PROGRAM TRANSMISSION CIRCUITS 



245 



In the third place, the usual listening conditions impose a definite limit 

 on the useful volume range. The loudest passages in the music of a sym- 

 phony orchestra correspond to a sound level of about +95 decibels at a point, 

 say one-third the way back in an auditorium, but most people in their 

 homes prefer a level which is lower than this b}' 5 to 10 decibels. Figure 8 



99.99 



25 30 35 40 45 50 55 60 65 

 Room Noise -db Above Reference Sound Level 



Fig. 8 — Residence room noise with radio sets silent 

 Average 43 db. Standard deviation 5.5 db. 



shows the results of an extensive survey"* of acoustic room noise in homes. 

 It will be noted that the average noise level is +43 decibels on the sound- 

 level scale, and that few hom.es are quieter than +30 decibels even in the 

 suburbs. The signal-to-noise range inherent in the listening conditions, 

 and allowing nothing for the noise contributed by the transmission system 

 or the room noise where the program is being produced, is therefore 



