306 



ARCHITECTURAL ACOUSTICS 



reflected sound picked up by a velocity or unidirectional microphone in 

 which fi = 4x/3 is shown in Fig. 12.14C. The generally reflected sound 

 picked up by an ultradirectional microphone in which Q, = vr/lO is shown 

 in Fig. 12.14D. The effectiveness of a directional sound collecting system 

 in overcoming reverberation and undesirable sounds is graphically depicted 

 in Fig. 12.14. 



Directional microphones, in addition to discriminating against noise and 

 generally reflected sounds, have been found to be extremely useful in ar- 

 ranging actors in dialogue and for adjusting the relative loudness of the 

 instruments of an orchestra. 



VELOCITY 

 MICROPHONE 



UNIDIRECTIONAL 

 MICROPHONE 



PLAN VIEW 



A 



VELOCITY 



\ /^^ MICROPHONE jr-^X^^ M'C 



CAMERA ^ ^ SOUN 



H iX ^^^J-'^SOURCI 



1'°""" A IT n 



PLAN VIEW 



B 



UNIDIRECTIONAL 

 MICROPHONE 



ELEVATION VIEW 



c 



ELEVATION VIEW PLAN VIEW 



D 



Fig. 12.15. Examples illustrating the use of directional microphones. 



A plan view ^^ of a velocity microphone and a number of sound sources 

 is shown in Fig. \1.\SA. Suppose that sources 2 and 5 represent two actors 

 who are carrying on a dialogue. In view of the fact that this microphone 

 receives with the same efficiency in two directions, it is possible to have 

 the actors face each other, which is an advantage from a dramatic stand- 

 point. Suppose that the sources of sound 1, 2, 3 and 5 represent the 

 instruments of an orchestra. All the sources are located at the same dis- 

 tance. This means that 1 will produce 0.7 times the voltage output pro- 

 duced by 2 for the same loudness. In the same way 3 will be 0.5 of 2. 

 Source 4 is considered as objectionable and is placed in the zero reception 



26 Olson, H. P., Proc. Inst. Rad. Eng., Vol. 21, No. 5, p. 655, 1933. 



