摘要:

The fundamental relationships between acoustic array parameters and the noise field are reviewed to establish the connection among the various processing techniques for estimation of the ambient‐sea‐noise directionality. The analyses, based on the concept of multidimensional space, conclude that basic information about the ambient‐sea‐noise directionality can be obtained directly from the cross‐spectral matrix of the array’s hydrophone outputs. The angular resolution of the processed noise field depends on the array structure, the stationarity of the noise field, and the precision in numerical computation. The cross‐spectral data also can be used to indicate the dominant coherent noise sources in a certain multidimensional representation. Examples of a simulated noise field and actual sea data are illustrated for the directional AUTOBUOY.

ISSN:0001-4966    

DOI:10.1121/1.381631

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The behavior of the resonant frequencies of a quartz crystal, coated with electrodes and tabs of the same material, is investigated both theoretically and experimentally. It is pointed out that, when the thicknesses of the tab exceeds the sum of the thickness of the electrodes, the tab behaves like a resonator acting independently of the resonator determined by the conventional electrodes. In the model, which describes this phenomenon, use is made of trapped energy theory on thickness‐twist modes. The results of numerical calculations on the theoretical model developed in this paper are in excellent agreement with the results obtained form the experiments. The additional resonant frequencies created by the presence of the tab together with the resonant frequencies related to the electrodes could possibly be used in the field of simultaneous mass and temperature determination. The principle of such a method is given in the paper.

ISSN:0001-4966    

DOI:10.1121/1.381632

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Transmission loss in cylindrical shells due to a finite region of discontinuities is considered. The analysis considers a free traveling wave encountering finite number of stiffeners. The material and geometric properties of the stiffeners and the spacing may vary. Numerical examples are presented. The transmission efficiency and the reflection efficiencey are found for two cases of interest.

ISSN:0001-4966    

DOI:10.1121/1.381633

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

By using the resonant vibrations of metal spheres it is possible to separate the contributions involving different amounts of shear, hydrostatic, and longitudinal strain merely by choosing the appropriate resonant frequencies. Birch [J. Geophys. Res. 80, 756–764 (1975)] has applied this method to the radical, spheriodal, and torsional modes of metals, glasses, and rocks. He has shown that if there is no loss connected with the hydrostatic component of vibration, the ratio of theQof the radial mode to theQof the torsional modes should be 9 to 1 whereas his measurements of steel indicated a ratio of about 3 to 1. We have measured several cubic metals (Al, Fe, Ta, Nb, W, V, and α‐brass) and have found that this ratio ofQ’s varies systematically with elastic anisotrophy. It is shown that the difference in the elastic constants of adjacent grains introduces a shearing stress in the body of the material which adds a component of the internal friction proportional to the anisotropic factor minus one which accounts for the drop inQfor a longitudinal vibration. For the radical mode the much larger effect has not been explained and the value ofKfound is experimental.

ISSN:0001-4966    

DOI:10.1121/1.381634

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

The semiopen‐type Exhibition Hall with more than 3500 seats was built in the Yamaha Sportland TSUMAGOI with the area of 1 700 000 m2. Since this hall is expected to be used for indoor sports and musical performances, it was required to make designs from the point of view quite different from the traditional auditoriums. In view of the control of sound field by the electroacoustical means, therefore, new tools have been adopted such as (1) the movable proscenium loudspeaker, (2) movable sound absorbing canvas, (3) artificial reverberation adding system, (4) multichannel public address console and delay/reverberation control console, and (5) other various types of electrical and spatial reverberation adding devices. This paper describes the idea of design for the Exhibition Hall meeting the requirements of the latest popular music involving electric musical instruments and explains the details of design and acoustic characteristics of those electronic equipments.

ISSN:0001-4966    

DOI:10.1121/1.381635

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

In cross‐sensor beamforming the narrow‐band quadrature signal at one sensor is multiplied by the complex conjugate of the narrow‐band quadrature signal at a second sensor to form a stable element of the cross‐sensor field. After suitable time averaging, the beam response can be calculated as the weighted correlation between the cross‐sensor field that is measured and the field that is expected. IfNsensors form a sparse line array, thenNlines form a sparse square array. Examples are given showing the performance of a sparse square array and a random planar array in resolving a realistic multiwave signal plus noise field. A simple adaptive algorithm is used to resolve weak signals close to strong signals and to reduce sidelobe problems associated with a random array.

ISSN:0001-4966    

DOI:10.1121/1.381636

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

This study was made to compare a variety of signal‐processing methods that can be used with arrays of sonic or ultrasonic transducers to produce images. Four types of holographic methods are compared with conjugate or beam‐scanned systems. Effects of amplitude quantization, phase quantization, uncorrelated noise, element spacing, and shading are illustrated. Signal‐processing comparisions in the literature often consider only a single point source or a pair of equal strength sources. The authors used a line array of hydrophones 30 wavelengths long to image a set of 10 point sources of varying amplitudes and phases. The composite signal received on each element of the array was calculated. Computer‐generated plots of signal level in decibels versus pattern angle are given for each processing method. The different processing techniques are evaluated on the basis of the range of target signal strengths that could be successfully imaged. Holographic processing requires twice as many transducers to obtain the same quality of image as conjugate processing. Amplitude or phase quantization makes it difficult to detect weak targets in the presence of strong signals.

ISSN:0001-4966    

DOI:10.1121/1.381637

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

A recently proposed echo‐analysis technique based on a power‐series expansion of the target transfer function and an optimally Doppler‐tolerant transmitted waveform is discussed. Specific problems with the technique including sensitivity of the extracted parameters to time delay and Doppler changes in the received waveform are identified. An analysis is conduced of relatively low‐frequency echoes from a number of simple submerged targets, and the results are reported. An iterative generalization of the proposed technique is introduced which substantially improves its performance.

ISSN:0001-4966    

DOI:10.1121/1.381638

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

Using a tone‐on‐tone masking procedure to just mask a compound actionpotential (AP) evoked by a 10 dB SL short toneburst yields frequency‐intensity combinations for the tonal masker called AP tuning curves. This procedure is used in addition to the standard electrocochleography procedure to obtain information about the peripheral frequency selectivity. Both methods were performed on a (normal) group of patients having normal or nearly normal (within 15 dB) thresholds for frequencies above and including 1 kHz, and in patients having hearing losses of sensorineural origin exceeding 40 dB HL. In normal ears, the characteristic two‐segment tuning curves are obtained. For pathological ears having a hearing loss of cochlear origin, tuning curves broadening by the loss of their sharp tips are obtained. There is some indication that in predominant neural hearing loss most of the sharp tuning is preserved. The changes in tuning associated with recovery from sudden deafness to almost normal hearing are reported. The overall conclusion is that the results obtained are in agreement with those from AP tuning curves reported in animal studies [P. Dallos and M.A. Cheatham, ’’Compound action potential (AP) tuning curves,’’ J. Acoust. Soc. Am. 59, 591–597 (1976)] as well as with changes in single‐fiber tuning in reversible hearing loss [E. F. Evans, ’’Auditory frequency selectivity and the cochlear nerve,’’ inFactsandModelsinHearing, edited by E. Zwicker and E. Terhardt (Springer–Verlag, New York, 1974)].

ISSN:0001-4966    

DOI:10.1121/1.381639

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP

摘要:

To examine the question of whether the distortion product 2fl−fhis unique—whether a special nonlinear mechanism is responsible for its production—estimates of 2fl−fhand of 2l+fhamplitudes were obtained in three listeners. Threshold shifts measured with a tone‐on‐tone masking paradigm for each distortion product suggest that each have similar properties and are masked paradigm or each distortion product suggest that each have similar properties and are masked by other tones as if they had a physical realization in the cochlea. Their masking is not a function of stimulus fine‐time structure. The 1 dB/dB growth of 2fl−fhwas not changed by rendering it inaudiable as previously suggested. Possible explanations of the 1 dB/dB growth of 2fl−fhcompared with the accelerated growth of 2fl+fhare examined.

ISSN:0001-4966    

DOI:10.1121/1.381640

出版商:Acoustical Society of America    

年代:1977

数据来源: AIP