What is wrong with a sub?

Better ones are damn heavy.

Subwoofers are absolutely audiophile. I think at times they get a bad rap because people don’t take the time to set them up correctly and all you hear is bass that sucks the detail and music out of the lower octaves. A properly set up subwoofer should simply extend the bass down to the lowest frequencies and you shouldn’t “hear” it - it should just sound like your mains play deeper. It also adds a nice tactile feel to your music, which is present in the live recording session.

There are are many benefits of a sub and mains over just mains. First, few mains can get as deep as a subwoofer. Second, the optimal place for a sub doesn’t always correlate with the location of the mains. Third, you can relieve your mains of sub duty which can improve clarity and give that duty to your sub which is made for it.

PS: If you go with a sub, use DSP so you can adjust the curve to account for peaks and valleys in the sound due to room effects. Or better yet, use multiple subs. Two is great. Four is better yet. 😀

@mkgus, thanks for that.  My one REL i7 I rarely hear.  Sometimes I do mess with the volume on it and pump it up beyond the music levels, but normally just because I want to wake everyone up.  

Got me thinking if 2 and 4 are better, is there any reason they should all be the same?  Could you mix an i7 with i9 or other brand?  I would tend to shy away from mixing brands.  But when I think of "real" bands and or orchestra there are different low end sounds of different power coming from different locations.  Maybe they balance those, just the base drums are not always center.  

I don't know what DSP is relative to subs.  I assume this? 

I mix 2 RELs from the same UK made era, a down-firing 100 watt Q108MKII, and a front firing Q150e...the synergy and tonal similarity between these two is remarkable, and they sound great.

Subs fill in the 'bottom' that the majority of speakers can't 'reach', w/out distorting their 'upper' frequencies.  Case in point:
 
I happened to be @ a instrument b&m store where some musicians started goofing about with various 'toys'.  While the 'regular frequencies' (80hz+) were covered by the monitors Just Fine, the 'subs' (which had 'ribbons' @ their ports, wagging about...) were 'filling in' the bassline that the monitors 'faded' from.  So, I took that as an 'instructive moment' that Any speaker shouldn't be expected to cover Everything....esp. when it came to moving 'bass line air'....since bass is mostly 'air movement' @ a major (and physical) process.  The aforementioned 'ribbons' were wagging about, in and out of their ports.  It's just how much 'air' you can excite, pure physics....

You want 'concert sound'?  Subs.