摘要:

The authors previously reported that American shad (Alosa sapidissima) can detect sounds from 100 Hz to 180 kHz, with two regions of best sensitivity, one from 200 to 800 Hz and the other from 25 to 150 kHz [Mann et al., Nature389, 341 (1997)]. These results demonstrated ultrasonic hearing by shad, but thresholds at lower frequencies were potentially masked by background noise in the experimental room. In this study, the thresholds of the American shad in a quieter and smaller tank, as well as thresholds for detecting simulated echolocation sounds of bottlenosed dolphins was determined. Shad had lower thresholds for detection (from 0.2 to 0.8 kHz) in the quieter and smaller tank compared with the previous experiment, with low-frequency background noise but similar thresholds at ultrasonic frequencies. Shad were also able to detect echolocation clicks with a threshold of 171 dBre: 1 μPa peak to peak. If spherical spreading and an absorption coefficient of 0.02 dB/m of dolphin echolocation clicks are assumed, shad should be able to detect echolocatingTursiops truncatusat ranges up to 187 m. The authors propose that ultrasonic hearing evolved in shad in response to selection pressures from echolocating odontocete cetaceans.

ISSN:0001-4966    

DOI:10.1121/1.423255

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Bats, which echolocate using broadband calls, are believed to employ the passive acoustic filtering properties of the head and pinnae to provide spectral cues which encode 3-D target angle. Microchiropteran species whose calls consist of a single, constant frequency harmonic (i.e., some species in the familiesRhinolophidaeandHipposideridae) may create additional acoustic localization cues via vigorous pinna movements. In this work, two types of echolocation cues generated by moving a pair of receivers aboard a model sensor head are investigated. In the first case, it is supposed that a common 3-D echolocation principle employed by all bats is the creation of alternative viewing perspectives, and that constant frequency (CF) echolocators use pinnamovementrather thanmorphologyto alter the acoustic axes of their perceptual systems. Alternatively, it is possible rhinolophids and hipposiderids move their ears to create dynamic cues—in the form of frequency and amplitude modulations—which vary systematically with target elevation. Here the use of binaural and monaural timing cues derived from amplitude modulated echo envelopes are investigated. In this case, pinna mobility provides an echolocator with a mechanism for creating dramatic temporal cues for directional sensing which, unlike interaural timing differences, do not degrade with head size.

ISSN:0001-4966    

DOI:10.1121/1.423256

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The aim of this paper is to clarify the effect replicated sources in two-dimensional radiation problems. In fact, it will be shown that the discrete pressure computed by using the angular spectrum approach is equal to the analytical pressure plus error terms arising from the convolutions of replicated spectra of the original spectrum and the Green’s function. A similar result is obtained for the far-field discrete pressure. For the later case, it will be shown that errors can be eliminated by choosing a sampling step smaller to that given by the Nyquist criterion.

ISSN:0001-4966    

DOI:10.1121/1.423302

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Some comparisons of C. E. Bradley’s and W. L. Nyborg’s theories on acoustic streaming are given.

ISSN:0001-4966    

DOI:10.1121/1.423303

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

Experimental results for the absorption of ultrasonic waves in pure cyclohexanol and aqueous solution of cyclohexanol in the frequency range 0.06–150 MHz and at temperatures 30, 40, 50, and60 °Care reported. The ultrasonic relaxation spectra of pure cyclohexanol investigated show two relaxation processes in contrast to those aqueous solutions of cyclohexanol, which indicate a single relaxation process. One relaxation process is located in the frequency range 0.01–1 MHz and the second in the range 0.8–10 GHz. The process with the lower relaxation frequency has been assigned to the “chair”–“chair” molecular conformations.

ISSN:0001-4966    

DOI:10.1121/1.423244

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

The vibration of a membrane shaped like a simply connected figure eight is studied. The domain is simplified to a single circle region using the internal matching method. The results also include the circular membrane with one segment constrained.

ISSN:0001-4966    

DOI:10.1121/1.423304

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

A spontaneous otoacoustic emission spectrum may contain equally spaced emission peaks. Then, two peaks, at frequencies,f1andf2,respectively, apparently generate a distortion product atfd=2 f1−f2[or2 f2−f1].For the three emission peaks of nine of such triplets (in six emission spectra), the phasesφ1(t),φ2(t)andφd(t)were computed, respectively. The phase differenceΔφ(t)=φd−(2φ1−φ2)[orΔφ=φd−(2φ2−φ1)] tends to lock at a plateau valueφlock(modulo 2π), but occasional jumps up or downn×2πto a neighboring plateau. Apparently, the emission at position2 f1−f2[or2 f2−f1] synchronizes to the cubic distortion product generated by the primariesf1andf2,but occasionally slips out of the synchronized regime. This behavior is consistent with a model consisting of a self-sustained oscillator in the presence of weak noise, driven by a periodic force.

ISSN:0001-4966    

DOI:10.1121/1.423287

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

摘要:

An expression is derived which can be used to determine the extent of the near field for a given microphone array size and operating wavelength. This expression is based on the distortion of the near-field array response, and approximates the distance at which the magnitude response error due to plane-wave beamforming is 1 dB.

ISSN:0001-4966    

DOI:10.1121/1.423289

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.423281

出版商:Acoustical Society of America    

年代:1998

数据来源: AIP