DISPERSION OF SOUND 



289 



siderable amplification which increases the tendency for feedback. In 

 cases where difficulties are experienced, due to acoustic feedback, a further 

 reduction in coupling can be obtained by employing directional microphones. 

 Furthermore, the stage collecting system should not be responsive to 

 sound originating in the orchestra or audience. In case the micro- 

 phones are located in the footlights, the shielding effects of the apron, to- 

 gether with a velocity microphone. Fig. 12.5, are in general sufficient to 

 accomplish this objective. Where it is impossible to shield the micro- 

 phones in this manner the unidirectional microphone has been found to be 

 very useful, as will be seen from a consideration of the directional charac- 

 teristics of this microphone shown in Fig. 12.5. 



, PLANE OF 

 VZERO RESPONSE 

 DIRECTIONAL 

 CHARACTERISTIC 



MICROPHONE 



ABSORBING 

 MATERIAL 



Fig. 12.5. Arrangements depicting the use of directional loud speakers and microphones 

 for reducing feedback between the loud speaker and the microphone. The arrangement 

 on the left employs a velocity microphone. A shield is used to reduce sound pickup from 

 the orchestra and audience. The arrangement on the right employs a unidirectional micro- 

 phone. The directional characteristics of this microphone are particularly adapted for 

 collecting sounds on the stage and discriminating against sounds coming from the orchestra 

 and audience. 



In order to " cover " the action from any part of the stage several micro- 

 phones are employed, usually spaced at intervals of ten feet. The output 

 of each stage microphone and orchestra microphone is connected to a sepa- 

 rate volume control on the mixer panel. This mixer and volume control 

 system is located in the monitoring box. By means of this system the 

 operator follows the action by selecting the microphone nearest the action 

 on the stage. The operator also controls the ratio of the volume of the 

 stage sound to that received from the orchestra when there is an orchestral 

 accompaniment as well as the overall intensity of the augmented sound. 



