Which subwoofer should I get?

Many subs can move lots of air. But integration tools (DSP PEQ) to tame room modes can make a less expensive air-mover sound magnitudes better than many very expensive air-mover that operates, more or less, open loop at the mercy of standing waves.

@misterbobman While DSP can certainly help a lot and is very convenient, proper room placement and carefully dialing in the sub’s controls can achieve the same thing or better in taming modes/nodes (DSP can’t do anything about nodes BTW) and achieving excellent results — just takes a little research and effort, and it’s not all that hard.

@mswale  I agree with @big_greg if you heard boom boom from the SB3000 and highly likely that sub wasn’t dialed in properly.  I’m not saying it’s on the same level as the better RELs or JL Labs subs, but it’s definitely not a boom boom sub if set up properly.  Read any review — they all say it works very well for music and no mention of bloom or bloat.  The cynic in me thinks the dealer may have done that on purpose to make the pricier subs sound better because this just doesn’t sound right.  I’ve got an SB2000 and there’s no boom boom whatsoever when the volume/crossover is set properly.  Something stinks here. 

My personal evaluation of Rels Neutrik hi-level input application is based on 25 years of ‘personal’ knowledge. I am still currently using two Rel T9i’s so my opinion is they work exceedingly well for me using hi-level for hi-fi.

@mylogic  Most other excellent lower-priced subs from the likes of Paradigm, Perlisten, etc. also only use low level inputs — are they just home theater subs too?  Silly.  Doubt you’ve even heard a decent sub in your room with low level inputs, so coming here and stating that subs with low level inputs are only for home theater is ignorant and frankly just a ridiculous statement, but you’re certainly entitled to your opinion just as I am to question it.

ln my opinion hi level for hi-fi and low level for home theatre only.

@mylogic  That might be your opinion, but most of the top subwoofers extant from the likes of Magico, Wilson, and JL Labs whose top subs venture well north of $20k only have line level inputs.  Hmmm.  Pretty sure these guys know what they’re doing, and if they thought high-level inputs were in any way better they would’ve included them in subs at this level.  Or maybe you can explain to Alon Wolf and Daryl Wilson why their uber-expensive subs are just for home theater.  You know what they say about opinions…

Given that the T/5x's are only rated -6dB at 32 Hz, I wonder if this is enough low end given my speakers and room? On the other hand, I'm a little concerned that a pair of Carbon Specials may be overkill for my situation (and a lot more expensive). Thoughts about this given my room size and need for music only?

Some thoughts — a sub that’s down 6dB at 19Hz at the price of the REL Carbon Special is nothing “special” at all when many other very good subs at less than half the price go down to an honest 20Hz and below.  A lot of spatial cues that get unearthed down there will be lost by many REL “subs.”   Many don’t realize that while not many instruments play down into the 20Hz region, there is still important recorded musical information that resides down there that plays a big part in improving imaging and an expanded 3D soundstage.  I wouldn’t worry about overkill for your room — just buy good subs that can get you to an honest 20Hz (-3dB) and if properly dialed in not only will they not overpower your room, they will work much less hard and with less distortion than smaller subs.  As for SVS subs being too sluggish for a 2-channel system — horse hockey!  I and many others here have gotten excellent results with SVS subs when properly dialed in, and all reviews back this up.  But you already got pleasing results even with a ported PB2000 so you probably already know this.  Just my experience and $0.02 FWIW. 

Much better to get two subs than one, especially for music. I’d take two SVS SB2000 subs over one SB4000, and with their risk free trial period that might be a good option to try. If you liked one PB2000 then two SB2000s would be a significant improvement over that. The Rhythmic F12G offers big performance/$ but doesn’t have integration software like SVS but does offer speaker-level inputs like REL but much higher value as they sell direct. REL is expensive for what you get and better to go with Rhythmik IMHO (compare the specs to REL). Best of luck.

https://www.rythmikaudio.com/F12G.html