摘要:

Sound absorption measurements in pureCO2at atmospheric pressure and 22°C have been conducted which, together with measurements by others, confirm the collision theory of anomalous absorption as developed by Einstein, Kneser, and others. The absorption coefficient is appreciable at frequencies as low as 2000 cycles, and increases to a maximum of 0.317 per wave‐length at 77,000 cycles. This maximum is higher than values obtained by previous workers, and indicates that both the deformation and symmetrical valence vibrations participate in the exchanges between translational and vibrational energy. Small impurities, as water or alcohol vapors, affect the absorption greatly; the entire absorption band is shifted to higher frequencies. Measurements in mixtures ofCO2inO2andCO2inN2indicate that neither theO2norN2is appreciably excited by collisions withCO2. Measurements inCS2reveal an absorption similar to that forCO2except that the absorption begins at about 10,000 cycles. In mixtures ofCS2andO2, the observed absorption at frequencies below 10,000 cycles is accounted for by assuming that only the vibration ofO2molecules is excited by collisions withCS2molecules; at higher frequencies theCS2molecules also are excited, principally by collisions with otherCS2molecules.

ISSN:0001-4966    

DOI:10.1121/1.1915961

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

摘要:

Serious difficulties have been encountered in attempts to measure the absorption coefficients of sound absorbing ceilings in large offices. An analysis of the sound field is made and it is concluded (1) that the reverberation time formula is usually invalid if the absorption is concentrated on one surface of the room, (2) that the energy density formula is not subject to such a restriction and (3) that under such conditions there is no apparent field method of determining the absorption coefficient that will serve as an accurate check on laboratory measurements.

ISSN:0001-4966    

DOI:10.1121/1.1915962

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915963

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

摘要:

The fundamental problem of absolute sound measurements in liquids is discussed. Regarding acoustic determinations, reference is made to certain inherent differences between air and water. An outline is presented of three methods now available for sound determination. A modified radiation pressure apparatus is described which permits a dual check of the basic measurements involved, and at the same time makes possible microphone calibration for secondary standards.

ISSN:0001-4966    

DOI:10.1121/1.1915964

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915965

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

摘要:

A portable tertiary frequency standard, adjustable over a small range, is described. The frequency determining element is a tube‐maintained tuning fork, adjustment of whose frequency over a relatively small range is accomplished by changing the position of movable weights on the prongs. Calculations are simplified by the design of the fork, which permits the assumption of lumped constants.The weights may be moved while the fork is running without interfering with its operation. Indication of their position is by means of a pointer reading on a scale graduated directly in frequency units. A precise method of calibration is given. Mechanical arrangements are described for obtaining a uniformly spaced scale, and the possibility of using such a scale in correcting for the temperature coefficient of the fork material is discussed.The relative accuracy of such a fork is greater, the smaller the range of frequency adjustment. In the present development, adjustment may be made over a range of plus and minus three percent of the mean frequency, that is, a musical interval of one semitone, or 100 cents total change. Incorporation of this fork in the chromatic stroboscope has resulted in considerable simplification as well as an increase in the reliability of the instrument.

ISSN:0001-4966    

DOI:10.1121/1.1915966

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915967

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915968

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915969

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1915970

出版商:Acoustical Society of America    

年代:1938

数据来源: AIP