Sub Question. One higher quality sub or two lesser quality? (Rythmik vs HSU)

I looked a Rythmik before purchase two REL S2 SHO subwoofers.  I thought REL's high level connection made sense.  My goal was to have the best of two worlds, home theater and music.  I like REL's technology because it makes more sense to blend subwoofer's with the main speaker so they act like additional woofers to extend the bass seamlessly.  I also think two are better than one to help balance things out.

TWO..or more,HSU and SVS both good as I am sure the others mentioned are too.
SVS lets you have free shipping both ways..in case you wanted to send it back,
SVS Also has 1 year trade up policy.Example,
You buy 2 PC2000[Pro version Now but they have the PC2000's at this time]..
and if later in the year you want to go bigger then send them back
and
you get FULL credit towards the Subwoofers that are higher up the price line.'
Free Shipping all the way around.
Power Sound Audio seems to make nice Subwoofers also,
I have a friend that has one and enjoys it.
He[Tom] used to be Part of SVS some years back.

I'm a little disappointed to hear that with two 15" woofers you are even looking for subs. I am considering the CW's. I understand they don't get down to the lowest octave. Not going to derail the subject but could I ask how big your room is? Might have missed it. 

@onhwy61 - Have built OB subs? HAve you used the GR Research servo amp and drivers in a project?


@mijostyn - you and I have mixed interactions, I probably misunderstood the very first question you asked me and the rest was, well...awkward.
I do have questions regarding your post on the previous page, as I am actually like the OP ozzy62, trying to research on this very topic.

HSU all the way. 2 of those tuned properly will be unbeatable for the price. 

definitely one sub of higher quality is any day better than two of lower quality.
in subwoofer more than sheer SPL , integration and matching to the main speaker is a far more important criteria.if you get a better sub the chances  and probability of a seamless integration are far higher

Mark

The speakers have great bass on their own. The room is 25 x 15. I am just looking for those lower octaves. The cornwalls are NOT bass shy.

I ordered the Hsu VTF-15 II yesterday. Thanks for all the input from everyone.

Oz

At this point it's moot, but do Klipschorns go lower than the Cornwalls.  If so, get a pair of of the corner horns and only run the woofer sections.  This setup would provide excellent matching of dynamics, speed and timbre.

I would NOT add subs to those Cornwalls, with 15" woofers, ports, and high efficiency horns.

You could easily mess up what you have, it’s very hard to add just the lowest ...... down to ....

You are looking at specs that say down to 34hz. that is in a test space, open air, your’s are in a room, sound waves contained, reflected, your bass is maintained below 34 I suspect.

I strongly suggest you buy a decent sound meter, see what you are actually getting, and where. Look for any weak/too strong spots, standing or cancelling waves.

With that sound meter, if you add subs, (or change speaker placement) you will be able to measure/adjust the crossover/blend from your listening spot.

2 channel system: 1 pair of subs, directional, located next to the cornwalls, forward facing. Bass is stereo, and the overtones of all low frequencies also give directional cues.

+10
Adding a sub to the Cornwall will be an exercise in frustration. Very little program exists below 30Hz, so work on placement. Depending on the room, REW’s room simulator [https://roomeqwizard.com] or Loudspeakers Calculator at Dr J. Hunecke’s Room Acoustics can assist in determining optimum location

I ordered the Hsu VTF-15 II yesterday.

you'll be sorry...
Get REW and a microphone and discover the bottom end phase response is a bucket of sludge.

Since you gone and done it, please read  http://www.ielogical.com/Audio/SubTerrBlues.php for some help on setting up. Read the links as well.
Bonne chance!

congrats... and,you can a second one later on when budget presents itself

neither subs are a waste of Money.

Go with the two Hsus (but depending on your main speakers, consider the  VTF-15H MK2 as well - goes lower and has a bit more output. Maybe better if your main speakers have decent bass and you want to cross over lower down.

mapman:" If you have large full range speakers that go down to the mid 30s, if you add subs, you need larger ones that deliver output below that range in that there is little to gain to start with otherwise and you don’t want to merely add to the frequencies already there.

Hello mapman,
     Your statement generally makes sense to me but only if the bass sound waves down to the mid 30s, that are being launched and reproduced by the pair of large full range and properly positioned stereo speakers, arrive intact at the listening position and are perceived as good quality bass. 
     It's well understood by acousticians, and has been proven scientifically, that deep bass frequency soundwaves behave very differently than midrange and treble frequencies behave in a given room due to physics.  Full cycle, or complete cycle, deep bass soundwaves are omnidirectional in their radiation patterns. are very long (a 20 Hz full cycle soundwave is 56' long), are not localizable at frequencies below about 80 Hz and are therefore perceived by us as mono. 
     Full cycle, or complete cycle, midrange and treble sound waves, by comparison, are highly directional in their radiation patterns, are much shorter (a 1200 Hz midrange full cycle soundwave is under a foot long and a 20,000 Hz  high treble full cycle soundwave is under an inch long), typically begin to be localizable at the higher bass frequency of about 80 Hz and the sound waves continue to become progressively shorter and more easily localizable as the frequencies increase beyond 80 Hz up to the generally cited upper audible limit of 20,000 Hz. 
     This  localizable full cycle soundwave threshold bass frequency of about 80 Hz is also the common threshold at which stereo perception begins when discrete L+R mono channel signals exist and are reproduced through discrete and properly positioned L+R speakers. 
     My main point, finally presented, is that individuals typically position their pair of main speakers in the room, and in relation to their designated listening position/seat, in order to optimize their midrange and treble performance perception along with their stereo image perception.  This results in individuals rarely, if ever, positioning their main speakers in their rooms, and in relation to their LP, in order to optimize their perceived bass performance.  Individuals are unable to optimize the bass and the rest for the simple reason that the bass drivers on the full range speakers are permanently attached to the cabinet containing the other, equally permanently attached, midrange and treble drivers, and are therefore not capable of being independently positioned.
     Obviously, this creates a Catch-22 like dilemma.  I believe most individuals, formerly including myself, just position their main speakers to optimize their perception of the midrange, treble and stereo imaging at their LP and resign themselves to accepting whatever unoptimized bass performance they perceive at their LP.  Since bass performance at the LP is also known to be highly dependent and influenced by physics and the room itself, the quality of the bass perceived there is also highly dependent on the physical relationship of the main speakers to the LP.
     l  strongly believe through personal experience,  I know along with many others, that multiple independently positioned subs are a good solution to this dilemma.  This solution is very effective whether it's achieved through the utilization of as few as a pair of subs or up to 4. used with a pair of larger full range or smaller limited low frequency range main speakers and can be configured to work well in virtually any size or shaped room.
     I also don't dismiss the effectiveness of bass line arrays, open baffle, planar-magnetic or horn-loaded type subs, I just have a total lack of personal experience with utilizing these thus far.
     I also wanted to state that I believe you agree, or at least already have a good understanding of, what I discussed above.  I mainly posted for the benefit of other possibly less knowledgeable and experienced readers of this thread.

Tim 

I manufacture bass guitar speaker cabinets and sometimes that gives the impression that I'm a bass player. But I'm not.   

" Who's you're hero, inspiration? "  

One need not be a bass player to be inspired by Geddy Lee. 

Duke, Your Bass cabs look solid, nice.

I get stoke from most Bass players, past and present. 
From Guitar player turn Bass player Kathy Valentine of the Go-Go's to Christian McBride, its all good. 
 
In '64 and JBL's DIY plans I cobbled together two 4530 'Scoops' and drove them using a Fender Deluxe with a modified line output to a Marantz 8B for amplification very loud. Lots of plywood on stages in those years.
These days shop dust collection is everything, over build it. Don't mess around. 

Over the years I went through the 360/361, Magnavox SVT, BAG END w/ELF-M sub QSC, Bergantino, Mesa 400+, Tone Tubby, etc. scattered around the house.
Small venue FOH gear came and went, I still have an older Tom Danley horn.

Don't laugh my current rig is an Acoustic Image Focus driving an old 12" drum shell fitted with a BAG END 10" Coaxial and x/over upshot.
Amp and speaker fit in a back pack, my Fiddle leaves me a free hand and just one trip to the car. So I began and ended up using DIY cabs. Life, eh?

In early spring you should tour the full function Masa Boogie operation in Petaluma California on your way up to the valley to pick up a few bottles of Sinskey and Plump Jack. The mustard grass is pop-in that time of year and hardly any tourist. 
Make a reservation well in advance for La Ciccia a down to earth family run restaurant in SanFrancisco's Noe Valley. Don't eat all day. 

@mapman 

I know this is off topic but I've been looking all over the Internet for someone who still has a Klipsch sw308. I sent you a private message, I'm interested in buying it. Let me know if you'd be willing to sell it to me.