WOW...there is a LOT of good info in that thread!
I just wanted to add, regarding the original question of this thread, that there is a school of thought that reads something like this:
A direct radiating (front firing) sub has the advantage of delivering it's output to the listener's ear BEFORE any and all reflected info, whereas a down firing sub can only deliver reflected bass info.
I'm not saying either method is better, but I do recognize it as a simple truth. I also think it may add to the direcionality of a sub vs. a downfiring sub...anyone have thoughts/facts on this? It may help Mike, and I think it's at the center of his original question.
Regarding 2 subs and the 6 dB advantage, I still contend that having a discrete LFE sub system and a RB sub will more than offset that advantage by not asking either sub to reproduce the brutal Dolby LFE+10+RB from 5 channels, summed mono bass signal.
SH: I've just finished connecting 2 subs plus 1 LFE sub as follows:
6 CH BYPASS, analog BM switched 'OFF'
SW output from the player to the LFE sub system (so no LFE ever enters the 950)
SW output from the 950 left empty.
FL from 950 to channel 1 of the Rane AC23B crossover and FR from 950 to channel 2.
Channel 1 LF output to sub #1, channel 2 LF output to sub #2
Channel 1 HF output to FL, channel 2 HF output to FR.
Crossover set at 80 Hz for Ch 1 & 2.
Subs are perfectly equidistant, and painstakingly phase aligned.
LFE sub is easily muted and/or volume adjusted on-the-fly, while the stereo subs are LFE signal-free.
I listened a bit last night to Diana Krall's MC SACD 'When I Look Into Your Eyes'. Though I can't know the method of mic configuration used, I am sure it's a mic'ed upright bass and I'm equally sure there is little, if any, of the bass in the other 3 channels.
MAN, I gotta tell ya...the dude was in my room playin' bass!! Again, with this particular disc, there's no way to know if it's a dual mono signal in each of the FL/FR channels or a true stereo mic'ed affair, but the effect is instantly noticeable.
Adding a touch of LFE in the third sub actually adds to the sense of a truly live sound.
Maybe it's this or that...I don't know, but I intend to manually graph the differences in FR, phase adjustment, filter slope, placement, etc., between a single, conventionally BM'd sub and this setup, as well as trying different source material that I know is stereo mic'ed (I have friends in the biz who will burn anything I ask them to...maybe I'll even lay down the bass lines for an experiment where I positively know what it SHOULD sound like.
In any case, very cool stuff! Thanx again for all your help.