摘要:

The general equation of heat conduction inside a fluid‐filled chamber takes two forms, which correspond to zero and infinite acoustic impedance of the driving source, respectively. By means of a simple transformation, it is possible to convert this equation to the standard diffusion equation with simple initial and boundary conditions. Special solutions to this equation are used to derive transfer functionsE, which relate the impressed temperature to the resultant average temperature. The equation of state of the fluid is then used to determine the relationships between pressure and volume changes in terms ofE. These relationships take the form of two different acoustic impedancesZpandZvwhich correspond to zero and infinite source impedance, respectively. In general, the chamber impedance is a function ofZp,Zv, and the external impedances. The above results can be used to extend the validity of acoustic circuit diagrams to zero frequency. The infrasonic acoustic impedance is an R C network, and numerical values of the components can be calculated in a simple manner.

ISSN:0001-4966    

DOI:10.1121/1.1919219

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

If a piston compresses and heats gas in a chamber that is larger than a few cubic inches, then the heat exchange between the gas and the wall is governed by convection. The simultaneous, nonlinear partial‐differential equations of free convection are given. Application of dimensional analysis to these equations indicates that the convection process can be described in terms of three dimensionless variables: the Grash of number, the Prandtl number, and the thermal‐diffusion number. A simplified model of the process of free convection is derived and it is shown that the geometrical constants of the model can be expressed in terms of the Grashof and Prandtl numbers. The chamber lengthland the boundary‐layer thicknesslbplay a key role. Mathematical solutions for the chamber pressure that follows a step piston displacement are derived and they agree within 1% with the measured pressure.

ISSN:0001-4966    

DOI:10.1121/1.1919220

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The method of describing the propagation of finite‐amplitude waves based on the introduction of coordinates “accompanying” the wave system is used for the consideration of the radiation of a compression wave by a sphere that is expanding at a constant rate in a perfect medium. To estimate the degree of accuracy of this method, the results are compared with the exact solution of G. I. Taylor. [Proc. Roy. Soc. (London)A186, 273–292 (1946)].

ISSN:0001-4966    

DOI:10.1121/1.1919221

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The signal‐detection capabilities of an array that is essentiallyDIMUSin nature are analyzed for the situation in which the background‐noise power from hydrophone to hydrophone is not the same. The signal to be detected is assumed to be a plane‐wave random time function. The signal power at different hydrophones is assumed to be constant. The performance of the DIMUS system, with infinite clippers, is compared to that for a similar array with purely linear signal processing. Results indicate that the performance of the system with infinite clippers is generally superior on a signal‐to‐noise basis and on the basis of normalized signal output.

ISSN:0001-4966    

DOI:10.1121/1.1919222

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

International reference‐zero levels for pure‐tone audiometers have been recommended by the International Organization of Standardization (ISO) and are under consideration for inclusion in a new American Standard for Audiometers. The new ISO levels are desirable because (1) the shape of the threshold contour is more accurate, (2) the threshold levels are reproducible from laboratory to laboratory and from country to country, and (3) they represent the only apparent escape from permanent ambiguity and confusion in the international exchange of audiometric information. The new ISO levels differ significantly from the American Standard values of 1951, but readings on one of these bases can readily be transferred to readings on the other base by a simple arithmetical adjustment. For instance, for the determination of percentage impairment of the ability to hear speech by calculation from the average of the decibel readings at 500, 1000, 2000 cps, an adjustment of 11 dB in the average of these readings provides the transfer from one base to the other.

ISSN:0001-4966    

DOI:10.1121/1.1919223

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The effects of varying the crosscorrelation of a noise masker upon the detection of a 500‐cps tonal signal were investigated. The correlation was varied by introducing a time delay into the channel to one ear. Ten delays yielding various positive and negative correlations and nine delays yielding zero correlations were employed with in‐phase and reversed‐in‐phase signals. A two‐interval forced‐choice procedure was used to obtain MLD's relative to the diotic condition. The function relating MLD's to delay is periodic, the largest values occurring for the antiphasic conditions and the smallest for the homophasic. The function for zero correlations is not periodic, but decreases regularly to a value near that found for uncorrelated noise. No difference is apparent between the two conditions of signal phase for zero correlations. The temporal interval over which the binaural system is able to effect a correlation between events occurring at the two ears is estimated to be at least 9 msec.

ISSN:0001-4966    

DOI:10.1121/1.1919224

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Nine subjects listened through one earphone of a binaural headset to 50‐word lists of common English words read to them at a rate of two words per second. They repeated the words that they heard while listening for an occasional word that might or might not be presented on the other earphone. This word, should it appear, was to be remembered until the conclusion of the 50‐word list, at which time it was to be recalled. No more than three target words were presented with any one 50‐word list for shadowing. The results indicate that shadowing performance is almost totally disrupted at the point of insertion of the target word, whether the target word is finally correctly remembered or not. Memory for the target word deteriorates as some function of the time between presentation and recall. Since time between presentation and recall and amount of intervening material between presentation and recall are directly correlated, it is impossible to say with certainty that the recall data support a decaying‐trace theory of immediate memory or an interference‐type theory. The results of a similar study using visual target words are cited to lend support to the position that an interference‐type theory is to be preferred in this case. Finally, these data further confirm the validity of the concept that man's perceptual system is basically a single‐channel one with a limited information‐handling capacity.

ISSN:0001-4966    

DOI:10.1121/1.1919225

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

In a series of experiments designed to compare the efficiency of human observers in amplitude‐discrimination tasks to their efficiency in frequency‐discrimination tasks, the behavior of one of the four observers suggested that he was completely insensitive to frequency differences. The procedure of the experiments was then diverted to conduct an experimental case study comparing the “tone deaf” observer to three observers with normal frequency discrimination under a variety of experimental conditions. In amplitude‐discrimination experiments in which he is detecting pulses of sine waves, he compares favorably. He far surpasses the other three observers when the signal is a sample of “white Gaussian” noise. An interesting aspect in the experiments reported is that the “tone deafness” of the participating observers suggests the possibility that these particular experiments may reflect culture‐bound conditions. A further program is planned that may yield data on the question of the environmental influences on sensory capabilities.

ISSN:0001-4966    

DOI:10.1121/1.1919226

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

Some experiments are performed to test the influence of rise time on loudness of a 750‐cps sinusoid and a broad‐band noise. Rise times, defined for a 50‐dB exponential variation in sound pressure level, were applied in the interval 0.025–1.6 sec. Maximum sound pressure level was 70–100 dB with duration 0.6 and 1.3 sec. A “paired comparison” method was used, and a decrease in loudness corresponding to approximately 3 dB in sound‐pressure level was found for the broad‐band noise. A smaller change was found for the 750‐cps sinusoid.

ISSN:0001-4966    

DOI:10.1121/1.1919227

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP

摘要:

The freefield resonant frequency and the deflection under given static pressure of a thin, circular, clamped‐edge diaphragm may be calculated theoretically by well‐known equations. Also, experimental means exist for a determination of these quantities. No satisfactory theoretical or experimental method has appeared, however, by which it is possible to obtain, for a complicated physical system, the diaphragm deflection as a function of the frequency of an applied sinusoidal pressure, over a frequency range that includes the natural diaphragm resonance. An experimental method is described by which a piezoelectric driver is employed to generate a sinusoidal pressure of variable frequency in a confined gas, to which one side of a test diaphragm may be exposed. Equations are derived describing the gas‐coupling medium and the piezoelectric driver. By use of these equations, it is possible to predict the characteristics of the apparatus. A study is made of the dynamic response of a series of thin, circular, clamped‐edge diaphragms. Since the diaphragm geometry is simple, the resonant frequency may be calculated theoretically. A shock‐excitation technique is also employed to determine the resonant frequency. Comparison is then made between the latter two methods and the result given by the apparatus. The static‐pressure dependence of the resonant amplitude and resonant frequency of the diaphragms is studied and discussed. The magnitude of the dynamic‐pressure amplitude is determined, employing a calibrated commercial pressure gauge below its own resonance. Modifications of the apparatus are reported that extend the dynamic‐pressure amplitude and the useful frequency range, and the possibility of utilizing the apparatus for dynamic calibration of pressure gauges is noted.

ISSN:0001-4966    

DOI:10.1121/1.1919228

出版商:Acoustical Society of America    

年代:1964

数据来源: AIP