摘要:

The problems involved in laboratory and field calibrations of high‐amplitude dynamic‐pressure measuring systems are discussed. A novel method is described which utilizes the vibration sensitivity of the transducer for the generation of high amplitude dynamic pressures at a frequency suitable for calibration. The design, construction, and evaluation are described for a simple hand‐held calibrator based on this principle and providing over all system calibrations ±12.5 psi and ±5 psi, at 60 cps.

ISSN:0001-4966    

DOI:10.1121/1.1908136

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

An analysis is given for a method of measuring the bulk modulus of a liquid by means of a Helmholtz resonator driven by an oscillating diaphragm in the cavity wall. The influence of the pressure transducer on the resonant frequencies is considered. In addition to the bulk modulus, the viscosity can be estimated by measuring the “Q” of the cavity.One resonator was built, tested, and calibrated. Some difficulty was encountered in measuring resonant frequencies of the fluid‐filled cavity at atmospheric pressure because of the formation of vapor bubbles. The results obtained for five common liquids compared favorably with earlier measurements of bulk modulus found in the literature.This method is especially suitable for measuring the bulk modulus of corrosive liquids since the liquid may be completely sealed in the cavity under pressure and no measuring probes are moved through the liquid.

ISSN:0001-4966    

DOI:10.1121/1.1908138

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

PB word and sentence intelligibility tests were conducted with unfiltered speech and with speech filtered (1) by a 100–7000 cps bandpass filter, (2) by a 100–1600 cps bandpass filter, (3) by a 500 2000 cps bandpass filter, (4) by a 1000–2500 cps bandpass filter, and (5) by various configurations of one, two, or three bandpass filters, each 500 cps wide. The positions of the center frequencies of the bandpass filters 500 cps wide were systematically varied during the tests. If we use constant speech intelligibility as our criterion, the results indicate that the total “effective” bandwidth required for the best multiple pass band system is less than that required for the best contiguous pass band systems by a factor of 2. Also, a feature of the signal resulting from this multiple sampling in the frequency domain is that it sounds “natural” and the identity of a talker's voice appears to be maintained.

ISSN:0001-4966    

DOI:10.1121/1.1908140

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

A study is made of the ultrasonic absorption and velocity of longitudinal waves in water containing suspended algae in order to determine the effect of biological suspensions on sound propagation. The ratio α/f2is found to be independent of frequency and is linearly dependent on algae concentration. These results indicate that scattering is not a mechanism for absorption and also shows that there is negligible interaction between particles. It was also found that the excess loss due to algae had the same temperature dependence as the shear viscosity. However the magnitude of the excess absorption calculated from the shear viscosity is insufficient to account for the total loss. Assuming that the structural viscosity of the liquid is increased by either the presence of the suspended material modifying the structural viscosity of the pure liquid, or by a structural viscosity associated directly with the cell, it is found that the increase in structural viscosity is 44 times the increase in shear viscosity for a given increase in concentration.

ISSN:0001-4966    

DOI:10.1121/1.1908142

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The thermal relaxation absorption in carbon disulfide vapor at temperatures between 0° and 160°C has been obtained for frequencies between 50 kc and 4 Mc per sec per atm. The data were obtained by the tube method. The relaxation time, the transition probability, and the collision efficiency were determined as a function of temperature from the measured data. The collision efficiency as a function of temperature is adequately predicted by the Landau and Teller theory.

ISSN:0001-4966    

DOI:10.1121/1.1908144

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Detailed information is given for the construction of relatively simple, efficient pulse equipment. The repetition rate of the pulse generator varies between once in 10 sec and 25 000 times a sec with a pulse duration from13 μsecto 100 msec. Pulses of sinsuoidal oscillations may be generated in the frequency range from 50 cps to 100 Mc. The circuits are free from ringing at frequencies below 5 Mc. The power output for pulses of less than 2‐msec duration is between 50 to 250 w at frequencies below 10 Mc. A thyratron stage produces a triggering pulse to activate a monostable multivibrator. The adjustable‐width multivibrator pulse passes through a cathode follower and furnishes the screen voltage for the output tube. If the frequency is below a few Mc, the output tube may be used to gate a sinusoidal voltage supplied by a standard signal generator. But for high power or at high frequencies, the output tube is preferably driven as a gated, self‐excited oscillator.The receiving amplifier may be connected in parallel with the output of the pulse generator so that the same transducer can be used as both sound projector and microphone. This amplifier limits the large voltage of the driving pulse and is capable of full sensitivity immediately after this pulse has decayed. Some valuable experiences with acoustic transducers are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908146

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The results for vibrations of an elastic cylinder as predicted by a number of the approximate shell theories are compared with the results of the exact theory. It is found that the membrane theory of shells is accurate for predicting frequencies and displacement ratios of cylinders with appreciable thickness. Furthermore, the theories which include bending effects as well as membrane effects are good at even the shorter wavelengths; and the theories which include rotatory inertia and shear are accurate over most of the wavelength spectrum of the lowest branch of rather thick shells. However, for the very thick shell (with a ratio of inside radius to outside radius less than 0.5), only the exact theory shows the full characteristics of the displacement distribution.

ISSN:0001-4966    

DOI:10.1121/1.1908148

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

A photographic study employing smoke as the indicating medium has shown the existence of a new type of streaming near a heated horizontal cylinder in the presence of a horizontal transverse sound field. This phenomenon, called “thermoacoustic streaming,” is characterized by the development of two vortices above the cylinder; the fluid pattern resembles vortex shedding behind a cylinder in forced flow normal to its axis. In the presence of sound waves whose half‐wavelength is six or more times greater than the diameter of the heated cylinder, the formation of the vortex flow is a function of the sound intensity only; for such wavelengths the vortices begin to appear at 140 db (re0.0002 μbar) and become fully developed at 146 db. This type of streaming is a flow phenomenon which is much stronger than isothermal streaming for the same geometry and sound intensity. It appears that thermoacoustic streaming will have important practical applications, particularly in the field of heat transfer.

ISSN:0001-4966    

DOI:10.1121/1.1908151

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Measurements of the complex shear compliance(J* = J′ − iJ″)have been carried out for three polyethylene samples of increasing weight average to number average molecular weight ratios (M̄w/M̄n) of 19, 70, and 110. The measurements extended to temperatures well above the crystalline melting points of the polyethylenes and over a frequency range from 25 to 2500 cps. A sudden increase in compliance occurred at all frequencies at the melting points of each type of polyethylene; there were no marked differences in dynamic mechanical behavior below the melting points. Above the melting points values of storage compliance (J′) were very nearly the same for all the polyethylenes but differences in the loss compliance (J″) were found. In particular at higher frequencies (1300 cps) values ofJ″ diverged with temperature in ascending order asM̄w/Mnincreased. Values of mechanical loss tangent (J″/J′) showed sudden jumps at the melting points but them was no evidence of maxima or peaks at these temperatures. Attempts to superpose the data in the melt were unsuccessful as values ofJ″ at various temperatures could not be shifted into coincidence even though values ofJ′ superposed fairly well. The superposition anomalies are tentatively ascribed to the presence of a secondary maximum in the loss compliance vs frequency characteristics of the materials while the secondary maximum, in turn, is attributed to either (1) a split molecular weight distribution with two separate maxima, or (2) a β mechanism involving the motion of very long branches.

ISSN:0001-4966    

DOI:10.1121/1.1908152

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

A general theory of mean square stability of random linear systems is developed when several system parameters vary as white noise stochastic processes. It is found that stability in mean square is determined from the character of the roots of a determinantal equation involving the Fourier transforms of double products of the weighting functions of the “average” system and the spectral densities of the parameter processes.The general theory is applied to the mean square stability of an RLC circuit in which the resistance and capacitance have purely random fluctuations.In the course of the study, a new type of dynamic stability is predicted, namely, the possibility of stabilizing unstable deterministic systems with random noise. Preliminary experimental studies appear to confirm this theoretical prediction.

ISSN:0001-4966    

DOI:10.1121/1.1908154

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP