ISSN:0001-4966    

DOI:10.1121/1.2143407

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The diffraction of a plane harmonic sound wave by an aperture in an infinitely thin rigid plane screen is investigated theoretically. Variational principles for the diffracted spherical wave amplitude at large distances from the aperture are derived. In the first of these, the stationary property is exhibited for the class of functions comprising the normal derivative of the aperture velocity potentials, whose distributions are governed by a generally insolvable integral equation. The second involves functions which characterize the discontinuity in velocity potentials at the screen (or their deviation from infinite screen distributions), and are specified by another integral equation. A comparison of the two variational principles is given, which indicates that their over‐all agreement following use of approximate functions, is a measure of the accuracy obtained. The plane wave transmission cross section of the aperture is related to the imaginary part of the diffracted amplitude in the direction of incidence and is cast in stationary forms. Particular attention is given to the low and high frequency behavior of the various forms of cross section, including comparison with Kirchhoff theory predictions.

ISSN:0001-4966    

DOI:10.1121/1.1906574

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The reciprocity pressure response formula is derived from the equations of motion of the electroacoustic systems involved in reciprocity measurements in which only two of the three transducers are coupled at a time to the chamber. The formula includes the acoustical impedances of the three transducers. When it is assumed that the acoustical impedances of the transducers are large relative to the chamber impedance an approximate formula is obtained which includes the acoustical impedance of only one of the transducers, the one whose response is given by the formula.

ISSN:0001-4966    

DOI:10.1121/1.1906575

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The equivalence between the problems of the change of cross section and the biforcation of a cylindrical tube, previously stated as exact, is only approximate. An exact solution to the latter problem (for a circular tube) has been given by Bailin, and the results are compared with recent calculations for the change of cross section. The approximate equivalence between the two results is found to be sufficiently close for many applications but to be far from exact.

ISSN:0001-4966    

DOI:10.1121/1.1906576

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906578

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1906580

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

The heterodyne filter, developed at the RIT, Stockholm, Sweden, is a laboratory transmission system for the speech frequency range. It can be used as a band pass filter with continuously variable low frequency cut‐off and high frequency cut‐off of very steep attenuation characteristics, 1–2 c.p.s. per db and 60‐db attenuation outside the band pass range. The two cut‐off frequency settings can be chosen independently in the frequency range 0–4000 c.p.s. One frequency dial on the panel controls the band width, another controls the low pass cut‐off. A band suppression action can also be obtained. In this case the band width is restricted to 2 alternative values. The mid‐frequency will be continuously variable, 0–4000 c.p.s. The heterodyne filter is meant for articulation and hearing tests in acoustic research work but can also be used as a wave analyzer with continuously variable band‐width of 50 c.p.s.‐4000 c.p.s. in the frequency range of 20–12,000 c.p.s.

ISSN:0001-4966    

DOI:10.1121/1.1917126

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

An artificial mastoid for testing bone conduction receivers is described. It consists essentially of a stiff metal bar having a fundamental resonant frequency above the measurement range, with a strain‐sensitive translating element fastened to the under side and a compliant pad on top. The translating element is a slab of activated ceramic, which is essentially invariant to humidity and temperature variations. The compliant pad generally used is Koroseal ♯74, which simulates the flesh over the mastoid prominence reasonably well. Koroseal ♯15 simulates flesh better but is less rugged. Calibration methods are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1917132

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

In 1933 Sivian and White closed their paper in the Journal of the Acoustical Society with the statement that at low frequencies the difference between the thresholds for minimum audible field and minimum audible pressure could not be explained. To investigate this problem further monaural field thresholds and monaural pressure thresholds have been obtained, the latter for cavities varying from 6 cc to over 800 cc. A probe tube, attached to a W.E. 640‐AA condenser microphone, was inserted near the ear drum and the sound pressure determined with the probe remained invariant under transformations of volume. Similarly the same probe was used to determine the pressure for free field. When sufficient care is taken to eliminate muscle noises, breathing noises, etc., and to insure monaural listening, there appears to be no significant difference between minimum audible field and minimum audible pressure at low frequencies. This result is based on measurements made with a limited number of subjects; however, to secure more representative data measurements are being continued with a larger number of subjects.

ISSN:0001-4966    

DOI:10.1121/1.1917141

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP

摘要:

Absolute and thermal noise masked pure tone thresholds were obtained for 3666 people at the 1948 San Diego County Fair. For groups having equal absolute hearing losses, slightly greater masked losses were found for the older age groups (over 40), females, and individuals who had not worked in noise, had not had musical training, and who were aware of hearing difficulty. It was further found that those with predominantly low frequency losses had greater masked losses than those with predominantly high frequency losses. Ratios of the intensity of the tones to intensity per cycle of the masking noise were obtained for masked thresholds of people whose corresponding absolute thresholds varied over a seventy‐db range. These ratios are plotted as a function of absolute hearing loss.

ISSN:0001-4966    

DOI:10.1121/1.1917142

出版商:Acoustical Society of America    

年代:1950

数据来源: AIP