A NON-DIRECTIONAL MICROPHONE 



409 



effect, made more serious by the wavy character of the response, while 

 the variation in response for the sphere is much less and the waviness 

 has practically disappeared. 



I DIA 271 

 2"DIA 135 

 4" DIA 68 



0.06 0.1 0.2 0.6 1 2 



RATIO OF DIAMETER TO WAVELENGTH OF SOUND 

 813 1355 2710 8129 13,548 27,096 



406 677 1355 4064 6774 13,548 



203 339 677 2032 3487 6774 



FREQUENCY IN CYCLES PER SECOND 



81,288 

 40,644 

 20, 322 



Fig. 4 — Calculated diffraction effect at the center of the end form of a cylinder, cube, 

 and sphere for sounds coming from different directions. 



It appears then that a very small sphere would be the most desirable 

 shape, but it was found impracticable to reduce the microphone housing 

 below a 2>2 inch sphere and to reduce the diaphragm diameter below 

 1 inch. The field response of the resultant microphone without the 

 acoustic screen for various angles of sound incidence is shown in Fig. 5. 



