摘要:

A simple test procedure for determiningA‐weighted sound power emission from household vacuum cleaners was systematically developed. Representative units were tested in various configurations and on different carpets to determine the sensitivity of noise emission to various operational factors. With a single configuration selected, these units were then tested in various acoustic environments, using direct and comparison methods, to evaluate the effects of the test environment. Tests were also run with fewer microphones. Concurrently, human response tests were conducted to determine whether a pure tone correction was indicated. An analysis of modal overlap in relation to tonal content was undertaken, and several existing standards were reviewed. The resulting test procedure is a comparison sound power measurement, using four microphones in a “semi‐reverberant” room similar to the ISO 3743 “special test room,” but less restrictive. A round robin conducted using this procedure has indicated a measurement precision of about 1 dB.

ISSN:0001-4966    

DOI:10.1121/1.2017260

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Spectral analysis of complex waveforms is the basis of many instructive demonstration and laboratory experiments in teaching acoustics and wave motion. Fourier analysis may employ either digital or analog techniques. Digital techniques, such as the fast Fourier transform algorithm, are easily carried out on hand calculators, and there are a number of real‐time spectrum analyzers which make use of these methods. Analog techniques include the use of multiple filters, a swept‐frequency filter, or a heterodyne arrangement. Limitations on the sweep rate of a filter can be circumvented by employing the time‐compression technique. These various techniques for Fourier analysis will be compared and a number of analyzers costing from $38 to $20 000 will be described and demonstrated.

ISSN:0001-4966    

DOI:10.1121/1.2017268

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The transient response of ultrasonic biomedical transducers and arrays is becoming increasingly important as a result of the wideband excitations which are currently envisaged for various biomedical applications. In the present paper, a computer model is developed to evaluate the transient transmit/receive response of multielement beam steered arrays of acoustically coupled piezoelectric thickness expander transducers. Each transducer is represented by a distributed parameter model which includes the effects of mechanical backing and matching materials. A set of coupled convolution integral equations are developed from the model to characterize the transient transmit/receive response of an army and scatterer configuration. These equations are an extended version of earlier work [P. Stepanishen, J. Acoust. Soc. Am.50, 964–974 (1971)] and can be readily solved using recursire techniques. Numerical results are presented to illustrate typical transient acoustic field and receive phenomena which result from the short pulse excitation of phased arrays of ultrasonic transducers in the MHz range of biomedical interest. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2017271

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

According to the prediction of theories, both acoustic power flux distribution between the right and left acoustic ports emitted from LFM IDT is asymmetric. By means of optical diffraction, we have detected the distribution of acoustic fields excited by the LFM IDT. Three unapodized LFM IDT which have different parameters are studied. These transducers with aluminum electrodes were deposited on the piezoelectric substrates ofYZ‐LiNbO3. The experimental results show that the SAW power run radiated from the high frequency port of LFM IDT is found to be stronger than that from the low frequency one. The asymmetry increases with the number of the finger pairs, but decreases with the band width. In general, the asymmetry increases with the excited frequency but the relation is not monotonic. Some theoretical models are taken for numerical evaluation of the asymmetric distribution. The comparison between the theoretical curves and the experimental results are presented and discussed briefly. However, in the theoretical calculations the mode‐conversion from SAW into BAW induced by the interdigital electrodes, has not been taken into consideration.

ISSN:0001-4966    

DOI:10.1121/1.2017276

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

A high precision cylindrical resonator has been employed to study the effects of impurity gases on the molecular absorption in oxygen. The resonator is capable of handling temperatures up to 500°C and pressures up to 100 atmospheres covering an effectivef/prange from 10 to 250 000 Hz/atm. The effects of4HeandCO2gases on the molecular absorption in oxygen within these experimental regions will be presented and compared with previous measurement using other techniques, such as the direct absorption method [Bass, J. Chem. Physics,58, 4783 (1973)] and shock interferometry [Millikan and White, J. Chem. Phys.39, 3209 (1963)]. [Work supported by NASA.]

ISSN:0001-4966    

DOI:10.1121/1.2017282

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The present report tends to summarize progress of the propagation of sound in foggy air since 1940s, with emphasis on the relaxation absorption and dispersion induced by mass transfer of fog droplets. Both theory and experiment in this report will be discussed in some details.

ISSN:0001-4966    

DOI:10.1121/1.2017286

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Recent work which established the acoustical conditions for ease of ensemble on stage [A. H. Marshall, D. Gottlob, and H. Alrutz. J. Acoust. Soc. Am.64, 1437–1442 (1978)] has been applied in two designs for arena stages. The first design has been constructed in the existing Christchurch Town Hall [A. H. Marshall, J. Acoust. Soc. Am.65, 951 (1979)]. A set of surfaces based on the reported work was installed above and around the stage in May 1978. At the first concert following, critics noted the excellence of ensemble playing and a questionnaire to the orchestra, which previously had expressed some difficulty with ensemble, elicited an overwhelmingly favorable response. The second part of the paper reports progress on the design of the stage and “ensemble” surfaces in the Wellington Town Hall. General conclusions about the design of arena stages for orchestral use are drawn.

ISSN:0001-4966    

DOI:10.1121/1.2017293

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

When a small musical group, such as a string quartet, performs on a large stage, it is usually placed downstage center, in order to achieve close contact with the audience. In this location there are no nearby sound reflecting surfaces to give acoustical support. If the audience is seated “out in front,” as in a proscenium theater the musicians can be helped by surrounding them at the sides and rear with a temporary folding screen, to provide close‐in sound reflections and reinforcement of their music. At the same time, it provides a suitable visual background to prevent their appearing lost on the large stage. So long as the height of the screen exceeds about six feet, the acoustical requirements are satisfied and the exact height is a matter only of visual concern. However, when the audience surrounds the stage, as in a number of new concert and recital halls, this approach does not work because the musicians are hidded from view for the audience around the stage. This paper discusses a recital screen for use in surround halls whose height is very much less than is customary. Examples are presented and the acoustical performance is discussed.

ISSN:0001-4966    

DOI:10.1121/1.2017296

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

The absorption produced by the audience in concert halls is considered a random variable. Beranek's proposal [L. L. Beranek,Music, Acoustics and Architecture(Wiley, New York, 1962), p. 543] that audience absorption is proportional to the area they occupy and not to their number is subjected to a statistical hypothesis test. A two variable linear regression model of the absorption with audience area and residual area as regressor variables is postulated for concert halls without added absorptive materials. Since Beranek's contention amounts to the statement that audience absorption is independent of the seating density, the test of the hypothesis lies in categorizing halls by seating density and examining for significant differences among slopes of regression planes of the different categories. Such a test shows that Beranek's hypothesis can be accepted. It is also shown that the audience area is a better predictor of the absorption than the audience number. The absorption coefficients and their 95% confidence limits are given for the audience and residual areas. A critique of the regression model is presented.

ISSN:0001-4966    

DOI:10.1121/1.2017300

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP

摘要:

Side‐scan sonar is the equivalent of synthetic‐aperture radar, a University of Michigan development in the 1950's. Then classified, it was first described in the open literature in 1966 in communication theory terms. The similarity of the synthetic aperture technique to holography was pointed out by the author in 1967, and a 1968 paper co‐authored by laser holography pioneer Emmett Leith (a co‐author of the 1966 synthetic aperture paper) noted that “the holographic viewpoint has led to designs which are not easily explicable from the communication theory viewpoint.” Because radar and sonar are both echo‐location systems, papers on the use of synthetic aperture concepts in sonar began appearing in 1968, including a 1974 paper describing synthetic‐apertureB‐scan sonar techniques in medical applications, and a 1970 U.S. patent on synthetic‐aperture ultrasonic imaging techniques. The present paper reviews the side‐scan principles, its recent advances and applications and briefly describes the possibilities of holographic space‐frequency equivalence [W. E. Kock, International Optical Computing Conference (I.O.C.C. 78), London, England, September 6, 1978] in side‐scan sonar. [Work supported by the Herman Schneider Laboratory.]

ISSN:0001-4966    

DOI:10.1121/1.2017308

出版商:Acoustical Society of America    

年代:1979

数据来源: AIP