摘要:

The diurnal variation of volume reverberation at frequencies from 3 to 30 kHz in the upper 600 m of the California current is analyzed. The variation is attributed to the vertical movements of resonant and nonresonant scatterers. A distribution model is developed which characterizes the sizes and population concentrations of six groups of scatterers.

ISSN:0001-4966    

DOI:10.1121/1.1913603

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Integrated scattering‐strength measurements describing the backscattering of sound from the ocean volume in winter were obtained along a triangular track running west from the southern tip of Vancouver Island, British Columbia, thence south to Hawaii and then roughly northeast on a return leg to Vancouver Island. Thirty stations were occupied enroute, alternately at midnight and midday, weather permitting. The data were analyzed to yield spectral characteristics of the backscattering from various depth ranges at all station locations. The integrated scattering strength is seen to decrease and the daytime deep scattering layer to become shallower as one proceeds north from Hawaii. Differences between daytime and nighttime scattering and distinctive spectral characteristics associated with sub‐tropic and sub‐arctic water masses are illustrated.

ISSN:0001-4966    

DOI:10.1121/1.1913604

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A study has been made of three sound sources, each of which is constructed out of a plane wire gauze (positive electrode) and a great many needles (negative electrode) pointing toward it. Direct current coronas have appeared when a high de potential has been applied to the sound sources in the atmosphere. Various experiments have been performed on the acoustical characteristics of the sound sources as they are supplied with an ac current in the frequency range of 0.2–10 kHz, which is superposed on a de current. The sound sources are each considered as consisting of a resistance shunted by a capacitance, so far as the ac current is concerned. Theoretical formulas are obtained from the assumption that the sound is produced by a vibratory force which acts directly on the air between the electrodes and which has an rms value (d/b)I′, wheredis the gap length,b= 2.2 cm2/V‐sec andI′ is the rms value of an ac current through the resistance. It has been found the experimental results for 0.2–1 kHz are in good agreement with the calculated ones obtained from the formulas.

ISSN:0001-4966    

DOI:10.1121/1.1913605

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This paper presents the maximum‐likelihood signal processor for steering a vertical array in the vertical direction. The major application is to the estimation of the depth of a distant narrow‐band continuous point source in the waveguide. The eigenfunctions of the guide are used to match the array to the received signal The error of the depth estimate is derived as a function of the aperture and geometry of the array, the covariance function of the ambient noise received by the array, and the observation period; assuming that the source and medium are stationary during that period. The processing technique can be applied to any perfect waveguide in which a signal source is detected by an array of sensors.

ISSN:0001-4966    

DOI:10.1121/1.1913606

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The ultrasonic intensity threshold for producing lesions in mammalian brain tissue is not a strong function of frequency (over the range of 1–10 MHz) for exposures longer than 1 sec. A model is presented to explain this apparent lack of frequency dependence. It is assumed that the maximum temperature developed in the lesion volume for a given pulse duration is determined (1) by the absorption coefficient of that tissue, and (2) by the distribution of the acoustic intensity over the treated volume (sharpness of the beam). The former is observed experimentally to be nearly linearly dependent upon frequency in the range 1–10 MHz, and the latter, for a good lens, is related inversely to frequency. Temperature calculations which account for heat loss by diffusion as well as the frequency dependence for the beam geometry and the absorption coefficient are presented. These lead to nearly frequency independent curves for threshold dosages beyond 1‐sec exposure, giving credence to the suggestion that thermal processes may be predominant for such exposures.

ISSN:0001-4966    

DOI:10.1121/1.1913607

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The response of two simple systems, such as beams or plates, strongly coupled at a point is discussed. Two models of a mass, spring, and gyroscopic coupling mechanism are treated. It is shown that the result of statistical energy analysis (SEA) relating power flow to differences in modal energy can be obtained even when the coupling is strong. For one model of the coupling mechanism, the power flow can be expressed in terms of changes in modal resonance frequencies caused by the coupling.

ISSN:0001-4966    

DOI:10.1121/1.1913608

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The fundamental equation of Statistical Energy Analysis (SEA) states that the average power flow between two coupled vibrating systems is proportional to the difference in their average modal energies. Under certain circumstances one can estimate the proportionality constant by modifying system boundary conditions on the separated systems and calculating or measuring changes in the systems. Newland's estimate, based upon blocking part of the system, is reexamined and limitations are discussed. Three alternative methods which circumvent blocking are presented. These were applied to predict power flow in experiments on coupled beams and on coupled plates wherein power flow through the coupling was measured directly as a product of force with velocity. The measurements support the fundamental SEA relation, including the null power point where the average modal energies are equal. Measured and predicted proportionality constants are compared.

ISSN:0001-4966    

DOI:10.1121/1.1913609

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Articulation scores and stapedius reflex responses to the same speech phrases were determined in subjects with unilateral stapedius muscle paralysis. Understanding of the speech sounds deteriorated significantly for maximal levels above 100 dB SPL, which was just above the threshold for the stapedius reflex. We conclude that the stapedius muscle extends the dynamic range of the ear by 15–20 dB.

ISSN:0001-4966    

DOI:10.1121/1.1913610

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

Recent neurophysiological experiments make it clear that some neurons in the auditory systems of the cat and monkey are responsive to interaural time differences that are larger than the maximum value possible for animals with their headwidths. Discussed here are several possible ways such neurons could be activated in real‐world situations, and it is suggested that these neurons might be involved in the suppression of erroneous localization information, the suppression of reverberation, and/or in the analysis for periodicities in the acoustic stimulus.

ISSN:0001-4966    

DOI:10.1121/1.1913611

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This letter reviews recent research on speaker identification by means of comparisons of speech spectrograms by human observers. Various factors affecting the reliability of identification are discussed, particularly those that would be present in practical forensic situations. Our interpretations of the new data lead us to reiterate our previous conclusion: that the degree of reliability of identification under practical conditions has not been scientifically established.

ISSN:0001-4966    

DOI:10.1121/1.1913613

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP