Volume 47, Issue 3A, March 1970
Index of content:
47(1970); http://dx.doi.org/10.1121/1.1911949View Description Hide Description
Cremer's theory of sound transmission for a single‐leaf wall is transformed into a more general formulation in which the exciting pressure is expressed in terms of the spatial cross‐correlation. The correlation coefficient was measured in a reverberation room just in front of the wall under test. The sound‐transmission loss of a single gypsum‐board wall was calculated employing these diffusivity measurements and compared with experimental data. Agreement between theory and experiment is good, especially in the frequency range below the coincidence frequency. Finally, a few fictitious quasidiffuse sound fields are investigated further study of the influence of the degree of diffusivity upon transmission loss.
47(1970); http://dx.doi.org/10.1121/1.1911950View Description Hide Description
The use of single number ratings in describing the acoustic performance of various building elements is very common. Examples of this are the sound‐transmission class (STC) of a wall or the impact‐noise rating of a floor. In the STC rating method, a transmission‐loss (TL) curve of irregular shape is compared to a standard‐reference curve. The contribution of various frequency bands depends on the shape of the standard curve and the method of comparison. An experiment has been carried out to determine the relative subjective importance of the various frequency bands and how the change in subjective rating due to irregularities in a TL curve compares with the rating obtained by using the standard curve and fitting rules. Results indicate that the present STC rating system is overconservative in rating changes in a TL curve and that narrow coincidence‐type dips are not very important.
47(1970); http://dx.doi.org/10.1121/1.1911951View Description Hide Description
Statistical energy analysis is used to study the transmission of random‐incidence sound waves through two independent panels separated by an air space. The analytical model consists of five linearly coupled oscillators arranged, room‐panel‐cavity‐panel‐room. Both nonresonant and resonant transmission for the panels are included. The cavity is considered to behave as a resonant system and its modal density and loss factor are determined, analytically. Absorption material is placed around the edges of the cavity. The sound energy transmitted is found to be strongly dependent upon the radiation resistance of the panels, the panel spacing, and the panel and cavity loss factors. Agreement between the theoretical results and experiments for several different double panel systems is found to be good.
47(1970); http://dx.doi.org/10.1121/1.1911952View Description Hide Description
In 1962, Bryn derived the optimal processor for detecting a Gaussian signal in Gaussian noise with a three‐dimensional array. Unfortunately, knowledge of the cross‐spectral‐density‐function matrices for both the signal and the noise must be known before the detector can be implemented. Consideration of the optimal processor for narrow‐band processes received on two units leads to the derivation of a detector that requires no a priori knowledge of the noise or signal characteristics, and that is significantly better than the standard detector when the noise is coherent. The direct extension of these results to larger arrays has thus far not been accomplished, but a simple application of the two‐detector technique a uniformly spaced linear array indicates that even a rather crude innovation may achieve some improvement in detection.
47(1970); http://dx.doi.org/10.1121/1.1911953View Description Hide Description
This paper develops a theoretical method of obtaining the frequency response and electrical equivalent circuit of piezoelectric sources and detectors in which the piezoelectric stress hD is not spatially uniform. A wave equation is derived from a one‐dimensional formulation of the piezoelectric relations, and Green's functions are used to obtain solutions for the generated stress waves in terms of the Fourier transform of the spatial distribution of piezoelectric stress. Both acoustically matched and unmatched sources are treated. The complex electrical impedance is also developed. Expressions are obtained for the voltage and current generation in detection, and conditions for maximum power transfer are considered. Illustrative examples include sources with uniform, sawtooth, and Gaussian distributions of piezoelectric stress, both matched and unmatched. Optimization of response by choice of source distribution is illustrated. Arrays of sources are also treated, both with and without piezoelectric interactions between sources.
47(1970); http://dx.doi.org/10.1121/1.1911954View Description Hide Description
General expressions are developed for determining the beam patterns and directivity index of arbitrary configurations of hydrophones and results given in the special case of a cylindrical shell array. The limiting case of a continuous distribution of hydrophones is considered and integral relationships are derived for volume and shell distributed array. Closed‐form solutions are obtained in the case of a sphere and cylinder, and results show the response of the volume array to be superior to that of a corresponding shell array. Comparisons also show the directional characteristics of a cylindrical shell array to agree quite well with those of a corresponding discrete array whose phone spacing is less than one‐half wavelength.