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BELL SYSTEM TECHNICAL JOURNAL 



This paper will discuss the factors relating the dimensions of a 

 condenser-type microphone system with the several types of field 

 distortion, and will describe a miniature system designed to practically 

 eliminate such distortions over a wide frequency range. 



Diffraction of Sound Around an Obstacle 

 The shapes of condenser microphones alone or in association with 

 amplifiers are so irregular that it is impossible to calculate their effect 

 as diffractors of sound waves. It will suffice, however, to assume 

 some regular shape approximating actuality, for which calculations 

 can be made. The diffraction effects so obtained for the regular shape 

 will be substantially the same as those caused by the actual irregular 

 shape, provided their areas projected on the plane of the incident 

 sound-waves be equal. Cavity resonances, of course, may be quite 

 different in the two cases. But these can be treated as separate 

 effects, and will be so considered in a later section of the paper. In 

 this section, only those disturbances of the sound field, caused by the 

 smooth envelope of the microphone alone or with its amplifier, will 

 be considered. 



The case of diffraction of plane sound waves around a spherical 



Fig. 1 — X'ariation in pressure on rigid sphere due to diffraction of plane sound waves. 



