摘要:

The radiated energy from a vibrating wall is measured and compared to the value calculated from a knowledge of the correlation of the vibrational velocity over the wall surface. Detailed measurements were made on a single wall, but it is shown that the case of a double wall may be predicted with fair accuracy.

ISSN:0001-4966    

DOI:10.1121/1.1914359

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In this paper an impedance tube technique is described and evaluated for the measurement of the characteristic impedance and propagation constant of porous acoustical materials. In this method, data are determined under dynamic conditions through the investigation of the standing wave patterns existing in a tube driven at one end by a sound source and terminated at the other end by (1) a sample backed by a rigid wall; (2) a sample backed by an air space, a quarter‐wave long, itself terminated in a rigid wall. The validity of the method is assessed by comparing values of characteristic impedance and propagation constant for Owens Corning Fiberglas, type 705, density 6 lb/ft3, obtained in this way to values obtained by two other well‐known techniques: Beranek's method and Scott's method. Data were obtained at 800, 1200, and 1600 Hz. The analysis performed on the data obtained by the impedance tube technique and Beranek's method are in agreement at all frequencies. Comparable analyses on the data obtained by Scott's method show agreement with data obtained by the other two techniques only for values of the propagation constant at 1200 Hz and 1600 Hz. The discrepancies observed are attributed to experimental difficulties inherent in Scott's method.

ISSN:0001-4966    

DOI:10.1121/1.1914360

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The radial shear forces transmitted to the cuticular plates of cochlear sensory cells are investigated by means of a mathematical model. The model is based on the fine anatomy of the hair cells and their supporting structures. It predicts that the inner hair cells are stimulated by a viscous force which is linearly proportional to, and in phase with, basilar membrane velocity. The outer hair cells are stimulated by a shear force which is linearly proportional to, and in phase with, basilar membrane displacement at low frequencies (e.g., less than 700 Hz for a midbasal turn cell). At higher frequencies, the shear force transmitted to the outer hair cells is a function of both displacement and velocity. This outer hair‐cell shear force is at least an order of magnitude greater than the corresponding inner hair cell force for the frequencies and cochlear positions studied. These results compare favorably to recent cochlear microphonic data from normal and kanamycin‐treated guinea pigs for frequencies less than 4000 Hz. Shear force amplitude envelopes are presented for 800‐ and 1600‐Hz pure tones. The results suggest that the “velocity‐sensitive” inner hair cells are candidates for “place‐mechanism” receptors while the outer hail cells are candidates for “frequency‐mechanism” receptors. The model predicts no mechanical fine tuning in the force transmission.

ISSN:0001-4966    

DOI:10.1121/1.1914361

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The critical band in the stapedius‐muscle reflex was investigated by means of two‐tone complexes of variable frequency separation. In confirmation of an earlier study, the results indicate that the reflex critical band is several times larger than the critical band known in psychophysics. More specifically, it was found to be numerically equal to the center frequency of the complexes. Outside the critical band, the reflex threshold for the complexes was 10 dB lower than for their components presented separately. The difference is equal to that found in loudness experiments.

ISSN:0001-4966    

DOI:10.1121/1.1914362

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The resolution of frequency and amplitude is better at low signal‐to‐noise ratios with out‐of‐phase signals than with in‐phase signals when the noise in which the signals are presented is the same at both ears. On the other hand, at high signal‐to‐noise ratios, the effects of the interaural phase of the signals are negligible. These findings are discussed in terms of the predictions of a modified version of Durlach's Equalization and Cancellation Model and the Webster‐Jeffress Model of the binaural masking level difference.

ISSN:0001-4966    

DOI:10.1121/1.1914363

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Five squirrel monkeys were exposed to pure tones at intensities and durations sufficient to produce permanent threshold shifts (PTS s). One animal was exposed to a 1 kHz tone at 130 dB SPL for 4 h. Two were exposed to a 1 kHz tone at 140 dB SPL, for respectively, 3 and 4 h. Two were exposed to a 2 kHz tone at 140 dB SPL, for respectively, 3 and 4 h. Pre‐ and post‐exposure behavioral testing was similar to that described in an earlier study (Hunter‐Duvar and Elliott, 1972). Following the exposure, testing was carried out at frequent intervals until recovery was no longer evident. Final thresholds were then determined. Animals were next sacrificed, their cochleas were fixed, and surface specimens prepared. Using a phase microscope, missing and severely damaged hair cells (those with fractures of the cuticular plate and obviously displaced nucleii) were determined for each of the inner and outer rows from a point 1 mm from the apex to a point 19 mm from the apex. Hair cells were inspected at all levels. Wide variations in hearing losses and hair‐cell damage were found, and were uncorrelated. Hearing losses ranged from less than 20 dB to greater than 50 dB; hair‐cell damage ranged from no apparent damage to complete loss of outer and moderate loss of inner cells. Little if any correlation was found between exposure‐tone characteristic (frequency, intensity, duration) and hearing loss or hair‐cell damage.

ISSN:0001-4966    

DOI:10.1121/1.1914364

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Intensity discrimination of filtered clicks was investigated. For broadband and high‐pass filtered clicks, the data are consistent with Weber's law. For low‐pass filtered clicks, however, the Weber fraction decreases with increasing click intensity. In contrast to earlier findings, the addition of background noise to a broadband click raised the threshold for detection but did not markedly affect the Weber fraction. Theoretical implications of these results are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1914365

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Two wavevector filters were designed for investigating the nature of the pressure field induced on a flat boundary by a highly subsonic turbulent boundary layer. The wavevector filters were designed specifically for investigation in the spectral range where the spectral density of the pressure field is high. Preliminary experiments have been carried out, and the results relating to the convection velocity are reported. The major objective of the paper is, however, to present an analysis that makes it possible to properly interpret the results and allows for a more satisfactory comparison between the results reported in the paper and the available data in the literature.

ISSN:0001-4966    

DOI:10.1121/1.1914366

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

In order to accurately describe the operation of capacitance microphones, it is necessary to have solutions for both the static and dynamic deflections of the moving electrode. The present paper describes an application of finite difference methods to the differential equations describing the dynamic membrane motion due to the acoustic excitation. The authors have previously presented numerical solution approaches to the static deflections caused by the electrical biasing of the microphone [J. Acoust. Soc. Am.52, 711–719 (1972)]. The dynamic solution approaches presented here include the effects of the static deflections and the motion of the thin air film between the microphone's electrodes. The numerical results are compared with published results for simplified stationary electrode geometries and with experimental data on more complicated geometries at different tension levels. The predicted mode shapes change greatly, depending upon the magnitudes of the membrane tension and microphone's back chamber volume. Owing to the accuracy of these methods, they have applications in microphone optimization and characterization of the time dependent properties of electret microphones.

ISSN:0001-4966    

DOI:10.1121/1.1914367

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A series of noise control modifications was made to the HH‐43B helicopter. Modifications were made to the aircraft engine, drive, and rotor systems. Significant reductions were achieved in all octave bands of interest, i.e., 63 Hz to 4 kHz, with an average reduction exceeding 8.5 dB. A total of ten distinct aircraft configurations were tested and their respective noise control modifications evaluated. Greatest reductions in noise resulted from engine and rotor system modifications. Turbine engine noise reductions were obtained through the use of reactively lined inlet and exhaust silencers. Rotor system modifications included blade geometry changes and reduced tip speed.

ISSN:0001-4966    

DOI:10.1121/1.1914368

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP