from instruments discussed in Section 4.5

shall be recorded. Explanatory notes shall be made

describing the test cycle.

Instrumentation - a complete list of instrumentation shall be

provided including models and serial numbers.

Data Sheets - data called for in Section 7.4 shall be

recorded on the accompanying data sheet (Figure A2). A

sketch shall be provided showing the microphone locations,

tool orientation, location of power source, etc.
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FIGURE A1

Height Applied to Portable Pavement Breakers to Simulate the

Designed Doun Force

Height may vary. See Manufacturers’ Instruction Manuals for the Designed Dovm

Force.

DATA SHEET

iOOr. DATA:

Model ^/rracle Name SIC p.1

Catalog Part #

TEST DATE:

-ay. f>/7 SManufacturer Swiss Industrial Gas

Address

Serial r

c/o American Jenback Corp. , Box Kuriington, NO 27715

Drill Diameter

Do’./n Force

m. Drill Bit

31.8 kg.

TEST FACILITIES: (Include photograph of test set-up)

Locat ion 'Bplvm'r, VA

Vi’ork Material Concrete

’ Date Poured

Compress ive Streng th 5692 kpa(psi) Date Tested" 9/6/78

power Source Chicago Pneumatic

Manufacturer Model/Trade Nam<

IKSTRU^iE^^^ATION : Sound Level Meter B&K 2203 Serial f 579906

liicropnone Fi gnrp A4

Length of Cable 7 ^

Vyindscreen .P&K.JIA02.3I.. Calibrator Type Pistonphone

Gnnrinuad for serial numbers)

Serial T 236169

Manufacturer/Model Bruel & Kjaer / 4220

Flow Meter Wallace & Tiernan Serial # none

Manu facturer/i lodel

* Correction Factor for Temp V^A60 +T)/530

\/SI

Tape Recorder Honeyxv^ell 5600 c

** Pressure

Serial # 01 o 4 lf^ 6LM77

"

TEST CONDITIONS: See Table I

Air Temperature C Dry Bulb

Barometric Pressure ^ Kind Speed

C Ket Bulb bRH

HG

m/sec

TEST DJvTA: See Table I

Operating Line Pressure (Voltage)

Operating Line Temperature (Fov;er Factor)

Operating Volumetric Flow Rate (Amperes)

A-V?eighted Sound Levels at 7 meters from Tool

dBA re 20 microFascals

1. Background Ambient Sound . Level-dEA (one only)

2. Sound Level dBA with Power Source Operating

3. Sound Level dEA v/ith Tool Operating

average; SC/JND I.CVEL:^

* Temperature in °F

dBA

Pressure in psig.

Figure A4 - Exanp'*c data r.Voet

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.EQUIPMENT

SERIAL

NUMBERS^

44

Figure

A4- (

concluded) 1

Certain

commercial

equipment

is

identified

in

this

paper

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

material

or

equipment

identified

is

necessarily

the

best

available

for

the

purpose.

WERT bookbinding

MIDDLETOWN, PA SEPT 81

‘ re Quel/lr Sound