摘要:

For a circular plane piston of radiusa, producing an ultrasonic beam with propagation constantk(or 2π/λ), an expression is derived for the velocity potential or the acoustic pressure, averaged with respect to magnitude and phase over a “measurement circle” equal in area to the piston and centered in the beam. The expression should be highly accurate forka⩾ 100, at distanceszfrom the source governed by(z/a)3 ⩾ ka. It agrees well with results computed, in another way, by Huntington, Emslie, and Hughes. The assumption that relatively near the source there is a collimated beam of plane waves is shown to be not very accurate; the averaged pressure falls off monotonically over all distances considered. The velocity potential at the rim of the “measurement circle” is also computed, and compared with the plane wave assumption.

ISSN:0001-4966    

DOI:10.1121/1.1906722

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

An apparatus is described for measuring acoustic wave fronts in water at frequencies in the vicinity of 1 mc. The sound waves are radiated by a piezoelectric crystal and are picked up by a movable microphone. The voltage output from the microphone is compared in phase with the voltage feeding the piezoelectric source, by means of a phase discriminator. The signal at the microphone is due both to the transmitted acoustic wave and a stray electric signal. These two are combined in the microphone in such a way as to produce a full wavelength modulation in the resultant electric signal. A wave front in the sound wave is then traced by moving the microphone along such a line or surface as will cause the phase discriminator to indicate constant phase difference. A mathematical analysis of the problem is given and the method of measuring the shape of acoustic wave fronts in water is described. The apparatus and method which are described reduce the time required for measuring wave fronts to about one‐third that previously needed. Typical experimental results are given.

ISSN:0001-4966    

DOI:10.1121/1.1906733

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

A phenomenological theory of volume viscoelasticity formulated, resulting in an equation recently used by Hall. Application of this equation to the dispersion and absorption of sound in fluids is extended to the whole range of frequencies. Results of calculations of the volume viscosity and the instantaneous and relaxational compressibilities for gases and liquids from certain available absorption data are given. The bearing of this theory on the classical theory of hydrodynamics is pointed out.

ISSN:0001-4966    

DOI:10.1121/1.1906718

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

A technique is described which makes use of Bragg reflection of x‐rays to give a “picture” of the vibration pattern on the face of a crystalline plate. The dependence of this pattern on the direction of the x‐ray beam is illustrated, and a comparison between dust patterns and x‐ray patterns for a vibrating bar fairly well establishes that the local curvature of the crystal is responsible for the observed increase in x‐ray reflection. Reference is made to quantitative measurements on statically bent quartz and to an approximate theory treating the effect.

ISSN:0001-4966    

DOI:10.1121/1.1906720

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

With the knowledge now available concerning the mechanical properties of the cochlea, it is possible to understand how movements of the stapes footplate are transmitted to and along the cochlear partition. But we know little about the electrical constants inside the cochlea (the resistances and capacitances). It is difficult therefore to draw conclusions about how voltages at a given point are transmitted to other parts of the cochlea, for instance, how microphonic voltages are transmitted to the round window. This paper tries to show that for parts of the cochlea near the two windows the cochlear tube (consisting of the two scalae and the cochlear duct) can be considered electrically as a transmission line. The characteristic values of this transmission line are measured for different distances from the windows. In this way, a start has been made toward the development of a type of electroanatomy. The impedance values of the cochlear partition are important for determining the electrical energy losses in the cochlea.

ISSN:0001-4966    

DOI:10.1121/1.1906721

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

A vibrating electrode has been developed, with which the microphonics produced at a single point on the cochlear partition can be measured. With this electrode, which can be made to vibrate in any of three orthogonal directions, different places on the cochlear partition were investigated. The basilar membrane is more sensitive to displacement in the radial direction than in the direction perpendicular to its plane. The important question is whether microphonics are produced by a constant stationary displacement or whether they are produced only during the movement of the cochlear partition. With the aid of trapezoidal waves it was possible to show that in a fresh cochlear preparation only the static displacement produces the microphonic voltage. A single displacement of the basilar membrane produces astatic voltage lasting for several seconds. This fact has an important bearing on the energetics of the microphonics.Preliminary experiments suggest that the same technique may be used to investigate the inner parts of the cochlear partition.

ISSN:0001-4966    

DOI:10.1121/1.1906723

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

Ear wardens in form of ear plugs acting as acoustic low pass filters are described. They allow a part of speech frequencies to pass through into the ear and in this way improve the speech intelligibility in comparison with other ear plugs. Nevertheless their protective action against noise was proved to be sufficient.

ISSN:0001-4966    

DOI:10.1121/1.1906724

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

“Tone‐pips” were produced by brief rectangular electrical pulses being delivered through two sound‐effects filters in cascade with both high and low cut‐offs set at 2000 cps. Nearly all of the acoustic energy of the final signal was found to be concentrated in a band about an octave wide and centering at 2000 cps. The pulsing frequency was varied independently between 90 and 150 pips per second.Listeners describe the resulting sound as a “metallic buzz.” Listeners vary greatly in their ability to identify the two “pitches” present in this sound and in the accuracy with which they match with a pure tone either the pulsing frequency (about 130 per second) or the band‐pass frequency (2000 cps in the present series). Errors of exactly one octave are particularly common.In the theoretical discussion we argue that the “pitch” of a pure tone is a double attribute compounded of “buzz” (correlated with frequency of volleys of nerve impulses) and “body” (correlated with position of maximum stimulation on the basilar membrane).

ISSN:0001-4966    

DOI:10.1121/1.1906725

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The vowel sounds are produced by vibration of the vocal cords and are modified by the filtering effect of the resonant cavities. Thus, in the case of voiced speech sounds and of the sounds of singing, two factors play a part in the final shaping of the sound picture: the cord‐tones and the resonators. The present paper deals with the cord‐tones and with the peculiarities of vibration of the vocal cords.

ISSN:0001-4966    

DOI:10.1121/1.1906726

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The art of “voicing” an organ pipe, that is, treating it in order to produce a satisfactory musical tone, is highly developed, but on an entirely empirical foundation. Flue pipes only are dealt with here, chiefly the open diapason, an open metal cylindrical pipe. The several tone‐producing mechanisms in it are described, and some two dozen different variables, each of which can affect the tone, are described with reference to the stage in manufacture in which they occur. Some account is given of the interrelationship of the various adjustments. Finally mention is made of the place of any one pipe in the tonal structure of a complete organ.

ISSN:0001-4966    

DOI:10.1121/1.1906727

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP