Eh hem!...Subwoofers... What do ya know?

millercarbon, others:

I suspect many of you have a far larger listening space than what I am discussing. I am not meaning to contradict your advice for what I never experienced.

As per the instructions i received . I put a powered sub on my listening seat and then played a 30hz tone . While it and only it was playing i went around the room with a measurement app on my iphone . I looked for hotspots reaching high and low everywhere . The locations were oddly NOT symmetrical to the room . One 10” is 13ft to the right of my right main against the wall . The other 10” is up high in the far left back corner almost 30ft away , the 15” subs are downstairs to my left fore and aft to me and the 18” subs are opposing each other between the sweet spot and the mains under the floor . But when all the subs were placed in those locations and wires ran and tweaked for output it is incredible . I used to have my 18” jbls under my mains . They are no longer there as there was a hot spot in front of ONE main and not the other . Due to the size of these subs (12cuft) i removed them both for aesthetic reasons .  The mid and high detail as well as the 3d image is very engaging . The placement went against everything i thought i knew about sound. Completely makes sense now. 

Unless you really need the deepest room shaking notes found on that occasional track or action movie sound track- a full range (or near full range) speaker driven by plenty of power is a better solution for me.  
100 watts driving the main speakers just won't compete with subwoofer amplifiers of 500 to 1000 watts or more. 
Drive your main speakers with 200 / 250 watts at 8-ohms and the need for a subwoofer greatly diminishes and becomes a better case set of compromises than even the best subwoofer setup. 
You have $ to invest in a subwoofer system? invest in a bigger amp instead IMHO.   

REL, REL , REL, oh did I mention REL, and the post that started this thread is correct, you must first understand what bass really is, how it is distributed, and how to properly integrate it i to (your system).
Every system dynamics are different due to room size etc, and as mentioned before if you know where the bass is coming from you have set it up incorrectly, not only will a properly set up sub allow your main speakers sound like they are bigger then life ( not only bass but in mid range also), also learn what High level connections can do for you when it comes to a sub. I recently upgraded to a line array system for my 2 channel system (if I could post pics here I would) , and was simply blown away , granted They consist of 28 6.5" woofers and 38 3" Motorola ceramic piezo tweeters in each column , using one REL Britannia B1 sub (yes its older but works as it should), the sound is phenomenal , and breathe taking , speakers and sub are controlled through a Samson S3 crossover network, and of course bi amped . 
Subs rule , but IMHO buy from a manufacturer who only builds subs for the best quality and technological attributes towards your systems dynamics.
  

Correction 28 tweeters , mis type