206 



MICROPHONES 



UNIDIRECTIONAL I FOOT 



FREQUENCY 



100 

 FREQUENCY 



UNIDIRECTIONAL 2 FEET 



UNIDIRECTIONAL 5 FEET 



C°20 



>2 



-100 

 FREQUENCY 



1000 D 20 



100 

 FREQUENCY 



Fig. 9.26. A. The relative voltage output of a velocity (or pressure gradient) microphone as 

 compared to a nondirectional pressure microphone for distances of 1, 2 and 5 feet. B, C, 

 D, the relative voltage output of a unidirectional microphone as compared to a nondirec- 

 tional pressure microphone for distances of 1, 2 and 5 feet and for various angles of the 

 incident sound. 



B. Efficiency of Energy Response to Random Sounds of the Unidirec- 

 tional Microphone as a Function of the Relative Sensitivities of the Bidirec- 

 tional and Nondirectional Microphones'^^. — The unidirectional microphone 

 consists of the combination of a bidirectional microphone, in which the 

 output is a function of the cosine of the angle of incidence, and a non- 

 directional microphone. In general, it is customary to make the output 

 of the bidirectional microphone for 6 = equal to the nondirectional 

 microphone. For this condition the directional characteristic is a cardioid 

 of revolution. In the case of both the bidirectional and the cardioid uni- 



28 Olson, H. F., Broadcast News, No. 30, p. 3, May, 1939. 



