200 



MICROPHONES 



a circular baffle is shown in Fig. 9.20. It will be seen that for small values 

 of R/\ the directional characteristic corresponds to a cosine function. Be- 

 tween R/\ = f and f the directional pattern is sharper than a cosine char- 

 acteristic. Then for R/\ larger than f the characteristics broaden and 



.9 



.8 



« .7 



I- 

 _i 



O 

 >.6 



_l 



2 .. 



Z 3456789 2 3456789 2 3456789 



.01 .1 I' 10 



R. 



x; 



Fig. 9.19. Measured open circuit voltage response frequency characteristic of a mass con- 

 trolled, electrodynamic ribbon located in a large circular baffle. 



assume irregular shapes. The theoretical directional characteristics em- 

 ploying equations 9.45, 9.50 and 9.51 are shown in Fig. 9.21. It will be 

 seen that the agreement with the experimental results of Fig. 9.20 is quite 

 good. There is some deviation for D/\ = f . It is in this region that 

 deviations occurred between the theoretical and experimental results for 

 the pressure, Figs. 9.14 and 9.15, and for the response. Figs. 9.18 and 9.19. 

 The theoretical directional characteristics for a doublet, Fig. 9.12, becomes 

 progressively broader for R/\ = f , | and f and does not agree at all with the 

 experimental results. For R/X = f , | and 1 the shape of the theoretical 

 directional characteristics of the doublet does not correspond with the 

 experimental results. Summarizing, the theoretical directional characteris- 

 tics of a ribbon microphone with a circular baffle agree within a few per 



