摘要:

Detection probability for 1‐kHz test tone‐bursts was estimated at 1‐sec intervals following exposure of subjects to a 1‐kHz continuous tone. Immediately after the exposure tone, detection probability is depressed. Recovery to preexposure probability is well fit by a single rising exponential function. These psychophysical data are compared with the recovery of discharge rate in single fibers of the cat's auditory nerve following similar exposures. For both sets of data the time constant of recovery decreases with increasing test tone‐burst level; the decrease is significantly faster for detection probability recovery than for recovery of discharge rate. This difference can be accounted for by a simple model relating discharge rate in ensembles of auditory‐nerve fibers to detection probability. Whereas the recovery time constant of discharge rate increases monotonically with exposure level, the recovery time constant of detection probability increases up to about 40 dB SPL and then decreases as exposure level is increased. We could not explain this difference on the basis of existing data.

ISSN:0001-4966    

DOI:10.1121/1.1914452

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

It is shown that both the Cremer‐Ising and Coltman mechanisms for sound production in organ pipes are comprehended by a more general approach, based on conservation of linear momentum. By calculating force per unit area exerted by the jet on a control volume containing the mixing region, and equating this to the difference in pressure along the pipe axis, it is possible to derive an expression for acoustic particle velocity in the standing wave as a function of the jet driving flow spectrum. The momentum model of the jet‐pipe interaction is able to explain the Coltman radiation symmetry effect, and also accounts for the role of entrained air in sound production. Additional spectral interaction terms, not previously noted, are found to play a significant role in the production of sound‐pressure fluctuations in the pipe. The fluctuating lift force at the edge is found to contribute to the sustenance of the pipe‐cavity oscillation below resonance, opposing it above resonance. In the near vicinity of the resonant frequency, edgetone effects are relatively small.

ISSN:0001-4966    

DOI:10.1121/1.1914453

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The effect of multiple barriers on the propagation of noise in urban and industrial environments is described by a cell model. The cell boundaries are formed by walls, machinery, etc., and each cell contains noise sources. The noise field both within and outside the souce region is discussed. A comparison with the results of previous investigations shows that the cell model correctly predicts the residual background level in traffic‐free zones in urban areas.

ISSN:0001-4966    

DOI:10.1121/1.1914454

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

A theory is developed which predicts the acoustic radiation of an axial‐flow fan stator due to interaction with rotor viscous wakes. Calculations are compared in detail with experimental data. Both the harmonic and broadband noise‐spectrum components are calculated from a unified model using methodology from the theories of random pulse amplitude modulation, PAM, and pulse position modulation, PPM. The stator is modeled as a circular array of pulsed dipoles. The amplitude and arrival time of each pulse are random variables whose means correspond to the values calculated from harmonic rotor‐stator interaction theory. The standard deviations of these random variables are measures of the turbulence levels in the blade wakes. For the model proposed the solution is exact: when PAM is imposed on a periodic stator source, new broadband energy is generated whose spectrum shape is similar to the envelope of harmonics at high frequencies and the harmonic radiation is unchanged; however, when PPM occurs, new broadband energy is radiated but at the expense of harmonic energy. At frequencies significantly above duct cutoff it is shown for a fixed stator solidity that the spectrum is essentially independent of the number of stator vanes.

ISSN:0001-4966    

DOI:10.1121/1.1914455

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

An investigation is made of the sound attenuation in a lined annular duct with flow. The eigenvalue equation in the presence of uniform flow is derived by matching the radial component of the particle displacement and acoustic pressure across a vortex sheet located an infinitely small distance from the facing sheet of an acoustic lining. The eigenvalue equation in the presence of shear flow is developed by matching the acoustic pressure and the radial component of the particle displacement at the interface between the regions of uniform flow and shear flow. Theoretical prediction of the sound‐attenuation spectrum is based on an acoustic‐energy flow in which the effect of the mean flow is taken into account. The results presented in this paper are limited to those which are typical for the geometry of an annular duct. Effects of mean flow Mach number, boundary‐layer refraction, and acoustic impedance on the sound attenuation for a given duct configuration are found to be similar to those in rectangular‐ and circular‐duct problems.

ISSN:0001-4966    

DOI:10.1121/1.1914456

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

This paper reports the results of an experimental and analytical investigation of a possible mechanism for exciting vibrations of the vocal cords. In order to test various approximations for describing the flow past the vocal cords and to demonstrate the importance of the upstream impedance in the excitation mechanism, the vocal cords are first represented by the simplest possible model, namely a simple vibrator of fixed shape. It is shown that if the pressures at the upstream and downstream ends of the channel formed by the vibrator wall are constant, the aerodynamic forces take energy from the vibrational motion. If, on the other hand, the output impedance of the system upstream of the channel is negative imaginary, vibrations of the channel walls can be excited. Experimental results agree with the predictions of the flow analysis for the simple vibrator. It is then argued that the respiratory system upstream of the larynx can be described as a tube 20 cm long in which the wave speed is reduced because of the distensibility of the bronchi, and which opens into the large reservoir of the lungs. Results of experiments in which the input impedance at the mouth was measured are consistent with this description. With this upstream impedance it is found that the simple vibrator would only be excited in a limited frequency range and would not allow many of the significant features of the vocal cord vibrations to be represented. Consequently a two‐degree‐of‐freedom model for the vocal cords is introduced. The flow analysis and impedance description are used in calculating the forces acting on the two‐mass model. It is predicted from the model that vibrations of the vocal vords are self excited over a range of frequencies. The properties of the self‐excited oscillations described by the model agree with the observed properties of the self‐excited vibrations in an experiment using a rubber membrane to represent the vocal cord, and are also consistent with several properties of the voice.

ISSN:0001-4966    

DOI:10.1121/1.1914457

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

High‐speed photography of the vibrating laryngeal structures was done on one female subject simultaneously with a direct recording of the vibratory air‐pressure variation in the trachea. The glottal dimensions and pressure data were obtained from this film using a semiautomated digital‐reduction technique. It was observed that the peaks of the subglottal‐pressure waves correspond with the dips in the glottal‐area waves, and also that the fundamental periodicity of the subglottal‐pressure wave represents the glottal‐area periodicity with good accuracy. Relations between the glottal‐area function and the glottal‐width function were considered. It is suggested that the glottal‐width function may be considered to be an approximate estimate of the glottal‐area function if the vibrating structure in the larynx is unaffected by pathology.

ISSN:0001-4966    

DOI:10.1121/1.1914458

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

TheB‐scan technique, which is used in ultrasonic medical diagnosis and in materials testing, suffers from a low lateral resolution because of the large diameter of the ultrasound beam. The present paper describes a beamforming device which focuses the beam over a large depth, i.e., the well‐known depth of focus problem is circumvented. An experimental device is described which gives a lateral resolution of 2 to 3 mm at a frequency of 2 MHz (λ = 0.75 mm in water).

ISSN:0001-4966    

DOI:10.1121/1.1914459

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

The elements of a symmetrical matrix for the eigenvalue problem for vibrational relaxation times in a mixture ofntwo‐state gases are given. These elements depend upon the reaction rates for the various transitions and upon the mole fractions of the gases. Calculations for the three‐gas mixtureO2/H2O/D2Oare compared with experimental results for these mixtures. The large effect of a 50%D2O/H2Oimpurity on the relaxation time ofO2is attributed to a three‐step energy‐exchange chain: the near‐resonantV Vtransfer of vibrational energy fromO2toH2O, then a rapid exchange of vibration betweenH2OandD2O, followed by the de‐excitation ofD2ObyO2, which is an order of magnitude faster than the de‐excitation ofH2ObyO2.

ISSN:0001-4966    

DOI:10.1121/1.1914460

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP

摘要:

It is shown that a single light intensity measurement does not allow the determination of the sign of the ratio of strain‐optical constants determined ultrasonically. However, if an experiment is performed in which the ratios are overdetermined, it is possible to determine the signs by applying the criterion that the results of the various measurements must be consistent. The equations which must be satisfied for the criterion of consistency are obtained for nine of the 32 crystal classes. The application of the technique is presented with numerical values for the case of NaCl.

ISSN:0001-4966    

DOI:10.1121/1.1914461

出版商:Acoustical Society of America    

年代:1973

数据来源: AIP