摘要:

Interaural time differences (ITDs) were measured from 400–7000 Hz on cats in order to provide quantitative data for use in physiological/behavioral studies on sound localization. ITDs derived from clicks and the initial portion of tone bursts showed a pronounced roughness and frequency dependence. This frequency dependence is most evident at higher angles of incidence and indicates that a single ITD will not always represent a single position on the azimuth. Controls demonstrate that most of the roughness in these functions was due to reflections off the surface supporting the animal and that the measured ITDs corresponded to predictions made by steady‐state theory. Measurements made with and without the pinnae in position indicate that they have relatively little effect on these ITD functions, particularly for frequencies below 2500 Hz and for small angles of incidence. In spite of acoustic limitations exemplified by the roughness and frequency dependence of these functions, ITDs generated by sound sources situated close to the midline provide reliable localization cues that are much better than those derived from sources well out on the azimuth. Finally it is noted that another ITD, the group ITD, can be ascribed to an acoustic signal. Calculations based on the measured steady‐state ITDs show differences between the group and steady‐state ITDs over a given range of frequencies. Differences between the group and steady‐state ITD can be significant, and it is argued that: (1) the group ITD can provide a localization cue to the auditory system that is distinct from the steady‐state ITD; and (2) it is possible these group ITDs are used by the nervous system to localize sound sources in realistic situations.

ISSN:0001-4966    

DOI:10.1121/1.385196

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

A series of three experiments with 15 normal‐hearing listeners measured temporary threshold shifts (TTS) as a function of various parameters of impact noise exposure. A criterion of 15 dB TTS at 4, 6, and 8 kHz, measured 3 min after exposure was adopted. Results indicated that; (1) the growth of TTS is a power function of the peak level of impact noises, (2) recovery from TTS appears to proceed linearly with the logarithm of the time in quiet, (3) the amounts of TTS3are exponentially related to the logarithm of the decay time (oreduration:te) of the impact sound pressure envelope, (4) with constant total amounts of energy and a constant repetition rate, increasing the number from 60 to 1000 increases the final amount of TTS; the derived trading relationship involves a 12.7‐dB level change for a tenfold change in the number of impacts, (5) repetition rates ranging between 0.5 and 1 pps (pulse per second) are the most harmful to hearing and, (6) daily exposure to 100 impacts (te: 200 ms; repetition rate: 0.5 pps) should be limited to a 130‐dB peak level, in order to protect 90% of the exposed people. Results are discussed in terms of the possible use of the equivalent continuous noise level as an index in setting safe limits of occupational impact noise exposure.

ISSN:0001-4966    

DOI:10.1121/1.385197

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

One of the basic questions which has persisted in the field of hearing theory is the still unresolved mechanical action of hair‐cell transduction. The fundamental problem that has historically plagued researches is the discrepancy between mechanically measured tuning of basilar membrane motion and neurally measured tuning. In this paper we show that the difference between these two measures appears to be accounted for by a specific, physically motivated, micromechanical model. This model gives rise to a spectral zero which we identify as the ’’second‐filter’’ of cochlear transduction. For high‐frequency fibers this zero resides at a fixed frequency ratio below CF (characteristic frequency) while for fibers having low‐frequency CF’s the zero appears to go to zero frequency faster than CF. In this paper we first present and analyze the assumed mechanical model. We then briefly discuss a possible specific physical realization for the nonlinearity of cochlea mechanics. The nonlinear model is based on dynamical variations in outer hair cell stereocilia stiffness.

ISSN:0001-4966    

DOI:10.1121/1.385198

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Derived narrow‐band brainstem responses were obtained for click levels of 10–60 dB SL in normal hearing subjects. The amplitudes and latencies of the wave I, wave III, and wave V components in the derived BSER were studied as a function of click intensity. Characteristic differences were found between the input–output behavior of waves I and III on one hand and wave V on the other hand, especially for the low‐frequency narrow bands (center frequencies of 0.5 and 1.0 kHz). While the wave I and wave III (peak‐to‐succeeding trough) amplitude showed a small (20–30 dB) dynamic range with saturation effects, the wave V amplitude continued to increase across the intensity range studied. At the high‐frequency end (narrow‐band center frequencies of 4 and 8 kHz), wave V also showed saturation. It is suggested that this difference across center frequency (place of origin along the cochlear partition) is responsible for the dominance of wave V at low‐frequency stimulation (e.g., with tonebursts). The latencies of the three waves studied maintained their constant interwave delays across the observed intensity range in each narrow band. Quite large (up to 3.5 ms) increases in the narrow‐band latencies were found for decreasing click levels; this is comparable in value with those for the unmasked BSER although the mechanism seems to be different. The major contribution to the BSER which determines its latencies, originates at 60 dB SL from the 8‐kHz region but at low SL (10 and 20 dB) from the 2‐kHz region. At these low intensity levels, the contribution from the apical part of the cochlea, however, is still of the same size as that from the high‐frequency end.

ISSN:0001-4966    

DOI:10.1121/1.385199

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Techniques were developed for measuring sound pressure in the cochlea with calibrated, liquid‐filled, piezoelectric probe microphones. Sound pressures were measured in scala vestibuli and scala tympani in the basal turn in 25 cats for tones from 20–10 000 Hz. Control experiments indicated that intracochlear pressures were essentially uninfluenced by the measuring technique, and were conducted to the cochlea via the ossicular chain. Intracochlear pressures are linearly related to pressure at the tympanic membrane for tone levels at least as high as 105 dB SPL, and are relatively independent of depth of probe insertion in the scalae. The transfer ratio of sound pressure in scala vestibuli to that at the tympanic membrane increases in magnitude over the frequency range 50–1000 Hz to reach a maximum value of 15–30 dB, and decreases at higher frequencies, thus demonstrating that the middle ear provides a frequency‐dependent pressure gain. At frequencies below 40 Hz, the pressures in scala vestibuli and scala tympani are approximately equal and are both determined by the round‐window membrane compliance. At frequencies above 100 Hz, the round‐window membrane impedance is small compared to the acoustic input impedance of the cochlea, and the pressure in scala vestibuli considerably exceeds that in scala tympani; consequently, the pressure difference across the cochlear partition is approximately equal to the pressure in scala vestibuli.

ISSN:0001-4966    

DOI:10.1121/1.385200

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

An existing adaptive beamforming technique, known as frequency‐domain adaptive interference rejection (FAIR), is examined for robustness with respect to nonsystematic array errors. It is concluded that, for array position errors below ±10% of the mean spacing, the FAIR technique continues to be effective. However, for special situations where large errors are encountered or where the noise situation is so favorable that better interference rejection is worthwhile, error compensation might become necessary, and a self‐calibration scheme is briefly described.

ISSN:0001-4966    

DOI:10.1121/1.385201

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

Standard methods of presentation of sonar signals to operators have not maximized the capabilities of the auditory system. This report describes a dichotic method of sonar signal presentation to operators based on the masking‐level‐difference (MLD) principle in hearing. Using a Bekesy tracking procedure, twenty‐six listeners of varied experience detected recorded broadband sonar targets and low‐frequency pure tones that were embedded in 100 Hz–4 kHz recorded and synthesized backgrounds. The signals were either homophasic or antiphasic and the backgrounds were always homophasic. Average detection thresholds for the antiphasic sonar signals were 5–7 dB better than their homophasic counterparts. Pure tone antiphasic detection thresholds were also 6–11 dB better than in the homophasic presentation. The sonar signals show similar MLD’s as those found with speech signals.

ISSN:0001-4966    

DOI:10.1121/1.385202

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The sidelobe level sensitivity of multistage modulation scanning sonar systems to internal electronic phase errors is examined by means of a ’’scanning function’’ approach and also by a hardware oriented analysis of a particular sonar system. It is shown that the later internal stages of such modulation scanning systems are the most sensitive to phase error. A general approach to calculating scanning sidelobe levels with phase error present is discussed.

ISSN:0001-4966    

DOI:10.1121/1.385203

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

This paper investigates the mapping capabilities of a linear receiving array of acoustic sensor pairs that measure both the pressure and pressure gradient along the array axis. It is demonstrated that unambiguous pressure maps of remote sources can be obtained even if the separation between sensor pairs is one wavelength (twice the spatial Nyquist sampling interval). The effect of additive noise—both correlated and uncorrelated at each sensor pair, but uncorrelated between sensor pairs, is studied and found not to be a major problem. In the second half of the paper an analysis of the cross correlations of the output voltages from the various sensor pairs reveals that each pair providesthreedistinct cross correlations. Accordingly from data obtained from an array with sensor pairs spacedthreehalf‐wavelengths apart an unambiguous map of the source intensity distribution can be formed. Examples of such maps are provided.

ISSN:0001-4966    

DOI:10.1121/1.385204

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP

摘要:

The spectral structure of pressure measurements made in a ducted combustion test facility are studied. Dispersion and attenuation of acoustic plane waves may occur in the duct at low frequencies due to combustor emissions and affect the spectral structure. A model that considers the propagation of plane waves through a cloud of particles in a flowing gas, and which includes heat transfer between soot particles and the gas, is discussed. Experimental results are compared with theory.

ISSN:0001-4966    

DOI:10.1121/1.385205

出版商:Acoustical Society of America    

年代:1980

数据来源: AIP