COLLECTION OF SOUND 307 



zone. With this microphone the relative loudness of these sources can be 

 adjusted by the angular position relative to the microphone axis as well 

 as the distance. Obviously, this is a great advantage in balancing the in- 

 struments of an orchestra. In the case of a nondirectional microphone, 

 the relative loudness can only be adjusted by the distance. 



The same procedure ^^ for balancing the instruments of an orchestra 

 may be used in connection with a unidirectional microphone (Fig. 12.15^). 

 The unidirectional microphone is particularly useful when all the instru- 

 ments are grouped in front of the microphone and the objectionable sounds 

 originate behind the microphone. 



The directional characteristics of the velocity microphone are useful in 

 overcoming objectionable noises.^^ It is possible to orient the microphone 

 so that the objectionable noise lies in the plane of zero response of the 

 microphone as shown in Fig. 12.15C 



In certain types of recording ^^ it is desirable to place the microphone at 

 the center of action directed upwards and collect sounds over an angle of 

 360° with respect to the microphone. (Figure 12.15D illustrates the use 

 of a unidirectional microphone for this application.) 



Other examples of the use of directional microphones are shown in 

 Fig. 12.5. 



B. Broadcasting Studios. — In the early days of broadcasting it was cus- 

 tomary to make the reverberation time of the studios as low as possible. 

 This imposed quite a strain upon the orchestra and singers to keep in tune. 

 The almost universal use of directional microphones during the past few 

 years has eliminated the necessity of extremely dead studios. As a result, 

 the quality and artistic effects of the collected sound are materially 

 enhanced. 



The studios in a large broadcasting station should be graduated in size 

 and in corresponding acoustical condition to accommodate anticipated 

 loading to the best advantage. The control booths should be provided 

 with sound proof windows located so that the studio engineer has an un- 

 obstructed view of the studio. 



The studios should be insulated against all types of extraneous noises. 

 Cinder composition has been found to give very good insulation. Resihent 

 mounting of the walls, floor and ceiling reduces mechanical transmission. 



Air borne noises carried in the air conditioning ducts may be suppressed 

 by lining the ducts with felt, rock wool, etc., to obtain suitable attenuation. 



27 Olson, H. F., Jour. Soc. Mot. Pic. Eng., Vol. 27, No. 3, p. 284, 1936. 



28 Olson, H. F., Jour. Soc. Mot. Pic. Eng., Vol. 16, No. 6, p. 695, 1931. 



29 Olson, H. F., Jour. Soc. Mot. Pic. Eng., Vol. 27, No. 3, p. 284, 1936. 



