PHYSICAL FACTORS 257 



Principal Conclusions 

 The principal conclusions that have been drawn from these inves- 

 tigations may be summarized as follows: 



1. Of the factors influencing angular localization, loudness difference 

 of direct sound seems to play the most important part; for certain 

 observing positions the effects can be predicted reasonably well from 

 computations. When large quality differences exist between the 

 loudspeaker outputs, the localization tends toward the more natural 

 source. Reverberation appears to be of minor importance unless 

 excessive. 



2. Depth localization was found to vary with changes in loudness, 

 the ratio of direct to reverberant sound, or both, and in a manner not 

 found subject to computational treatment. The actual ratio of direct 

 to reverberant sound, and the change in the ratio, both appeared to 

 play a part in an observer's judgment of stage depth. 



3. Observers in various parts of the auditorium localize a given 

 source at different virtual positions, as is predicted by loudness com- 

 putations. The virtual source shifts to the side of the stage as the 

 observer moves toward the side of the auditorium. Although quan- 

 titative data have not been obtained, qualitative data on these effects 

 indicate that the observed shift is considerably greater than that 

 computed. Moving backward and forward in the auditorium appears 

 to have only a small effect on the virtual position. 



4. Because of these physical factors controlling auditory perspective, 

 point-for-point correlation between pick-up stage and virtual stage 

 positions is not obtained for 2- and 3-channel systems. However, 

 with stage shapes based upon the ideas of Fig. 7, and with suitable 

 use of quality and reverberation, good auditory perspective can be 

 produced. Manipulation of circuit conditions probably can be used 

 advantageously to heighten the illusions or to produce novel effects. 



5. The 3-channel system proved definitely superior to the 2-channel 

 by eliminating the recession of the center-stage positions and in re- 

 ducing the differences in localization for various observing positions. 

 For musical reproduction, the center channel can be used for inde- 

 pendent control of soloist renditions. Although the bridged systems 

 did not duplicate the performance of the physical third channel, it is 

 believed that with suitably developed technique their use will improve 

 2-channel reproduction in many cases. 



6. The application of acoustic perspective to orchestral reproduction 

 in large auditoriums gives more satisfactory performance than probably 

 would be suggested by the foregoing discussions. The instruments 

 near the front are localized by every one near their correct positions. 



