REPORT NO. DOT-TST-75-71

TRUCK NOISE - IB

SPECTRAL AND DIRECTIONAL CHARACTERISTICS

OF NOISE GENERATED BY TRUCK TIRES

WILLIAM A. LEASURE, JR.

DANIEL M. CORLEY

FINAL REPORT

SEPTEMBER 1974

Availability is unlimited. Document has been

released to the National Technical Information

Service.Operation's Division, Springfield,Va. 22151,for sale to the public

PREPARED FOR

DEPARTMENT OF TRANSPORTATION

OFFICE OF THE SECRETARY

OFFICE OF NOISE ABATEMENT

WASHINGTON, D.C. 20590

NBS-114A (REV. 7-73)

U .S. DEPT. OF CO.MM. BIBLIOGRAPHIC DATA

SHEET

1. public:ation or repor i no. 2. Gov't Accession

No.

3. Recipient's Accession No.

4. TITLE AND SL'BTITLI-:

Spectral and Directional Characteristics of Noise

Generated by Truck Tires

5. Publication Date L 1 ^ 7 V

6. Performing Organization Code

7. AU rHOR(S) 8. Performing Organ. Report No.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No. DOT-AS -10004

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

U. S. Department of Transportation

Office of the Secretary

Office of Noise Abatement

Washington, D. C. 20590

13. Type of Report & Period Covered

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRAC;T (A 200-word or less (actual summary of most si^ilicant information. If document includes a significant

bibliography or literature survey, mention it here.)

This report is the third in a series of reports published as a result

of Department of Transportation sponsored truck tire noise research conducted

by the National Bureau of Standards. The previous reports (OST-ONA-71-9

and OST/TST-72-1) contained details of the test design, test procedures , and

an inventory of maximum A-weighted sound level data for typical rib, crossbar, and retread type truck tires. A test sample of nine tread designs,

estimated to represent 70-80% (based on discussions with fleet owners) of the

truck tire population on the road today, was investigated considering noise

levels as a function of the following variables: wear, loading, speed,

pavement surface, and tire location. Test vehicles included both singlechassis vehicles and tractor trailers. The existing data base is expanded

in this report to include one-third octave band spectral data, directionality

data in the form of equal A-weighted sound level contours and other refined

analysis of the data. Such data can serve as the groundwork for understanding the generation mechanisms by which tires produce noise — the first

step in developing the necessary data to design quiet tires scientifically.

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

)

Acoustics, noise measurement, noise pollution, noise (sound), sound transmission,

tire noise, transportation noise, truck, urban planning.

18. availability [X_ Unlimited

I

' For Official Dist ribution. Do Not Release to NTlS

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

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USCOMM-DC 29042-P74
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FORM NBS-JMA (REV. 7-731 USCOMM-DC 29042-P74
Table of Contents •

Page

1. Introduction 1

2. Test Results 2

2.1. Directional Characteristics . . 2

2.2. Spectral Characteristics 2k

3. Conclusions 39

k. Appendix A. Parametric Study Results hi

5. Appendix B. Description of the Procedure for the

Development of the Directionality Contours . 128

6. Appendix C. Results of Narrow-Band Spectral

Analysis Investigation . 131

7. Appendix D. Synopsis of DOT Reports

0ST-0NA-Tl-9[l] and 0ST/TST-72-l[2] -176

8. References l80

1
List of Fig-ares and Tables*

Page

Figure 1. Equal A-veighted sound level contours characteristic of fully-worn, pocket-tread tires mph

on asphalt ) , , h

Figure 2. Equal sound pressure level contours for the 31.5

and 63 Hz octave bands for new, rib-B tires 7

Figure 3. Equal sound pressure level contours for the 125

and 250 Hz octave bands for new, rib-B tires .... 8

Figure h. Equal sound pressure level contours for the 500

and 1000 Hz octave bands for new, rib-B tires .... 9

Figure 5- Equal sound pressure level contours for the 2000

and UOOO Hz octave bands for new, rib-B tires .... 10

Figure 6. Equal sound press\ire level contours for the 31.5

and 63 Hz octave bands for new, cross-bar-F tires . . 11

Figure T. Equal sound pressure level contours for the 125

and 250 Hz octave bands for new, cross-bar-F tires. . 12

Figure 8. Equal sound pressure level contours for the 500

and 1000 Hz octave bands for new, cross-bar-F tires . 13

Figure 9. Equal sound pressure level contours for the 2000

and UOOO Hz octave bands for new, cross-bar-F tires . 1^1

Figure 10. Equal sound pressure level contours for the 31.5

and 63 Hz octave bands for new, retread-I tires ... 15 •

Figure 11. Equal sound pressTire level contours for the 125

and 250 Hz octave bands for new, retread-I tires. . . I6

Figure 12. Equal sound pressure level contours for the 500

and 1000 Hz octave bands for new, retread-I tires . . IT

Figure 13. Equal sound pressure level contours for the 2000

and UOOO Hz octave bands for new, retread-I tires . . 18

Figure lU. One-third octave band soimd pressure levels versus time (representative cross-bar tread pattern) .... 19

* Unless otherwise noted, all Figures and Tables correspond to a loaded

single-chassis vehicle coastby at 50 mph on a concrete surface.

ii
Figure 15. Maximiam A-weighted sound level contours as measured

at the 25, 50, 80 and 130 foot microphone locations

(various rib tires) 21

Figure 16. Maximum A-veighted sound level contours as measured

. at the 25, 50, 80 and 130 foot microphone locations

(various cross-bar tires) 22

Figure IT- Maximum A-weighted sound level contours as measured

at the 25, 50, 80 and 130 foot microphone locations

(various retread tires) 23

Figure I8. Test tires of rib tread design with the major tread

element spacing identified 27

Figure 19- Test tires of cross-bar tread design with the major

tread element spacing identified 28

Figure 20. Test tires of retread (block and pocket) design with

the major tread element spacing identified 29

Figure 21. Narrow band (2 Hz bandwidth) so\ind pressure levels

versus frequency for the range 0-500 Hz as measured

at the 50 foot microphone location at the time

corresponding to the occurrence of the maximum

A-weighted sound level (new, rib-A tires) ...... 32

Figiare 22. Narrow band (2 Hz bandwidth) soimd pressirre levels

versus frequency for the range 500-1000 Hz as measured at the 50 foot microphone location at the

time corresponding to the occurrence of the maximum

A-weighted sound level (new, rib-A tires) 33

Figure 23. Narrow band (2 Hz bandwidth) sound pressure levels

versus frequency for the range 0-500 Hz as measured

at the 50 foot microphone location at the time

corresponding to the occirrrence of the maximum

A-weighted sound level (new, cross-bar-F tires). ... 3^

Figure 2h. Narrow band (2 Hz bandwidth) sound pressure levels

versus frequency for the range 500-1000 Hz as measured at the 50 foot microphone location at the

time corresponding to the occurrence of the maximum

A-weighted sound level (new, cross-bar-F tires). ... 35

Figure 25. Narrow band (2 Hz bandwidth) sound pressure levels

versus frequency for the range 0-500 Hz as measured

at the 50 foot microphone location at the time

corresponding to the occurrence of the maximum

A-weighted sound level (new, retread-H tires) 36

iii
Figirre 26. Narrow band (2 Hz bandwidth) sound pressure levels

versus frequency for the range 500-1000 Hz as measured at the 50 foot microphone location at the

time corresponding to the occurrence of the maximum

A-weighted sound level (new, retread-H tires) 37

Table 1. Predicted and measured fundamental tire noise

frequencies based on major tread spacing

considerations 30

iv
Appendix A

Appendix A contains the detailed plots of one-third octave band soiind

pressure levels as measured at the 50 foot microphone location at the time

corresponding to the occurrence of the maximum A-weighted sound level as well as the equal A-weighted sound level contour plots for all runs made with the

single-chassis vehicle. The plots correspond to a vehicle speed of 50 mph while

running on both a concrete and an asphalt surface. Tread design, degree of wear,

loading conditions and n\imbers of tires were the variables investigated during

the parametric study.

T~\T~10 T~> Mil DEGREE NUMBER OF

FIGURE TREAD DESIGN OF WEAR TIRES LOADING Tl A TTl rAGE

Figure A-1 Rib-A New Dual Loaded U2

1' igure A- id IDA "U A Kl b—

New Dual Unloaded

Figure A-^ Rib-A iMew Single Unloaded HO)i Figure A-h Rib—

i'lew Dual Loaded 40

T7I * AC rigure A

Rib-B Mall -Worn T>- - A "1 Dual Loaded CZ P50

Figure A-6 nl D—L New T^T -1 #-1 n Dual Loaded 52

i! igure A- ( Rl D—

nail —Worn Dual Loaded 5^

Figure ARlD-L Fiilly-Worn Dual T ^ ^ J ^ J Loaaea 5d

Figure A—nl D—wew Duai Unloaded 50

r Igure A—JLU rvl D—L/ nan —worn "Pit Duai t o 1 Unloaded DU

TP ~\ rm ~K» ^ A ^ ~l "I r j-gu_L c >i~J__L JaJ, U —o r uiiy—wox n "Dm Q 1 ^?

r Igure ±\.—±^ JAl D—i"jew Single uniodciecL DM- r Igure ii— ±o R-i x\l"KD—P

xiaii — worn Single unioaQeo- DD

Figure A—lU Pnnl P D—

Fully—Worn Single Unloaded DO

Figure A—15 Cross—Bar—

New Dual Loaded V P(0

Figure A—l6 Cross—Bar—nail —worn Dual T^T T J-1 "I Loaded TO

Figure A-IT Cross-Bar-D Fully—Worn Dual Loaded 1 4 Figure A—l8 Cros s—Bar—

ri ew Dual Loaded 1 D

r Igure A— ±y Cros s—Bar—nan —worn T^T Dual T O 1 Loaded 1 0

rigure A-idO Cross-Bar-E Fully-Worn Dual Loaded RpOU

TP ^ A ^ "I Figixre A- 21 Cross-Bar-F Wew Dual Loaded Aoo2

Figure A-22 Cross-Bar-F Half-Worn Dual Loaded o4

Figure A-23 Cross-Bar-F Fully-Worn Dual Loaded Ob

TT'-J -ri. ...... . A Oil figure A-24 Cross-Bar-r New Dual Unloaded 00

rigTxre A- 2

/~t TTl Cross-Bar-F Half-Worn Dual Unloaded 90

-figure A- 2d T~l TTl Cross-Bar-F Fully-Worn T^, , „ n Dual Unloaded 92

r Igure A-2 f oL n TT* Cross-Bar-r T\T A- - JNew Single Unloaded 0)1 94

rigure A— 20 Lross-Bar-r Mall -Worn Single Unloaded 9d

Figure A-29 /"I T^ TTl Cross-Bar-r Fully-Worn Single Unloaded pQ90

Figure A- 30 Retread-G New Dual Loaded 100

Figure A- 31 Retread-G Half-Worn Dual Loaded 102

Figure A- 32 Retread-H New Dual Loaded 10^

' Figure A- 33 Retread-H Half-Worn Dual Loaded 106

Figure A- 3^ Retread-H Fully-Worn Dual Loaded 108

Figure A- 35 Retread-I New Dual Loaded 110

Figure A- 36 Retread-I Half-Worn Dual Loaded 112

Figure A- 37 Retread-I Fully-Worn Dual Loaded llU

Figure A- 38 Retread-I New Dual Unloaded 116

Figure A- 39 Retread-I Half-Worn Dual Unloaded 118

Figure A-kO Retread-I Fully-Worn Dual Unloaded 120

Figure A-iil Retread-I New Single Unloaded 122

Figure A-U2 Retread-I Half-Worn Single Unloaded I2I; Figure A-1+3 Retread-I Fully-Worn Single Unloaded 126

V
Appendix B

Page

Figure B-1. A graphical representation of the matrix

from which the equal sound level directionality contour plots were generated 130

Appendix C

Appendix C contains the detailed plots of the narrov-band (2 Hz bandwidth)

sound pressure levels as measured at the 50 foot microphone location at the time

corresponding to the occurrence of the maximum A-weighted sound level for select

rTxns made with the single-chassis vehicle. The plots correspond to a vehicle

speed of 50 mph. Tread design, degree of wear, loading conditions, number of

tires and the pavement surface were the variables investigated during this study

JJiiiuniljil] TP"DTPnTTTP"[\T i^V fyDTT" A "Pi Ur Ur L/UAJJliMb"

FIGURE RANGE "r\T7i(~* T T\T DESIGN WEAR TIRES /~i T\T "p\ T m~r r\ tvt CONDITION SURr ACE rAGE

n "1 U-pUU Kl D—

In Single Unloaded Concrete 1J2

L-2 n r\r\ ~\ r\r\r\ 500-1000 Rib-A New Single Unloaded Concrete TOO 133

^-6 U— ^UU nl D—

Single Unloaded Asphalt 134

500-1000 Rib-A I\T „ New Single Unloaded Asphalt nor" 135

C-5 0-500 Kl b--D New Dual Loaded Concrete 13d

n C L-D 500-1000 Rib--B New Dual Loaded Concrete 137

C-Y 0-500 Rib-C T\T r^T -r Dual Loaded Concrete 130

C-O 500-1000 Rib-C IMew Dual Loaded Concrete 139

u-9 0-500 Klb-0 iMew Dual Unloaded Concrete 140

U—±U 500-1000 Rlb-0 Dual Unloaded Concrete ±41

U-11 0-500 Rib-C New Single Unloaded Concrete "I 1 1 o 14<d

C-12 500-1000 Rib-C New Single Unloaded Concrete 1^3

C-13 0-500 Rib-C New Single Unloaded Asphalt lUli

C-lU 500-1000 Rib-C New Single Unloaded Asphalt 1^5

C-15 0-500 Rib-C Half-Worn Single Unloaded Concrete ihG

C-l6 500-1000 Rib-C Half-Worn Single Unloaded Concrete ll+T C-IT 0-500 Rib-C Fully-Worn Single Unloaded Concrete ll+8

C-18 500-1000 Rib-C Fully-Worn Single Unloaded Concrete ll+9

c-19 0-500 Cross-Bar--D New Dual Loaded Concrete 150

c-20 500-1000 Cross-Bar

-D New Dual Loaded Concrete 151

C-21 0-500 Cross-Bar--E New Dual Loaded Concrete 152

C-22 500-1000 Cross-Bar--E New Dual Loaded Concrete 153

C-23 0-500 Cross-Bar--F New Dual Unloaded Concrete 15^

C-2U 500-1000 Cross-Bar--F New Dual Unloaded Concrete 155

C-25 0-500 Cross-Bar--F New Single Unloaded Concrete 156

C-26 500-1000 Cross-Bar--F New Single Unloaded Concrete 157

C-2T 0-500 Cross-Bar--F New Single Unloaded Asphalt 158

C-28 500-1000 Cross-Bar--F New Single Unloaded Asphalt 159

C-29 0-500 Cross-Bar--F Half-Worn Single Unloaded Concrete 160

C-30 500-1000 Cross-Bar

-F Half-Worn Single Unloaded Concrete 161

vi
DEGREE NUMBER

frequency TREAD OF OF LOADING

FIGUEE RA.NGE DESIGN WEAR TIRES CONDITION SURFACE PAGE

C-31 0-500 Cross-Bar-F Fully-Worn Single Unloaded Concrete 162

C-32 500-1000 Cross-Bar-F Fully-Worn Single Unloaded Concrete 163

C-33 0-500 Retread-I New Dual Loaded Concrete I6U

C-3^ 500-1000 Retread-I New Dual Loaded Concrete 165

C-35 0-500 Retread-I New Dual Unloaded Concrete 166

C-36 500-1000 Retread-I New Dual Unloaded Concrete i6t

C-3T 0-500 Retread-I New Single Unloaded Concrete 168

C-38 500-1000 Retread-I New Single Unloaded Concrete 169

C-39 0-500 Retread-I New Single Unloaded Asphalt 170

c-ko 500-1000 Retread-I New Single Unloaded Asphalt 171

C-Ul 0-500 Retread-I Half-Worn Single Unloaded Concrete 172

c-Up T?X\C0HOx—K* »^t:cxU.~_L a (^TMX Hd-L-L ""WUX ii 0 J. Xl^Xt: Uil_LUctU.t:U. VyOiiL-I troc: J-

"1 7^1 J C-U3 0-500 Retread-I Fully-Worn Single Unloaded Concrete

c-kk 500-1000 Retread-I Fully-Worn Single Unloaded Concrete 175

Appendix D

Page

Figure D-1. Test tire tread designs I78

Figure D-2. View of test section showing instrumentation

placement plus vehicle path 179
Abstract

This report is the third in a series of reports published as a result

of Department of Transportation sponsored truck tire noise research conducted

by the National Bioreau of Standards. The previous reports ( OST-ONA-71-9

and OST/TST-72-I) contained details of the test design, test procedures, and

an inventory of maximum A-weighted sound level data for typical rib, crossbar, and retread type truck tires. A test sample of nine tread designs, es- timated to represent J0-80% (based on discussions "with fleet owners) of the

truck tire population on the road today, was investigated considering noise

levels as a function of the following variables: wear, loading, speed,

pavement surface, and tire location. Test vehicles included both singlechassis vehicles and tractor trc-.ilers. The existing data base is expanded

in this report to include one-third octave band spectral data, directionality

data in the form of equal A-weighted sound level contours and other refined

analysis of the data. Such data can serve as the groundwork for understanding the generation mechanisms by which tires produce noise — the first

step in developing the necessary data to design quiet tires scientifically.

viii
1. Introduction

The goal of this tire noise research program is the identification and

quantification of the physical parameters which affect the noise generation

characteristics of truck tires and the development of an information base

that may lead to standardized tire-noise procedures and to highway noise re- duction criteria, standards, and regulations.

An extensive data hase of maximum A-weighted sound levels due to truck

tires has been established as a result of a field study carried out in two

phases during the summer/fall of 1970 ^^'^ 1971- These data, previously reported in earlier DOT reports [1,2]— , supplemented the existing data on

total truck noise and in conjunction with data developed concerning testing

procedures can serve as the basis for meaningful vehicle noise regulations.

This report expands the existing data base to include spectral data —

one-third octave band andTiarrow band, and directionality information in the

form of octave-band and equal A-weighted sound level contours . These data

serve as additional information to our superficial understanding of tire noise

generation mechanisms — understanding which is vitally necessary if the

tire engineer is to be provided with the data to design quiet tires scientifically. In addition, this Information can be utilized by the urban planner

as input data for the prediction of noise levels in nearby communities at

various distances from present and proposed highways. The highway designer

also can utilize these data as the basis for optimum location of roadwaysand for the proper design of roadside barriers to lower overall community

noise levels.

Since this report serves as a companion document to the initial reports

in this series [1,2], the details of the program, including a discussion of

the test design, the operational aspects of the test, and the test procedure,

which were discussed in detail in the earlier reports, are not repeated here.

However, a summary of the pertinent material covered in the previous reports

is presented In Appendix D.

— FigTires in brackets indicate the literature references at the end of this

report

-1-
2. Test Results

The initial reports [1,2] in this series presented the maximum Aweighted sound level data for typical rit, cross-bar, and retread type

truck tires in various degrees of wear. This data "base has "been expanded

to include the spectral and directional characteristics of these tires and

the results are reported herein. The detailed results are presented in

graphical form in Appendix A. In this section the general trends are investigated and the implications of the data are discussed.

.

'

' ' 2.1 Directional Characteristics

The directionality characteristics of truck tire noise are important

since such data provide some insight into the noise generation mechanisms for

tires and also provide additional information for urban planners and highway

designers who are responsible for: (l) determining optimum highway routes

to ensure minimum environmental impact; (2) specifying noise barrier materials, dimensions and locations; (3) and predicting community noise levels

resulting from new highways or changing traffic flow patterns on existing

roadways

One would like to study a single tire at near maximum rated load

running on typical road surfaces at various speeds. Ideally, at a given

instant of time a large number of measurements would be made simultaneously

at various angles and distances in the horizontal plane surrounding the

tire.— , • . , ,

, ;

It was not possible, however, to test a single tire. In all cases

the test tires were mounted on single-chassis vehicles (four or six tires)

or tractor trailer combination vehicles (eighteen tires). Since the singlechassis vehicle approaches the single tire goal more closely than does the

tractor-trailer, the directionality contours shown in Appendix A are for

coasting (engine shut off) single-chassis vehicles equipped with quiet

tires on the steering axle and either two (single) or four (dual) test

tires on the drive axle. The DOT/NBS test program was designed such that

while the test vehicle, equipped with the tires of interest, coasted through

the 1000 foot test section, voltages corresponding to the sound pressures

at six microphone locations, at different distances from the path of vehicle

travel, were recorded on magnetic tape in analog form. In addition to the

microphones, which were located midway in the test section on a line perpendicular to the path of the vehicle (see Appendix C for a detailed

description of the test section), a photosensor system (five photosensors

located 250 feet apart along the vehicle path activated by a light source on the test vehicle — which provided truck position and sp^ad data versus time) was designed and utilized. By sampling the analog data — and utilizing

the photosensor data to convert the A-weighted sound level versus time

data to A-weighted sound level versus distance data, it was possible to

simulate an instantaneous measurement at a large number of microphone

locations

— Results of feasibility studies [l] indicated that the A-weighted sound level

was relatively independent of angle — for ranges of 0° - 25° — in the vertical

direction.

—3/For details on the procedure utilized in the development of the equal Aweighted sound level contoTxr plots, see Appendix B.

-2-
It shoiild also "be noted at this time that the major concern at the

onset of this program was the establishment of a data base of maximum Aweighted sound levels for typical truck tires. The directionality information, which was acquired during the same parametric study, was to be primarily utilized to assess the impact of tire noise on the community. For

these reasons, the dynamic range of the instrumentation system was established such that the maximum A-weighted sound level was measured at each

microphone location. This decision resulted in a limited amount of data

being recorded for the 6 and 12 foot microphone locations. At these two

positions , the maximim A-weighted sound level was recorded but little information was obtained on the noise level as the truck approached or receded

from the microphone array due to the available dynamic range [approximately

UOdB] of the data acquisition system. Therefore, the contour plots shown

in Appendix A are derived chiefly from data for the remaining four microphones. These plots identify the sideward lobe of the characteristic

directionality patterns for truck tires. Such lobes of maximum noise would

have a greater effect on community noise levels, in general, then lobes

fore and aft of the vehicle along the roadway.

Even though the emphasis was on community noise, it is important to

gain a better understanding of the shape and magnitude of all of the lobes

that exist in a characteristic directionality pattern for a given set of

tires — lobes to the front and rear of the vehicle as well as those to

the side. Accepting the constraints imposed by the dynamic range of the

instrumentation system, the following procedure was utilized to develop

the directionality contour map shown in Figure 1. Two identical coastby

runs were made at h'^ mph on an asphalt surface. Four fully-worn, pockettread tires were mounted on the drive axle of the loaded, single-chassis

vehicle. Neutral rib tires were mounted on the steering axle. During

the first run the 6 and 12 foot microphones were set up to read the maximum A-weighted sound level during the passby. During the second run,

these two microphones were allowed to satiirate in the vicinity of the

microphone array, however, they measured the sound level as the truck

approached the microphone array and as the truck receded from the array.

The data resulting from these two runs were merged to form the basis for

the directionality pattern shown in Fig\ire 1.

Four significant observations can be made from reviewing this directionality contour plot: —

1. Tire noise is directional.

2. The forward lobe (along the vehicle path) is of short duration

compared to the lobe behind the tires.

— The scales chosen for the ordinate and abscissa are not identical and it

should be noted that the sideward lobe is exaggerated by the scale selection.

-3-
^ *>ionai lAiodd aoNvisia

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-4-
3. A double-peaked lobe is present to the side of the truck (peaks

at approximately +_ h3° fore and aft of the perpendicular, drawn

through the zero point) as veil as a possible third side lobe

at a shallow angle (approximately 2°) with the roadway to the

rear of the vehicle.

h. The maximum sound level is recorded after passage of the rear axle

of the test vehicle past the microphone point (zero represents

the centerline of the drive (rear) axle of the truck).

With the exception of the foiarth observation, this is the characteristic

pattern for all tires. Tire noise is directional. A majority of the

contours exhibit the double peak to the side of the vehicle although

some are much more pronounced than others. With the exception of the

pocket-tread (retread-l), which served as the basis for the contour

shown in Figure 1, the^maximum level one would measure at 50 feet occurs prior to the passage of the tires past the microphone point. Due to the

manner in which the contours were constructed, the third sideward lobe

and the lobes fore and aft of the truck are not evident in the data in

Appendix A and the angles at which the lobes are observed are not constant

among tires.

At first, it was surprising that the maximum A-weighted sound level

occurs prior to the passage of the tires past the observation point. Subjectively most people associate tire noise with the highly tonal tires

whose high-pitched "singing" persists long after a truck has passed.

Recently an analysis of tire tread noise based on tread element impact

with the road surface was reported in the literature [3]. The analysis

resulted in an equation for the impact energy loss. Part of this energy

must be radiated from the tire as sound and it would seem that, since the

impact occurs on the front end of the contact area, the front part of

the tire is the principal radiating surface.

The directionality contour plots shown in Appendix A indicate that

even at a distance of 130 feet from the noise source — which is many times

the length of the noise source — one does not observe a constant decrease

in sound level as the distance from the source is doubled along any given

angle. Thus, the widely utilized rule of thiomb that far-field conditions

exist roughly at distances of more than one wavelength away from a source

or at 2 to 3 times the largest linear dimension of the noise source,

whichever is the greater, should be applied with caution.

Although small changes are observed in the characteristic A-weighted

sound level directionality contours for a given tire type as parameters

such as load or pavement surface are varied, gross changes are not typical.

In general, the effect of parameter variation is evidenced only by a change in the location of any given contour with respect to the source.

-5-
Departures from relatively smooth contours — evidenced by the existance of

irregularities in contour shape — are observed on occasion. One expects the

contours further from the source to be irregular since the distance is such

that one is approaching the limits of available signal-to-noise ratio. However, a review of the tabiilar data from which the directionality contours were constructed indicates that, in general, in those cases where the

irregiilarity is confined to a single contour line, these irregularities

are caused by isolated atypical data points which the contour plotting

routine does not ignore.

To further investigate the directional characteristics of truck

tires, a representative tread design was selected from each of three

generic tread catagories — rib (rib-B), cross-bar ( cross-bar-F ) and

pocket (retread-l) type tread designs — and equal sound pressure level

contoior plots were generated for the eight octave bands between 31-5 Hz

and k kHz. The resultant contour plots are shown in Figures 2-13. Octave

band rather than one-third octave band plots were developed to avoid the

difficulty of tonal components shifting from one band to an adjacent

band due to Doppler shifts as the truck passed through the test section.

Figure ih shows a plot of one-third octave band sound pressure level

versus frequency versus time for a truck passby as measured at a 50

foot microphone location. The truck was equipped with tires with a representative cross-bar type tread pattern. The Doppler shift of the

fundamental from one third-octive band to another is obvious.

As might be expected, the contours, in general, are rather omnidirectional

at the lower frequencies and more directional at higher frequencies. However,

the contour map for the octave band containing the fundamental is very complex

and highly directional. Similar, although not as pronoiinced, effects are seen

in octave bands containing harmonics of the fundamental which represent

significant peaks in the spectrum for that tire. It should be obvious

that use of the A-weighting network tends to mask some of the detailed

information which will be necessary to identify the tire noise source mechanisms .

-

At this point in time our understanding of the tire noise generation

mechanisms is such that we have no basis to attach any further meaning

to these contours, especially since they do not represent (due to practical

reasons) the directionality contour for a single tire.

The directionality plots also provide data pertinent to the establishment of minimum requirements for measurement test sites suitable for

tire certification testing. The important factors in tire certification

testing are that the vehicle be at the proper speed and that the maximum

noise generated by the tire be observed at the microphone while the

vehicle is in the test zone. For the majority of the data reported in

the literature, no information is reported regarding vehicle position

when maximum noise is recorded during a passby. In this study, however,

care was taken to ensure that vehicle position and speed were recorded

throughout the series of tests.

-6-
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11.1

THIRD OCTAVE BAND CENTER FREQUENCY, kHz

Figiire ih . One-third octave band, sound pressure levels (in dB re 20 yPa) versus

time for a truck coastby as measured at 50 feet. The truck was equipped with tires with a representative cross-har type tread pattern.

-19-
utilizing this data base, equal A-weighted sound level contours

whose levels corresponded to the maxim\airi A-weighted sound level observed

during the truck passby at the specific microphone locations at 25, 50,

80, and 130 feet were generated for each tire tread design in that state

of tread wear which corresponded to the maximum noise level produced by

that tire. These plots, shown in Figures 15-17 ? correspond to the loaded

single-chassis vehicle coasting at a speed of 50 mph on a concrete surface

The test tires were mounted in dual pairs on the drive axle of the truck

while neutral rib (rib-A) tires were mounted on the steering axle. These

contours are supplementary to those presented in Appendix A.

From these data it is evident that for a 50 foot measurement location the maximum A-weighted ["FAST" response] sound levels generated by

truck tires are typically measured prior to the passage of the drive axle

of the truck past the microphones when tires with rib or cross-bar tread

patterns are moionted on the vehicle. On the average, such maximum noise

levels are recorded 30 to hO feet prior to the passage of the drive axle.

The lobe of maximum noise for pocket tread tires (retread-l) is usually

the rearward lobe and maximum sound levels are typically measured 50 to

75 feet behind the truck (or after passage of the drive axle).

Realizing that these pocket-tread tires are presently being phased

out, it would appear that the minimum vehicle path should be 100 feet

[+_ 50 feet on either side of the microphone location] if one hopes to

achieve a measurement of maximum tire noise on a 50 mph coastby of a single drive axle, loaded vehicle utilizing a 50 foot microphone location. If other vehicle speeds or microphone locations are utilized in

the future, the minimum test site requirements stated here may not be

valid; therefore, the situation would have to be reevaluated based on the directionality contours characteristic for the chosen vehicle speed

and microphone location.
o 1 00

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HALF-WORN

72 DB

DB \

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DISTANCE FROM TRUCrt, FT

DIRECTION OF TRAVEL 1

100 150

Figure 15 • Maximim A-weighted sound level contours as measured at the 25, 50, 80,

and 130 foot microphone locations. These plots correspond to a loaded

single-chassis vehicle coastby at 50 mph on a concrete surface with

various rih tires mounted in dual pairs on the drive axle.

-21-
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84 DB \

90 DB \ /

-100 -50 0 50

DI3TRNICE FROM TRUCK FT

100 150

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CROSS-BAR-F

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0I3TRMCE: FReri TRucr^, ft

DIRECTION OF TRAVEL

1 00 150

Figure l6. Maximuin A-weighted sound level contours as measured at the 25, 50, 80

and 130 foot microphone locations. These plots correspond to a loaded

single-chassis vehicle coasthy at 50 mph on a concrete surface with

various cross-har tires mounted in dual pairs on the drive axle.

-22-
-150 -100 -50 0 50 100 150

DISTRNCE FROn TRUCK, FT

toQ 0 I 1 -ISO -IQO -50 0 50 100 150

DISTRMCE FROn TRUCK, FT

RETREAD

NEW

-150 -100 -50 0 50 100 150

oi3Tf)McE rreri tj^uck, ft

DIRECTION OF TRAVEL

Figure 17- Maximum A-weighted sound level contours as measured at the 25, 50, 80,

and 130 foot microphone locations. These plots correspond to a loaded

single-chassis vehicle coasthy at 50 mph on a concrete surface with

various retread tires moimted in dual pairs on the drive axle.

-23-
2.2 Spectral Characteristics

In order to gain an understanding of the mechanisms by which tireroad interaction noise is generated, one cannot simply look at single

numlDer descriptors such as the A-weighted sound level but must analyze

the noise in finer detail through spectral analysis. The data for all runs have been analyzed in one-third octave bands. These data, for the

single-chassis vehicle at the time corresponding to the occurrence of

the maximum A-"weighted sound level, are reported in Appendix A. Spectral

measurements on tire sounds by a stationary observer along the roadway

are complicated by the motion of the so\irce of sound — the spectrum

changes with time as the relative positions of the tire and the observer

change. The Doppler effect contributes an additional shift in frequencie

which also changes as the relative position of the tire and observer

change

The evaluation of tire noise source mechanisms is a very complex

task. At present, three generic types of tire noise source mechanisms

have been postulated — aerodynamic, air pumping and vibration.

Aerodynamic sources refer to unsteady flow over the tire, attributable largely to the whole-body motion of the tire through nearlystationary air. Siddon [h] speculates that fluctuating pressures from

vortices generated at the trailing edge of a tire near the road are sufficient to contribute substantially to roadside noise. While this

may be the case for smooth tires operating on smooth roads, it hardly

seems likely to be a major source in view of the overwhelming data

demonstrating a dependence of tire noise on road roughness and tread

design.

Investigators are in general agreement that air pumping is a major

contributor to tire noise. As a tire tread segment contacts the road

surface, air is squeezed out of the small depressions in the road and

tire interstices. As the tread segment leaves the surface, air rushes

back to fill the voids. Hayden [5] modeled this oscillating flow by

assuming a compact array of monopole sources of noise associated with

the leading and trailing parts of the contact area and developed an expression for estimation of the overall sound pressure radiated by a single tire as:

Where, 6 = tread depth, w = width of a single cavity or groove in the

tread, S = circumferential distance between tread grooves, v = vehicle

velocity, f = fractional change in cavity volume, m = cavities per tire

width and r = distance from tire to observation point.

(1) + 20 log f + 10 log m - 20 log r

-24-
A similar expression applies when one treats the roadway depressions

in the same manner as the tread interstices.

Vibration of the tire carcass (caused by tire/road interaction) is

believed to be a third soirrce of noise. There exist numerous possible

excitation and radiation mechanisms as well as types of tire response

that could characterize tire vibration and attendant sound generation.

An initial excitation mechanism that should be considered is the

interaction of the tread elements with roadway surface irregularities.

As a tire rotates, the tread is pulled radially by centrifugal force for

a large percentage of travel and then comes suddenly to rest on the ground.

An impact occurs that is semi-elastic in natiare and some of the energy must

be lost through the tire tread and walls in flexural vibration which is

radiated as sound. This mechanism is likely to be of major importance.

Of probable lesser significance are nonuniformities of tire construction

which give rise to fluctuating values of radial stiffness, with attendant

force variations. The fundamental component associated with tire nonuniformities corresponds to tire rotation rate, which at highway speeds is

very low frequency. It is unlikely that harmonics of this will be significant in the frequency range of substantial sound radiation.

Tire vibrational characteristics and mechanisms of sound radiation

may be evaluated together in three frequency regimes. At low frequencies,

below the first carcass mode, one would expect the tire to respond only in

the vicinity of the contact area. This mechanism is not likely to be of

consequence because these frequencies are so low. At higher frequencies-,

the carcass responds in a modal manner. Tire modes are inefficient radiators since the wavelength corresponding to the frequency of vibration is

much greater than the distance between the contracting and expanding parts

of the tire. At still higher frequencies, waves in the carcass will be

generated at the roadway interface. If the phase velocity of these waves

is above critical (i.e., above the speed of sound in air) the waves will

radiate very efficiently. However, even subcritical waves may radiate

significant sound levels owing to low wavenumber components associated

with the excitation point.

Tire tread and carcass vibration as a source of tire noise is actively

being investigated by researchers at North Carolina State University [ 6 ]

This on-going analytical and experimental program, under the sponsorship of

the Office of Noise Abatement, Department of Transportation, should provide

considerable insight into the role of tire vibration as a tire-noise

source mechanism.

Since both the vibration and air pumping mechanisms result from

the interaction of the tire with the roadway surface, the tire tread

design and the surface texture of the roadway are very important determinants of the noise generated by a given tire. Many truck tire manufacturers do not use tread patterns possessing imiform pitch. In general

randomized pitch lengths are utilized so as to produce a more pleasant,

or at least less intrusive, sound than the pure tones associated with

regular tread spacing.

-25-
The tire noise spectrum is composed of two parts: a periodic variation due to the tread pattern and tire nonuniformities and an aperiodic

variation due to the road surface cavities. The periodic component exhibits

spectral peaks at discrete frequencies and the aperiodic component exhibits

a more continuous spectrum. The frequencies of the spectral peaks are associated with the tire design (tread spacing) and the tire rotational rate.

The fundamental frequency can be predicted by calculating the number of

tread elements which pass through the footprint per second. If the distance

between consecutive tread elements is 'uniform, the sound produced is nearly

a pure tone whose frequency is given by [?]:

^ ^ 1T.6V

a

where, f = fundamental frequency, Hz

V = vehicle speed, mph

-'

_ a = tread spacing, in.

Most tire manufacturers, however, do not utilize a uniform element spacing.

The pitch lengths are usually varied in some manner so as to produce a less intrusive sound than a pure tone. The difficulty is defining the

so-called tread spacing. Modern tires are produced by molding into the

tread major grooves (in the case of rib tires major grooves are oriented

in the circumferential direction while for cross-bars the grooves are oriented in the lateral direction) and secondary grooves or slots called

siping, all of which contribute in some unknown way to the complex

acoustic signature of the tread pattern.

Table 1 shows the major tread spacing for the tires tested when new,

the predicted frequency of the fundamental based on major tread spacing,

and the one-third octave frequency band in which the fundamental was actually measured. The calculations are based on a vehicle speed of 50

mph. Since there is some question as to what is meant by the term "major

tread spacing", footprints of the tires tested along with identification

of the major tread spacings as defined for the purposes of this report

are presented in Figures l8, 19, and 20 for rib, cross-bar and retread

tires, respectively. Although present understanding of tire noise source mechanisms does not allow one to identify the mechanism — air pumping

and/or vibration — excited by the tread elements interacting with the

road surface, in most cases the one one-third octave band in which the

maximum signal level could be found was predictable on the basis of

tread spacing considerations.

A reasonable question to pose at this time is whether one-third

octave band analysis provides the discrimination necessary for pinpointing particular frequencies associated with noise generation mechanisms.

Identification of specific frequencies rather than a range of frequencies

should assist in the identification of the mechanisms associated with the

frequencies observed. To address this question, a minim-um of one run for

each tire tread type studied (with the exception of retread-G) was selected

for narrow band analysis. —

—^The work was performed \mder contract with Hydrospace Research Corporation,

Rockville, Maryland.

-26-
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-28-
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-29-
Tire

Major Tread

Spacing

in

Predicted Fundamental

Frequency

Hz.

Band Limits

Of One-Third Octave

Band(s) Containing The

Measured Fundamental

Frequency, Hz

nl D—

,

, Kid—i> 2. 01 - 2. 28 386 - 1+38 354 .

)i )i <c 0

Klb-L 1.93 - 2.95 298 - U56 2(0. 5 — 44d 0

Cross—Bar- pi -u 3.35 263 oo"i n - 279 0

Cross-Bar--E 2.76 319 278.5 - 351 5

Cross-Bar--F 2.hh - 2.91 302 - 361 278.5 - 351 5

Retread-G 1.56 56U 1+1+2.0 - 558 0

Retread-H 1.89 1+66 35I+.O - 558.0

Retread-I 2.1+8 355 278.5 - 351 5

Table 1. Predicted and measured fundamental tire noise frequencies

hased on major tread spacing considerations corresponding

to a vehicle speed of 50 mph.

Each truck passby of interest, which had "been recorded in the field

in analog form, was previewed in order to determine the time delay between

the second photocell (data start) and the occurrence of the maximum Aweighted sound level measiored for that particular run. The software

that was utilized to perform the analysis required an 0.5 second data

sample and this sample was selected such that the maximum A-weighted

sound level observed was approximately centered within the sample. The

analog data were then digitized to produce a digital voltage versus time

array. This array was Fourier transformed, utilizing software in the

computer, into 512 channels, each of 2 Hz bandwidth, covering the frequency gange from 0 - I05I+ Hz. The computer utilized was a Varian

620/i. — The plots in this report are for those data covering the frequency range 0-1000 Hz only.

— Commercial instruments are identified in this report in order to adequately

specify the experimental procedure. In no case does such identification imply

recommendation or endorsement by the National Bureau of Standards nor does it

imply that the equipment identified is necessarily the best available for the

piirpose

-30-
It is important to provide an indication of the statistical significance of these narrow-hand spectra; that is, hov much error is incurred

"by using practical analysis equipment with finite hand widths and finite

averaging times. As stated earlier, the analysis utilized a handwidth (B)

of 2 Hz and a sample record (T) of 0.5 seconds; therefore, the statistical

uncertainty associated with the narrow hand spectra is 3dB {c= 1/2/bt).

Aliasing errors are estimated to he less than 0.6 dB.

To provide an indication of the results, the narrow band spectra for

ri"b-A, cross-har-F and retread-H are shown in Figures 21-26. These data

are for new tires mounted in dual pairs on the loaded (i+i+30 Ihs/tire),

single-chassis vehicle for a' nominal speed of 50 mph. The pavement surface

was concrete. The narrow-hand spectra for the remaining twenty-two runs which were investigated are presented in Appendix C.

The one-third octave hand data for rih-A (Figure A-1 of Appendix A) are rather hroad hand in nature with no pronounced spectral peaks. This

tire has a tread pattern consisting of straight circumferential grooves

that run parallel to each other around the circumference of the tire. This

tire was originally chosen for this test program since it was felt that

due to the total ahsense of sipes and cross-hars this tire would provide

a lower hound on truck tire noise level among current production tires. It

has been reported [6] that circumferentially grooved treads exhibit slightly

higher noise levels than smooth treads and that the sound levels generated

by both smooth and circumferentially grooved treads depend heavily on the

road siirface. The narrow band spectra (Figures 21 and 22) — are also

broad band in nature as expected.

In the case of cross-har-F (Figure A-21 of Appendix A) , the one-third

octave band data show a fundamental at 315 Hz and a secondary plateau ranging

from 630 - 1000 Hz which includes the apparent second and third harmonics.

This tire, which has a circumferential tread face centers (central rib) with

shoulders of laterally aligned bars with sipes, possesses a randomized tread

pattern with the major tread spacing ranging from 2.hh - 2.9I in. For this

spacing, with a vehicle speed of 50 mph, equation 2 would predict a fundamental between 302 and 36l Hz. These frequencies are contained in the one- third octave bands centered at 315 and hOO Hz. The narrow band data (Figures

23 and 2h) show seven major peaks — 270, 308, 3^8, 386, 582, 656 and 89U Hz.

The maximum in the narrow band spectrum at 308 Hz is in the range of the

predicted fundamental. Although evident in the spectrum, the second and

third harmonics of this peak — 616 and 92h Hz — are not prominent (more

than 20 dB below the fundamental) . The maxima at 3^8 Hz (which is IT dB

down from the level at 308 Hz) is also in the range of the predicted fundamental. The remaining peaks, whose influence is visible in the one-third

octave band data, are not accounted for by major tread spacing considerations.

A review of the narrow hand data seems to indicate that the more randomization evident in the tread pattern the more likely one is to see numerous — All frequency components below ^0 Hz in the narrow-band spectra are neglected

since comparable data do not exist for the one-third octave spectra.

-31-
200 300

FREQUENCY, Hi

500

Figure 21. Narrow "band (2 Hz bandwidth) sound pressure levels versus frequency

for the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped with

neutral rib (rih-A) tires on the steering axle and dual, new,

' ' rib-A tires on the drive axle. The 50 mph coastby was on a concrete surface.

-32-
700 800 !000

Figure 22. Narrow "band (2 Hz bandwidth) sound pressure levels versus frequency

for the range 500-1000 Hz as measured at the 50 foot microphone location

at the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped with

neutral rib (rih-A) tires on the steering axle and dual, new,

ri"b-A tires on the drive axle. The 50 mph coastby was on a concrete s^urface.

-33-
100 200 300

FREQUENCY, HZ

400 500

Figure 23. Narrow band (2 Hz bandwidth) sound pressure levels versus frequency

for the range 0-500 Hz as measured at the 50 foot microphone location

at the time corresponding to the occurrence of the maximiim A-weighted

sound level. The loaded single-chassis vehicle was equipped with

neutral rib (rib-A) tires on the steering axle and dual, new,

cross-bar-F tires on the drive axle. The 50 mph coastby was on a concrete surface.

-34-
600 700 800

FREQUENCY, HZ

900 1000

Figiire 2h. Narrow band (2 Hz bandwidth) sound pressure levels versus frequency

for the range 500-1000 Hz as measured at the 50 foot microphone location

at the time corresponding to the occixrrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped with

neutral rib (rib-A) tires on the steering axle and dual, new,

cross-bar-F tires on the drive axle. The 50 mph coastby was on a concrete sixrface.

-35-
200 300

FREQUENCY .HZ

500

Figure 25. Narrow band (2 Hz bandwidth) sound pressure levels versus frequency

for the range 0-500 Hz as measured at the 50 foot microphone location

at the time corresponding to the occurrence of the maximiim A-weighted

sound level. The loaded single-chassis vehicle was equipped with

neutral rib (rib-A) tires on the steering axle and dual, new,

retread-H tires on the drive axle. The 50 mph coastby was on a concrete surface.

-36-
70

RETREAD-H, NEW, DUAL, LOADED, CONCRETE

CO

'^^00 600 700 800 900 1000

FREQUENCY. HZ

Figure 26. Narrow tand (2 Hz bandwidth) sound pressure levels versus frequency

for the range 500-1000 Hz as measured at the 50 foot microphone location

at the time corresponding to the occurrence of the maximum A-weighted

soimd level. The loaded single-chassis vehicle was equipped with

neutral rib (rib-A) tires on the steering axle and dual, new,

retread-H tires on the drive axle. The 50 mph coastby was on a concrete surface.

-37-
lower level peaks in the nsirrow "band spectrum rather than a few higher level

ones. This seems logical since the piirpose of tread randomization is the

breakup of the noise energy that would "be concentrated in a few single frequency "bands (if the tread pattern was repetitive) and distri"bution of this

energy at lower levels over a broader frequency range. The characteristic

of the tire noise appears to depend on the lengths and distribution of

lengths of the tread elements.

Retread-H, the final tire to be considered, does not possess a ran- domized tread element pattern but has a major tread spacing of I.89 in.

The one-third octave band data (Figure A-32 of Appendix A) show a maximum

in the spectrum at 500 Hz (fundamental) and a second harmonic at 1000 Hz.

For a vehicle speed of 50 mph, one would predict a fundamental at U66 Hz.

The narrow band data (Figures 25 and 26) clearly indicate a double peak

in this region — kho and hhd Hz — and the second harmonic at 896 Hz.

Other major peaks occur at 96, 278 and U32 Hz. A comparison of the data - for cross-bar-F with the data for retread-H clearly shows the spectral

differences that can be expected when a narrow band frequency spectra for

a tire with a fixed, repetitive tread pattern is compared with another

tire with a randomized tread element pattern.

Since our knowledge of tire noise mechanisms is limited, it is

difficult to evaluate the total significance of the data resulting from

the narrow-band analysis. The situation is complicated by the fact that

the data being analyzed are for a set of six tires (two steering, four

drive) rather than a single tire. Narrow-band analysis will, however,

be a necessity when we reach the point where we are evaluating a single

tire and are attempting to pinpoint frequencies associated with specific

vibrational, air p-umping, or other tire noise source mechanism.
3. Conclusions

Many of the phenomena exhihited by the data presented in this report

are not fully explainable at present due to our limited knowledge of the

mechanisms of tire noise generation. However, it is important that such

data be placed into the public domain since: (l) further evaluation of

these data may lead eventually to explanations of the presently unexplainable phenomena and, thus, to an understanding of tire noise generation

mechanisms, and (2) on-going and future experimental and analytical research

in tire noise must account for such experimentally observed phenomena, e.g.

the double-peaked sideward lobe observed in the directionality patterns.

In reviewing the data, one could easily be mislead into thinking that

the mechanism question is simply one associated with tread design alone,

however, the apparent attainable "limit" with present structural design - a blank tire (full tread depth but no tread pattern) on a smooth surface -

is only a few decibels lower than current original equipment rib tires of

quiet design. Therefore, to accomplish significant levels of tire noise

reduction it is necessary first to evaluate thoroughly the presently postulated tire noise source mechanisms — aerodynamic, air pumping and vibration — and others that may evolve through appropriate research. By com- bining the results of such research with other aspects of tire performance,

it is expected that tires may be designed for safety, longevity and quiet.

-39-
THIS PAGE BLANK.

-40-
h. Appendix A. Parametric Study Results

This appendix contains the expanded data base on the noise generated

by rib, cross-bar and retread truck tires tested during the field efforts

conducted at Wallops Station, Virginia in 1970 and 1971-

Test results for the single-chassis vehicle are presented in a series

of figures comprised of two separate facing pages. One page contains (l) a computer generated plot of one-third octave band sound pressure levels

versus frequency as measured at the 50 foot microphone location at the time

corresponding to the occurrence of the maximum A-weighted soiond level and

(2) a tire footprint of one of the actual test tires utilized (scale l:h)

showingythe characteristic tread element pattern in its given state of

wear. — The accompanying pages present directionality information in the

form of equal A-weighted soimd level contours. The zero point on the contour plots correspond to the center line of the drive (rear) axle of the

test vehicle. These plots correspond to a vehicle coastby at 50 mph on both a concrete and an asphalt surface. The specific tread design and

associated degree of wear are defined in the title at the top of the page.

Also identified are the loading condition and information as to whether

the tires were mounted in dual pairs or singly. Tires with identical

tread designs were mounted at each position on the drive axle of the

test vehicle. These were the test tires. New neutral rib (rib-A) control tires were mounted on the steering axle for all tests.

Pertinent tire data such as tread depth and Shore hardness (rubber

hardness), which were taken for each test tire, were tabulated and reported

in the previous reports [1,2].

It should be noted that on several occasions one or more microphones

were inoperative dirring the truck passby and therefore, data are not available in these instances. Also, data for retread-G should be used with

caution. Note the difference in tread patterns shown for the new and halfworn tires. Examination of the tire footprints for retread-G tires showed

that one of the half-worn tires had a different tread pattern than the

other tire (footprints were made for a dual pair of identical tread designs).

The different tread patterns resulted from a misaligned tire mold. A discussion of the problem was presented in an earlier report [2]. No knowledge

exists as to how many of the retread-G tires had these tread variations.

— No footprint was made of the tread element pattern for rib-C in a fully-worn

state. The footprint which is shown with data corresponding to the fullyworn tires is that for a half-worn rib-C.

-41-
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5 . Appendix B

Description of the Procedure for the

Development of the Directionality Contours

The equal A-weighted sound level contours presented in this report

were generated according to the follo-wing procedure.

An array of six microphones, which were placed along a line perpendicular to the line of travel of the test vehicle, was utilized in the

data acquisition portion of the program to record tire noise levels as the test truck coasted through a 1000 foot test section. Five photosensors, activated "by a light "beam produced "by a spotlight mounted on the

truck, were located 250 feet apart along the test lane parallel to the

path of the vehicle. The photosensors provided information on truck posi

tion versus time. (See Appendix D for a summary description of the test

section, instrumentation placement and test procedure.) During analysis,

each analog tape was played back a channel at a time through a one-third

octave band real-time-analyzer interfaced to a mini-computer. One-third

octave band sound pressiore levels and A-weighted sound levels were

digitized and stored on magnetic tape. Analysis was initiated at the

first photosensor — when the truck was 500 feet from the microphone

array — and the analog data were sampled approximately every 20 feet

throughout the 1000 foot test section. The time constant utilized for one-third octave analysis was 0.2 second above 200 Hz; below 200 Hz the

time constant increased with decreasing frequency to 2 second at 20 Hz.

The time constant for the weighting networks was TO milliseconds. For

nominal speeds from 30-60 mph, this was accomplished by increasing the

sampling rate as vehicle speed increased. The sampling rates utilized

were: (l) ^00 milliseconds at vehicle speeds of 30, 35 and ^0 mph, (2)

300 milliseconds at U5 and 50 mph, and (3) 200 milliseconds at 55 and 60

mph. As an example, for a vehicle speed of 30 mph {hh ft./sec), data

were sampled every 0.^ seconds after the initial photosensor or approximately every I8 feet during the passby. In this manner, A-weighted sound

level versus time data were generated for each microphone location for

each passby.

A major goal of the program was the measurement and tabulation of

the maximum A-weighted sound level at each microphone position. This

goal conflicted somewhat with the requirements for developing directionality contours, especially for the two near-field microphone locations at

6 and 12 feet. For these two locations, the dynamic range available in

state-of-the-art instrumentation did not allow for the recording of both

the maximum sound level and the sound level data as the truck approached

and receded from the microphone array; therefore, only the data from the

remaining four microphones were utilized for the generation of the direct

ionality plots.

The A-weighted sound-level-versus-time data for each microphone of

interest were then transformed to A-weighted sound level versus distance

data utilizing the information provided by the photosensor system. The

-128-
five photosensor placements plus the time of arrival at each microphone

location gave four measurements of distance versus time, plu^ th^ zero

point, to which a cuhic polynomial in time of form X=A+Bt+Ct +Dt was fitted by the method of least squares. The reason for the choice of the

cubic polynomial was the fact that the velocity versus time data obtained

by differentiation of the distance versus time data deviates from a straight line, although only slightly. The speed of the ^ruck at any

given time t is calculated as follows: v = B + 2Ct + 3Dt where B, C, and

D are the constants found above in the fitted distance versus time data.

A typical set of data now consisted of A-weighted sound level versus

distance for four microphones at seven different nominal speeds from 30 to

60 mph in 5 mpb increments. It is desirable to compare directionality contours at identical truck speeds, e.g., 50 mph; therefore, for each speed

from 30 to 60 mph, an interpolation scheme was utilized to find A-weighted

soTond level versus distance data every 20 feet along the 1000 foot test

section for each microphone of interest. Thus for each microphone at 51

locations along the line of travel we have T data points of A-weighted

sound level versus speed. A parabolic interpolation of A-weighted sound

level versus speed was performed to obtain 51 data points all at a con- stant speed of 50 mph. The parabolic fit was chosen because it was utilized

previously [1,2] in fitting A-weighted sound level data versus speed. We

now have a U x 51 dimensional matrix — the k columns representing the h

microphone locations at 25, 50, 80 and 130 feet and the 51 rows representing the 51 locations every 20 feet along the line of travel. These data

showed that the majority of the information was contained around the

microphone array location; therefore, for the purposes of this report,

contours were drawn from -250 to +25O feet rather than the total distance

of -500 to +500 feet.

All that remained was to draw the desired equal A-weighted sound level

contours. This involved two steps. First, in order to generate a contour

map with the truck in the center and contour levels surrounding it, the

distance scale had to be reinterpreted. When the truck was at -250 feet, the

microphone was in front of the truck and vice versa at +250 feet. Therefore,

the scale must be reversed if we wish to draw the contours properly, e.g.,

the direction of travel of the test vehicle was from -250 feet to +250 feet.

Second, to draw the actual contours a bi-variate spline contouring routine

available at NBS on the Univac — IIO8 Exec. VIII system was utilized. This

routine essentially searches the data for equal values of A-weighted sound

level and draws a smooth curve through the points.

— Commercial equipment are identified in this report in order to adequately

specify the experimental procedure. In no case does such identification im

recommendation or endorsement by the National Bureau of Standards , nor does

imply that the equipment identified is necessarily the best available for t

purpose

-129-
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6. Appendix C

Results of Narrow-Band Spectral Analysis Investigation

As discussed earlier in this report, a limited number of mns was selected for narrow-band analysis. The piirpose of this investigation was

to address the question of whether one-third octave band analysis provides the discrimination necessairy for identifying particular frequencies

associated with noise generation mechanisms.

A total of twenty-five runs was selected. Data resulting from three

of the runs were discussed in Section 2.2. The remainder of the data is

presented in this Appendix. It should be noted that the choice of runs which were analyzed allows one to evaluate the effects of tread design,

degree of tread wear, pavement siorface, load and the number of tires on the drive axle. For example, a comparison among the spectra shown in

Figures Cll-12, CI5-I6 and CI7-I8 allows for the evaluation of wear as a parameter for rib-C tires. In these cases the speed, niomber of tires,

load and pavement surface were held constant.

Since our present knowledge of tire noise source mechanisms is superficial at best, no in-depth analysis of the narrow-band spectral data shown

in this appendix has been undertaken at this time. However, it is important

that such data be placed into the public domain since the tire noise source models resulting from ongoing and future tire noise investigations should

account for the phenomena shown by these data.

-131-
70

I RIB-A, NEW, SINGLE, UNLOADED, CONCRETE

ccto

FREQUENCY, HZ

Figure C-1 Narrow tand (2 Hz 'bandwidth) soimd pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rih-A) tires on the steering axle and new, single,

rib-A tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-132-
00 600 700 800

FREQUENCY , HZ

900 1000

Figure C-2 Narrow "band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rih (rib-A) tires on the steering axle and new, single,

rib-A tires on the drive axle. The 50 mph coastby was on a concrete

surface

-133-
Figure C-3 Narrow band (2 Hz "bandvidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-veighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rih (rib-A) tires on the steering axle and new, single,

rib-A tires on the drive axle. The 50 mph coastby was on an asphalt

surface

-134-
700 800

FREQUENCY, HZ

900 1000

Figiire C-h Narrow band (2 Hz bandwidth) sound pressiire levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

rib-A tires on the drive axle. The 50 mph coastby was on an asphalt

surface

-135-
30.

100 200 300

FREQUENCY, HZ

400 500

Figure C-5 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at the time corresponding to the occirrrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

rib-B tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-136-
700 800

FREOLfENCY.HZ

1000

Figure C-6 Narrow "band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as ineas\u:-ed at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

rib-B tires on the drive axle. The 50 mph coastby was on a concrete

surface

-137-
200 300

FREQUENCY. HZ

500

Figirre C-T Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

rib-C tires on the drive axle. The 50 mph coastby was on a concrete

surface

-138-
%0 600 700 800

FREQUENCY. HZ

900 1000

Figure C-8 Narrov "band (2 Hz iDandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

with neutral rib (rih-A) tires on the steering axle and new, dual,

rilD-C tires on the drive axle. The 50 mph coastby was on a concrete

surface

-139-
200 300

FREQUENCY. HZ

500

Figure C-9 Narrow band (2 Hz bandwidth) soiind pressirre levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

rib-C tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-140-
600 700 800

FREQUENCY. HZ

900 1000

gure C-10 Narrow tand (2 Hz bandwidth) souad pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rih-A) tires on the steering axle and new, dual,

rih-C tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-141-
too 200 300

FREQUENCY, HZ

400 500

Figure C-11 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

rib-C tixes on the drive axle. The 50 mph coastby was on a concrete

surface.

-142-
00 600 700 800

FREQUENCY. HZ

900 1000

Figure C-12 Warrov band (2 Hz "bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-veighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

rib-C tires on the drive axle. The 50 mph coastby was on a concrete

surface

-143-
RIB-C, NEW, SINGLE, UNLOADED, ASPHALT

0 100 200 300

FREQUENCY, HZ

400 500

Figure C-13 Narrow tand (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

rib-C tires on the drive axle. The 50 mph coastby was on an asphalt

surface.

-144-
60

RIB-C, NEW, SINGLE, UNLOADED, ASPHALT

to

Figure C-lk Narrow band (2 Hz bandwidth) soimd pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

soiind level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

rib-C tires on the drive axle. The 50 mph coastby was on an asphalt

surface

-145-
200 300

FREQUENCY. HZ

500

Figiire C-15 Narrow "band (2 Hz bandwidth) soimd pressiore levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occ\rrrence of the maximiam A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and half-worn, single,

rib-C tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-146-
70

RIB-C, HALF -WORN, SINGLE, UNLOADED, CONCRETE

ure C-l6 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and half-worn, single,

rib-C tires on the drive axle. The 50 mph coastby was on a concrete

surface

-147-
100 200 300

FREQUENCY. HZ

400 500

Figure C-17 Narrow "band (2 Hz tandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

- ' with neutral rib (rib-A) tires on the steering axle and fully-worn, single.

rib-C tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-148-
00 600 700 800

FREQUENCY ,HZ

900 1000

Figure C-l8 Narrov band (2 Hz bandwidth) soTond pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and fully-worn, single.

rib-C tires on the drive axle. The 50 mph coastby was on a concrete

surface

-149-
80

CROSS-BAR-D, NEW, DUAL, LOADED, CONCRETE

CO^70-

FREQUENCY.KZ

Figure C-19 Narrow band (2 Hz "bandwidth) sound presstire levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

soimd level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual, cross-

. , bar-D tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-150-
700 800

FRSUUtNCY .HZ

1000

Figure C-20 Narrow band (2 Hz bandwidth) soimd pressure levels versus frequency for

the range 500-1000 Hz as measiired at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

soiind level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual, cross- bar-D tires on the drive axle. The 50 mph coastby was on a concrete

svorface.

-151-
100 200 300

FREQUENCY. HZ

400 500

Fig\ire C-21 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

'

' with neutral rib (rib-A) tires on the steering axle and new, dual, cross- bar-E tires on the drive axle. The 50 mph coastby was on a concrete

surface

-152-
700 800

FREQUENCY. HZ

1000

Figure C-22 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual, cross- bar-E tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-153-
200 300

FRlQUENCY ,HZ

500

Figure C-23 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

soTond level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual, cross- bar-F tires on the drive axle. The 50 mph coastby was on a concrete

surface

-154-
700 800

FREQUENCY, HZ

900 1000

gure C-2h Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual, cross- bar-F tires on the drive axle. The 50 mph coastby was on a concrete

surface

-155-
200 3O0

FREQUENCY, HZ

500

Figure C-25 Narrow band (2 Hz iDandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

' v., .. sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single, cross- bar-F tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-156-
00 600 700 800

FREQUENCY .HZ

900 1000

Figure C-26 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single, cross- bar-F tires on the drive axle. The 50 mph coastby was on a concrete

surface

-157-
70

CROSS-BAR-F, NEW, SINGLE, UNLOADED, ASPHALT 1

fl

gure C-2T Narrow band (2 Hz bandwidth) soimd pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

.

: sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single, cross- bar-F tires on the drive axle. The 50 mph coastby was on an asphalt

surface

-158-
700 800

FREQUENCY, HZ

1000

Figure C-28 Warrov band (2 Hz "bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single, cross- bar-F tires on the drive axle. The 50 mph coastby was on an asphalt

surface

-159-
80 CROSS-BAR-F, HALF-WORN, SINGLE, UNLOADED, CONCRETE

-Ja:

ICQ 200 300 400 500

FREQUENCY. HZ

Figure C-29 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and half-worn, single,

cross-bar-F tires on the drive axle. The 50 mph coastby was on a concrete

surface

-160-
80

CROSS-BAR-F, HALF-WORN, SINGLE, UNLOADED, CONCRETE

^§00 600 700 800 900 1000

FREQUENCY. HZ

•e C-30 Narrow band (2 Hz "bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral ri"b (rih-A) tires on the steering axle and half-worn, single,

cross-har-F tires on the drive axle. The 50 mph coasthy was on a concrete

surface.

-161-
100 200 300

FREQUENCY, HZ

400 500

Figure C-31 Narrow "band (2 Hz "bandwidth) so-and pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

soiond level. The unloaded single-chassis vehicle was equipped

with neutral rih (rib-A) tires on the steering axle and fully-worn, single,

cross-bar-F tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-162-
700 800

FREQUENCY, HZ

1000

Figure C-32 Narrov band (2 Hz bandwidth) soimd pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

soimd level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and fully-worn, single,

cross-bar-F tires on the drive axle. The 50 mph coastby was on a concrete

s\irface

-163-
100 200 300

FREQUENCY. HZ

400 500

Figure C-33 Narrow band (2 Hz bandwidth) sound pressiire levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

- - retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface

-164-
FREQUENCY. HZ

Figure C-3^ Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The loaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-165-
70

RETREAD-I, NEW, DUAL, UNLOADED, CONCRETE

-JCE

C/5 ^60 •

FREQUENCY, HZ

Figure C-35 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as meas^ured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

• ' sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface

-166-
70 r RETREAD-I, NEW, DUAL, UNLOADED, CONCRETE

FREQUENCY. HZ

Figure C-36 Narrow band (2 Hz "bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measiored at the 50 foot microphone location at

the time corresponding to the occurrence of the maximim A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, dual,

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-167-
80

200 300

FREQUENCY. HZ

500

Figure C-37 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

, the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface.

-168-
00 600 700 800

FREQUENCY, HZ

900 1000

Figure C-38 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface

-169-
200 300

FREQUENCY, HZ

500

Figure C-39 Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

retread-I tires on the drive axle. The 50 mph coastby was on an asphalt

surface

-170-
80

RETREAD- I, NEW, SINGLE, UNLOADED, ASPHALT

600 700 800

FREQUENCY. HZ

900 1000

Figure C-hO Narrow band (2 Hz bandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rib-A) tires on the steering axle and new, single,

retread-I tires on the drive axle. The 50 mph coastby was on an asphalt

surface

-171-
200 300

FREQUENCY, HZ

500

Figure C-hl Narrow "band (2 Hz iDandwidth) sound pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-veighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rih (rib-A) tires on the steering axle and half-worn, single

^ .

.

, retread-I tires on the drive axle. The 50 mph coasthy was on a concrete

surface

-172-
RETREAD-I, HALF-WORN, SINGLE, UNLOADED, CONCRETE

600 700 800

FREQUENCY. HZ

900 1000

Figure C-U2 Karrov band (2 Hz Toandwidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rih (rib-A) tires on the steering axle and half-worn, single,

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface

-173-
70

RETREAD-I, FULLY-WORN, SINGLE, UNLOADED, CONCRETE

CE

<_) V3£60-

FREQUENCY, HZ

Figure C-h3 Narrow band (2 Hz "bandwidth) soimd pressure levels versus frequency for

the range 0-500 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

. with neutral rib (rib-A) tires on the steering axle and fully-worn, single,

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

surface

-174-
70

RETREAD-I, FULLY-WORN, SINGLE, UNLOADED, CONCRETE

CO

^00 600 700 800 900 1000

FREQUENCY. HZ

Figure C-hU Narrow band (2 Hz "bandvidth) sound pressure levels versus frequency for

the range 500-1000 Hz as measured at the 50 foot microphone location at

the time corresponding to the occurrence of the maximum A-weighted

sound level. The unloaded single-chassis vehicle was equipped

with neutral rib (rih-A) tires on the steering axle and f\illy-worn, single

retread-I tires on the drive axle. The 50 mph coastby was on a concrete

sirrface

-175-
T. Appendix D. Synopsis of DOT Reports OST-ONA-Tl-9 [l]

and 0ST/TST-T2-1 [2]

The first two reports, published as a result of Department of Transportation sponsored truck tire noise research conducted by the National Bureau of

Standards, contain details of the test design, test procedures and inventory

of maximum A-weighted sound levels generated by truck tires. Both singlechassis vehicles and tractor-trailers were utilized as test vehicles while

the effect of tread design, tread wear, loading, speed, pavement surface and

tire location on the noise generated by truck tires was investigated. The

following is a brief synopsis of the program design and the data contained

in the first two reports.

A review of the data from past studies indicated that although numerous

parameters contribute to tire noise levels the following parameters are believed to be the most influential: tread design, degree of wear, type of

pavement surface, vehicle speed, loading and tire location. These were the

study parameters for this investigation. Secondary parameters such as carcass design, rubber composition, inflation pressure and other design features

also influence tire noise; however, the limited available data indicated that

their contribution would be significantly less than that of the principal

parameters cited above. Test matrices for both single-chassis and tractortrailer test vehicles were developed based on the principal parameters.

This study attemipted to select a relatively small sample from the

hundreds of tread patterns that exist for truck tires. Discussions with

fleet operators provided an opportunity to gain and apply their knowledge,

acquired through years of experience, toward the proper selection of representative tire types. Utilizing their expertise in the field, a total of

nine tread designs was chosen (figure D-l). In our estimation these exact

tread designs represent 70-80^ of the total truck tire population in use on the road today.

In accordance with standard operating procedure, the tires utilized

during this test program were not balanced. The tires were inflated to the

pressures recommended by the Tire and Rim Associations for the particular

load range. Tires were not considered acceptable test specimens until they

had undergone a break-in period of 100-200 miles under actual driving conditions. The break-in procedure ensured the removal of all mold marks and

manufacturing irregularities. Immediately prior to actual test of a given set of tires, a warm-up procedure was followed. It required the

driver to operate the test vehicle until he no longer could sense any

"thumping" or "heavy vibration" which could be expected when the tires were

cold (a phenomena referred to as flatspotting)

Prior to finalization of the overall test design, a feasibility test

program was conducted to develop an accurate and appropriate measurement

methodology. Various microphone array configurations (microphones placed

along a line perpendicular to the path of the test vehicle) were utilized

-176-
to evaluate the following parameters: microphone height and vertical directionality, hard versus soft reflecting surface and the attenuation effect

of rubber mud flaps on the propagation of the noise generated by truck tires.

The evaluation of the feasibility test data led to the establishment of the

following test design and measurement methodology which was utilized throughout the parametric study.

Two test sections, each 1000 feet in length, were established on the

research runway at the Wallops Island, Virginia facility of the National

Aeronautics and Space Administration. The test section surfaces were smooth

concrete and textured asphalt. The microphone array, located midway in the

test section, consisted of six microphones placed along a line perpendicular

to the path of the test vehicle. The microphones were mounted on tripods

at a height of U8 inches above the hard reflecting surface of the runway.

They were spaced at distances of 6, 12, 25, 50, 80, and 130 feet as measured

from the centerline of the lane in which the truck travelled (see figiire D-2).

The photosensor system for the determination of truck speed and position with

time was located along the test lane parallel to the path of the vehicle.

Microphones and photosensors were connected by coaxial cables to the recording and monitoring equipment which was housed in an instrumentation van located 500 feet from the edge of the runway. The van was so located to avoid

unwanted reflection effects.

For a given test run, the driver of the test vehicle accelerated the

truck to slightly more than the desired speed to compensate for the deceleration characteristics of the particiilar test vehicle. The characteristic

deceleration for the loaded single chassis test vehicle was a loss of 1 mph

every 200 feet. Since tire noise was being investigated, the driver shut

down the engine before entering the test section and coasted through the

test area. As the truck passed the initial photocell, which was interfaced

with the analog tape system, the tape transport and record electronics

were remotely activated. This initial photocell was located so that when

the truck passed the second photocell the tape recorder was up to speed and

data could be recorded. Data from each microphone were recorded on one of

six channels of an F.M. tape recorder during the entire passby over the 1000

foot test section. A light source on the truck activated the photocells,

generating voltage spikes which were recorded on the seventh channel (direct

record) of the tape recorder. Photocells number 2, 3, ^, 5, and 6 were

located 250 feet apart along the test section; the signal produced by these

photocells provided information on truck position with time which was used

for the calculation of vehicle speed. As the truck left the test section, a final photocell was triggered which remotely stopped the tape recorder. Each

analog tape recorded in the field was returned to the National Bureau of

Standards for reduction and analysis

The detailed maximum A-weighted sound level data for all the runs were plotted versus vehicle speed and microphone distance. The data were

also presented in tabular form. Also included were tire footprints of one of the actual test tires utilized, showing the characteristic tread

element pattern in its given state of wear and the associated tread depth

and rubber hardness. For ease of comparison and establishment of general

trends, summary plots of the data were developed showing the effect of the

various parameters on tire noise levels.

-177-
NEUTRAL RIB

RIB-A RIB-B RIB-C

1

CROSS-BAR-D CROSS-BAR-E CROSS-BAR-F

RETREAD-G RETREAD

RETREAD - I

Figure D-1 Test tire tread designs. These exact tread patterns represent 10-Q0%

of the total truck tire population in use on the road today. Scale-l:l6

-178-
TEST SECTION

VEHICLE PATH

O O O OP.4 O O O

P-1 P.2 P-3 P-5 P-6 P-7

aM-6

e D-2 View of test section showing instrumentation placement plus vehicle

path. (not to scale)

-179-
8. References

Anon., Truck noise-I, peak A-weighted sound levels due to truck

tires, U. S. Department of Transportation Report OST-ONA-Tl-9

(National Bureau of Standards, Washington, D. C, 19T0). Available

from the National Technical Information Service, Springfield,

Virginia, Accession No. PB 20^188.

Leasure, Jr., W. A., Corley, D. M. , Flynn, D. R. , and Forrer , J. S.,

Addendum truck noise-I, peak A-weighted sound levels due to truck

tires, U. S. Department of Transportation Report 0ST/TST-T2-1

(National Bureau of Standards, Washington, D. C, 1972). Available

from the U. S. Department of Transportation, Washington, D. C.

Archibald, F. R. , An elementary analysis of a vehicle tire tread

noise source, Jo\u:'nal of Sound and Vibration 3h_ (2), 285-286 (19T^).

Siddon, T. E. , Noise generation mechanisms for car tires, presented

at the 8Uth meeting of the Acoustical Society of America, Miami,

Florida (19T2).

Hayden, R. E., Roadside noise from the interaction of a rolling

tire with the road surface. Proceedings of the Purdue Noise Control

Conference, Purdue University, West Lafayette, Indiana (l9Tl)«

Reiter, W. F., Jr. and Eberhardt , A. C. , Truck tire vibration noise.

Society of Automotive Engineers, Inc., Paper T^0609 (Society of

Automotive Engineers, Inc., New York, New York, 197^)-

Truck tire noise. Society of Automotive Engineers, Inc. Report SP-373

(Society of Automotive Engineers, Inc., New York, New York, 1972).

-180-