HIGHLY DIRECTIONAL MICROPHONES 



221 



The response characteristics of the units with the filter systems are shown 

 in Fig. 9.39. Figure 9.40 illustrates the principles used in obtaining uniform 

 directional characteristics. Figure 9.40^^ is the directional character- 

 istic of line 3 at 700 cycles. Figure 9.405 shows the directional charac- 

 teristics of lines 2 and 3 at 950 cycles. The resultant of these characteris- 

 tics is also shown in Fig. 9.405. The same is shown in Fig. 9.40C for 1250 



FREQUENCY IN CYCLES PER SECOND 



Fig. 9.39. Voltage response frequency characteristics of the unit sand filter 

 system shown in Fig. 9.38. 



cycles. In Figs. 9.405 and 9.40C the directional characteristic of line 2 

 is broader than Fig. 9.40y^ while the characteristic of line 3 is narrower. 

 The resultant of lines 2 and 3 is a directional characteristic very close to 

 Fig. 9A0yi. The directional characteristics of the microphone shown in 

 Fig. 9.38 for the range from 85 to 8000 cycles, except for the small lobes 



as TO 8000 CYCLES 



Fig. 9.40. y/.Thedirectionalcharacteristicof line 3 at 700 cycles. 5. The directional character- 

 istics of lines 2 and 3 and the resultant at 950 cycles. C. The directional characteristics of 

 lines 2 and 3 and the resultant of 1250 cycles. D. The directional characteristics of the 

 microphone shown in Fig. 9.38 for the range from 85 to 8000 cycles fall within the shaded 

 area. 



for angles greater than 90°, fall within the shaded area of Fig. 9.40D. 

 Considering that this microphone has a frequency range of 6| octaves, it 

 is a remarkably uniform characteristic. 



C. Directional Efficiency of a Directional Sound Collecting System. — 

 The ratio of energy response of a nondirectional microphone as compared 

 to a directional microphone for sounds originating in random directions. 



