摘要:

The influence of a turbulent air stream on the sound attenuation in ducts, lined with sound absorbing materials or structures of different kinds, has been experimentally investigated. For linings consisting either of porous materials or sufficiently damped Helmholtz resonators, decrease of absorption with increasing flow velocity has been observed, together with an increase of the frequency of maximum absorption in the case of the resonators. Somewhat surprising results have been obtained for undamped or weakly damped Helmholtz resonators, where an attenuation minimum is observed above the resonant frequency, the frequency of which increases linearly with increasing flow velocity, and which—for undamped resonators—even reaches negative attenuation values. Aside from the negative attenuation, a self‐excitation of the duct is observed under certain conditions, the frequency of which is not identical with the attenuation minimum.

ISSN:0001-4966    

DOI:10.1121/1.1909527

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

In this paper the design, construction, acoustical testing, and articulation testing of a listening studio, giving reasonably constant listening conditions, is described. The reverberation time has been measured by several methods, and was found to be equal to about 0.5 sec. A comparison of the individual results is presented.

ISSN:0001-4966    

DOI:10.1121/1.1909529

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The burst level of a periodically, abruptly interrupted, white noise, necessary to match a continuous noninterrupted white noise in loudness, was examined over a wide range of interruption conditions. A procedure for calculating the required burst level, with knowledge only of the time‐intensity characteristics of the interrupted noise, is outlined.

ISSN:0001-4966    

DOI:10.1121/1.1909531

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Measurements of the propagation velocity of flexural waves in the human skull performed in three different studies are discussed and compared with each other. The analysis leads to the conclusion that the existing discrepancies may be due to individual differences in skull thickness. For frequencies around and above 1000 cps the highest measured velocity amounts to 570 m/sec and the lowest to 260 m/sec.

ISSN:0001-4966    

DOI:10.1121/1.1909533

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A rubber noise shield was developed which significantly improves the speech‐to‐noise ratio at a military microphone. The construction and evaluation techniques are described, and the advantage of introducing acoustic damping material is shown.

ISSN:0001-4966    

DOI:10.1121/1.1909535

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

The frequencies of the lower modes of vibration of the Indian drums, the right‐ and left‐hand thabalas which have circular drumheads loaded concentrically in the former and eccentrically in the latter have been computed by the method of variation of parameters incorporating the variation of the surface density of the drumheads in the normalizing integral. The boundary value problem is first formulated in terms of a modified form of bipolar coordinates suitable for the eccentrically loaded left‐hand thabala, the boundary value problem of the right‐hand thabala being obtained as a special case when the eccentricity parameter vanishes. It is then shown that the harmonic character of the modes of vibration is primarily determined by the ratio of the radii of the loaded and unloaded regions, the eccentric placement of the loaded region in the left‐hand thabala merely bringing about a small separation between the frequencies of the even and odd modes.The computed frequencies are compared with previous calculations. In the case of the right‐hand thabala where exact values are known the agreement is as good as 1% and in the case of the left‐hand thabala where only approximate values are known the agreement is about 10%.

ISSN:0001-4966    

DOI:10.1121/1.1909537

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Several message procedures, designed to improve speech communications under extremely unfavorable speech‐to‐noise ratios, were examined. A message procedure based upon the informational principle of successive selections among a reduced number of alternatives was strikingly superior to a message procedure based upon the repetition of a single selection among a larger number of alternatives. Information, alone, is not the entire story because message diversity, without change of information, may produce nearly equivalent results.

ISSN:0001-4966    

DOI:10.1121/1.1909539

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

A dynamically controllable electrical analog of the vocal tract capable of synthesizing sequences of speech sounds is described. The acoustic transmission line between the glottis and lips in the human vocal tract is realized electrically by eleven electronically controlled variableLCsections plus three fixed sections. Each variable capacitor is realized by means of the Miller effect, and the inductors are saturable reactors. Both elements of each section are controlled by a single voltage in a manner that constrains theLCproduct to remain constant, and varies the ratioL/Cto simulate changes in effective cross‐sectional area. The analog can be excited by a buzz source to simulate the glottal tone, by a noise source inserted at various distances from the glottis to simulate the noise of turbulence, or by both together. Thus, vowels and most consonants can be produced with equal facility by the dynamic analog. Control voltages are derived from a resistance network in which a series of desired articulatory configurations is stored. A timing arrangement chooses the excitation and articulatory configurations in the proper sequence, and smoothing circuits are used to assure natural transitions from one configuration to the next.

ISSN:0001-4966    

DOI:10.1121/1.1909541

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Thermodynamic data on specific heat, and thermal expansion coefficient of glycerol in the liquid and glass state are used to investigate the origin of the ultrasonic volume viscosity losses and associated dispersion in liquid glycerol. It is shown that the volume relaxation effects cannot be accounted for on the basis of a thermal relaxation involving either the vibrational specific heat or the structural specific heat. It is concluded that the volume viscosity in glycerol (and most probably in all the associated liquids) has an origin similar to that found for water, namely, a relaxing isothermal compressibility.

ISSN:0001-4966    

DOI:10.1121/1.1909543

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP

摘要:

Methods for measuring α, the sound amplitude absorption coefficient in liquids, using two matched quartz crystals are outlined. A standard signal generator drives one of the crystals continuously. The amplitude of the resulting pressure waves is measured at the other crystal by means of a communications receiver and a voltmeter. Partial wave analysis allows the voltage observed at the second crystal to be expressed in terms of the absorption coefficient. Three cases are identified: low, high, and intermediate absorptions, and the above expression is simplified for each of these cases. Data, obtained by these methods, are presented. The internal consistency encountered suggests an accuracy of ±3%.

ISSN:0001-4966    

DOI:10.1121/1.1909545

出版商:Acoustical Society of America    

年代:1958

数据来源: AIP