摘要:

Chinchillas were trained for behavioral audiometry and then exposed to a schedule of 6 h of noise and 18 h of quiet for a nine‐day period. The thresholds at 0.5, 2.0, 5.7, and 8.0 kHz were measured immediately before and after each exposure. The decay of threshold shift after the ninth day was followed until stable thresholds were again observed. This procedure was repeated at six levels (57, 65, 72, 80, 86, and 92 dB) of an ocatve band of noise centered at 4.0 kHz. The threshold shift measured after 4 min of quiet appears to reach asymptote (ATS4) after the first or second exposure. ATS4increases with the level of the octave‐band noise for daily 6‐h exposures with the same slope as does ATS4for continuous exposures. For frequencies exhibiting the greatest loss (5.7 kHz), ATS4increases 1.7 dB for every decibel increase in the noise, if ATS4is greater than 10–15 dB. The decay of TS was related to the level of the noise and, thus, the amount of ATS4. For exposures of 57 and 65 dB, the decay of TS during the 18‐h period of quiet was nearly complete. The exposures at 72 and 80 dB required three to five days for complete recovery, while those at 86 and 92 dB were very slow and not complete with average values of PTS of about 6 and 13 dB, respectively.

ISSN:0001-4966    

DOI:10.1121/1.3437298

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Changes in the threshold of hearing and suprathreshold loudness judgments have been reported under conditions in which the contraction of the middle ear muscles (MEM) has been induced. These psychophysical changes have been accounted for variously on the bases of contributions of contralateral direct masking, contralateral remote masking (CRM), binaural loudness summation (LS), and the effects of changes in transmission caused by MEM contraction. Experimental conditions were devised to determine the influence of the contraction of the MEM on suprathreshold loudness judgments at 250, 500, and 1500 Hz by controlling the possible influences of CRM and LS. The relative loudness of two sequentially presented 50‐msec pulses (identical frequency) was judged by subjects with normal sensitivity (hearing and MEM) using the method of constants during three basic experimental conditions. In Condition A (reference condition), the test stimuli were presented monaurally separated by a 1400‐msec interstimulus interval. Condition B was identical to Condition A except that a 1250‐msec narrow‐band noise (2900–5000 Hz) was presented contralaterally with an onset delayed 200 msec relative to the first test pulse. In Condition C an identical contralateral noise was used but with the onset of the first test pulse simultaneous with the onset of the noise. For each of these three conditions two reference tone intensities (60 and 100 dB SPL) and two narrow‐band noise stimulus intensities (70 and 105 dB SPL) were employed. Essentially no suprathreshold loudness changes were observed between the two pulses among the various. conditions. We conclude that MEM contractions did not effect the suprathreshold loudness judgment.

ISSN:0001-4966    

DOI:10.1121/1.3437301

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The acoustic measurement of middle ear function is presently accomplished with electroacoustic instruments which measure the difference in flow of acoustic energy through the middle ear as a function of variable air pressure gradient across the tympanic membrane. The result is displayed in the form of a curve called a tympanogram, which may be analyzed by its configuration, or may provide the computational basis for the determination of static acoustic impedance or its parameters. Descriptive data has previously been defined in reactive or resistive components of the acoustic impedance, or the acoustic impedance itself, depending upon the instrumentation used. The present study explores the clinical measurement of acoustic admittance, which is the reciprocal of acoustic impedance, and compares the results of this measurement on 100 normal human middle ears with the previously developed normative data. Normal ranges for the acoustic susceptance and acoustic conductance, as well as the complex acoustic admittance, are developed which will serve as ranges for the clinical study of static acoustic admittance of the middle ear. The results compare well with data previously developed with mechanical acoustic instrumentation and also provide evidence of the source of variability in certain pathological conditions.

ISSN:0001-4966    

DOI:10.1121/1.3437303

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Spectra of reverberation from deep scattering layers in Baffin Bay, Davis Strait, and the Labrador and Norwegian Seas were measured using explosives and hydrophones operating near the sea surface. Results from four experiments carried out between 1966 and 1972 were used to form a composite picture of reverberation in northern waters in late summer. This reverberation differs from that in the main North Atlantic Basin in that there is usually much less diurnal change in spectrum and considerably more scattering at low frequencies. Exceptions, when they occur, are in the more northerly regions. Towards the south there is a considerable backscattering of sound in the frequency range 1–3 kHz, caused presumably by layers of fish a few tens of centimeters in length. Concentrations of these fish are relatively constant over distances of hundreds of miles but decrease markedly over short distances in the neighborhood of oceanographic boundaries.

ISSN:0001-4966    

DOI:10.1121/1.3437310

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The bearing error obtained from a bottom bounce sonar is proportional to the bottom slope in the direction perpendicular to the line of sight between the source and the target. Therefore, it is necessary to know the variance of the bottom slopes in order to estimate the magnitude of the bearing errors to be expected in a given ocean region. The bottom slopes can be completely described statistically by their wavenumber spectrum, which is simply related to the spectrum of the bottom depth fluctuations obtained from fathometer data. The slope spectrum represents the variance of slope per unit bandwidth, so that integration of the slope spectrum yields the total slope variance. For the purpose of estimating bearing errors, it is necessary to cut off the slope spectrum integration at a wavenumber inversely proportional to the width of the first Fresnel zone, because scattering from outside this region makes up a negligible portion of the measured return signal. Typical slope spectra in various regions will be presented. [Supported by Navy Science Assistance Program.]

ISSN:0001-4966    

DOI:10.1121/1.3437313

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The results of a computer investigation of the angular distribution of the normal modes of vibration of rectangular rooms is reviewed. The importance of angular distribution for several specific types of room uses is discussed.

ISSN:0001-4966    

DOI:10.1121/1.3437321

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A comparative evaluation was performed on test methods to simulate the acoustic response of shroud‐enclosed spacecraft structures. The evaluation was based primarily on vibro/acoustic test results obtained from a single “baseline” model of spacecraft, attach fitting, shroud, and “lower structure.” Emphasis was placed on (1) the magnitude of test input change required to generate comparable responses, both by a spacecraft/attach fitting “alone” acoustic test and a vibration test, to those responses produced by the shroud‐installed acoustic test of the baseline model, and the difficulty in producing such a change, and (2) the degree of mis‐simulation that can result from performing a particular “less than optimum” test. Conclusions are drawn with regard to the advantages and disadvantages derived from the use of input spectra adjustment methods and lower structure simulations. Test guidelines are also developed for planning and performing a launch acoustic environmental test.

ISSN:0001-4966    

DOI:10.1121/1.3437325

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Honeycomb sandwich panels are highly anisotropic, layered media predicted to have unique dispersion characteristics for flexure wave frequencies above a few kilohertz. The phase velocity of flexural waves traveling along a l‐in.‐thick honeycomb sandwich panel has been experimentally determined from 170 Hz to 50 kHz using three techniques: measurement of resonant frequencies of beam‐shaped samples in forced vibration, measurement of nodal spacing in standing‐wave patterns on beam‐shaped samples, and measurement of the change in time delay of a particular phase feature of a wave packet as a function of propagation distance in large plate samples. The data are in good agreement with two models, a plate theory and an elasticity theory, each of which treats the core as a continuum. Above SO kHz, the predictions of the two models diverge and the experimental phenomena become more complex. A brief description of these results is given.

ISSN:0001-4966    

DOI:10.1121/1.3437328

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Initial research started ten years ago or the extraction of non‐verbal speech parameters as numerical assessors of emotional/physical states of the speaker. Initial research concentrated on energy changes occurring in different frequency regions when the speaker or the experiencing emotional stress. It was determined that the optimal frequencies were the 100–120 and 500–800 Hz regions. Subsequent research and field studies explored additional parameters and other emotional states of the speaker. A second parameter has been shown to be correlated with the tension of the speaker. It has been shown to successfully discriminate different levels of confidence of the speaker in his statements and his attitudes to social issues as well as the different emotional stress levels occurring in polygraph examination. The precise property of speech corresponding to the second parameter has not as yet been identified, although active research is continuing. A current study shows excellent correlation with interpretations of polygraph data, although the voice parameter does not appear to correlate highly with any of the three conventional physiological parameters used in polygraph examination. The first and second speech parameters discussed in this paper appear to be independent (Pearson product moment correlation equals +0.05).

ISSN:0001-4966    

DOI:10.1121/1.3437333

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The effects of shear flow on the modal phase velocity, the group velocity, and the cutoff frequencies of acoustic modes propagating in ducts are studied analytically. The convection effect of the shear flow is found to be equivalent to the convection effect of a uniform mean flow with some effective Mach number. Using the effective Mach number, the uniform mean flow dispersion relation can be generally used to express the relation between the space‐time parameters for any shear flow Mach number distribution. Acoustic duct modes which may be expected to propagate under the assumption of uniform mean flow will decay because of shear flow effects. The calculated propagation constant of different modes propagating upstream or downstream in annular, circular, or two‐dimensional ducts are compared with all available data calculated by time‐consuming sophisticated techniques and published by previous investigators. The comparison shows an excellent agreement. By using the effective Mach number to obtain the propagation constant, the solution of the sound field in the duct—and thus the refraction effects of the shear flow—becomes a simple matter of integrating an ordinary differential equation. [Research supported by National Research Council of Canada.]

ISSN:0001-4966    

DOI:10.1121/1.3437338

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP