摘要:

Two rectangular plates with approximately clamped boundary conditions were used as spatial filters to measure the low wave number components of the wall pressure fluctuations beneath a turbulent boundary layer. The plates were designed to provide low wave number measurements at higher frequencies and wave numbers than previous plate experiments in order to provide data comparable to measurements made using microphone arrays. Measurements were made in the lower test section wall of the MIT low turbulence subsonic wind tunnel under zero pressure gradient and adverse pressure gradient conditions. The zero pressure gradient data lies in the wave number frequency range 2.5<ωδ*/U∞<10 and 0.5

ISSN:0001-4966    

DOI:10.1121/1.2016405

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Sound transmission through a fluid layer which is imbedded in lighter density fluid is analyzed in terms of a resonant transmission theory. Expressions for the transmission coefficient (T) have been obtained indicating that T can be decomposed into resonance terms corresponding to symmetric and antisymmetric propagation modes in the layer. A computer progarm is utilized to compute both total T and T for each resonance for several cases of interest. Dispersion curves for the layer are obtained and compared to calculations and experimental data in the literature. The resonance widths are also calculated and an interpretation of total T as a function of angle of incidence and frequency thickness product is made in terms of these individual resonances. A similar but more complicated analysis holds for the elastic plate.

ISSN:0001-4966    

DOI:10.1121/1.2016408

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The design of compliant tube gratings for acoustic decoupling in water requires considerable detailed modeling of tube elastodynamics, array acoustics, grating resonant frequency, resonant bandwidth, elastomer loading, and tube stresses induced by uncompensated hydrostatic loading. Since the stresses depend on the same tube parameters as the acoustic characteristics it becomes necessary to simultaneously consider all grating factors including weight, thickness, and cost. For obvious reasons, however, tube strength must be given top priority in any design, and fundamental to estimating strength is a knowledge of stress risers in uniformly loaded oval shells. For conventional shaped tubes, such as those used by NUSC, the maximum stress is compression on the inside at the center of the curved ring segment. For very thick curved ends the ordinary thin shallow shell model is inappropriate and should be replaced by a more precise model. This paper presents the theoretical and emperical highlights of a detailed stress analysis of compliant tubes, including the flexural stress at the tube ends as well as the ring stresses.

ISSN:0001-4966    

DOI:10.1121/1.2016413

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Auditory units that responded to sound only when it originated from a limited area of space were found in the lateral and anterior portions of the midbrain auditory nucleus (nucleus mesencephalicus lateralis pars dorsalis, MLD) of the owl. The response properties of these units were studied in five barn owls (Tyto alba) using a remotely controlled, movable sound source under free‐field, anechoic conditions. The area of space to which such a unit responded was virtually independent of the nature (tone, click, or noise) and the intensity of the sound stimulus, and was defined as the unit'sreceptive field. Within a unit's receptive field could be found a small area to which the unit would respond with greatest vigor. This area of space was termed the unit'sbest area. Units in the lateral and anterior portions of MLD were systematically arranged according to the azimuth and elevation of their best areas. Units with contralateral best areas were located posterolaterally; units with ipsilateral best areas were located anteromedially. Elevation was arrayed along the dorsoventral axis with high best areas located dorsally and low best areas ventrally. [Work supported by NIH.]

ISSN:0001-4966    

DOI:10.1121/1.2016420

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Microelectrode recording techniques and the anterograde transport of tritiated amino acids (TAA) were utilized to demonstrate the projections of AI, AII, and the anterior auditory field (AAF) to the inferior colliculus (IC). Microinjections of TAA into AI resulted in two restricted, labeled laminae in the central IC of both sides: one in the dorsomedial division of the central nucleus (ICC) and one in the pericentral nucleus (ICP). The location and orientation of the projection arrays, as a function of the best frequencies of the cortical injection sites, were consistent with best frequency‐position data obtained in microelectrode mapping studies in the ICC. With injections in AII near the border of AI, very sparse, diffuse labeling in ICP and in the dorsal and medial aspect of IC was observed. No projection to IC was observed in four AAF cases. These results indicate that (1) of these three fields, AI has the greatest descending input to IC; (2) the projection from AI is topographic (cochleotopic); and (3) the projections to the dorsomedial division of ICC are laminar and the position and orientation of the the laminae are appropriate with their being continuous with the morphologically laminated ventral lateral division. [Supported by NIH grant NS‐10414.]

ISSN:0001-4966    

DOI:10.1121/1.2016424

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A new electrode was developed for recording the electrocochleogram (ECochG) from the ear canal. The electrode has a self‐retaining assembly, is placed without the aid of an otoscope, requires no anesthesia, and can be used under an earphone. The electrode,per se, is of the surface type and is placed on the floor of the ear canal about12‐cmfrom the eardrum. The focus of this report is on observations carried out in normal hearing subjects in which the ear canal recording was referenced to an electrode located on the forehead at hairline (which for purposes of recording the brainstem responses is not much different from the vertex). The interest in this configuration was in examining the potential for, in effect, combining the ECochG and the BSER (brainstem evoked response) in a single recording. This technique has been found to provide fairly reliable brainstem responses, however, with an appreciable facilitation of the eighth nerve response (N1or wave I). Unfortunately, the latter has proven to be quite variable, independent of the overall sensitivity of the recording. Possible sources of this problem and the relative limitations versus merits of this recording technique are discussed.

ISSN:0001-4966    

DOI:10.1121/1.2016427

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The critical band may be viewed as an indication of the bandwidth of the internal auditory filter. The bandwidth of a filter, as a measure of its frequency selectivity is not easily compared with the bandwidths of other filters. One useful measure of frequency selectivity, however, can be found by dividing the bandwidth of a filter at some arbitrary point below the peak, into the center frequency of the filter. This so called “Q” measure is valuable because it represents a ratio and thus can be compared among filters of different center frequencies. We have assumed that indirect measures of the critical band (the critical ratio) represent the bandwidth of the internal filter at a consistent point below the peak. We have thus calculated a Qcritical ratiofor all the available data points in the parakeet. Psychophysical tuning curves (PTC) have been empirically obtained for eight different probe frequencies in the parakeet. A Q10 dBwas calculated for each of these tuning curves and compared with the data describing Qcritical ratio, at ten different frequencies. The plot over frequency of Qcritical ratioand Q10 dBof the PTC's, although differing in absolute values, were nearly identical in shape. Frequency selectivity is poor in the low frequencies, raises sharply between 2.5 and 4.0 kHz, and then becomes poor again at higher frequencies. The results will be discussed with regard to the relation between the critical band and psychophysical tuning curves and frequency selectivity in the parakeet. [Work supported by NSF.]

ISSN:0001-4966    

DOI:10.1121/1.2016433

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

In many cases, dolphin tanks, like auditoriums, are designed with no special effort directed toward achieving acoustical perfection. Our measurements were to be made in a small pen in a large semicircular tank which was divided much the same as a railroad roundhouse, and contained seals and sea lions as well as dolphins. The walls were smooth concrete. Our object was to measure dolphin echolocation signals, and both reverberation and isolation presented serious problems. A wood lining which is echo suppressing in the frequency range of 10–150 kHz was developed and installed. The lining was constructed in 6‐ft square curtain panels, which were made up from small (3.5 × 7 × 2.5‐in.) blocks. This built‐up construction was necessitated by the particular grain orientation and pressure treatment of the wood required. The development of a satisfactory surface configuration and grain orientation was carried out in a small laboratory tank using 12‐in. square panels. Echo‐reduction measurements made in the USRD Lake Facility on full‐size panels and in the dolphin tank on the completed lining are in good agreement with the small‐tank data and show about 15–30 dB echo reduction over the entire frequency range. Transmission loss increases from about 15 dB at 10 kHz to 40 dB at the high frequencies.

ISSN:0001-4966    

DOI:10.1121/1.2016438

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Uses of the tactile sense to aid speech reception (usually in conjunction with lipreading) are reviewed. In the noninstrumental approach, the receiver's hands are placed on the talker. In one Instrumental approach, the unprocessed speech waveform or its envelope is transduced by a single vibrator. In those approaches guided by Helmholtzian place theory (“tactile vocoders”), the acoustic spectrum is analyzed into frequency bands and their envelopes are represented in an ordered, usually linear, spatial array on the skin. In the perceptual approach, auditory‐perceptual dimensions relevant to speech are mapped onto tactile‐perceptual dimensions In a manner arbitrarily selected by the experimenter. Observations at Central Institute for the Deaf will illustrate issues pertinent to the development and eventual clinical use of tactile aids. These are: problems of aid evaluation including appropriate training of subjects, criteria for selection of clients, and practial problems associated with daily use (safety, reliability, feedback, noise, and cost). A review of the accomplishments of the last 15 years substantiates that progress has been made toward clinical application. [Supported by NS 03856 and RR 00396.]

ISSN:0001-4966    

DOI:10.1121/1.2016449

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

This paper discusses some possible implications for deaf persons of several areas of computer‐related research and development. For the most part, this research and development has not been motivated by an interest in facilitating communication by and with deaf people. We argue that some of the results of these activities do have the potential for facilitating such communication, but that the potential will probably not be realized without explicit efforts to apply those results to the needs of deaf persons. The research and development areas that are discussed are: speech compression and speech synthesis, speech understanding systems, and computer‐mediated message technology.

ISSN:0001-4966    

DOI:10.1121/1.2016452

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP