摘要:

Spatial fluctuations of sound in reverberant rooms are examined theoretically for the case of a fixed source and movable receiver. The approach is to describe statistics of the time‐averaged squared sound pressure, as a function of frequency. These statistics apply to reverberant rooms at high frequencies, such that the modal overlap (ratio of modal bandwidth to the average spacing between modes) is larger than about 3, and for regions sufficiently removed from the source that the reverberant field prevails. Within these bounds of frequency and space, squared sound pressure may be profitably viewed as a stochastic process over frequency. At each frequency in this range, squared sound pressure is a random variable obeying an exponential probability law over space. The family of random variables obtained by considering all frequencies in this range defines a stochastic process. The process is employed to derive formulas for the spatial variance of squared sound pressure for the cases of single tone, multitone, warbletone, and narrow‐band noise excitation. Experimental confirmation and suggested applications are given in many instances. In general, the variance is small when the product of bandwidth and reverberation time is large, as long as reverberation time is not so large as to prevent high modal overlap.

ISSN:0001-4966    

DOI:10.1121/1.1911287

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Subjects were exposed in one ear for 5 min to13‐octband noise centered at either 2, 3, 4, or 6 kHz at 110 dB SPL. The resulting aftersensation, called “noise‐induced short‐duration tinnitus” (NIST) was matched for pitch and loudness in the nonstimulated ear. It was found that the pitch of NIST bears a constant relation to the frequency of the stimulus and that the difference between the equivalent frequency of NIST and the frequency of maximum threshold shift was equivalent to one critical band.

ISSN:0001-4966    

DOI:10.1121/1.1911288

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Most, if not all, models of binaural hearing predict a dependence of the magnitude of the masking‐level difference (MLD) on signal frequency. Specifically, the size of the MLD is expected to increase as the signal frequency is decreased. The results of many experiments in which signal frequency was varied, however, do not support the above prediction. The magnitude of the MLD appears to decrease at frequencies below 300 cps. The present experiment was designed to re‐examine the decrease in the size of the MLD at low frequencies and to test a qualitative explanation of this phenomenon based on the concept of internal noise. To do so, the size of the MLD in the N0Sπ masking condition and the N0S0 masking condition was estimated relative to the NMSM masking condition at signal frequencies of 150 and 300 cps at several masker spectrum levels. The results indicated that the magnitude of the MLD at both frequencies is dependent upon spectrum level of the masker. The results further indicate that the dependence of the size of the MLD on spectrum level varies as a function of the signal frequency. The size of the MLD at 150 cps is much more sensitive to changes in masker spectrum level than is the MLD at 300 cps. Both results agree with predictions based on the internal noise hypothesis.

ISSN:0001-4966    

DOI:10.1121/1.1911289

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Four experiments were conducted to develop and test a method of determining the frequency‐response characteristic of the observer when he listens for single‐frequency signals presented against a continuous background of wide‐band noise. After observers were trained to detect primary signals of a single frequency, probe signals of various other frequencies were presented infrequently, in lieu of the primary signal. Primary signals and all probe signals were presented with very similar amplitudes that would be expected to render them all equally detectable if presented alone in single‐frequency experiments. Estimates of the detectability of the signals of the various frequencies were obtained concurrently in a two‐alternative forced‐choice procedure. The results from 14 observers were quite similar and show differences in detection as a function of signal frequency when the primary signal was of 1000 or of 1100 Hz. In general, the primary signal was correctly detected 75%–90% of the time while signals with frequencies at approximately 150 to 200 Hz on either side of the primary‐signal frequency were detected at the chance level, 50% correct. In as few as three experimental sessions, the observer's frequency‐response characteristic was obtained using the probe‐signal method.

ISSN:0001-4966    

DOI:10.1121/1.1911290

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Subjects were exposed, on different test days, to 166‐dB (peak normal‐incidence) impulses 34, 58, 72, or 96 μsec in duration spaced 1 sec apart. For each pulse duration, the subjects were first exposed to one pulse, then the number of pulses was doubled on successive days until the temporary threshold shift (TTS) following exposure exceeded 30 dB. Intercorrelations of numbers of impulses required to reach criterion TTS at each duration were obtained; they were highest when durations were similar. At the largest pulse duration, a median of only four impulses was required to achieve criterion, some individuals exceeded criterion at one impulse, while others required hundreds. No evidence was seen of a 4‐kHz notch; maximum shift was at high frequencies (10–15 kHz) and relatively independent of impulse duration. There is reason to believe that if one exceeds allowable TTS in the speech‐range frequencies with this kind of impulse noise, there is a chance of producing permanent high‐frequency loss.

ISSN:0001-4966    

DOI:10.1121/1.1911291

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Average evoked responses were recorded from human vertex in response to tone pulses presented at intersignal intervals (ISI) ranging from 0.25 through 10 sec. Tone pulses were 20 msec in duration with 20‐msec rise and decay times. Frequencies investigated were 500, 1000, and 2000 Hz. Response amplitude was found to be a linear function of log10ISI. Response latency did not change significantly with ISI, except perhaps in componentN2of the response, which appeared to increase in latency as ISI increased. These relations obtained regardless of frequency.

ISSN:0001-4966    

DOI:10.1121/1.1911292

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Difference limens were obtained for the discrimination of pure tones from 62.5 Hz to 12 kHz, and for short pulses from 1 to 4 kHz. In logarithmic coordinates, the data fitted straight lines with different slopes for the high‐frequency, the low‐ and medium‐frequency, and, for pulses, the very low‐frequency ranges. An analysis was made to show that the discrimination of duration and the discrimination of pitch are both based on time‐measuring processes.

ISSN:0001-4966    

DOI:10.1121/1.1911293

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

Sounds of sufficient intensity and duration can produce decrements in the cochlear microphonic (CM). It was the purpose of these experiments to determine the extent of such changes and the rate at which they occurred. Cat ears were exposed to 5.0‐kHz tones at intensities from 99 to 138 dB SPL (re0.0002 μbar) for periods totaling 80 min. Losses in CM sensitivity (measured with a round‐window electrode) occurred for tones ranging from 0.1 to 10 kHz with the greatest losses at 3.0 or 4.0 kHz. Changes occurred at a rate that was linear in time for the lower intensities and linear in time at the higher intensities.

ISSN:0001-4966    

DOI:10.1121/1.1911294

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

A laser interferometer, designed and constructed in this laboratory, was evaluated with respect to its applicability to measurements of amplitudes and phases in the ear. The instrument measures continuously up to a maximal amplitude of 0.92×10−5cm, and higher at selected points. With respect to vibrations of the tympanic membrane, measured in an open sound field, the vibration isolations of the instrument was ample. The prevailing S/N ratio made it convenient to routinely measure amplitudes of 1 × 10−7cm in living animals. At low frequencies, this corresponds to SPL's of approximately 60 dB. In fresh cadavers, however, while there was no immediate change in the magnitude of the responses, readings were extended to 1 × 10−9cm, owing to the absence of pulse and breathing, giving a dynamic range of 80 dB. In all experiments, repeatability was excellent, and between‐animal variations were low. The resulting transfer characteristics obtained in living animals, with the tympanic bulla closed, was generally similar to those obtained earlier, with some noted exceptions. The amplitude curve failed to show the slight hump around 1 kHz found earlier. The phase curve was much more complex than earlier ones and cannot be approximated by the assumption of simple network models.

ISSN:0001-4966    

DOI:10.1121/1.1911295

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP

摘要:

An interferometer is described. It is designed for measurements of submicroscopic displacement amplitudes of small biological structures in living animals. Its output is frequency independent. The instrument may be used for measuring: (1) absolute displacement amplitudes as low as 3 × 10−10cm between 20 and 20 000 Hz; (2) phase angles of the displacements with respect to that of the applied sound signals; (3) transient responses of the vibrating structure. Theory of operation is discussed. Fabrication of microscopic mirrors and construction details of the interferometer are given. Experiments performed with the aid of an earphone as a vibrating object are included to show the characteristics of the interferometer. Calibration is precise (within 1 dB) and repeatability is excellent, both with respect to amplitude (within 1 dB) and phase (within 5°). Experiments on living animals and cadavers, giving amplitude and phase data, will be included in a separate paper.

ISSN:0001-4966    

DOI:10.1121/1.1911296

出版商:Acoustical Society of America    

年代:1968

数据来源: AIP