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ARCHITECTURAL ACOUSTICS 



the vertical coverage angle is very small, which means that practically 

 any system will have a distribution angle sufficiently broad to supply the 

 required vertical spread. However, for conservation of power the vertical 

 spread of the loud speaker should correspond to the vertical angle subtended 

 by the audience at the loud speaker. Since the distance of those nearest 

 the loud speaker to those farthest removed (that is, considering the vertical 

 angle only) is very nearly the same, the sound intensity from the loud 

 speaker will be practically the same for all parts of the audience through 

 any vertical plane and the use of compensation by means of the directional 

 characteristics for change in distance in the vertical plane to obtain uniform 

 response is not necessary. In the horizontal plane the spread of the loud 



\--i S S 8 8- 



FIELD 



LOUD SPEAKERS 



PLAN VIEW 



ELEVATION VIEW 



Fig. 12.9. Two arrangements of sound systems for addressing assemblages in large grand- 

 stands. For the stadium on the left a large number of loud speakers are used, each loud 

 speaker covering a small portion of the total area. For the ball park on the right, a single 

 loud speaker cluster is used to supply the entire grandstand. 



speaker should correspond to the angle subtended by the stands at the 

 loud speaker. Since the center line is farthest removed, a directional 

 characteristic of the shape shown is necessary for obtaining the same sound 

 level in all parts of the grandstand. To eliminate any difficulties due to 

 feedback, a velocity microphone is used and oriented so that the plane of 

 zero reception passes through the loud speaker system. 



The sound level required for public address work of the type considered 

 above will be determined by the noise level of the maximum crowd. In 

 general, it is not practical to employ a system with sufficient power to 

 override the sound level during cheering, applause, etc. However, the 

 power should be sufficient to override the general noise during relatively 



