SUMMARY 
STATEMENT OF PROBLEM 
Determine some of the theoretical properties of the multipole sound fields generated 
by both free turbulence and turbulence in the presence of solid boundaries at distances that 
are less than a wavelength from the turbulence. Compare the frequency spectra and spatial 
properties of the induction near-sound fields with the frequency spectra and spatial properties 
of the far-sound fields of these multipole sound sources. 
FINDINGS 
There are significant differences in the frequency spectra and the spatial properties 
of the various multipole components of the sound field at distances greater than and less than 
a wavelength from a turbulent region. Approximate corrections to datataken in the near-sound 
field of multipole sound sources can be made if the geometric extent, type, and orientation of 
the multipole sources are known or can be estimated. 
RECOMMENDATIONS 
If possible, measurements of the sound from multipole sound sources should be taken 
at a distance that is many wavelengths and many ‘‘diameters’’ from the sound sources. If 
this is not possible or desirable, information about the geometric extent, type, and orientation 
of the sound sources should be obtained. 
