摘要:

Thirteen normal‐hearing observers were exposed to 60 high‐intensity pulses presented at 4 different interpulse intervals: 1, 3, 9, and 30 sec. Temporary threshold shifts (TTS) were measured at frequencies from 500 to 13 000 cps. Results indicate that the TTS produced by 1‐, 3‐, and 9‐sec interpulse intervals are essentially equivalent. Considerably less TTS was produced by the 30‐sec interval during the first minute or two of recovery, but by 5 min after cessation of the pulses, this difference had nearly disappeared. This supports the hypothesis of Hirsh and Bilger that two separate fatigue or recovery processes are involved in TTS. It is concluded that total number of impulses is more important than exposure timeper sein predicting TTS (and so, presumably, permanent loss) from impulse noise.

ISSN:0001-4966    

DOI:10.1121/1.1918309

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

When an electro‐acoustic transducer is added to a circumaural ear defender the requirements of minimum sound transmission and maximum earphone sensitivity are partially incompatible. The transmission and response of simple (single cavity) and compound (two cavity) systems have been determined by an analog method. The preferred system is a rigid structure with resistive coupling between the two cavities. This system has maximum effective coupling volume at low frequencies thus providing maximum noise attenuation and a smaller effective volume at high frequencies affording increased earphone response. When the cavities contain suitable porous materials and are coupled by an annular slit, the two cavity system becomes a lossy waveguide. Analysis of hemispherical and plane wave acoustical models indicates an effective volume which is constant up to a transition frequency and decreases steadily with further increase in frequency. The theory is supported by measurements on an experimental earphone having complementary transducer and cavity characteristics leading to constant response over a wide‐frequency range. Probe microphone data show that above 1 kc the real ear response of circumaural earphones is generally greater than the flat‐plate coupler response.

ISSN:0001-4966    

DOI:10.1121/1.1918311

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

A unified analysis of ultrasonic delay lines is presented with particular attention paid to the characteristics of direct‐current pulse transmission. The analysis can be applied to any delay line, whether piezoelectric or magnetostrictive, regardless of whether the mode of transmission is longitudinal, shear, or torsional, as long as the motion is adequately described by the one‐dimensional theory on which the equivalent circuits are based.Characteristics in the time domain are obtained in terms of the time‐shift operators of Laplace transform calculus. This makes it possible to easily obtain the output waveform for any arbitrary input. Three transducer configurations are discussed; namely, a line with transducers in the middle of the delay medium (Case A), a line with one of the transducers at the free end of the delay medium (Case B) and a line with transducers at both free ends of the delay medium (Case C).The latter two configurations are especially useful for a delay line made of a ferrite or piezoelectric ceramic, both of which are available in limited length only due to manufacturing difficulties. Cascading of several pieces of material in order to obtain a longer delay than that which is available using a single piece is discussed. The effects of acoustic mismatching at bonding points on the signal‐to‐noise ratio and on the ringing in the output are presented.

ISSN:0001-4966    

DOI:10.1121/1.1918313

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The theory of acoustic propagation in porous media is extended to include anisotropy, viscoelasticity, and solid dissipation. A more refined analysis of the relative motion of the fluid in the pores is also developed by introducing the concept of viscodynamic operational tensor. The nature of this operator is analyzed by applying variational and Lagrangian methods. Viscoelasticity and solid dissipation are introduced by applying the correspondence principle as derived from thermodynamics in earlier work by the author. Various dissipative models are discussed and the corresponding operators and relaxation spectra are derived. The physical chemistry of the multiphase porous medium including surface effects lies within the scope of the thermodynamic theory. The nature of thermoelastic dissipation and electrokinetic effects in relation to the thermodynamic theory is also brought out.

ISSN:0001-4966    

DOI:10.1121/1.1918315

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The sound power radiated by acoustically slow waves scattered by a beam is computed. An acoustic radiation resistance per unit length of beam is computed based on the radiated power and the mean‐square transverse plate velocity in the absence of the beam. For a diffuse reverberant vibrational field and supported, clamped, or edge supported lines, explicit expressions for the radiation resistance are obtained. The reduction of radiation coupling due to beam vibration is also computed.

ISSN:0001-4966    

DOI:10.1121/1.1918317

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

When the errors in a previous paper are corrected and the method of attack is somewhat modified, a remarkably straightforward analysis yields an expression for the attenuation of repeated saw‐tooth waves. The expression is in substantial agreement with those obtained by other methods.

ISSN:0001-4966    

DOI:10.1121/1.1918319

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An analysis made of plane wave propagation in different directions of quartz with possible piezoelectric effects considered. A method of determining the zero‐field elastic moduli is described which should be suitable for measurements versus temperature and hydrostatic pressure. Values for elastic moduli obtained at 25°C are compared with the literature.

ISSN:0001-4966    

DOI:10.1121/1.1918321

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The precision of centering a noise signal in the head is improved by switching the earphone channels; either by communicating them, or by switching from a single channel for both ears to one channel for one ear and one for the other. Switching reduces both random errors and bias errors.

ISSN:0001-4966    

DOI:10.1121/1.1918323

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Forced choice between the tempered scale and one of the just scales in an atypical melody does not provide an adequate test of tuning preferences. Experiments by other methods indicate that small whole number ratios do operate in melody.

ISSN:0001-4966    

DOI:10.1121/1.1918325

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An ultrasonic microscope operating at 9 Mc and using phase contrast has been described which can detect a polyethylene strip112thousandths of an inch thick and 40 thousandths of an inch wide.

ISSN:0001-4966    

DOI:10.1121/1.1918329

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP