摘要:

Detection thresholds were obtained for short duration rising tone glides and falling tone glides for normal hearing listeners in quiet and with varied levels of background, broadband noise. For signal durations 50 ms, or greater, pure tones were detectable at lower levels than were rising and falling tone glides; no level effects were observed. For signal durations less than 50 ms an interaction between background noise level, signal duration, and signal class was observed. The previously reported tendency for short duration rising glides to be detected at lower sound pressures than pure tones or falling tone glides appears to be unique to a limited range of noise levels (40–75 dB).

ISSN:0001-4966    

DOI:10.1121/1.391606

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

NoSo and NoSπ thresholds for a 500‐Hz signal were determined as a function of masker level for masking noises having 600‐ and 50‐Hz bandwidths centered on 500 Hz. Noise levels of 0, 10, 20, 30, 40, 50, and 60 dB/Hz were used for the 600‐Hz bandwidth, and noise levels of 0, 10, 20, 30, 40, 50, 60, and 70 dB/Hz were used for the 50‐Hz bandwidth. The So thresholds increased as a function of increasing noise level with a slope close to 1.0, for both the 50‐ and 600‐Hz masker bandwidths. For the 600‐Hz‐wide masker, the Sπ thresholds increased with a slope less than 1.0 for masker levels from 0 dB/Hz to approximately 20 dB/Hz, but increased with a slope close to 1.0 for masker levels above approximately 20 dB/Hz. For the 50‐Hz‐wide masker, the Sπ thresholds increased with a slope less than 1.0 for masker levels from 0 dB/Hz to approximately 40 dB/Hz, but increased with a slope close to 1.0 for masker levels above approximately 40 dB/Hz. The results are discussed in terms of different binaural processes involving interaction between monaural critical bands centered on the signal frequency, and interaction involving monaural critical bands outside the monaural critical band centered on the signal. It was suggested that the narrow‐band noise results are probably more appropriate than the wideband noise results when considering binaural interaction involving monaural critical bands centered on the signal frequency.

ISSN:0001-4966    

DOI:10.1121/1.391616

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Several experiments are described in which subjects were required to discriminate differences in the spatial distribution of concurrently active sound sources in stereophonic arrays. For pure tone stimuli and binaural listening, systematic discrimination functions were observed when relatively small intersource frequency differences (approximately 30 Hz) were present. For tonal stimuli, this discrimination task was reliably performed only for frequencies below 1500 Hz. Additional tests were conducted with amplitude‐modulated tonal stimuli, low‐ and high‐frequency uncorrelated noise, correlated low‐frequency noise, and, with the uncorrelated low‐frequency noise, for stimuli presented in both the vertical plane and under monaural listening conditions. The results of all of these manipulations support the notion that the spatial distribution of sources in a stereophonic array can be appreciated if disparate low‐frequency energy is available from the sources in a horizontal configuration. The implications of these results are discussed relative to acoustic processing in the natural environment.

ISSN:0001-4966    

DOI:10.1121/1.391617

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Spontaneous oto‐acoustic emissions (SOAEs) were detected in eight of 19 ears from 12 persons with normal hearing. On a subset of these individuals, additional characteristics of SOAEs were studied including the suppression of SOAE level caused by an external tone. For suppressor tones below and slightly above the frequency of an SOAE, suppression is quite abrupt (about 5 dB of SOAE level reduction per dB increase in suppressor level); however, as suppressor frequency increases above the SOAE, the rate of suppression decreases. Areleasefrom suppression was demonstrated by the interaction of an SOAE with two external tones. When a tone above the SOAE frequency causes suppression, a second tone above the suppressor frequency can cause the SOAE to increase nearly to its ambient level. This finding is interpreted as the second tone having suppressed some aspect of the intracochlear influence of the first tone. The growth rate of this secondary suppression appears to be near 1 dB/dB, a value similar to rates derived from existing measures of two‐tone suppression observed in auditory‐nerve‐fiber recordings in laboratory mammals.

ISSN:0001-4966    

DOI:10.1121/1.391618

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

High data‐rate signaling with acoustic pulses along an elastic plate is made difficult by the conversion of a transmitted pulse into many component pulses that arrive separately during a time span that can exceed the travel time of the first component pulse to arrive. In addition, the amplitude of the received signals fluctuates widely with changes in pulse center frequency. But to obtain high data‐rate signaling, many pulses with different center frequencies must be transmitted at closely spaced time intervals. It is important in these circumstances to understand the principal features of the component pulses that originate from a single transmitted pulse. This paper derives analytical expressions for the arrival times, the peak envelope amplitudes, and the center frequencies of the arriving component pulses that are transmitted by wideband line forces acting normal to the plate surface. Each component pulse is the manifestation of a different mode of propagation. By carefully picking the bandwidth and center frequency of the launching pulse, the number of its component pulses (or, alternatively, excited modes) that have significant amplitude can be minimized, if the pulse center frequency is low enough. If the frequency is high enough, so that more than about six propagating modes can exist, then the number of arrivals cannot be reduced significantly. At higher frequencies, several of the modes merge to form the Rayleigh wave, which is centered within both earlier and later modes. A series of photographs show how transmitted Gaussian pulses look when the pulse center frequency is picked to illustrate three regimes; where the Rayleigh wave is not formed; where it is partially formed; and where it is fully formed.

ISSN:0001-4966    

DOI:10.1121/1.391619

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

We consider the inverse problem for a two‐dimensional, spatially incoherent random source. Under these assumptions, we show that an exact inversion formula can be derived for recovering the source spectral intensity, as a function of position, fromnearfieldmeasurements of the emitted radiation recorded on the circumference of a circle enclosing the source region. Although solutions to the inverse random source problem have been reported in the past, these results have almost always employed farfield approximations. After deriving the inversion formula in two dimensions, we discuss an efficient method for numerically evaluating this formula using the fast Fourier transform algorithm. Finally, a generalization of the inverse problem to a three‐dimensional source enclosed by a spherical recording surface is given.

ISSN:0001-4966    

DOI:10.1121/1.391620

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

This article presents the results of a simulation experiment comparing the behavior of four noise background normalization schemes. The four schemes are the two‐pass mean, the split three‐pass mean, the split average exclude average, and the order truncate average normalizers.

ISSN:0001-4966    

DOI:10.1121/1.391621

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

An analysis is presented for the free vibration of a cantilever folded plate. For this purpose, the deflection displacements of the plate are written in a series of the products of the eigenfunctions of a cantilever beam and a cranked free–free beam parallel to the clamped edge of the plate. The kinetic and strain energies of the plate are evaluated analytically, and the frequency equations are derived by the Ritz method. The method is applied to cantilever folded plates with and without structural symmetry, and the natural frequencies and the mode shapes of vibration are calculated numerically giving the results.

ISSN:0001-4966    

DOI:10.1121/1.391622

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Calculations have been made which predict sound amplification under certain conditions when propagated through a gas with an overpopulation of vibrationally excited states. Three metastable states have been analyzed, where the vibrational temperature is varying slowly on the scale of the sound period. The first is that of a long‐lived vibrational mode in a diatomic gas. Calculations were made for N2, CO, O2, and Cl2. The second is that of a fast v–v exchange followed by a slow v–t. Calculations were made for CD4as an example of this situation. And the third is that of a slow v–v followed by a fast v–t. Calculations were made for a mixture of N2/CO2/He as an example of this situation. Some of the difficulties in experimentally observing the gain are discussed.

ISSN:0001-4966    

DOI:10.1121/1.391623

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP

摘要:

Harmonic generation of 30‐MHz ultrasonic waves in small solid samples is analyzed to establish a technique for evaluating combinations of third‐order elastic constants of samples which cannot be grown large enough to allow one to make the infinite plane‐wave approximation. Results are reported for CsCdF3and KZnF3.

ISSN:0001-4966    

DOI:10.1121/1.391002

出版商:Acoustical Society of America    

年代:1984

数据来源: AIP