At one time I read several Audio Engineering Society papers on the subject of detection of low frequency sources, and came away with the understanding that a crossover frequency of 80 Hz was acceptable as long as the low-pass filter's slope was steep enough. Tones below 80 Hz could not be localized by ear, but if the crossover wasn't steep enough then sufficient lower midrange energy would leak through to give away the sub's location. Subwoofer systems that meet the 80 Hz/steep slope (4th order) criteria can be placed pretty much anywhere in the room.
If the crossover has to be above 80 Hz and/or is not very steep, then it's best to keep the sub(s) near the main speakers and probably fairly symmetrical. That being said, I have used a satellite/sub system that had a 150 Hz crossover with a relatively shallow slope (12 dB per octave) and I could not detect the sub's location when it was off-center to the left or right of the centerline, as long as it was in between the satellites.
Duke
dealer/manufacturer
If the crossover has to be above 80 Hz and/or is not very steep, then it's best to keep the sub(s) near the main speakers and probably fairly symmetrical. That being said, I have used a satellite/sub system that had a 150 Hz crossover with a relatively shallow slope (12 dB per octave) and I could not detect the sub's location when it was off-center to the left or right of the centerline, as long as it was in between the satellites.
Duke
dealer/manufacturer