摘要:

The air chamber is treated as a boundary value problem which results in the solution of the wave equation for the general case in which the horn throat enters the air chamber in any circumferentially symmetrical manner. The following specific cases are analyzed: (1) the case in which the horn throat enters the air chamber by means of a single orifice, (2) the horn throat enters the air chamber by means of a single annulus of radiusrand widthw, and (3) the horn throat enters the air chamber in “m” annuluses of radiir1⋯rmand widthsw1⋯wm. The analysis reveals that the radial perturbation caused by the horn throat excites higher order modes. At the resonant frequencies of these modes the horn throat pressure becomes zero and the loudspeaker does not radiate. By suitable choice of annulus radii and widths the first “m” modes may be suppressed and the corresponding nulls in the output pressure eliminated.

ISSN:0001-4966    

DOI:10.1121/1.1907038

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

A method has been developed for measuring the acoustic power output in watts and the frequency spectra of ventilating fans operating into ducts. Both the inlet and the exhaust noise are determined as a function of back‐pressure. The fan is ideally connected to a circular section of duct about equal in diameter to the fan diameter and five to ten diameters in length. Three to six diameters from the input end of this duct an air straightener is located. The acoustic measurements are made with a condenser microphone enclosed in a wind screen located four to eight diameters from the inlet. The outlet end of the duct couples through an exponential connector to an anechoic wedge structure two feet square. This is backed by a plenum chamber containing an array of holes that can be progressively closed to produce increased back‐pressure. Sound pressure level measurements are made in frequency bands and converted to acoustic watts per band. The inlet noise is measured over a hemispherical surface outdoors to obtain the directivity pattern and the acoustic power for each frequency band. Engineering formulas and charts for applying the data to prediction of the noise produced in rooms are presented, including the effects of room characteristics, duct losses, and the distance from the ventilating grille in the room. Criteria for permissible noise levels in various types of rooms and auditoriums are presented.

ISSN:0001-4966    

DOI:10.1121/1.1907039

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Using the apparatus described by Beranek, Reynolds, and Wilson, measurements were made of the acoustic power in watts in twenty‐four bands each one‐third octave wide for three vaneaxial‐type and two centrifugal‐type fans of graded sizes. Formulas were derived empirically, enabling the computation of the over‐all acoustic power of the noise for the exhaust end of a fan where the input power, the number of blades, blade‐tip speed, and other design characteristics are known. The directivity pattern and acoustic power generated for each of the twenty‐four bands was also measured at the inlet with the fan mounted in one end of a long duct outdoors. The effects of back pressure were also determined. As a second stage of this investigation, the acoustical characteristics of unlined ducts were studied. The attenuation effects of one and two, 90° unlined bends placed in the ten‐inch by twelve‐inch duct system were determined. The greatest amount of attenuation was found in those frequency bands that contained the frequencies for which the width of the duct, in the direction of the bend, was 0.5 wavelength and 1.5 wavelength.

ISSN:0001-4966    

DOI:10.1121/1.1907040

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

The impedance introduced by an abrupt change of circular cross section of a tube has been examined. It is shown that in the case of an ideal viscousless fluid the effect of the discontinuity is to introduce an inductance in series with the acoustical transmission system. The discontinuity inductance has been determined as a function of the ratio of the tube radii and has been plotted for different values of this ratio. The problem of a small tube or constriction inserted between two larger tubes has also been treated. It is shown that the constriction inductance is equal to the sum of the discontinuity inductances of each end taken separately to a very good approximation. The constriction inductance can be considered as a correction term to be added to the analogous acoustical inductance of the tube and can be interpreted physically as an increase in the equivalent length of the tube.

ISSN:0001-4966    

DOI:10.1121/1.1907041

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

In the absorption of 4 mc/sec sound in liquids the complete conversion of sound energy into thermal energy is substantiated.

ISSN:0001-4966    

DOI:10.1121/1.1907043

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

An experimental method of measuring the attenuation of sound in a circular tube for gases at reduced pressures has been developed. Since the tube effect is inversely proportional to the square root of the pressure, a reduction in pressure increases the attenuation and thus increases the experimental accuracy. The tube attenuation was measured for the frequency over pressure ratio of 8 to 2000 kc/atm. The measured attenuation was found to be 4.5 percent greater than that predicted by the Kirchhoff formula.

ISSN:0001-4966    

DOI:10.1121/1.1907044

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1907046

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP

摘要:

Temporary birefringence, induced by ultrasonic stress, causes a depolarization in a plane polarized light beam traversing a transparent quartz plate. Detection of this depolarization allows the complete sound field to be made visible. Photographs taken by this technique are shown.

ISSN:0001-4966    

DOI:10.1121/1.1907047

出版商:Acoustical Society of America    

年代:1953

数据来源: AIP