摘要:

The City of Boulder, Colorado, has had an active noise control program for three years. The levels set for vehicles are more stringent than those of California and the enforcement statistics have shown that these lower levels can be reasonably applied at the present time‐even to motorcycles. Enforcement is accomplished primarily outside the Police Department using the “soft fuzz” approach. The techniques used to maximize compliance with minimum personnel will be described. The educational program for civic groups and students, an important part of the enforcement program, are discussed. The City is currently spending about 23¢ per capita per year on noise control and may be second only to Inglewood, California. The results of a survey of citizenry taken two years after the passage of the ordinance are given. The experience has resulted in the writing of a more comprehensive ordinance, which is described. Agreements among city departments for noise prevention planning are described.

ISSN:0001-4966    

DOI:10.1121/1.3437447

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The most‐favored of traditional approaches to statutory regulation of excessive noise has been the subjective or qualitative statute. We present an analysis of the legal problems of qualitative municipal noise ordinances. While such an enactment is a valid exercise of a state or municipality's police powers, a case study of the Provincetown, Massachusetts, experience demonstrates the statute's vulnerability on constitutional grounds. In Provincetown, prosecution under the subjective “disturbing the peace” ordinance was used to silence an unpopular retailer's amplified music. A sound truck ordinance in Kovcas v. Cooper and an auto muffler statute in Smith v. Peterson have been upheld out of apparent necessity rather than constitutional soundness. By prohibiting noise described merely as “unnecessary” or “annoying,” authorities leave a citizen without notice of precisely what conduct is violative of the statute, as is required by due process guarantees of the 14th Amendment. At the same time, there are obvious dangers of discriminatory enforcement where one noise may be less popular than another at equal emission level if measured on an objective decibel scale. A quantitative noise statute permitting objective measurement according to widely recognized acoustical standards obviates the legal pitfalls.

ISSN:0001-4966    

DOI:10.1121/1.3437452

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

ANSI Standard SI.21‐1972, “Methods for the Determination of Sound Power Levels of Small Sources in Reverberation Rooms,“ represents a significant departure from its predecessor S1.2‐1962 in that it requires a performance evaluation to demonstrate the qualification of a reverberation room measurement system for measurement of discrete frequency sound. Experience in preparing this type of performance requirement was provided to many members of the working group through their association with ASHRAE and ISO writing groups who prepared or were in the process of preparing similar types of standards. Data on a number of facilities were available from round‐robin evaluations sponsored by ISO. A forthcoming paper by Ebbing and Maling [“Reverberation Room Qualification for Determination of Sound Power of Sources of Discrete‐Frequency Sound,” J. Acoust. Soc. Am.54, No. 4 (1973)] provides an extensive discussion of the theoretical basis for the standard and presents some of the round‐robin data. In this presentation, the data available to the writing group at the time of preparation of the standard are reviewed. As might be expected, the performance requirements represent a compromise between desirable measurement accuracy, and achievable measurement conditions in reasonable size rooms. The selected performance requirements of S1.21‐1972 are discussed in the context of this compromise, and the data available on existing rooms. Finally, some estimates of the achievable accuracy of power level measurement of an arbitrary source are related to the performance requirements.

ISSN:0001-4966    

DOI:10.1121/1.3437460

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

In the following presentations, pertinent data on a number of facilities are presented to give some indication of the breadth in types of spaces and techniques which are being used to achieve qualified rooms. Data to be presented include: (1) size and shape of room; (2) description of rotating diffuser (if used); (3) room absorption (reverberation time versus frequency) and a discussion of modifications to the absorption if used; (4) general instrumentation used, and discussion of techniques used to obtain an estimate of space average sound pressure level; (5) a discussion of source position (s) used and their relationship to other characteristics of the space; (6) a brief summary of any unique or unusual problems encountered in the qualification of the facility. The facilities to be discussed include: (a) National Bureau of Standards, Applied Acoustics Section, Washington, D. C. 20234 (by David S. Pallett); (b) Kodaras Acoustical Laboratories, 75‐02 51st Ave., Elmhurst N. Y. 11373 (by M. W. Blanck); (c) Riverbank Acoustical Laboratories, Geneva, 111. (by D. Zadonis); (d) Bolt Beranek and Newman Inc., Research Acoustic Test Facility, Cambridge, Mass. 02138 (by C. I. Holmer); (e) Airtemp Division Acoustic Laboratory, Chrysler Corp., P. O. Box 1111, Dayton, Ohio 45401 (by Dale T. Chambers); (f) Delco Products Div., Acoustics Laboratory, General Motors Corp., 2000 Forrer Blvd., Dayton, Ohio 45401 (by John M. Guinter); (g) IBM Acoustics Laboratory, Poughkeepsie, N. Y. 12602 (by G. C. Maling, Jr.)

ISSN:0001-4966    

DOI:10.1121/1.3437466

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The threshold for 500‐, 200‐, 100‐, 50‐, 20‐, and 10‐msec tones was measured with the tracking method at 250, 1000, and 4000 Hz in a group of five listeners who simulated a hearing loss of about 40 dB. A sample of listeners presenting with temporal lobe lesions was also examined. The results on both groups of subjects were remarkably similar to one another. That is, where the threshold difference between a 20‐ and 500‐msec tone is expected to be 10 dB, the differences observed here were in excess of 20 dB. In each instance, these aberrant results are interpreted not to be a result of a deficiency in the summing mechanism, but rather are due to a modification of the detection process.

ISSN:0001-4966    

DOI:10.1121/1.3437470

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

When monkeys are trained to release a response key to the onset of a pure‐tone stimulus, latency of key release is inversely related to tone intensity. Equal values of the behavioral measure (latency) can be said to reflect equal subjective intensities (loudness) and can be used to determine loudness matches. This technique was used to assess the extent of occurrence of loudness recruitment in the presence of noise‐induced TTS and during tone‐on‐tone masking. Under these conditions, latencies measured at lower intensities are lengthened, while latencies at high intensities remain unchanged. When a conductive loss is produced, latencies at all intensities are increased such that the latency‐intensity function appears to be shifted by a constant number of decibels. The data obtained are, in general, consistent with human data on loudness recruitment. Both TTS‐producing exposures and tone‐on‐tone masking result in complete recruitment 20–30 dB above the shifted threshold. With both TTS and masking, overrecruitment is occasionally observed. [Research supported by grants from NIH.]

ISSN:0001-4966    

DOI:10.1121/1.3437476

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The temporal and spatial variations of the index of refraction, μ, cause fluctuations of sound phase and amplitude that can be understood only by defining μ in terms of the duration, location, and range of the acoustical experiment. A “universal” isotropic spatial correlation function of μ has been derived from a simplified form of the Kolmogorov‐Batchelor spectrum of temperature fluctuations in a turbulent medium. However, such a correlation function, although more accurate than the popular Gaussian form, appears to be correct only for spatial lags less than 1 or 2 m at sea. Furthermore,in‐situexperiments have confirmed that the common presence of ambient bubbles in the upper several meters of the ocean produces a microstruc‐ture of the index in which the temperature is much less important than the bubble distribution. In this bubble‐dominated region the average speed of sound, the variance, and the frequency spectrum of the fluctuations of the speed are all strong functions of the sound frequency, the ocean wave spectrum, and the depth of the experiment. The phase fluctuations due to propagation in the upper ocean volume are compared with those occuring during forward scatter from the surface itself. [Research support by Naval Ship Systems Command.]

ISSN:0001-4966    

DOI:10.1121/1.3437480

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

One of the most prominent characteristics of acoustic signals transmitted from one point to another in the ocean is the fluctuation of the signal, in both space and time. This is true for both fixed and moving source and receiver. Postulated mechanisms and controlling parameters for various modes of propagation and types of environment are discussed. The environment includes the nature of reflectors and scatterers and their influence on the fluctuation. Examples of appropriate measures of fluctuation are offered. Experiments for testing mechanisms and obtaining descriptive data are discussed. Some problems of prediction are outlined.

ISSN:0001-4966    

DOI:10.1121/1.3437483

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The effects of a signal coherence which decreases exponentially with sensor separation are examined for a number of line array processors. For the conventional beamformer the limiting gain as the array is made infinitely long is simply (1 + ρ)/(l − ρ), where ρ is the signal coherence between adjacent sensors. The gain of the optimum processor is presented. A simple suboptimum processor which incoherently combines the outputs of a number of subarrays is found to provide near optimum performance. The performance of the split‐beam multiplicative processor is shown to degrade rapidly as signal coherence decreases. [This work was done at the University of California, San Diego, Marine Physical Laboratory of the Scripps Institution of Oceanography, San Diego, California 92132.]

ISSN:0001-4966    

DOI:10.1121/1.3437490

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The surface properties of a solid can sometimes be different from the bulk properties because of near surface gradients in such variables as chemical composition, metallurgical microstructure, degree of cold work, etc. Since surface or Rayleigh acoustic waves sample the surface elasticity to a depth comparable to the wavelength, these waves can be used to determine such a property gradient in a nondestructive way by measuring the velocity of propagation as a function of frequency. A theoretical expression relating the frequency dependence of the wave velocity to the gradient in elastic constants and density has been derived using perturbation theory, and several cases of practical interest have been calculated. Experiments on quench‐hardened steel in which the property gradient is the hardness have been carried out to verify the theory.

ISSN:0001-4966    

DOI:10.1121/1.3437496

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP