308 BELL SYSTEM TECHNICAL JOURNAL 



"tempo" signal to the assistant director leading the orchestra that 

 could be operated during the rendition of the music. The switches 

 for the auxiliary circuits and the order wire subset are shown at the 

 control operator's position at the left in Fig. 6. 



That a reproducing system may have quite different characteristics 

 in different auditoriums is well illustrated in the case of the two halls 

 considered here. From Fig. 3 it may be seen that in Constitution 

 Hall the stage is built into the auditorium itself, and that there is no 

 back stage space. The Academy of Music, however, has a large 

 volume back stage. When the orchestra plays in the Academy the 

 reflecting shell shown in Fig. 2 is used to concentrate the radiated 

 sound energy toward the audience. When the reproducing system 

 was set up in the Academy the shell could not be used because of the 

 stage and lighting effects desired, and a large part of the energy radi- 

 ated by the loud speakers at the low frequencies was lost back stage. 

 The loss of low frequency energy is attributable partly to the fact that 

 the loud speakers cannot well be made as directional for the very low 

 frequencies as for the higher. The loss amounts to about 10 db at 

 35 c.p.s., and becomes inappreciable at 300 c.p.s. or more, as measured 

 in comparable locations in the two auditoriums. This difference in 

 characteristics emphasizes the fact that for perfect reproduction the 

 acoustics of the auditorium must be considered as a part of the system, 

 and that in general the equalizing networks must have different charac- 

 teristics for different auditoriums. 



References 



1. "Acoustics of Broadcasting and Recording Studios," G. T. Stanton and F. C. 



Schmid. Jour. Acous. Soc. Am., v. 4, No. 1, part 1, July 1932, p. 44. 



2. "Acoustic Pick-Up for Philadelphia Orchestra Broadcasts," J. P. Maxfield. Jour. 



Acous. Soc. Am., v. 4, No. 2, Oct. 1932, p. 122. 



3. "Optimum Reverberation Time for Auditoriums," W. C. MacNair. Jour. Acous. 



Soc. Am., V. 1, No. 2, part 1, Jan. 1930, p. 242. 



4. "Acoustic Control of Recording for Talking Motion Pictures," J. P. Maxfield. 



Jour. S. M. P. E., V. 14, No. 1, Jan. 1930, p. 85. 



5. "A High Speed Level Recorder for Acoustic Measurements," E. C. Wente, E. H. 



Bedell, K. D. Swartzel, Jr. Unpublished paper presented before the Acous. 

 Soc. Am., May 1, 1933. 



6. "The Effect of Humidity Upon the Absorption of Sound in a Room, and a Deter- 



mination of the Coefficients of Absorption of Sound in Air, V. O. Knudson. 

 Jour. Acous. Soc. Am., v. 3, No. 1, July 1931, p. 126. 



7. "Absorption of Sound in Air, in Oxygen, and in Nitrogen — Effects of Humidity 



and Temperature," V. O. Knudson. Jour. Acous. Soc. Am., v. 5, No. 2, 

 Oct. 1933, p. 112. 



