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Journal of the Acoustical Society of America

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Oct 1974

Volume 56, Issue 4, pp. 1043-1309

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Ray trace acoustics in unsteady inhomogeneous flow

Ray Engelke

J. Acoust. Soc. Am. Volume 56, Issue 4, pp. 1291-1292 (1974); (2 pages)

Online Publication Date: 12 Aug 2005

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The differential equations governing acoustic ray trajectories for space‐ and time‐dependent flow are derived. The derivation requires only a generalized Huygens's principle and geometrical constraints. The Huygens's principle states that a ray's velocity is the vector sum of the sound speed along the wave normal and the particle velocity vector. It is found that the ray differential equations for unsteady flow have the same general form as those for steady flow. Earlier work is briefly reviewed.

Disk parametric acoustic array

James C. Lockwood

J. Acoust. Soc. Am. Volume 56, Issue 4, pp. 1293-1294 (1974); (2 pages)

Online Publication Date: 12 Aug 2005

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A parametric acoustic array, the primary field of which is a thin disk of cylindrically spreading waves, is analyzed. It is shown that the half‐power beamwidth of difference‐frequency radiation perpendicular to the disk exceeds the beamwidth of the corresponding collimated plane‐wave parametric array by a factor of 1.316. The radiated intensity is less than in the plane‐wave case by a factor of α0/k for the same total acoustic power in the primary waves, where α0 is the absorption coefficient at the mean primary frequency and k is the wavenumber at the difference frequency.

Speed of sound and transmission loss in silicone rubbers at ultrasonic frequencies

D. L. Folds

J. Acoust. Soc. Am. Volume 56, Issue 4, pp. 1295-1296 (1974); (2 pages) | Cited 4 times

Online Publication Date: 12 Aug 2005

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The speed of sound as a function of temperature (0°–3°C) and the transmission loss in 2.5‐cm‐thick samples of 13 different RTV silicone rubbers have been measured in the frequency range 500 kHz–1 MHz. The range of measured sound speeds for the various materials was between 960 and 1110 m/sec at 0°C. The thermal coefficients of sound speed were approximately −3 m/sec °C for all samples. The transmission losses ranged from near 0 dB for RTV‐602 to 14 dB for RTV‐90 at 1 MHz.

Statistical correlates of the energy‐equivalent sound level

D. A. Driscoll, W. J. Webster, F. G. Haag, and J. W. Farinacci

J. Acoust. Soc. Am. Volume 56, Issue 4, pp. 1297-1299 (1974); (3 pages)

Online Publication Date: 12 Aug 2005

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The increased use of energy‐averaged, single‐number measures of environmental noise (e.g., Leq and LDN) makes desirable careful comparison with the more easily obtained and more frequently used statistical levels (e.g., L10 and L50). Analysis of a variety of environmental noise distributions, as well as a theoretical analysis of normal distributions, indicates strong correlation between several of the statistical levels (particularly the L10 and the L15) and the energy‐equivalent sound level (Leq) for many types of environmental noise.
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