ISSN:0001-4966    

DOI:10.1121/1.1915760

出版商:Acoustical Society of America    

年代:1935

数据来源: AIP

摘要:

The transmission ratio, and thus the transmission loss in decibels, has been determined from a theoretical consideration of this problem, based on certain simplifying assumption such as zero stiffness compared with mass, an air layer between partitions small compared with the wavelength, etc. Three cases in particular are considered, the transmission loss being expressed as a function of wavelength of sound, weight per square foot of partitions, and distance between them: (1) Double partition wall; (2) Single wall (noting check with previous work); (3) Double partition and single partition loosely fixed to vibrating surface as a means of reducing sound radiation from that surface. Certain limitations of the theory are explained briefly.

ISSN:0001-4966    

DOI:10.1121/1.1915766

出版商:Acoustical Society of America    

年代:1935

数据来源: AIP

摘要:

With the aid of a vacuum tube “impulsator” the limits for which the integral law of apparent duration holds true, were determined; they are expressed by the value∫t1t2logIdt, for the extent of the apparent duration. Experiments with different impulses of tones of 1000 vib./sec., showed that the law holds true for limits of from 2 to 50 units of apparent duration. As a unit of apparent duration we take the apparent duration of a pure, constant tone which has sounded for one second at a loudness level of 1 db. Further experiments with tones of 50, 100, 500, 1000, 2000 and 4000 vib./sec. showed that the integral of apparent duration holds true for these tones and does not depend on the frequency of the tone. The musical optimum of reverberation corresponds to 37 units of apparent duration. As a result of the limits determined as indicated above, we can consider that the integral law of apparent duration in its unvaried form is applicable for the determination of the musical optimum of reverberation for halls up to 80,000 cu. m in volume.

ISSN:0001-4966    

DOI:10.1121/1.1915770

出版商:Acoustical Society of America    

年代:1935

数据来源: AIP

摘要:

It is well known that the vibrations of a violin are produced by those of the string, transmitted through the bridge, but that what we hear comes mainly from the top and back of the body, and from the enclosed air mass through the f‐holes. The resonant pitches of the body and of the air column are examined by a method due to Raman. With an automatic player which produces a steady tone the least weight needed to make the instrument “speak” properly has been measured at each frequency. A curve of these weights drawn against the frequency discloses the resonant frequencies. A simple method is described whereby the main air‐mass frequency can be distinguished from that of the body. The effect of the resonant pitches on the tone quality is briefly discussed, with reference to a few analyses obtained with the analyzer described at this meeting. Loading the bridge is shown to affect some of these resonant points; also the tension to which the whole instrument is subjected by the strings. Variations of the sound energy emitted in a definite direction with bow pressure, speed and distance from the bridge are given by graphs.

ISSN:0001-4966    

DOI:10.1121/1.1915776

出版商:Acoustical Society of America    

年代:1935

数据来源: AIP

摘要:

This paper stresses the noise elements in the application of fans, particularly those of the propeller type, where the apparatus must operate in quiet surroundings. The sources of such noise are divided into the inherent noise of the fan, and the five classes of noise which tend to modify this inherent noise as follows: (1) Noise increase due to improper flow conditions; (2) noise increase due to improper application or design of fan; (3) change of the inherent noise by other parts of the apparatus; (4) amplification by the fan of noise made by other parts of the apparatus; (5) noise increase due to improper mechanical design or construction. The inherent noise forms a base level for the required performance of a given design operating under the best possible conditions, and depends upon the static pressure against which the fan must operate. The first and second classes of noise result because of deviations from the best operating conditions. The third and fourth classes deal with the interrelation between the fan, its motor and the system in which it works. The result of the third class may either be an amplification or an absorption. The fifth class concerns mechanical vibrations usually in a form of resonance. Several illustrations are shown as practical examples of each class of noise.

ISSN:0001-4966    

DOI:10.1121/1.1915778

出版商:Acoustical Society of America    

年代:1935

数据来源: AIP

摘要:

The number and strength of loud speakers, their relative location, and the radiated sound spectrum must be examined relative to acoustical principles. It follows that uniform distribution throughout a room is not only uneconomical but does not lead to best audibility. In view of interfering sounds, formulae are developed allowing computation of the required number and strength of loud speakers and their most favorable location, and the intensity for each observer. It is further shown how the absorption in air is to be considered. Using different sound spectra in loud speakers, there arises a greater total loudness than would be computed on a straight energy basis. Very large auditoriums do not follow the generally accepted acoustical laws. Short examples show the practical use of the formulae.

ISSN:0001-4966    

DOI:10.1121/1.1915787

出版商:Acoustical Society of America    

年代:1935

数据来源: AIP

摘要:

When a solid body vibrates, the alternating strain within it induces a correlated dissipation of energy resembling internal static or rubbing friction. No material is purely elastic. Elasticity must be regarded as having a phase angle which varies little, or not at all, with frequency, and in metals is a small fraction of 1°. This friction introduces losses in acoustic apparatus in amounts depending on design, and also on choice and heat treatment of materials. Taking metals as a class, this dissipation is generally least in light materials like aluminum and duralumin, and greatest in the heaviest substances like lead. They may be varied by a factor of as much as 10 by heat treatment.

ISSN:0001-4966    

DOI:10.1121/1.1915790

出版商:Acoustical Society of America    

年代:1935

数据来源: AIP