Two subs or not two subs...

Use both. Until you're able to add more.

If you can make it work with two different subs, go for it.

I noticed this unit has outputs for a single sub, or a stereo pair of subs.

https://www.audiogon.com/listings/lis9bg0c-black-ice-audio-f360-tube-hybrid-preamplifier-tube

I'm a big fan of mains with no ports, full range for large rooms,

or, smaller mains with no ports, with stereo pair of front facing directional subs (self powered) for smaller rooms.

Bass is not mono as some believe, just listen to the placement of bass players in jazz groups, or listen to this!

https://www.amazon.com/Double-Bass-Niels-Henning-rsted-Pedersen/dp/B00000G62F/ref=asc_df_B00000G62F/?tag=hyprod-20&linkCode=df0&hvadid=312683822382&hvpos=1o1&hvnetw=g&hvrand=3655329634212047699&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9003511&hvtargid=pla-540093611693&psc=1&tag=&ref=&adgrpid=65958438881&hvpone=&hvptwo=&hvadid=312683822382&hvpos=1o1&hvnetw=g&hvrand=3655329634212047699&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9003511&hvtargid=pla-540093611693

IF ports, front facing.

Home theater, single self powered sub can be quite successful, but, if watching music concerts, then directional 2 channel full frequency mains or pair of stereo subs is advantageous .

powerful amps for subs are not just to push a lot of air, they are needed to stop/control the woofer, as important, so go for subs that can contain themselves.

Thanks for the thoughts, looking forward to the experimentation. :) 

Get rid of the Klipsch.  I owned a couple of their subs a few years ago and they were junk compared to anything you can get from HSU, SVS, PSA, Rythmik, etc.  Maybe they've gotten better over the years, but I doubt it.

You could use your VTF-15H with whatever new sub you get.  It has a volume control.  Turn it down and you won't overpower the space.  Or get two Rels.  Or get four smaller subs. 

@elliottbnewcombjr 

I'm a big fan of mains with no ports, full range for large rooms, or, smaller mains with no ports, with stereo pair of front facing directional subs (self powered) for smaller rooms.

I too like sealed (i.e., acoustic suspension) speakers and believe, in general, the bass roll-off and low frequency distortion are improved over ported (i.e., bass reflex) designs.  However, as with anything, there are excellent and not so good examples of each type.

A successful speaker designer has told me that in his opinion two subs operated in stereo can work very well.  Others here enjoy the Audiokinesis Swarm type bass systems using 4 (or more) subs summed to mono.  I can say my two high quality subs located at the front of the room and run in stereo are vastly superior to when I used one sub only.  I would still like to try one or two additional subs summed to mono and located in the back of the room.  I believe one reason this works well in my system is that my stand-mounted acoustic suspension speakers have dual 9-inch woofers and run reasonably flat to about 40Hz so I can roll the subs in at a relatively low frequency.

I use 2 REL subs, a Q150e and a Q108MKII, and they were inexpensive and sound excellent. The more the merrier as far as subs go, but 2 are plenty for my tastes. Note that the clear "position" of the bass player in a jazz group is determined by the "aural cues" of the higher frequency notes and overtones of a bass, not the sub frequency tone which is absolutely non directional.

I use 2 REL subs, a Q150e and a Q108MKII, and they were inexpensive

Inexpensive is better than the alternatives! :)

Thanks all, will setup the REL as a 2nd sub, will at least see how that goes in tandem with the Klipsche! 

The bad news about my particular RELs is that REL informed me that they don't service that model anymore, so if one stops working I'd have to fish around for a repair...oh well...the good news is they currently work perfectly.

Did you see this thread about a bee's hive of subs?

https://forum.audiogon.com/discussions/best-bass-in-earth-bass-that-just-smells-right

mitch2

I don't want to expose myself to more than my pair of 15" woofers, I might want it. No room. 

wolf_garcia

good point about the bassovertones giving location.

After a lot of years, I simply sum up my preference for tubes as "Analog gets the Overtones right".