摘要:

Average tuning curves of single auditory‐nerve fibers are compared with average cochlear‐microphonic (CM) tuning curves corrected for electrical filtering of the cochlea. Both the neural and CM data were obtained from Mongolian gerbils (Merionesunguiculatus) with the same acoustic system and similar corrections for middle‐ear effects. Under these conditions the CM tuning in the second and third cochlear turns in similar to the tuning of fibers whose characteristic frequencies (CFs) correspond to the CM best frequencies (2.5 and 0.5 kHz). Thus, little sharpening seems to take place for low CF fibers. CM tuning at the most apical electrode position is sharper than expected for frequencies below the best frequency—a result that may be due to the shunting effect of the helicotrema at low frequencies. Previous modeling results have confirmed that apical basilar‐membrane tuning may be appreciably affected by the mechanical impedance of the helicotrema. This helicotrema effect may account for the nearly symmetrical shapes of neural tuning curves of low‐CF fibers.

ISSN:0001-4966    

DOI:10.1121/1.382000

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The acoustical properties of the large anechoic chamber at the National Bureau of Standards were investigated by two methods over the frequency range 40–63 000 Hz. In the first method described, deviations of mean‐square sound pressure from an assumed inverse square law were measured as a sound source and microphone were moved apart. Over most of the frequency range, the deviations were found from a least‐squares curve‐fitting procedure by means of digital‐computer processing of the data. The effective acoustic centers of the sources were obtained as a by‐product of the procedure. In the second method, the source and microphone were kept at a fixed separation as they were moved together across the chamber, and deviations from the mean value of the sound pressure level were estimated from recordings. The significances of the two methods are discussed with a view towards their application.

ISSN:0001-4966    

DOI:10.1121/1.382001

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The sound field generated by an omnidirectional point source in an infinitely long, straight street is considered. The field is assumed to be the sum of a multiply‐specularly reflected field and a diffuse field that is fed from scattering at the walls at each reflection of the specular field. It is shown that scattering is important close to the source. The sound level depends on the width of the street and the height of the walls and on the reflection and scattering coefficients of the walls.

ISSN:0001-4966    

DOI:10.1121/1.382002

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A simple procedure, based on Love’s approximate theory [TheMathematicalTheoryofElasticity(Cambridge U. P., Cambridge, England, 1927), 4th ed.] for wave propagation in a bar, is proposed in order to consider dispersive effects in wave propagation in a thin‐walled, fluid‐filled, elastomer tube. It is assumed that the perturbation from steady flow in the tube is small enough that a linearized theory is valid, and that the elastic modulus of the tube is small compared with the bulk modulus of the fluid so that compressibility of the fluid can be neglected. The flexural rigidity of the tube wall, the inertia of the tube wall, and the radial inertia of the fluid are taken into account, and an approximate expression for the dispersion relation for the fundamental mode is obtained. In order to investigate the dispersive effects, resulting from inclusion of the inertia and flexural rigidity of the tube wall and the radial inertia of the fluid in the model, an initial value problem is considered in detail. The fast Fourier transform is used to obtain numerical solutions for small and intermediate times. Numerical results are presented in graphical form.

ISSN:0001-4966    

DOI:10.1121/1.382003

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

The effective ultrasonic Grüneisen parameter obtained from room temperature measurements of the attenuation in 12 cubic crystals is compared with calculations for the anisotropic elastic continuum model in terms of second‐ and third‐order elastic constants. The agreement between the calculated values and those derived from the ultrasonic attenuation is in most cases within a factor of 2 provided local equilibrium effects are included in the expression for the attenuation coefficient. The model accounts in general for the anisotropy and polarization dependence of the attenuation and can be used to estimate the magnitude of the sound absorption by acoustic thermal phonons from known elastic and thermal properties. Ultrasonic Grüneisen parameters are smallest for shear waves polarized along<001≳. Crystals with the NaCl structure show a larger and more anisotropic mean anharmonicity than covalent crystals and alkaline earth fluorides.

ISSN:0001-4966    

DOI:10.1121/1.382004

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

In an earlier article [J. Acoust. Soc. Am. 63, 353–365 (1978)], the authors presented a statistical theory of acoustic propagation in a canonical‐model random ocean, valid in the limit of low acoustic frequency. Here, numerical predictions of the theory are evaluated and compared to the results of a large‐scale Monte Carlo computer simulation. At each of the acoustic frequencies 50, 100, 200, 500, and 1000 Hz, 100 independent realizations of the random acoustic model are obtained. Sample statistical moments indicate that, at least up to 200 Hz, the theoretical predictions are quite accurate. For 500 Hz and above the theory breaks down, as expected for sufficiently high acoustic frequency.

ISSN:0001-4966    

DOI:10.1121/1.382005

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

This paper considers characteristics of plane‐wave reflection loss for a model of the ocean’s sub‐bottom consisting of a single inhomogeneous fluid layer (sediment) overlying a semi‐infinite solid (basement). It is found by direct computation that, under certain conditions of sediment sound speed gradient, density, and compressional‐wave speed ratios and attenuations, a large peak in bottom loss can occur over a narrow range of grazing angles. These angles occur below the shear and compressional wave critical angles; hence, they are not directly related to transport of energy by these wave fields. It is found, however, that the presence of shear waves in the substrate is necessary for such a peak to occur; that is, if the shear‐wave speed is set to zero in the substrate, the anomalous loss peak vanishes. Furthermore, these loss peaks are due to absorption rather than the transport of energy to infinity as evidence by the fact that, when all absorptions vanish, so do the anomalous peaks in bottom loss. The decay of pressure amplitude away from the sediment–substrate interface in both directions (for grazing angles in the neighborhood of the loss peak angles) suggests the presence of a surface or interface wave.

ISSN:0001-4966    

DOI:10.1121/1.382006

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Reverberation structure has been observed from research platform FLIP with a narrowbeam, high‐resolution 87.5‐kHz echo sounder. The system resolution indicates that the backscattering can be resolved as discrete targets. Targets strengths and scatterer densities suggest that the scatterers are probably fish and possibly squid and siphonophores. Although zooplankton may be observed acoustically if there are sufficient animal densities, they will not be the dominant scatterers below the mixed layer for small insonified volumes. A midnight migration was observed that corresponded with the passage of rain squalls.

ISSN:0001-4966    

DOI:10.1121/1.382007

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

Experiments were performed in a shallow two‐dimensional water tank to determine the effects of diameter, spacing, and material properties on acoustic scattering by rows of cylindrical obstacles. Cylinder diameters ranged from 0.17 to 0.39 times the wavelength, and center‐to‐center spacings up to 1.2 wavelengths were investigated. In the limit of small spacings, multiple scattering was found to be characteristically similar to sound wave transmission through walls. Analysis of the experimental data indicated that the acoustic properties and microstructure of the scatterers could be distinguished by the transmissivity response of the arrays.

ISSN:0001-4966    

DOI:10.1121/1.382008

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP

摘要:

A new model of swimbladder‐bearing fish has been developed in order to provide improved predictions of the resonance frequency and acoustic cross section of such a fish. The model consists of a small spherical shell in water, enclosing an air cavity which supports a surface tension. The shell is a viscous, heat‐conducting Newtonian fluid, with the physical properties of fish flesh. A comparison of the results obtained with the new model to experimental data indicates that the new model constitutes a definite improvement over previous models. The new model can predict the high values of damping and elevated resonance frequencies that previous models could not. The model appears to be most accurate for fish in which tension in the swimbladder wall has a minor effect on resonant scattering. This includes the fish which are of interest in studies of volume reverberation, and the new model should therefore be of considerable value in such studies.

ISSN:0001-4966    

DOI:10.1121/1.382009

出版商:Acoustical Society of America    

年代:1978

数据来源: AIP