摘要:

A synthesizer was constructed to produce simultaneously 100 pure tones with means for controlling the intensity and frequency of each one of them. The piano tones were analyzed by conventional apparatus and methods and the analysis set into the synthesizer. The analysis was considered correct only when a jury of eight listeners could not tell which were real and which were synthetic tones. Various kinds of synthetic tones were presented to the jury for comparison with real tones. A number of these were judged to have better quality than the real tones. According to these tests synthesized piano like tones were produced when the attack time was less than 0.01 sec. The decay can be as long as 20 sec for the lower notes and be less than 1 sec for the very high ones. The best quality is produced when the partials decrease in level at the rate of 2 db per 100 cps increase in the frequency of the partial. The partials below middle C must be inharmonic in frequency to be piano like.

ISSN:0001-4966    

DOI:10.1121/1.1918192

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

This exploratory paper describes a modification of the paired comparison technique for deriving a one‐dimensional scale for rating speech transmission systems on the basis of listener preferences. The numbers on the scale, which run from 0 to 100, are called “Transmission Preference Units” (TPU), and are intended to be used to evaluate any speech transmission system, regardless of the noise or distortions encountered, provided the system is less preferred than the reference condition, namely, real speech at 1 m. If the TPU ratings for two transmission systems are known, it is believed that the difference can be used to predict the percentage of users who would prefer the system with the higher rating.Subjective listening experiments have been conducted with a small group averaging seven observers for rating a large number of speech transmission conditions on the TPU scale. Equal preference contours were determined on speech level‐noise level planes for several different frequency bands. The listening tests require only simple A‐B preference comparisons of two brief samples of speech heard consecutively.The data suggest that the basic requirement of transitivity, essential for a simple useful one‐dimensional rating scale, may be satisfied for many types of transmission conditions. Thus if transmission condition A is judged to equal condition B in preference, and condition B equals C, then A and C were also found to be judged equal. This apparently holds even though A, B, and C are circuits differing widely in their physical parameters.This study is reported at this stage in the hope that other laboratories may become interested in checking and extending the limited scope of the work reported here. Such confirmation is necessary before a simple one‐dimensional TPU scale can be postulated and used with confidence for precise evaluations. For the purposes of this work, two circuits are considered to be equal in preference when half of the judgments of the group favor one and half favor the other circuit; it does not follow that individual observers are indifferent in their preferences for the two circuits.

ISSN:0001-4966    

DOI:10.1121/1.1918193

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Two schemes using piezoelectric plates to produce acoustic waves in liquid; in the kilomegacycle frequency region are described. The use of the thermoelectric method of detecting the acoustic energy in liquids is discussed briefly. Data obtained by these techniques are presented.

ISSN:0001-4966    

DOI:10.1121/1.1918194

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An acoustic resonance tube is described capable of operating at moderately high pressures and elevated temperatures: possibly 1000 atm and several hundred degrees centigrade. The frequency range is 500 to 15 000 cps, or correspondingly 0.5 to 15 000 cps/atm or higher, thus filling a significant experimental gap in acoustical instrumentation. The wall absorption in this tube is about 10% above the calculated classical value, and is approximately independent of molecular weight or pressure of the gas. Details of construction and operation are given, and the application of the tube to problems of relaxation at low frequency/pressure ratios is indicated.

ISSN:0001-4966    

DOI:10.1121/1.1918195

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The Karal‐Keller theory is applied to an explosive source in a spherical cavity where it becomes exact because the displacement series terminates after two terms. This solves the source problem as a necessary preliminary to considering both free surface reflection in a homogeneous media and propagation in inhomogeneous media. The dual problem of the purely rotational source is also solved. Collectively, the two problems illustrate how the asymptotic theory may, by terminating, yield an exact solution for an arbitrary waveform.

ISSN:0001-4966    

DOI:10.1121/1.1918196

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

The intensity and power radiated from circular ring sources and circular arrays of point sources are derived from first principles. The shape of the radiation patterns and efficiency of power output are studied as a function of phase changes between different parts of the source and of the ratio of the over‐all source dimensions to the wavelength of the sound field. These expressions are applicable to the reduction of noise from such sources as centrifugal and axial blowers and aircraft propellers. The relationship between the mathematical phase parameter and such mechanical quantities as the number of blades is described. As in the case of the linear source the radiated power drops if the phase parameter exceeds a certain critical value. However, the drop in the power for the circular source is greater than that for the line source. For the circular source alone the anomaly exists wherein the power—at most ratios of the source diameter to sound wave‐length greater than about 0.6—is greater for a source “de‐phased” by small amount than for one having all elements radiating in phase.

ISSN:0001-4966    

DOI:10.1121/1.1918197

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

A theoretical treatment of the motion of a piston in a fluid‐filled cavity is presented. Emphasis is on the steady‐state response of the piston to a sinusoidal driving force. Effects of finite amplitude and finite length of the cavity are taken into account; frictional damping is also considered. It is found that if the piston is driven hard enough in the neighborhood of resonance, the motion is markedly influenced by the nonlinearity of the equation of state (pressure‐density relation) of the fluid. The fluid‐filled cavity behaves as a nonlinear spring. The theoretical results show how measurements of the piston motion might be used to obtain data on the coefficients of the most important nonlinear terms in the equation of state of the fluid. Push‐pull as well as single‐sided piston‐cavity systems are analyzed.

ISSN:0001-4966    

DOI:10.1121/1.1918198

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

An analogy to architectural acoustics is used to characterize the localized damping at boundaries of structures in terms of absorption coefficients. These coefficients can be measured by a technique which has all the advantages and disadvantages of the reverberation chamber method of architectural acoustics. Experimental results show that the way in which absorption coefficients vary with frequency is primarily a function of the geometry of the boundary structure. Structures consisting of beams attached to plates, which are of practical importance, in some cases appear to dissipate energy by virtue of friction at the interface.

ISSN:0001-4966    

DOI:10.1121/1.1918199

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

A statistical method for estimating the response of ribbed panels to acoustic excitation is discussed. It is shown that the acceleration spectrum of the vibrational field is related to the pressure spectrum by a coupling factor which is a simple function of the radiation and mechanical resistance of the structure. The radiation resistance of a ribbed panel is studied as a function of frequency. The analysis predicts that ribbing increases the radiation resistance of the panel and hence its coupling to the acoustic field. The effect of various panel‐rib boundary conditions is also considered. The results of experiments which were conducted to test the theory are reported. The agreement between theory and experiments is shown to be satisfactory.

ISSN:0001-4966    

DOI:10.1121/1.1918200

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP

摘要:

Current procedures for predicting the response of dynamically nonlinear, resonant structures to random excitation are reviewed. Methods of analysis are summarized and limitations inherent in the methods and their application to practical structures are pointed out. The most important limitations are the neglect of nonlinear damping, and the description of the motion of a distributed structure in terms of a single mode.

ISSN:0001-4966    

DOI:10.1121/1.1918201

出版商:Acoustical Society of America    

年代:1962

数据来源: AIP