254 



BELL SYSTEM TECHNICAL JOURNAL 



the angular location of each position on the virtual stage results from a 

 particular loudness difference at the two ears produced by the speech 

 coming from the loud speakers. When three channels are used a definite 



20 



^ -20 



20 



-12 -10 



-4-2 2 4 



sr-sl in decibels 



Fig. 5 — Calculated and observed apparent angles for 2- and 3-channel reproduction. 



set of loud speaker speech levels exists for each position on the pick-up 

 stage. To create these same sets of loud speaker speech levels with 

 the 3-microphone 3-loud speaker bridging arrangement already dis- 

 cussed, it would be necessary to change the bridging gains for each 

 position on the pick-up stage. Hence it could not be expected that 

 the arrangement as used (i.e., with fixed gains) would create a virtual 

 stage identical with that created by 3-channel reproduction. How- 

 ever, with proper technique, bridging arrangements on a given number 

 of channels can be made to give better reproduction than would be 

 obtained with the channels alone. 



Experimental Verification of Theory 

 Considerations of loudness difference indicate that all caller positions 

 on the pick-up stage giving the same relative loud speaker outputs 



