shady, the 4 times number comes from a few sources 1 SVS , when I spoke with Ed Mullen he told me doubling the sub count can get you 4 times the output, 2 HSU's website, they publish that on the dual drive webpage brochures...
they say it a few different ways...
"
give you lower distortion and higher headroom, and better long term reliability because each sub needs only 1/4 the power to play as loudly as a single "
"
When you have
four, you get up to 12 dB (16
times) more
output than a single"
"When you have two, you get up to 6 dB (
4 times) more
output than a single"
Not to mention I HAVE 4 Dual sub set ups in my home, lol Dual subs on my jade 5's, duals on my evo40's, dual svs sb12's on my csb1's, and dual vtf2's in my ascend 5.2 system, so I have played with the settings, and db meter to get them balanced, and I notice the gain level is much lower with dual subs than it is with a single, it surprised me the first few times because common sense says 2 subs, half the gain, but it more like a 1/5th the gain...
ALSO- two subs sounds much better, all the way around, they will last longer, they will use less energy, they will look better
, ect ect ect...
I would put a single rythmic 15hp against dual vtf3's any day in every category!!!!!!!!! I know a few guys on here just love to disagree and promote what they own, I may be one of them, but with me I have already tried the rest, most guys, bought what they bought and that is all they know, I demoed and listened to many many subs before coming to the realization that HSU is bang for buck number 1... I own svs subs, and rythmic, I have heard the previous to the 15hp sub{I think it was a hv15?} and wasn't super impressed with it either for its price, lets face it any sub can do the job, I just want one that does it for less money, with HSU you get more all the way around for LESS money
....
To the OP, I am sure you will be happy with sub from any of the companies we have mentioned, SVS, Rythmic, HSU, ect do not sell junk, Ill bet if you bought a lv12 or vtf2 it would be enough, I know my vtf2 cracked my ceiling plaster {a few times} and it wasn't all the way up by any means. But if you wnat bang for your buck and great cs go with HSU, I have dealt with them all and bought the lv12 with the intentions of replacing my vtf2's with them, but ended up leaving it at my mothers house for her, and actually now its just shut off and has crochetting and knitting baskets on top of it, because my mother hates the house rattling, lol a $600 end table.... Me and my brothers turn it on when we go over, {always followed by a call on how to shut it off after we leave}.....