摘要:

A method for prediction of community noise exposure in the vicinity of a railroad yard, knowing its operations and layout, has been developed. Requirements of the technique were (1) applicability to a yard of arbitrarily defined operation and layout, (2) ability to accurately measure existing noise levels for use as reference data, and (3) consistency of methodology with possible government regulatory monitoring procedures. The method selected involves development of noise contours based upon the average maximumA‐weighted noise levels of individual events projected in the community. This method satisfied the needs for a workable noise prediction technique within the current state‐of‐the‐art. The advantages of this technique are as follows: (1) it may be accurately tailored to any yard configuration by a building block approach which allows inclusion of all significant sources of noise; (2) it utilizes easily measured quantities (in dBA) which are largely independent of the variables which affect noise output by virtue of usage of average maximum noise levels for each operation; (3) it does not require precise location of specific noise sources‐but rather assigns certain operations to broad areas of tracks over which these operations would logically occur; (4) it accounts for level of yard operation activity, and (5) it provides a conservative working instrument for railroads to assess the potential impact of their yard operations on the surrounding community. Supporting data were taken at four railroad yards in the Los Angeles area representing a broad range of yard activity.

ISSN:0001-4966    

DOI:10.1121/1.3437947

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Responses of single auditory‐nerve fibers of normal and kanamycin‐treated Mongolian gerbils indicate that inputs from inner and outer hair cells tend to cancel each other at frequencies below the characteristic frequency (CF). In normal animals, trapezoidal motion of the basilar membrane produces velocity and displacement responses which change systematically with CF. In kanamycin‐treated animals, two types of abnormal responses nearly 180° out of phase with respect to each other are found. Latencies of these responses and anatomical changes generally produced by kanamycin indicate that one type is produced predominantly by the inner, the other predominantly by the outer hair cells. Normal firing patterns can be reconstructed from these two kinds of responses. They appear to result from an excitatory input from the inner hair cells and an inhibitory input from the outer hair cells. This interpretation is consistent with the generally found hair‐cell directionality. The inferred interaction between the inner and outer hair cells points out a solution to the problem of neural sharpening of mechanical frequency analysis in the cochlea.

ISSN:0001-4966    

DOI:10.1121/1.3437948

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Fourier analyses have been conducted upon period histograms of responses of single cochlear nerve fibers to a pair of phase‐locked, equal‐amplitude tones whose frequenciesf1andf2in relation to the characteristic frequency (CF) of the nerve fiber under study are given by the ratio CF:f1:f2=i:j:k, wherei,j, andkare positive integers satisfyingi

ISSN:0001-4966    

DOI:10.1121/1.3437952

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The neural response of neurons in the medial superior olive was recorded to electrical stimulation of nervous processes in the osseous spiral laminae and also to antidromic stimulation from the inferior colliculi. The osseous spiral laminae were stimulated at the first, second, and third turns. Time of signal arrival differences (Δτ) at the two spiral laminae and also intensity differences (Δi) were varied. It was found that (1) electrical stimulation gives a regular neural response; (2) the neural response to changes in Δτ and Δiisnonlinear; (3) fine latency changes in the neural response can signal changes in Δrand Δi; (4) stimulations of different turns of the osseous spiral laminae (i.e., with different current flows) give different neural responses reflecting the anatomical tonotopic arrangement of the medial superior olive; and (5) changes in Δτ and Δimay be registered by theratioof the spike count in a short period following the stimulus to the spike count in a longer total period.

ISSN:0001-4966    

DOI:10.1121/1.3437956

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

Using the results of the single scatter study discussed in PartI, a valid multiple scatter solution was developed for the coherence function for an initial horizontal time‐harmonic plane wave incident on a random medium with horizontal correlation lengths that are orders of magnitude larger than vertical correlation lengths. Using this solution, we construct a qualitative description of the loss of spatial coherence due to the scattering of low‐frequency acoustic signals by the temperature microstructure. Simple algebraic expressions are presented for a characteristic coherence length, which can be used to estimate the maximum useful array size for the coherent summing of signals, for a horizontal temperature fluctuations spectrum that may be described by a single power law. In this way, the most significant environmental parameters are clearly identified.

ISSN:0001-4966    

DOI:10.1121/1.3437962

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A general method is proposed to treat rough boundary scattering in ray‐tracing propagation models. The angular intensity of the field reradiated from the rough boundary is interpreted as a probability density function of the angles of reflection. The influence of rough surface scattering on sound attenuation in shallow water is demonstrated for selected sound speed profiles by model calculations. The theoretical results are compared with experimental data.

ISSN:0001-4966    

DOI:10.1121/1.3437969

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

The analysis of PartI, “A Mathematical Analysis of a Free‐Flooded Finite Length Radiating Magnetostrictive Shell,” is continued. Acoustic radiation from a finite‐length free‐flooded circular cylinder is analyzed by numerical integration of applicable Helmholtz‐type integral equations. By matching acoustic boundary conditions, the modal vibration of the shell is integrated into the elastic and magnetostrictive response provided by PartI. For an input set of dimensions, electric drive, and required frequency range, the computer program delivers surface velocities, electrical and mechanical motional impedances, nearfield and farfield acoustic radiation, and acoustic power developed for a water‐loaded shell. Typical examples of computer output are given together with discussions. Comparison is made with selected experimented results.

ISSN:0001-4966    

DOI:10.1121/1.3437974

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

A technique is presented for the direct measurement of the cross‐correlation function of two mechanical quantities—at least one of which is measured with a passive‐type transducer. The technique obtains measurements of the cross‐correlation function without the sophisticated instrumentation normally utilized. Except for a suitable time delay unit, the necessary instrumentation is found in even the most basically equipped research laboratory. The paper describes the theoretical basis for the technique and discusses data resulting from application to measurement of the cross‐correlation of the motion at two points on a slender beam. The beam is driven by sinusoidal and by bandlimited random excitation. Additional applications such as measurement of the cross‐correlation between a sound field and the motion of an interacting structure are presented.

ISSN:0001-4966    

DOI:10.1121/1.3437980

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.3437983

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP

摘要:

We have built, from off‐the‐shelf arithmetic modules, an electronic cross‐correlator which measuresR = p1p2¯/(p12p22¯)12as a function of the distance from point 1 to point 2. It is compact, accurate, and stable. To illustrate its use, we have made surveys along a horizontal diagonal of the NBS reverberation room. Pure tones, FM signals, and13‐octavebands of noise were used at frequencies (or center frequencies) in the range 125–2000 Hz. In some cases microphone No. 1 was fixed and No. 2 was moved, but in most cases the microphone separation was fixed at λ/2, for whichR= 0 in the case of a three‐dimensional diffuse field, and the array translated slowly along the diagonal. The second method appears to be the better.

ISSN:0001-4966    

DOI:10.1121/1.3437985

出版商:Acoustical Society of America    

年代:1974

数据来源: AIP