摘要:

The acoustic properties of a deep scattering layer located north of Bermuda were examined over the frequency range from 0.4 to 6.4 kc/sec. Octave‐band scattering strengths were measured in the two octaves from 1.6 to 6.4 kc/sec. A broad peak in scattering strength was observed whose center frequency decreased over the sunset period from an average daytime value of 5.4 kc/sec to an average nighttime value of 4.8 kc/sec. The variations in measured scattering strengths, resonant frequencies of scattering‐strength peaks, and layer depths were consistent with those expected from a migrating layer of scatterers possessing swim bladders of constant volume.

ISSN:0001-4966    

DOI:10.1121/1.1918928

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Guidelines for selecting adequate test distances for sensitivity measurements involving two piston transducers are derived and discussed in terms of the transducer dimensions and the wavelength. Applicable correction factors are computed for use in either a reciprocity or a comparison calibration when short distances are necessary. Experimental data obtained at frequencies in the megacycle‐per‐second range are shown to support the validity of the analysis and the computations.

ISSN:0001-4966    

DOI:10.1121/1.1918929

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The interaction radiation resistance for a line array of two and three hairpin‐type, nickel, magnetostrictive‐stack transducers at an air‐water surface was measured. The transducers are resonant near 20 kc/sec and have square radiating faces whose sides are 0.38 of the wavelength of sound in water. The interaction, radiation resistance was studied as a function of number, separation, driving force, and phase of the interacting transducers. The circuit used to measure the radiation resistance is discussed, and the graphs of the interaction radiation resistance with transducer separation for several conditions are presented. It is shown that it is possible to have a transducer behave as a sink if the nearby transducers are different enough in driving force and phase.

ISSN:0001-4966    

DOI:10.1121/1.1918930

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Physical arguments are followed by mathematical developments to show how aerodynamic sound is generated as a result of the movement of vortices, or of vorticity, in an unsteady fluid flow. Changes in circulation or area of a vortex ring give rise to a dipole sound field, the former being illustrated by oscillating flow about a fixed sphere, and the latter by a simple model for the aeolian tone attributable to the stretching of vortex rings. Because in a free flow there can be no change of the total vortex strength (circulation times area), there is no net dipole strength, but each moving element of vorticity still causes local dipolelike flow; each element of moving vorticity acts with some equal and opposite movement elsewhere in the flow so that together they form an oblique quadrupole, although the total effect must be reducible to an assembly of lateral quadrupoles. A cardinal result is that the vorticity in a slightly compressible fluid can be considered to induce the whole flow field, both the hydrodynamic part and the acoustic part. With vorticity taken as the common basis, a slightly compressible flow is compared to the corresponding incompressible one, which may be used in the evaluation of the sound‐radiation formula. The theory is particularly well‐structured to estimate sound from flows described in terms of vorticity: the sound field is determined for two rectilinear vortices spinning about an axis between them, and its basis for similarity methods is demonstrated in application to free shear flow and jet flow.

ISSN:0001-4966    

DOI:10.1121/1.1918931

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Single units in the accessory nucleus of anesthetized cats, isolated with tungsten microelectrodes, show a delicate sensitivity to interaural time and intensity differences. A click delivered to one ear produces a response that may be inhibited by a click presented with some time difference to the opposite ear. When a response occasionally does occur during such inhibition, its latency is increased significantly. Both the amount of this shift and the occurrence of inhibition are dependent upon the interaural time difference. In one well‐studied instance, when the interaural time difference was too large to produce inhibition, an increase in the intensity of the driving click produced effective inhibitory interaction. Monaural unit responses show such variations in latency to a click stimulus that, whenever the effects of time and intensity disparities are under investigation, time measurements should be made fromN1of each cochlea.

ISSN:0001-4966    

DOI:10.1121/1.1918932

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

This paper deals with the normal modes of vibration of a stiff piano string. The equations that govern the vibration of a solid string are developed along traditional lines. They are modified to apply to strings having a solid‐steel core upon which are wrapped one or two copper windings. The bass strings of most pianos are made this way. Two boundary conditions are considered: namely, (1) pinned by sharp knife edges at both ends and (2) clamped at both ends. Formulas for the partial frequencies for both of these conditions are developed. The partial frequencies that are calculated by these formulas are compared to the experimental values obtained on an upright Hamilton piano. The experimental values appear to agree somewhat better with the pinned boundary condition rather than the clamped boundary condition, although the differences are not much greater than the observational error. It was found that the formulafn = nf1[(1 plus; Bn2)/(1 + B)]12gives values of the partial frequencies that agree with the experimental ones wherenis the number of the partial,fthe fundamental frequency, andBa constant that can be calculated from the dimensions of the wire.

ISSN:0001-4966    

DOI:10.1121/1.1918933

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1918934

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

It is shown that one can find the radiation reactance if the radiation resistance is known at all frequencies, and vice versa.

ISSN:0001-4966    

DOI:10.1121/1.1918936

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

It is shown that for an arbitrary‐shape rigid piston in an infinite planar baffle, on which the boundary condition is (pressure) = (normal velocity) × (acoustic impedance of baffle), the radiation impedance of the piston, the baffle impedance, and the pressure amplitude in the far field, normal to the piston, are simply related.

ISSN:0001-4966    

DOI:10.1121/1.1918937

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

In a recent paper, Marin and Kroeger presented some test data comparing the responses of simple cantilever beams under an acoustical‐pressure field and under mechanically induced vibratory motions. This discussion offers some additional analyses intended to fulfill the objectives sought by the aforementioned authors. It is observed that proper correlations are indeed obtainable.

ISSN:0001-4966    

DOI:10.1121/1.1918938

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP