302 



BELL SYSTEM TECHNICAL JOURNAL 



Pick-Up Conditions 

 The source room is the auditorium of the American Academy of 

 Music in Philadelphia. This room has a volume of approximately 

 700,000 cubic feet, and a seating capacity of 3000. Measured reverber- 

 ation time curves for this auditorium, and preferred values ^-^ for a 

 room of this volume, are given in Fig. 1. It may be seen that with a 



yj 1.0 



500 1000 



FREQUENCY IN CYCLES PER SECOND 



Fig. 1 — Reverberation characteristics of Academy of Music, Philadelphia, Pa. 



full audience this room might be considered somewhat dead, but would 

 be considered generally satisfactory for pick-up either with or without 

 an audience. A floor plan of the Academy auditorium and stage, 

 showing the location of the three microphones used, is given in Fig. 2. 

 The microphone positions were selected after judgment tests using 

 several locations and are much nearer the orchestra than they would 

 be for single channel pick-up.^ The use of the microphones near the 

 orchestra results in picking up a high ratio of direct to reverberant 

 sound and thus reduces the effect of reverberation in the source room 

 upon the reproduced music. A high ratio of direct sound is desirable 

 in the present case also because of the use of three channels. The per- 

 spective effect obtained with three channels depends to a considerable 

 extent upon the relative loudness at the three microphones, and since the 

 change in loudness with increasing distance from the source is marked 

 for the direct sound only, and not for the reverberant, there would be 



