81ST MEETING ß ACOUSTICAL SOCIETY OF AMERICA

the race and discusses in detail the noise levels of the various vehicles.

2:30

T3. Noise Levels Encountered in Air and Surface Transporta- tion. DoN E. BR,¾, Department of Mechanical Engineering, University of Houston, Houston, Texas 77004.--Noise Levels have been obtained at passenger seat locations on airplanes, buses, and railcars while they were operating in regular service. The sound field at seating positions was found to be diffuse in most cases, and convenient measurements could be made with a hand-held sound-level meter. The data are

graphically illustrated first as typical time histories, second as separate groups with cruise noise levels shown in decibels (A) and, finally, as a point graph with cruise levels in decibels (A) versus the difference decibels (C) - decibels (A). This last graph shows three distinct clusters and illustrates in compact form the comparative differences in the frequency components of each group. Special interest items included are STOL aircraft, the Metroliner, and PATCO cars from Philadelphia's new Lindenwold Commuter line. Some com- parative data from other authors and a discussion of the particular noise sources are also included.

2:45

T4. Jet Noise Contribution to Wind Noise in Vehicles. C.-K. A. Yu ANY H. S. RZBN•.R, Institute for Aerospace Studies, University of Toronto, Toronto, Canada.--A source of "wind noise" in a vehicle with a slightly opened window has been modeled as a slit jet issuing from a plenum (idealized vehicle). The nondimensional power spectra measured inside and outside were quite similar; the curves collapsed together well when plotted against Strouhal number fD/U (f=fre- quency, D--slit width, U--jet nozzle velocity). The higher frequency sources of the jet noise, being closer to the slit, subtend a larger angle and would be expected to transmit more noise into the plenum. This expectation was confirmed, with inward transmission increasing with both frequency and slit width; at 10 000 Hz and 1.5-in. slit width (maxima for these experiments, with 80-fps jet velocity) the jet noise power transmitted inward through the slit reached 68% of the power emitted externally in the «-oct band. These were exploratory tests, and there was no external wind. [Work supported by Air Force Office of Scientific Research.-1

3:00

T5. Roadside Noise from the Interaction of a Rolling Tire with the Road Surface. R. E. HAYDEN, Bolt Beranek and Newman Incorporated, 50 Moulton Street, Cambridge, Mas- sachusetts 02138.--As noise from ground transportation vehicles continues to arouse public concern, physical under- standing of the various noise sources becomes essential in seeking means to quiet vehicles. Tires are one of the per- dominant noise sources on trucks and automobiles. This

study analyzes the various mechanisms by which noise can be generated by the interaction of a rolling tire with the roadway surface. Physical models are presented for the "air pumping" vibrational and aerodynamic noise mechanisms, which are then rank-ordered in sound-producing capability for several classes of vehicles. Results of limited experiments are discussed, and measured data are interpreted in terms of the physical models.

3:15

T6. Truck Tire Noise--A Measurement Program. W. A. Lv.•suR•., Applied Acoustics and Illumination Selection, National Bureau of Standards, Washington, D.C. 20234.-- Vehicular traffic noise continues to be a major source of complaint, especially near high-speed highways. Of all

vehicles on the road today, many consider trucks to be the lnajor offender. Engine operating noise, exhaust noise, brake noise, and tire noise each contribute to the over-all noise level produced by trucks; however, at speeds of 50 mph and greater, which is quite prevalent on today's interstate high- ways, the noise from tires predominates, provided the truck has a reasonably good exhaust muffler and is in a good state of repair. The lack of an information base of tire noise data available in the public domain has hampered the development of standardized tire-noise testing procedures and the establish- ment of highway noise reduction criteria, standards, and regulations. This investigation will provide an inventory of data on representative tires and will develop an appropriate and accurate measurement methodology. The test parameters of this investigation include: tread design, tread depth, type of pavement, speed, and loading. A discussion is presented of measurement and analysis techniques leading to the attain- ment of (1) peak A-weighted sound levels, (2) «-oct spectrum data, and (3) directionality information shown as equal sound- level contour plots for various truck tires.

3:30

T7. Noise Reduction by Earth Berms. P•ut• JE_•$EN, Bolt Beranek and Newman Incorporated, Cambridge, Massachusetts 02138.mAcoustical shielding of apartment buildings, town houses, and especially hospitals by walls or earth berms has been used extensively in Denmark during the last years. Acoustical measurements have been conducted to determine

the shielding properties of a rampart 30 ft high and 2100 ft long, situated along a highway and with a grassland field on the other side. The sound source was a mobile screw-compres- sor (usually used for starting up jet engines of airplanes) called an Air Partner. The Air Partner was placed both in the near side and in the far side of the highway. Measure- ments were obtained for these two source positions and six corresponding microphone positions. The measured results are compared with the theoretic formulas for noise reduction of barriers.

3:45

T8. Design of Acoustic Barriers for Highway Noise Reduction. GRANt S. ANDERSON, Bolt Beranek and Newman Incorporated, Cambridge, Massachusetts 02138, ANt) FREVERZC•C GOTZE- •OELLER, Skidmore Owings and Merrill, Washington, D.C. 20036.•By a technique similar to that of the Highway Re- search Board Acoustic Design Guide, the acoustic impact of 20 miles of future interstate highway through a large eastern city was evaluated. Where the Design Guide criteria indicated that the impact was excessive, roadside barriers were designed. Barrier design involves breaking the highway into straight- line elements and calculating their individual contributions to the A level at the receiver position. In this manner, the varying effectiveness of a roadside barrier in attenuating the sound from each element can be used to determine the neces-

sary barrier length and height (which may vary along its length). Roadside barriers and barriers that envelop the receiver may both be evaluated. Also, the method allows computation of the A level for highways of varying curva- ture, gradient, traffic count, and surface characteristics. The calculations are repeated for receivers at different posi- tions and heights. The technique predicts the barrier attenua- tion of both the 50-percentile and the peak A level. One of the recommended barrier complexes is used to illustrate the method.

4:00

T9. Noise Legislation and Regulation in Hawaii. J. C. Bur- GeSS, Department of Mechanical Engineering, University of Hawaii, ttonolulu, Hawaii 96822.--During 1970, legislation was enacted in Hawaii mandating the State Department of

The Journal of the Acoustical Society of America 113

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