DISPERSION OF SOUND 



293 



power to override any anticipated noise level of the maximum crowd, 

 and facilities available for microphones at predetermined points. 



A large stadium equipped with a public address system is illustrated by 

 the left portion of Fig. 12.9. Due to the size and configuration of the 

 audience area it is practically impossible to obtain satisfactory sound level 

 and coverage with a single loud speaker. Consequently, the loud speakers 



Table 12.2. noise levels for various sources and locations 



Source or Description 

 of Noise 



Noise Level 

 in Decibels 



Threshold of Pain 



Hammer Blows on Steel Plate 2 ft 



Riveter 35 ft 



Factory 



Busy Street Traffic 



Large Office 



Ordinary Conversation 3 ft, 



Large S tore 



Factory Office 



Medium Store 



Restaurant 



Residential Street 



Medium Office 



Garage 



Small Store 



Hotel 



Apartment 



House, Large City 



House, Country 



Average Whisper 4 ft 



Quiet Whisper 5 ft, 



Rustle of Leaves in Gentle Breeze 



Threshold of Hearing 



130 

 114 



97 

 78 

 68 

 65 

 65 

 63 

 63 

 62 

 60 

 58 

 58 

 55 

 52 

 42 

 42 

 40 

 30 

 20 

 10 

 10 

 



are placed at intervals near the boundary of the field sufficiently close to- 

 gether so that uniform response is obtained in the horizontal plane. The 

 elevation view of Fig. 12.9 shows how uniform sound distribution is ob- 

 tained in the vertical plane by means of the directional characteristics. 

 The microphones are usually located either on the field or in the press box. 

 A baseball field equipped with a public address system is illustrated by 

 the right portion of Fig. 12.9. As contrasted to the stadium, here a single 

 loud speaker station is used to supply the entire audience area. The dis- 

 tance between the loud speakers and the auditors is very large. Therefore, 



