By S. M. Baxter
The goal of this publication is to j.ir€'~ 0l'l\' a brand new procedure for the experimental research of the loose wave version sound box of acoustics. The process relies at the use of round harmonic capabilities of perspective. Acousticians usually stumble upon random sound fields whose homes might be heavily modelled by means of use of the "free wave" box. This version box is outlined by way of easy statistical houses: stationarity in time, and homogeneity in house. Stationarity signifies that any unmarried order statistic measured via a microphone within the box could be self sustaining of the time at which the recording is taken, whereas homogeneity signifies that the size can also be autonomous of the mic- phone's place within the box. additionally, moment order information bought from the measurements of 2 microphones will count purely at the time lapse among the 2 recordings, and the relative spatial separation of the micro telephones, and never at the microphones' absolute positions in area and time. The unfastened wave box can also (equivalently) be pictured as a set of aircraft sound waves which method an commentary place from all angles. those are the "free waves" of the identify, without correlation among waves at various angles and frequencies, even supposing there may perhaps exist an angle-dependant aircraft wave density functionality. it is a degree of the density of sound power returning from diverse angles. The loose wave box has proved to be an easy yet remarkably robust model.
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1». 16) showed good agreement of theory and measurement when a dipole surface source model (m=1) was used. 17) later showed that Cron and Sherman's deep water correlation results for their surface noise model also applied to correlation in regions near to the surface. 18) independently made a similar theoretical and experimental study. 19) suggested a different approach to the surface noise problem involving the correlation produced in deep water beneath a surface distribution of independent sources with a specified plane correlation.
If the weighting is dominated by a single peak, 111 describes the position of the peak, 112 describes its width, and so on. The more moments are known, the more detail of the weighting is specified. 28) cos v cos nv = (1/3)(sin - vl)/2. 29) The significance of these moments for the form of CCSD is illustrated by a consideration of the axial CCSD in a partially reverberant field. 24). e. 35) Thus the lowest-order moments of the plane wave weighting are reflected in the low-kr range of CCSD, so that if only a limited range of kr values were available, only the lowest-order features of the plane wave weighting could be observed.
DIRECT WEIGHTING ANALYSIS: SPHERICAL HARMONIC EXPANSIONS Only one restriction - large sampling position separations - was made on the CCSD data set necessary for the stationary phase analysis method described in the last section. Suppose now that the data set is still more limited, to a sparse irregular array of pOints which cannot be assumed to be far apart. An analysis method which will work even under these conditions is based on the spherical harmonic expansion of CCSD and weighting, and is discussed in this section.