摘要:

Acoustic spectra of a cornet have been measured with the instrument equipped with several mutes of types used mainly in dance orchestras. Data are presented showing the sound pressure levels of the first 10–15 partials of the instrument when fitted with each of the mutes. The instrument was blown naturally by a cornetist, with an attempt to obtain a normal characteristic tone for each mute. The sound spectrum of the muted instrument is compared to that of the open or unmuted instrument. The mutes tend to exhibit the same formants for several different notes, indicating resonance phenomena in the acoustic networks. The measurements were made by playing the instrument in a dead room, and recording the sound on tape, with a condenser microphone and a magnetic tape recorder of professional quality. The sounds were then analyzed by playback through a heterodyne wave analyzer. Two of the mutes, the Harmon and the Solotone, are equipped with cylindrical aluminum tubes, open at both ends. The formants for these mutes display families of resonance peaks corresponding to the calculated open pipe frequencies. These resonances are also observed when the mutes are driven with an electroacoustic transducer. All of the mutes themselves act as Helmholtz resonators at 200 to 300 cps, which is, however, in the frequency range of considerably reduced output when fitted to the instrument.

ISSN:0001-4966    

DOI:10.1121/1.1908353

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Evidence is presented which suggests that the noise of full‐scale helicopter rotors results mainly from conditions of unsteady flow. Measurements of the sound‐pressure levels and spectra are presented for test conditions where gear train, engine, and other propulsion system noises are minimized. These data cover a range of tip speeds from 100 ft/sec to 900 ft/sec for various rotor disk loadings. Results indicate that both tip speed and disk loading have an important influence on the noise radiated from the rotor. During stall, the sound pressure levels increased at all frequencies, but particularly at the high end of the spectrum. As a matter of special interest, a highly‐peaked wave form due to possible doppler effects was noted to be associated with high‐tip speed operation.

ISSN:0001-4966    

DOI:10.1121/1.1908355

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

Measurements of ultrasonic absorption and velocity were made in the molten saltsKNO3, NaNO3, AgNO3, LiNO3, CdCl2, and the molten salt mixtureNaNO3‐KNO3. The results indicate that these molten salts exhibit a structural viscosity similar to that found in water and associated organic liquids. The ratio of bulk to shear viscosity (ηB/ηS) ran high as 10 inKNO3and as low as 1.7 inCdCl2. In the Group I nitrates, the ratio ηB/ηSwas found to be directly proportional to the volume of the cation. The ln ηB/ηSwas found to be a linear function of the entropy of fusion. Consideration of the ultrasonic data in the primary alcohols showed that here also the ln ηB/ηSis a linear function of the entropy of fusion when considering an homologous series. These results indicate that the structural relaxation process in both the ionic and organic liquids involves considerable randomization of the quasi‐crystalline liquid lattice.

ISSN:0001-4966    

DOI:10.1121/1.1908357

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

As explained previously [J. Acoust. Soc. Am.31, 1527–1535 (1959)] the disturbances due to an initially step‐like pressure wave progressing down a channel carrying a compressible flow can be analyzed by a multiple reflection method. For the final “transmitted” and “reflected” pressures, this yields a power series expansion, successive terms representing the effect of higher order reflections. It is now shown that the coefficients of these series are connected to Euler's and Bernoulli's numbers, respectively, and convenient expressions for the coefficients are given. Whennis not small, the coefficientcn≃2(2/π)n+1. The infinite power series are shown to have sums simply like sechxand tanhx, respectively. This provides an easy means of numerical evaluation, and gives simple criteria for the accuracy of the approach using the leading term of each of the series. The results when reflections of all orders are taken into account are shown to be analytically identical to those of the “before” and “after” steady flow method.

ISSN:0001-4966    

DOI:10.1121/1.1908359

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The far‐field solution for a line and a point source near a tangential velocity discontinuity has been calculated by summing (integrating) the plane waves that make up the source. The exact field integrals were evaluated approximately by the stationary phase method, and this approximation gives the far field. It was found that the sound was strongly peaked in some directions, and considerably reduced in others. This angular dependence is shown graphically for certain cases. The physical significance of these results is discussed for both subsonic and supersonic motions, and the relationship to the jet‐noise problem is suggested.

ISSN:0001-4966    

DOI:10.1121/1.1908361

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The maximum peak velocity which can be developed at the free end of a slender rod driven at resonance in a normal mode of longitudinal vibration is given byv0 = c0Sxx, wherec0is the Young's‐modulus speed of sound(E/ρ)12andSxxis the limiting value of extensional strain for the rod material. The ratio of allowable stress to the maximum peak velocity is given byTxx/v0 = ρc0, where the characteristic specific impedance plays in this case the role of a transfer impedance relating the stress at a node to the velocity at an antinode. The same expressions describe, within half an order of magnitude, the relations between the maximum allowable stress or strain and the normal component of velocity at the antinodes of displacement for thin uniform bars or plates and for wedges or cones vibrating in flexure, and for an exponential solid horn vibrating longitudinally. By inductive extension it is argued that within the indicated precision the same velocity‐strain ratios prevail in the vibration of any elastic body however excited.

ISSN:0001-4966    

DOI:10.1121/1.1908363

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

In the compensatory form of loudness tracking, S keeps a loudness level constant in the face of programmed changes; in the pursuit form, he duplicates the loudness changes by manipulating an external source. Five subjects were required to track three tape‐recorded programs presented in eight test conditions, including both modes (compensatory and pursuit) and three channel types of reception (monotic, diotic, dichotic). The responses were obtained by dial‐writing techniques and a paper‐tape voltage recorder. Analysis of variances based on 120 tracings revealed the overall superiority of the compensatory mode (averaged momentary error 2.2 db) vs the pursuit mode (3.3 db). High accuracy and consistency obtainable in auditory tracking suggest its use for the purposes of suprathreshold audiometry and for human engineering tasks in compensatory and pursuit displays.

ISSN:0001-4966    

DOI:10.1121/1.1908365

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The dynamic properties of the vibration sense in the human skin were investigated by means of psycho‐physical methods using stimuli with different time courses. Sinusoidal deformations and deformations linearly increasing with time were used. Up to frequencies of 30 cps the results are described very well by a differentiating system having a time constant of about 30 msec. This is in good agreement with electrophysiological observations. Also in agreement with electrophysiological experiments, “rectifying” properties are found. Possible mechanisms underlying these phenomena are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1908367

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The theory of signal detectability is examined from the standpoint of determining a set of satisfactory assumptions for the purpose of developing an interpretive tool for use in psycho‐physical experiments. It is concluded that the assumption that the observer attempts to maximize the expected value of the outcome of the experiment is satisfactory for this purpose, and that a set of physical conditions can be established which justify a computation of the detectability of a signal in noise based on a finite sampling plan involving 2WTamplitude values over the open interval, 0 toT.

ISSN:0001-4966    

DOI:10.1121/1.1908369

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP

摘要:

The use of electroencephalograms for the evaluation of auditory function has proven to be invaluable, especially where the standard audiogram is not possible. In sleeping subjects there is a definable change in the EEG pattern upon the presentation of an auditory stimulus. One method of analysis of the brain's response to a tone is the measurement of shifts in frequency of the brain wave, recorded simultaneously with the electroencephalogram. This recording of frequency changes is later analyzed for indications of reception of the tones presented. An electronic frequency recorder which is used in conjunction with a standard polygraph is described. The cortex has indicated response when the recorder produces a shift in frequency. This shift occurs within a specified time interval after the presentation of tone (the “delay time” of the response).

ISSN:0001-4966    

DOI:10.1121/1.1908372

出版商:Acoustical Society of America    

年代:1960

数据来源: AIP