摘要:

Phase comparison at high ultrasonic frequencies is found to be particularly suited to velocity of propagation measurements (and hence measurement of elastic constants) for small solid specimens such as single crystals. Both longitudinal and transverse waves may be used, with accurate results possible even when the specimen loss becomes high.A pulse technique is used which allows exact determination of the number of wave‐lengths in the acoustic path, and a direct measurement of phase shift at reflecting interfaces. The use of λ/4 plastic coupling seals to minimize errors is explained; necessary theoretical analysis is included.Illustrative data for fused silica and single crystal germanium are given.

ISSN:0001-4966    

DOI:10.1121/1.1906618

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

An approximate theoretical treatment of the output from the simplest type of ultrasonic generator in the form of a laminated bar is first developed. The dumbbell generator is shown to be very similar to the simple bar type and the previously obtained relations are then employed for determining the relative output in terms of its face and neck dimensions.

ISSN:0001-4966    

DOI:10.1121/1.1906619

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The acoustic absorption of sand and soil with varying amounts of water (dry to saturated) has been investigated the 10‐ to 100‐kc range. Two methods were used. In one, the source and a number of equally spaced probe microphones were imbedded in the medium. In the other method the source and receiver were in air and the transmission loss was obtained for samples of varying thickness. The unsaturated media were found to have attenuation coefficients ranging from 2 db/cm for nodulous, loose soils to greater than 25 db/cm for finely divided soils and sand, the value for any particular sample depending in an important way on its flow resistance. In water‐saturated media the attenuation was found to depend markedly on the amount of gas present in the mixture. Air‐free mixtures prepared in an evacuated chamber had attenuation coefficients which were too small to be measurable—probably less than 2 db/cm. On the other hand, for mixtures prepared in the presence of air the attenuation coefficient immediately after mixing were extremely large. For one sample it ranged from 26 db/cm at 10 kc to 64 db/cm at 30 kc. When a source and microphone, separated by a distance of one centimeter, were immersed in such a freshly stirred mixture and then left undisturbed, the intensity level increased in time—as much as 50 db at 30 kc over a period of 100 hr.

ISSN:0001-4966    

DOI:10.1121/1.1906620

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The scattering of sound from a spherical fluid obstacle of size comparable to a wave‐length is considered, neglecting dissipation. Calculations of the acoustic pressure and the total energy in the scattered wave are presented graphically; sound velocities and densities of the sphere lie between 0.5 and 2.0 times that of the external medium. The limiting cases of Rayleigh scattering and scattering from a fixed rigid sphere are also shown for comparison. In the region where the diameter of the sphere is comparable to a wave‐length, the scattering is a complicated function of frequency, showing in some cases large maxima and minima. The amplitude of the scattered wave in the backward direction from a fluid sphere a few wave‐lengths in diameter exceeds twice that from a rigid sphere of the same size for the case of the sound velocity 0.8 and density equal to that of the surrounding medium.

ISSN:0001-4966    

DOI:10.1121/1.1906621

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A method for the calculation of viscous losses in acoustic wave guides and cavities is described, similar to that used by Carson, Mead, and Schelkunoff for electromagnetic waves. The loss in a plane wave in a round tube is discussed and the results agree with those previously obtained by others. The attenuation for two higher modes in hard wall guides is computed, as well as the decay constants for a cylindrical cavity for longitudinal and pure radial modes.

ISSN:0001-4966    

DOI:10.1121/1.1906622

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The flexural vibrations of a ring in its plane are studied by taking shear effect into account, and it is proposed to compute the deviation from the classical frequency formula, which is only valid for very small ratios of the thickness to the diameter. In a second chapter the possibility of extension is included, and in this procedure the frequencies of extensional vibrations are obtained as a by‐product.It is seen that the shear effect plays a predominant role in the deviation from the classical formula, and is more important than curvature effects and the rotational inertia. Extensibility influence is found to be very small.An interesting comparison can be made with the similar influence of secondary factors on the flexural vibration's frequencies of a straight beam.

ISSN:0001-4966    

DOI:10.1121/1.1906623

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Direct measurements of envelope delay have been obtained for a series of commercial and experimental loudspeakers. The modulation phase shift method of Nyquist and Brand has been adapted for direct indication of envelope delay by utilizing an electronic phase meter. A continuous record of the delay is obtained by an automatic level recorder suitably connected to the phase meter. Pressure‐amplitude curves measured under the same conditions provide data for a preliminary attempt to interpret the correlation between delay response and pressure response.

ISSN:0001-4966    

DOI:10.1121/1.1906624

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A heterodyne filter for the speech frequency range is described. It can be used as a band pass filter of continuously variable low and high frequency cut‐offs adaptable for any desired transmission band in the frequency range 40–4000 c.p.s. and with more than 60‐db attenuation and with cut‐offs of a maximal slope of 1 db per c.p.s.Band width and low frequency cut off are varied by two separate controls. Band elimination filtering can also be obtained with continuously variable mid‐frequency but with band width restricted to either 300 or 800 c.p.s.The variable filtering is performed by single sideband transmission with successive filtering in two modulation units and demodulation in a third unit. Distortion products from impurities in transmission and modulation are kept at a −60‐db level and random noise at a −85‐db level, relative to a single test tone.The filter was designed for articulation tests and general speech research purposes and also as a wave analyzer of continuously variable band width, 45–4000 c.p.s. in the frequency range 40–2000 c.p.s. The maximum permissible speed in analysis of sustained sounds, governed by the inverse square of band width law, is discussed with regard to the quality of the analyzing band pass filter.

ISSN:0001-4966    

DOI:10.1121/1.1906625

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

A technique is described for the dynamic calibration of accelerometers or other vibration‐measuring instruments. For each calibration frequency the accelerometer is attached to a free‐free bar driven electromagnetically at a known sinusoidal displacement. Displacement amplitudes are measured by means of strain gauges which are calibrated optically. The accelerometer output can be conveniently compared in magnitude and phase with the displacement as indicated by the strain‐gauge voltage. Instruments have been calibrated at frequencies between 400 and 2000 c.p.s. The error in determining phase angle was about ±2 degrees. The error in the optical measurement of displacement was about ±0.1 × 10−3cm. The percent error, however, could be made fairly small by calibrating the strain gauges at large displacements of the bar. For instance, the error in calibrating a 200‐g accelerometer at 1000 c.p.s. was about ±2 percent.

ISSN:0001-4966    

DOI:10.1121/1.1906626

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

One hundred and ten monosyllabic words, 10 for each of the 11 common American vowels, were spoken in isolation by each of 10 subjects. Most of the differences between the mean relative intensities of the vowels were found to be statistically significant. Among the words for a given vowel the intensity of that vowel was found to differ significantly in most instances, variation tentatively attributed to consonantal environment.

ISSN:0001-4966    

DOI:10.1121/1.1906627

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP