摘要:

A short periodically repeated train of torsional waves is transmitted along a glass or metal cylindrical rod. After reflection from the free end, these waves are sent back to the quartz crystal which serves as both transmitter and receiver. The phase shift and added attenuation caused by immersing the rod in the test liquid are measured by means of a special balancing arrangement, and yield a calculation of the impedance presented to the rod surface.From an analysis of wave propagation both in the rod and in the liquid, one can calculate the characteristic shear impedance of the liquid, and the dynamic viscosity and stiffness.Data for polyisobutylene liquids with static viscosities up to 2000 poises are given for the frequency range 25–150 kc. High frequency data (5–25 mc) for the same liquids obtained by a method previously reported on (see reference 10(b)) are correlated to the present work. Some results for polypropylene, polyisoprene, polybutadiene, and polypropylene sebacate are also given.

ISSN:0001-4966    

DOI:10.1121/1.1906904

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The theory of scattering of plane waves of sound is extended to scatterers in the form of thin elastic shells of cylindrical and spherical shape. As for all elastic scatterers, the scattering action is the resultant of: (1) “rigid body scattering,” i.e., the scattering which would be present if the scatterer were rigid and immovable; (2) “radiation scattering,” which represents the sound radiation from the shell undergoing forced vibrations under the influence of the incident wave pressure, and which is determined by the dynamic characteristics of the submerged shell. Contrary to solid scatterers, whose dynamic characteristics are little different in vacuum and in the fluid medium, the characteristics of shells are profoundly altered by fluid reaction. When the shell is excited near resonance, the scattering pattern resembles the dynamic response of the shell in that it is highly frequency sensitive.The mathematical analysis proceeds by correlating the general solution of the wave equation in the fluid medium with the Lagrange equations of the elastic shell; the correlation is obtained by applying one boundary condition and by expressing the energy exchange between the two media in terms of generalized forces. This method should be applicable whenever (1) the solution of the wave equation is known in the appropriate coordinate system; (2) the equations of motion of the elastic scatterer freely vibrating in vacuum can be derived and solved.

ISSN:0001-4966    

DOI:10.1121/1.1906905

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The explanation of the acoustical action of multiple Helmholtz resonators, except for one and two cavities, has not been developed. Application of Lagrange's method is made to obtain the equations of motion of the fluid displacements. The equation for the frequencies of resonance is obtained by placing the determinant of the coefficients of the displacements equal to zero. The calculations yield a number of resonances equal to the number of cavities in the system. These are found to be in agreement with the experimental results. This physical method of approach, rather than synthetic electrical circuit theory, affords, among other applications, a more direct and more informative method for explaining the resonances of the vocal tract.

ISSN:0001-4966    

DOI:10.1121/1.1906906

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

In order to obtain some further measure of the acoustic properties of a rectangular room, a brief subjective study is made of listener response to sounds having various degrees of modulation on their decay curves and to alternate sounds which differ only in the phase relation of a harmonic in the source with respect to the fundamental frequency. The data show that the average listener finds the decay of sounds pleasant in inverse proportion to the amount of modulation on the decay curves, and that a large majority of listeners cannot distinguish between two steady‐state sounds, alike except that in one sound the phase of a harmonic is changed with respect to that of the fundamental frequency. Also, an objective study is made of the modulation on decay curves. A switching device is used to insure a smooth cutoff at any predetermined phase of the fundamental frequency. The data show that, if the source includes the fundamental frequency and a harmonic at equal amplitudes, the modulation of the decay curve consists of two superposed modulations. The phase relations and amplitudes of these modulations are dependent on the phase relations and amplitudes of the driving frequencies which produce them.

ISSN:0001-4966    

DOI:10.1121/1.1906907

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Two piezoelectric accelerometers have been calibrated by an absolute reciprocity technique in the frequency range from 100 cps to 10 kc. A theoretical and experimental evaluation of the technique is given.

ISSN:0001-4966    

DOI:10.1121/1.1906908

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

Measurements were made of the first‐probability distribution and of various conditional probability distributions of the speech wave instantaneous amplitude. Results obtained for several speakers indicate that the first‐probability distribution varies exponentially with large values of amplitude and that increases in the conditional probabilities are noted for delay times of the order of magnitude of the pitch period.Measurements were also made of the first‐probability distribution of the duration of the speech‐wave zero‐crossing periods, and of the auto‐correlation function of clipped speech.These measurements were of the stationary, or “long‐time,” speech‐wave probability distributions. Most of the results are for speech waves recorded in an anechoic chamber. Some results are included for voices recorded in a live studio.

ISSN:0001-4966    

DOI:10.1121/1.1906909

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

An apparatus was developed that made it possible to push an electrode automatically with an absolutely even and smooth velocity through the cochlear partition of an anesthetized guinea pig. The ac and dc potentials of this perforating electrode were recorded during the perforation when sound was applied to the eardrum, or when an electrical generator was connected to the vestibular and tympanic channels of the cochlea. These measurements enable us to show that the endolymph is surrounded by an electrically insulating layer, and that the inner part of the organ of Corti is protected from external electrical potential fields. Further, it was shown that the microphonics produced by a vibration of the eardrum have larger values inside the endolymph than in the perilymph or near the round window. The microphonics seem to reach a maximum near the organ of Corti.The perforation measurements also made it possible to discriminate three types of tissues in the cochlea: (1) highly sensitive cells with large microphonics and dc potentials; (2) cells that do not produce large microphonics but still have in them large dc potentials; and (3) tissues that are electrically indifferent and can be represented by an electrical resistance. These distinctions and the measurement of the electrical conductivity of the endolymph permit a coarse description of the electro‐anatomy of the cochlear partition.

ISSN:0001-4966    

DOI:10.1121/1.1906910

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

The impedance of the human mastoid was determined by means of a vibrating piston, one end of which was placed in firm contact with the body surface. The impedances of several subjects were measured. The compliancecand the resistancerwere calculated from the results; the average values werec = 1.5×10−8 cm/dyneandr = 1.0×104 dyne/cm/sec, for an area of the piston base of 1 cm2and an application force of 250 g. It is shown how the impedance depends on the area and the application force of the piston. A critical review of the literature on the subject is given.

ISSN:0001-4966    

DOI:10.1121/1.1906911

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

摘要:

A viscous mechanism for the absorption of ultrasonic energy in tissue is considered. It is shown that the viscous forces acting between a suitably chosen distribution of suspended particles or structure elements and a suspending liquid can account for the experimentally observed linear relations between acoustic absorption coefficient and ultrasonic frequency. The frequency band over which linearity obtains is determined by the limits of the distribution of values for the parameters which describe the structure elements. Below the linear range the relation becomes quadratic, in agreement with experiment, and at “high” frequencies a limiting value is approached asymptotically.

ISSN:0001-4966    

DOI:10.1121/1.1906912

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906913

出版商:Acoustical Society of America    

年代:1952

数据来源: AIP