DISPERSION OF SOUND 



291 



ment is an important factor in the motion picture and sound re-enforcing 

 systems. The minimum intensity which these systems should be capable 

 of producing is 80 db. db = .0002 dyne per square centimeter. The 

 graph of Fig. 12.7 shows the acoustic power required, as a function of the 

 volume, in auditoriums to produce a level of 80 db. In large auditoriums 

 where the orchestra is also re-enforced the power available should be greater. 

 For example, to render full artistic appeal, the system should be capable 



■ 10^ lO* 10^ 10^ 10' 



VOLUME IN CUBIC FEET 



Fig. 12.7. Acoustic power required to produce an intensity level of 80 db as a function of 



the volume of the auditorium. 



of producing a level up to 100 db. This means a power of 100 times that 

 shown in Fig. 12.7. Systems for producing this sound level without dis- 

 tortion usually require special amplifiers and loud speakers. 



F. Noise at Different Locations. — The ease with which speech may be 

 heard and understood depends upon the noise conditions as well as upon 

 the other characteristics of a sound reproducing system. The full artistic 

 effects of musical reproduction can only be obtained with a wide volume 

 range. This volume range, of course, depends upon the noise level at the 

 listening point. The tolerable level of the noises generated in any repro- 

 ducing system depends upon the noise level at the reproducing point. 



The noise level " of residences, business offices and factories is shown in 



" Seacord, D. F., Elec. Eng., Vol. 58, No. 6, p. 255, 1939. 



