Quote Originally Posted by E-Stat
Perhaps with all the qualifications RG stated, that would be the case. I suspect the modest 12" powered subs I use in my HT system do not utilize such a steep slope. Even when I set the sub's crossover to 70 hz sourced from the LFE output, I find two blend better than one.
If you have read the writings of both Richard Greene(who comes here sometimes now) and Tom, according to both of them the ideal crossover point for subwoofer invisibility would be around 60-80hz with a VERY steep 24dbpo crossover. This is the parimeter that Tom Nousiane followed during his measurement of those many rooms.

Returning to the original question, I believe than unless you have largely full range speakers to begin with, buy a serious sub with an unusually steep crossover slope, you would be better off with a pair.

BTW, TtT - I notice you use a pair of 15 inchers.

rw
If you place full range speakers where the bass response is augmented(closer to the walls) then imaging suffers because of the added and early arrival of nearfield reflections. If you place full range speakers to acheive maximum imaging, it is likely to roll off early, and create peaks and valley in its freqeuncy responses do to late arriving reflections combining with early arriving reflections. That is why subs are so important no matter which kind of speaker you use.

You are right, I do use a pair of 15". Not for any reason other than to fullfill my audio requirements that the LFE speakers have 6db headroom over the loudest peak within that channel. A single of my subs could easily reach the loudest potential of the LFE channel(115db peak acousticall). Two subs located in each of the front corners on the floor reaches my goal of 6db. I otherwise would have used a single sub in my room if I didn't have these requirements. I require that all speakers in my system be able to handle at least 6db of headroom over the highest peak in that channel. Consequently I use VERY big speakers all of the way around, although I wouldn't consider my surrounds full range as they only go down to 50hz. Considering that there is not always alot of deep bass in the surrounds, that is low enough IMO to run full range. Only in the rarest of occasions have I seen bass at very high levels below 50hz in the surrounds. In the dubbing stage the surrounds are band limited at 80hz anyway, except if its being mixed at Skywalker sound which have surrounds that go down to 50hz or so.