摘要:

In order to examine the applicability to electromechanical transducers, fundamental characteristics of an MOS field‐effect structure with a movable gate electrode, or a ’’movable‐gate–air‐gap–oxide–semiconductor’’ system, are investigated. In this system, a channel current suffers field‐effect modulations by a mechanical displacement of a gate electrode. As a movable‐gate electrode, a metal plate, and a foil electret are used. Equations derived from an approximate treatment of MOS–FET equations are found to explain the experimental results. Based on these equations and experimental facts, design considerations for electromechanical transducers using this structure are made. As an example of applications, microphones utilizing foil electrets are constructed and their performances are discussed.

ISSN:0001-4966    

DOI:10.1121/1.382036

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The success of the ultrasonic pulse‐echo technique for measurement of the depth of burn necrosis in porcine skin [Med. Phys. 4, 259–263 (1977)] has led to the present investigation of the specific acoustic impedance difference between the necrotic (burn) tissue and the underlying viable (nonburn) tissue. Experimental results show that the ultrasonic group velocities and mass densities are approximately the same in these tissues yielding average values of (1.72±0.12) ×105cm/s for group velocity and (1.093×0.009) g/cm3for the density. The characteristic impedance (density times velocity) differs by at most 3% between necrotic and viable tissues. Measurements of acoustic attenuation show a difference of approximately 70% between these tissues. porcine skin is due primarily to the difference in acoustic attenuation.

ISSN:0001-4966    

DOI:10.1121/1.382037

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Observations of biological choruses in the ambient noise of tropical waters of the east Indian Ocean, the west Pacific Ocean, and the Timor Sea near Australia are described. These choruses occurred for a few hours at a time and had most energy at frequencies between 400 Hz and 4 kHz, with spectral peaks mainly at 800 Hz, 1.6–2 kHz, and 3 kHz. During choruses, noise spectrum levels rose up to 30 dB above the usual background noise. Statistics of occurrence of the evening choruses indicate that they would occur on most, if not all evenings at the locations of measurement and are probably fairly widespread in and near shallow waters of the region. As well as these regular evening choruses, there were also transitory choruses which were observed at various times of day over periods of a few days but not before or after. Possible sources of the choruses are discussed. There are at least three sources of the regular evening choruses, possibly fish or sea urchins. Some of the transitory choruses, spectrally similar to the regular choruses, were composed of intense clicking sounds, apparently from sperm whales.

ISSN:0001-4966    

DOI:10.1121/1.382038

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

In order to investigate the effect of level of presentation on subjects’ labeling of speechlike sound patterns, synthetic stimuli were constructed, varying systematically F0contours, VOT, and F2transitions. These stimuli were presented in random sequences at levels between 15 and 105 dB SPL to subjects with normal hearing. No significant response variation was observed in the range 40–100 dB SPL. Subjects’ labeling behavior suddenly breaks down below levels of around 35 dB SPL. The secondary findings of the study are also discussed in terms of different specific processing strategies for different specific speech features.

ISSN:0001-4966    

DOI:10.1121/1.382039

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Masked thresholds for constant and gliding tones were determined by the method of adjustment for durations between 0.5 and 5000 ms in three overlapping frequency regions between 0.25 and 3.3 kHz. The masker was a continuous white noise at 70‐dB SPL. Listening was monaural; subjects had normal hearing. Below 10 ms the thresholds for upward glides were lower and those for downward glides higher than the thresholds for constant tones. In the 10–300‐ms duration range, which encompasses formant transitions of speech, the highest thresholds are for downward glides and the lowest ones for constant tones. These differences could result from different time courses of neural decay and inhibition for constant tones, upward and downward glides. The differences between upward and downward glides indicate that the phase spectra influence sound detectability. The thresholds for constant tones reach minimum around 1 s. The thresholds for glides continue to decrease at least up to 5 s. The ’’critical’’ duration for constant tone integration can result from the overriding of integration effects by adaptation effects, the latter ones being eliminated by changing frequency. The curves for constant‐tone threshold between 10‐ and 1000‐ms duration were fitted by a product of exponential and hyperbolic functions.

ISSN:0001-4966    

DOI:10.1121/1.382040

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This paper describes a new approach to pitch perception. It focuses attention on the slight difference between the pitch of complex tone and the pitch of a pure tone with the same (fundamental) frequency. This approach is based on the assumption that pitch perception is based on both spatial and temporal cue analysis. In this study, the values provided by the temporal cue are calculated from physiological data from the auditory nerve fibers. The possible ratios of the pitch of complex tones relative to the pitch of pure tones at various frequencies are predicted. Psychophysical experimental results strongly support this prediction. In addition, another experiment suggests that the above psychophysical effect is not based upon a mutual masking effect in the spatial domain.

ISSN:0001-4966    

DOI:10.1121/1.382041

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Recordings were made of discharges in single fibers of the cat’s auditory nerve using single‐tone and two‐tone signals of varying frequency. The frequency of the single tone was varied stepwise from the fiber’s best frequency to about 1.7 times this value. One component of the two‐tone signal was varied in exactly the same manner while the frequency of the other was increased in such a way that the frequency of the cubic difference tone (CDT, 2f1−f2) generated within the auditory system was kept constant at the fiber’s best frequency. Responses in terms of discharge rate and period histograms were collected for both signals. The difference in spike rate between the response to the single tone and to the two tones could be ascribed to the CDT and was used to estimate the CDT level as a function of the signal level and frequency. It turned out that the CDT level relative to that of the primaries is about 15 dB smaller for frequencies beyond 10 kHz than for lower frequencies, and slighly decreasing for an increasing stimulus level. Period histograms of responses to CDTs of frequencies below 4 kHz made it possible to estimate CDT phase as a function of the frequencies and the level of the two generating tones. The intensity of the tones had no effect on the CDT phase. The varying frequency separation produced shifts in the CDT phase of several hundred degrees if its frequency was above 2.5 kHz. For lower frequencies the shifts were maller, and varied considerably between different preparations. The phase estimated from period histograms for acoustic tones and for CDTs of varying frequency turned out to change in an identical manner. This shows that the CDT must be subject to the same delays or phase shifts as the traveling wave in the cochlea produced by an acoustic tone.

ISSN:0001-4966    

DOI:10.1121/1.382042

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The characteristics of acoustic reflex adaptation were studied in human subjects. Contralateral stapedial reflex measurements were made by monitoring changes in acoustic conductance and susceptance with a 220‐Hz probe. The reflex activators included four tonal stimuli (500, 1000, 2000, and 4000 Hz) and broadband noise presented for 180 s at 96, 104, and 112 dB SPL. The data are presented as change in acoustic admittance and in percent of maximum admittance change. The static admittance of the ear was found to drift systematically toward lower admittance values in the absence of contralateral stimulation. All stimulus conditions demonstrated some reflex adaptation. The half‐life and time of onset of adaptation were found to vary directly with intensity and inversely with frequency. The effects of stimulus parameters on the rates of reflex adaptation are discussed. A previously described exponential model of reflex adaptation provided a reasonable first approximation to the data.

ISSN:0001-4966    

DOI:10.1121/1.382043

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A linear array can detect a plane wave signai at a wrong bearing if the signal wavelengths are shorter than twice the distance between the closest adjacent sensors. This penomenon, called spatial aliasing, is most pronounced when the bearing is near endfire. This paper presents a method for correcting spatial aliasing of broadband signals using the frequency‐wavenumber approach to array processing. Also presented is a method for averaging the ω–κ Fourier coefficients that will give a more accurate bearing estimator than the method presented by Clay, Hinich, and Shaman [J. Acoust. Soc. Am. 53, 1161–1166 (1973)]. The methods discussed in this paper can be used for a sparse unequally spaced array which is detecting a dispersive signal.

ISSN:0001-4966    

DOI:10.1121/1.382044

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A new technique is presented for the study of seismic reflection profiles. Previous investigations of the reflection of sound from marine sediments have been restricted to the determination of a specular reflection coefficient. This study is based upon the hypothesis that the entire reflected waveform, rather than just the amplitude, contains valuable information on the classification and characteristics of these sediments. The multivariate statistics technique of principal component analysis is proposed for analyzing the variability in the shape and amplitude of the reflected waveform. The results of this analysis are used in conjunction with an improved cluster analysis program to produce maps of sediment distributions for a section of Narragansett Bay, Rhode Island. The groupings produced are in basic agreement with previous studies of the area. Preliminary regression equations are presented for converting the principal components to percentages of sand, silt, and clay.

ISSN:0001-4966    

DOI:10.1121/1.382045

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP