摘要:

Natural resonant frequencies of prolate acoustical resonators with either perfectly soft or perfectly rigid boundaries are calculated by locating the zeros ofRmn(1)(h,ξ) andRmn(1)′(h,ξ). These resonances are normalized to those of the corresponding modes in a spherical cavity with the same volume and are presented for various ratios of major to minor axes.

ISSN:0001-4966    

DOI:10.1121/1.1912399

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The present study deals with an experimental and analytical investigation on the behavior of a cable system in the case of salvage recovery of objects embedded in ocean sediments or handling structures placed on the bottom of the ocean. Steady‐state and transient vibrations of the system are considered. The possibility of “snap” loads in the system is studied and some conclusions of practical interest are drawn.

ISSN:0001-4966    

DOI:10.1121/1.1912400

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

Frequency‐selective detection of acoustic sources in the upper atmosphere is shown to offer advantages over a broad‐band detector in improving signal‐to‐noise ratio. A model for an optimum frequency is developed using simplified assumptions: i.e., a source with a Fourier spectrum of uniform amplitude; attenuation by absorption during propagation; local turbulence as the noise source. An optimum frequency is found where the signal‐to‐noise ratio is maximum as a function of altitude. Experimental evidence confirms that a peak in the signal‐to‐noise ratio exits for acoustic sources in the upper atmosphere.

ISSN:0001-4966    

DOI:10.1121/1.1912401

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The propagation of random sound in a cylindrical duct has been treated theoretically. The conditions under which the simple wave equation applies to the transmission of sound generated by industrial air‐moving devices is made explicit. The acoustic forcing function and termination conditions are discussed extensively as well as the structure of the sound field in the duct. Equations for the power spectral density and pressure cross‐spectral density are derived in order to define the problems associated with deducing sound power, given sound pressure at two points. The results suggest that an anechoic termination is almost mandatory and that the modal spectra must be known, if accurate measurements are to be made. A number of simplifications to the theory were tested experimentally and found to apply. Modal spectra were measured and were used to compute sound power and predict pressure measurements. The predicted and observed were found to be within 1 dB, suggesting that a practical means for measuring ducted‐fan sound power can be found.

ISSN:0001-4966    

DOI:10.1121/1.1912402

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

This study deals with the design and analysis of an adaptive array processor in which the individual filters consist of tapped delay lines and adjustable gains. The gains are adjusted automatically by an iterative procedure which is a modified form of the stochastic approximation method of Robbins and Monro. The criterion for optimality is that the mean‐square error between filter output and an ideal signal be a minimum. However, it is shown that the ideal signal need not be available to the processor; it suffices that the signal autocorrelation function and spatial direction be available. General expressions are obtained for convergence of the iterative algorithm, and an explicit expression for an upper bound on the rate of convergence is derived. System performance is analyzed by considering a noise field consisting of a spatially isotropic component and a single directional component. It is shown that the adaptive system eventually acts to eliminate the effect of the directional component. The theoretical behavior of the system has been verified experimentally using actual sonar data and a six‐element array.

ISSN:0001-4966    

DOI:10.1121/1.1912403

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP

摘要:

The shadow‐graph method in the classical form used by W. C. Sabine seems better suited to wavefront photography in models of auditoriums than the more complex schlieren method. The former produces photographs in which the optical density is proportional to the density of disturbance within the model; the latter produces photographs that are sensitive to gradients within the model. The return to the techniques of Sabine and others who produced wavefront photographs in the earlier years of auditorium design is recommended as a means of avoiding detrimental effects produced by considerations of geometrical acoustics only.

ISSN:0001-4966    

DOI:10.1121/1.1912404

出版商:Acoustical Society of America    

年代:1971

数据来源: AIP