摘要:

Whereas some evidence indicates that spontaneous otoacoustic emissions (SOAEs) may be a manifestation of the normal functioning of an active feedback mechanism in the cochlea, other evidence suggests that emissions may be the result of the interaction of such a feedback mechanism with localized outer‐hair‐cell damage. The present study surveyed the incidence of SOAEs in children and infants. If SOAEs are correlated with outer‐hair‐cell damage, the incidence of SOAEs might be expected to be lower in these two groups than in adults. The results showed no difference in the incidence of SOAEs with age. They also showed a significant tendency for a higher incidence of SOAEs in females than in males. PACS numbers: 43.63.Kz, 43.63.La

ISSN:0001-4966    

DOI:10.1121/1.392924

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

This paper presents the results of a simulation experiment to determine the effect of improper normalization on the performance of an automated energy detector. The normalization algorithms investigated are the two‐pass mean, the split two‐pass mean, the split three‐pass mean, the split average exclude average, and the order truncate average normalizers.

ISSN:0001-4966    

DOI:10.1121/1.392925

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The effect of sound‐absorptive facings on the airborne‐sound transmission of panels is discussed. The response of a simple model, consisting of an infinite elastic plate with an attached sound‐absorptive facing, to acoustical excitation is calculated. Numerical calculations of the transmission loss, carried out for typical examples, show the influence of the main parameters involved.

ISSN:0001-4966    

DOI:10.1121/1.392926

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

An extensive series of sound absorption measurements were taken in air over a range of frequencies from 10–2500 Hz, of temperature from 10°–50 °C, and of relative humidity from 0.3%–92%, all at a pressure of 1 atm. The N2and O2vibrational absorption components were extracted from a relatively large background absorption by means of a differential technique using a background gas, 89.5% N2–10.5% Ar, which matches the sound speed of air but has no molecular absorption over the range of experimental frequencies. The measurements reveal: (1) The humidity dependence of the relaxation frequency of N2in air exceeds that in binary N2–H2O mixtures, possibly because the vibrational modes of CO2provide a competing relaxation path for V–V exchange between N2and H2O molecules; (2) the temperature dependence of the relaxation frequency of humid N2is nearly the same in air as in binary mixtures; and (3) at very low humidities the relaxation frequency of O2appears to approach a limiting value much lower than that determined from a prior study. The present experimental results, together with those of an earlier study at high frequencies, provide a substantial data base leading to revised formulas for standard values of the relaxation frequencies of N2and O2.

ISSN:0001-4966    

DOI:10.1121/1.392927

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

A method of steepest‐descents integration suitable for use when a pole may approach near to one of the saddle points in the complex plane of integration is applied to the problem of predicting the field resulting from a point source near to the interface between two semi‐infinite media. It has been shown that it is possible to obtain asymptotic approximations for the field above or below the interface to any desired degree of accuracy in a way that is more straightforward and less algebraically cumbersome than that which is employed when using the subtraction of the pole technique. Approximation for the case where the receiving medium has a high refractive index produces the expected result whereby the field below the interface is related to that incident on the interface according to Snell’s law. Measurements are made of the phase and amplitude of the sound field below the surface of a 0.5‐m‐thick layer of glass fiber material, relative to those of the field at the surface due to the point source close to the surface. Experiments are reported using continuous, swept‐tone burst and spark‐discharge sources. The measured data are compared with theoretical predictions. The predictions require knowledge of the complex propagation constant within the material. Use of an empirical formula together with measured flow resistivity is found to produce overestimates of attenuation, whereas use of a theory for propagation in a rigid porous medium based upon a classical capillary‐pore approach is found to enable tolerable agreement with measured data. This confirms directly the locally reacting nature of the boundary over the frequency range of the measurement.

ISSN:0001-4966    

DOI:10.1121/1.392928

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

A theory for the amplification of surface skimmingSHwaves, commonly known as surface skimming bulk waves (SSBW), in 90°‐propagating, rotated Y‐cut quartz is presented. In particular, the structure proposed utilizes a thin, continuous, isotropic dielectric film instead of an air gap as the medium separating the piezoelectric substrate and semiconductor. The effective permittivity function at the crystal surface, which contains all the necessary mechanical and electrical information about the structure, is derived to analyze the amplification coefficient. The results show that the amplification coefficient increases with film thickness. This is in contrast to the air gap separate piezoelectric/semiconductor configuration where the amplification coefficient decreases with increasing gap size. As a result, acoustoelectric devices, having the advantages of higher operational frequencies and better temperature stability characteristics of SSBW devices, might be realized.

ISSN:0001-4966    

DOI:10.1121/1.392929

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Measurements are presented that can be used to test theories that predict acoustical characteristics of outdoor surfaces. The specific acoustic impedances of forest soils, grass‐covered surfaces, and bare sandy soils have been measuredinsituusing an inclined track method. Best‐fit effective flow resistivities have also been deduced from the acoustical measurements. For grass‐covered and forest soils the soil stratification has been determined and measurements have been carried out to determine the acoustical significance of the different layers. Physical soil parameters have also been measured, including porosity; water, air, and solid matter content; soil texture; and directly measured air flow resistivity. It is found possible to classify investigated soils as acoustically soft, moderate, or hard, both according to the behavior of the reflection coefficient and impedance with frequency and to the corresponding best‐fit values of effective flow resistivities. Bare sandy soils are found to be acoustically hard surfaces. Forest soils may be classified, in most cases, as acoustically soft. For grass‐covered and forest soils, the real part of the acoustic impedance is relatively independent of frequency, while the imaginary part strongly decreases with frequency. Litter layers do not influence acoustical soil properties. The important role for humus and root layers that has been suggested is not always confirmed by air flow resistivity measurements reported in this paper. A classification of soils based on measured air flow resistivity is possible but is only roughly in agreement with the acoustical classification. Predictions of acoustic impedances, based on the equations of Delany and Bazley [Appl. Acoust.3, 106–116 (1970)] and on directly measured flow resistivities, are not always satisfactory. The predictions are particularly poor for forest floors.

ISSN:0001-4966    

DOI:10.1121/1.392930

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Underwater ambient noise is known to be wind dependent. Several mechanisms have been proposed to explain the nature of the transfer of energy from the wind to the acoustic noise field. Examples include wind and wave turbulence and nonlinear interactions between surface waves. This study examines these wind‐related mechanisms at the low end of the acoustic spectrum. Data from a long‐term investigation of ocean waves and the associated microseism response recorded ashore have provided evidence helpful in identifying the active processes. It is concluded that the noise field below 5 Hz is controlled by nonlinear wave–wave interactions and that existing theories account adequately for the effects observed.

ISSN:0001-4966    

DOI:10.1121/1.392931

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

Kochetal.’s [J. Acoust Soc. Am.73, 1567–1570 (1983)] formulation of the impedance boundary condition normal mode identification algorithm is used to develop the relationship between the normal mode and geometric ray quantities for low frequency, where previous analyses, employing WKB or other high‐frequency approximations, may not be valid. The result shows that mode normalization is not uniquely relatedapriorito a mathematically meaningful horizontal wavenumber derivative of mode number. Instead, some auxiliary conditions must be invoked to uniquely define cycle distance as a single mode quantity (as opposed to the range periodicity of interference between two modes) given by a mode number derivative and corresponding in appropriate limits to the geometric ray cycle distance. A suggestion for constructing from this result an optimal eigenvalue predictor for numerical eigenmode calculations is discussed.

ISSN:0001-4966    

DOI:10.1121/1.392932

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP

摘要:

The dispersion analysis of explosive signals and measurements of individual mode attenuation in the Yellow Sea is reported. By adjusting input parameters of a normal mode computer program and making the calculated results coincide with field data, the compressional wave velocity and attenuation in the sediment for the frequency range of 80–800 Hz is simultaneously deduced. The sea‐bottom velocity, attenuation, and its frequency dependence, probed from two sea areas with a different depth and sound velocity profile in the summer and the winter, are very close. Resultant sea‐bottom attenuation approaches the results of earlier workers at the upper end of the frequency band and joins with the data obtained by others at the lower end, and the absorption appears to have a nonlinear frequency dependence (α=0.37f1.84dB/m kHz). The errors due to the change of environmental parameters (such as water depth, water sound velocity profile, sediment density, and seafloor roughness) are discussed.

ISSN:0001-4966    

DOI:10.1121/1.393016

出版商:Acoustical Society of America    

年代:1985

数据来源: AIP