208 



MICROPHONES 



principal sources of phase shift between the two units, namely: a phase 

 shift due to a finite separation and a phase shift due to a difference in the 

 phase frequency characteristics. 



10 20 30 40 00 



Fig. 9.27. The ratio of energy response to random sounds of a directional microphone con- 

 sisting of a bidirectional and a nondirectional unit as a function of the ratio of the outputs 

 of the elements, as compared to the nondirectional microphone. End energy response of 

 a nondirectional microphone. Ed energy response of a directional microphone. Ri voltage 

 output of the nondirectional unit. R^ voltage output of the directional unit. 



BIDIRECTIONAL 



NONDIRECTIONAL - 



COMBINATION 



^M^ 



"^y^yQ 



ENERGY RESPONSE 

 TO RANDON SOUND 



Fig. 9.28. Directional diagrams of various combinations of bidirectional and nondirectional 

 microphones and the energy response to random sounds. 



Consider the case in which there is a phase shift 4> between the output 

 of the bidirectional and nondirectional units. The output of each sepa- 



