Originally Posted by rcohen
One caveat to this is that with 4 subs, you get more flexibility for symmetrical layouts, which can be really helpful for cancelling room modes and getting seat to seat consistency.
In addition with 4 subs you get greater overall in-room flatten frequency response. Here's Data-base.com measurements on 1-4 subs separate, identical subwoofers placed away from each other:
"It is easy to see that adding in the second subwoofer caused a gain larger than 6dB at the listening position in quite a few places – 12, 30, 40, 50 and 90Hz for example. Over some ranges output was actually lost (58-65Hz and 97-116Hz) most likely due to the phase relationship at those frequencies.
Looking at the gain seen from adding in the third subwoofer, note that again at 30Hz more than 6dB is gained and the system’s total radiation is not even doubling at this point by adding a third sub and at 80Hz we again see a slight loss.
By the time the fourth subwoofer is added in, the gain is between 2-4dB for the most part. However, note that the overall response has been flattened out and smoothed significantly
, fitting within a 12dB window from 5-120Hz, where it was about an 18.5dB window before with much more overall variation."
In the example given above, the green trace is one
subwoofer, red is two
, blue is three
and the black trace is all four
of them operating at once.