From SAC Newsletter Volume 9 Number 4
(Newsletter Volume 9, No.2, page 21, “Split Speakers? Reduce One Channel 3 dB,” credits CLEON WELLS of Chicago Recording with asking during our last Chicago class, “What happens if?”. Recently we were telling Cleon how pleased we are with his suggestion and he said the idea was first suggested to him by Mike King of Chicago Recording.)
This translates into concern whenever sound from two sources will arrive at equal levels but with time differences of 50 msec or greater (see the Doak and Bolt criteria, Fig. 7-46, page 130, of SOUND YSTEM ENGINEERING) or with time differences of l.0 msec or less. The area of from 3 msec up to 50 msec can, on occasion, be audible depending upon the number of accompanying reflections.
J. Blauert and P. Laws Criteria
This paper has had frequent referencing to it by many of the “literature researchers,” most of whom do no listening–just reading.
We are beginning to suspect that the Blauert and Laws criteria are in reality the upper curve for an “envelope” whose lower limit represents the area of one inch or less of time difference. In other words, time differences of less than one inch are audible-from one inch to about two feet are not audible and then over two feet they once again become audible.
The Haas effect usually takes over for equal level signals separated by anywhere from 3 to 30 or even 40 msec. We can’~ help but wonder how many “dead spots” are not due to lack of coverage but to too much coverage from unequal distances actually canceling each other
A Simple “Ear Opening” Experiment
Place two loudspeakers 1″ apart and feed them equal level signals. (See Illust. #2) Sit about ten feet away and listen. Have someone switch first one on and then both on. Move through the sound field and hear how broad the area is that is affected by this effect. Then with both units on, reduce one of them by 3 dB. Note the increase in both high frequency response and, but even more apparent, the rise in loudness.