Subwoofer Decision

I have narrowed my search to two choices though I am sure I will get comments steering me away from these.
Contrast Rythmik Audio 12G with Vandersteen 2Wq. I would like to get only one though I know a pair are best choice. Could maybe afford 2 Rythmik, but only 1 Vandersteen for now. The subwoofer would support Dali Helicons (4 ohms) biwired and driven by 2 mono McIntosh MC 252's at 500 watts each into 4 ohms. Living room size aprox. 24'x16'x8' placement not centered on 16' wall due to furniture (wife) constraints must stay put. Subwoofer placement needs also to stay there as well, I know this limits possible best choice for placement, my bad. There is room behind, next to, and between speakers. Any help help is appreciated.
773de154 8d26 4ee0 97f3 40a97799ea35lowfreqguy
I had the 2WQ's and sold them, Replaced with a pair of Rythmik 12's.
Tighter, lower and with more control. Also more flexible in set up. A pair is almost always better.
I've never heard anything bad about Rythmik subs, and they dig quite a bit deeper than the Vandersteen unit, handy if you like electronic or organ music.  

If your setup doesn't have any room correction for bass frequencies having two subs will let you even things out.  

The "G" version (paper cone woofer, courtesy of GR Research’s Danny Richie) of the Rythmik F12---man, you are hip! Excellent sub for music. The paper cone is slightly lower in moving mass than the aluminum cone (good for music), the aluminum a little stiffer (good for high excursion movie sound effects). Danny feels the paper cone woofer provides a little more resolution than the aluminum, and a more natural sound quality. All I know is the woofer reproduces the sound of a well-recorded upright bass like no other I’ve heard. As the player descends down the neck of his bass, I hear no change in the timing of the playing, or in the timbre and transparency of my Quad ESL’s & Eminent Technology Magnetic-Planars. The lowest note on a standard 4-string bass (the open E string) is at 42Hz, and has a lot of overtones. The (acoustic) upright bass is an excellent test of the capabilities of a sub and the woofer of a speaker, highly revealing of any coloration or excess weight/fat, and driver "overshoot" and slow "settling" time---returning to rest after excursion (which causes smearing---a lack of transparency and resolution of fine detail). Rythmik Subs are characterized as "stopping on a dime".

The Rythmik sub features Brian Ding’s patented "Direct" (no accelerometer) Servo-Feedback circuit, the Vandersteen Richard’s unique feed-forward circuit, both good approaches to creating higher performance and lower distortion. Two of the best music subs available, either will satisfy. I myself have four of the paper cone G woofers, but in a version optimized for Open Baffle applications, installed in pairs in OB/Dipole H-frames. The only subs I’ve ever heard good enough for use with planar speakers---ESL’s, magnetic-planars, and ribbons.

A good read on this topic reposted here:

The following article has been posted before and is rehashed again below - one of the finer reads in the subwoofer selection tree .... best article I've seen discussing this....

August 3, 2008 ... subwoofer/

"…And Why a Really Good Subwoofer is so Hard to Find

Audiophiles and music lovers are missing out on one of the most dramatic improvements they can make to their audio system: Powered Subwoofers.

Most audiophiles won’t even use the word “subwoofer” in public, let alone plug one in to their precious systems. There is a kind of snobbery that exists in the world of high-end audio aimed primarily at receivers, car audio, home theater and especially subwoofers. As a matter of fact, subwoofers are responsible for many people disliking both car audio and home theater, since it is the subwoofer in both of those situations that tends to call attention to the system and cause many of the problems.

The truth of the matter is that subwoofers have fully earned their bad reputation. They usually suck. Most of them sound boomy, muddy and out of control with an obnoxious bass overhang that lingers so long as to blur most of the musical information up until the next bass note is struck.

We have all had our fair share of bad subwoofer experiences, whether it’s from a nearby car thumping so loud that it appears to be bouncing up off the road, or a home theater with such overblown bass that it causes you to feel nauseous half-way through the movie. You would think that high-end audio manufacturers would be above all of that, but you would be wrong. In many cases, their subwoofers are almost as bad as the mass-market models because they too, are trying to capitalize on the home theater trend that is sweeping the land.

You see, it’s very difficult and expensive to build a good subwoofer. One reason is that a sub has to move a tremendous amount of air, which places big demands on the driver (or drivers). Moving lots of air requires a lot of power and that means an amp with a huge power supply, which can cost huge money.

Finally, in trying to move all of this air, the driver (or drivers) which operate in an enclosure, create tremendous pressure inside of the box itself. The cabinet walls must be able to handle this pressure without flexing or resonating. Building such a box involves heavy damping and bracing which gets very expensive. When you consider these requirements, you quickly realize that it is virtually impossible to build a really good subwoofer (I mean good enough for a high-end music system) for under $1000. Yet most of the subwoofers out there sell for between $500 and $900. Manufacturers do this because their marketing research has shown them that that is what people want to spend on a sub, never mind the fact that what people want to spend and what it takes to get the job done right may be two different things. The result is that even most high-end manufacturers are putting out poorly constructed subwoofers that just don’t sound very good.

I don’t want to give you the impression that anyone who really wants to can build a good subwoofer so long as they are willing to throw enough money at the problem, because that really isn’t true either. There are some pretty expensive and well-constructed subwoofers out there that you would never want to plug into your music system because they would most certainly make the sound worse.

Why? Because of their crossovers.

A crossover is inserted into your signal path in order to remove the lowest frequencies (the deep bass) from your main speakers so that they no longer have to do all of the dirty work. The deep bass will instead be dealt with by the subwoofer.

The #1 benefit of adding a high quality subwoofer to your system is not how it further extends the bass response, but how it can dramatically improve the sound of your existing power amp and main speakers from the midrange on up. That, my friends, is by far the most compelling reason to add a sub to your high-end music system. Once your main speakers are freed from the burden of making deep bass, they will sound cleaner, faster and clearer, especially in the midrange and midbass.

They will also image way better because there will be far less air pressure and therefore resonance and vibration affecting their cabinet walls.

And since the power required to make the deep bass is provided by the subwoofer’s built-in amplifier, your main power amp will be free from that burden and begin to sound like a much more powerful amplifier.

The one big problem with all of this is that you need a crossover to roll off the deep bass in your system and achieve all of these benefits. And the crossover that comes with almost every subwoofer on the market will cause more damage to your signal than can be overcome by these benefits. That is the main reason that audiophiles refuse to consider adding subwoofers, even very expensive ones with well built cabinets.

Enter the Vandersteen 2Wq 300 watt powered subwoofer. This is the only subwoofer that is specifically designed to be inserted into the highest of high-end music systems without doing any harm to the precious signal.

So how does Vandersteen do it?

Simply. In fact his crossover scheme is so ingeniously simple that it’s a wonder nobody else thought of doing it the same way. I’ll spare you an in-depth description and just say that the only thing you end up inserting into your system is a couple of high quality capacitors. That’s it, nothing more!

No additional wires or gadgets enter your signal path. Hell, you don’t even have to disconnect the wire between your amp and speakers to add this subwoofer. The model 2Wq sub uses the same basic crossover scheme as the $15,000 flagship Model 5As. As a matter of fact, you can even run the specially designed Model 5A crossovers (M5-HP) with the 2Wq if you want the most transparent sound imaginable.

So what about the other reason to add a subwoofer to your system: for more powerful and extended bass? I don’t care how big your main speakers are, they’re no match for a good subwoofer in the bass.

A really good subwoofer can run rings around the best floorstanding speakers when it comes to bass extension, power and control because it is designed to be good at that and nothing but that, whereas main speakers have to be good at higher frequencies as well. Ideally, you want two subwoofers so that you have true stereo separation down deep into the bass. Stereo subs can also help to lessen room interaction problems by providing two discrete sources of bass information. Remember, if you can’t afford to buy two subwoofers at once, you can always add the second one later. Adding a pair of 300 watt powered subwoofers is exactly like adding a pair of 300 watt monoblock amplifiers to your system and upgrading to a pair of better main speakers at the same time. The beauty is that you don’t have to replace your main power amp or speakers to do it.

But there is a problem here as well.

Everything comes at a price, and the price you pay with most subwoofers is that when you add them and their built-in amplifiers to your system, they don’t tend to blend or integrate well with the sound of your power amp and speakers. This is especially true if you own a tube amp, because the character of your amp is nothing like the character of the big solid-state amp that is built into most subwoofers.

The result is that your system sounds split in half. You can hear where one part of the system leaves off (namely your amp and speakers) and where the other part takes over (the sub and its amp). This is a HUGE problem for audiophiles who aren’t willing to destroy their system’s coherence for additional power and bass extension.

Fortunately, Vandersteen has the perfect solution for this problem that is, again, so simple, I wonder why nobody else thought of it first. His solution is to build a very powerful 300 watt amplifier that strictly provides the huge current needed to drive the subwoofer. You can think of this amplifier as only half of an amplifier; or just the power portion of an amplifier. The release of this power is controlled by the signal that is provided by your power amp. Vandersteen’s amplifier needs a voltage to modulate its current output, and what better place to get that voltage than from your main power amp? This way, your power amplifier is directly responsible for the sonic character of the deep bass coming from the subwoofer because it provides the necessary voltage signal. This voltage signal contains the unique and characteristic sound of your main power amplifier and insures that that character is maintained in the sound of the subwoofer itself. The beauty of it is that your amplifier is only providing a voltage reference and no actual current, so it is not taxed with the burden of “driving” the subwoofer in any way. As a matter of fact, your amplifier doesn’t even know that the sub is connected to it. The 2Wq’s potential is almost unlimited given that it will ratchet up its performance as you improve your power amp. Remember that you always want your subwoofer to sound just like your power amp. No better, no worse. NO DIFFERENT!

After having spent time with the amazing Vandersteen Model 5A loudspeakers with their 400-watt powered, metal cone subwoofers, we were reminded of the sound we had with the awesome Audio Research Reference 600 mono power amps. With the Ref 600s there was a sense of effortlessness, openness and unrestricted dynamic freedom that we have only otherwise heard with live unamplified music.

Listening to those monstrously powerful amps made us realize that all other systems sound compressed by comparison. Only when we heard the new Vandersteen Model 5As with their hugely powerful built-in subwoofers, did we again have a strikingly similar sonic experience. The reason is that the Model 5As provide a total of 800 high-quality watts, to which you have to remember to add the power of the amp we were using, the ARC VT-100, at 200 watts.

This means we were listening to about 1000 total watts of amplifier power – not far from the 1200 total watts provided by the Ref 600s. With the Vandersteen subwoofer crossover and amplifier, you are able to get those hundreds of subwoofer watts to blend seamlessly and even take on the character of the ARC VT-100. It’s amazing! What’s even better is that the price of the system with the Model 5As and the VT-100 is under half the cost of the Ref 600s alone! Since this discovery, we have achieved the same kind of unbelievable dynamics and seamless blending with ProAc loudspeakers and twin Vandersteen 2Wq 300 watt powered subs.

So, if you want the sound of Ref 600s but cannot afford them, buy a pair of Model 5As or your favorite pair of ProAcs plus a couple of 2Wq subwoofers and mate them with a VT100 and you’ll get surprisingly close.

You can cut the cost even further by running a pair of Vandersteen 2Wq 300-watt subwoofers with your existing speakers.

Or mate a pair of 2Wqs with your favorite ProAc. In any case, it is the magic of SUBWOOFERS that allows this to happen.

It is for all of the above reasons that there is only one subwoofer in existence capable of integrating seamlessly into a high-end music system, allowing you to reap all of the benefits of having a subwoofer, with none of the drawbacks.

And the Vandersteen 2Wq is the one. And just in case you think I am a biased source, our correspondent Blaine Peck (who, for all you know is also a biased source) recently wrote the following, with no discussion between us about the topic prior to his sending us his comments.

Whether reproducing the plucked string of an acoustic bass or the sound of an analog synthesizer, the Vandersteen 2Wq subwoofer is a seamless extension of any system. Nothing else need be added! With its internal 300-watt power amplifier, it is the perfect compliment to any sound system. Designed to take on the characteristics of your main stereo amplifier, the amp in the 2Wq will not sound foreign in your system. Also, through an extension of the Vandersteen design philosophy, a unique gradually sloping crossover system is implemented so you simply do not know where your main speakers stop and the 2Wq begins.

Now that your main speaker/amplifier combination need not concern themselves with those power demanding low frequencies, they are freed up to work in a more comfortable range. Yes, now what is coming from your main speakers will sound better than ever.

The 2Wq is not just another subwoofer. It consists of three 8″ floor-facing drivers, each with a massive motor. So why not a more typical single 12″ or 15″ design? Well frankly, the mass of a larger driver will not allow it to respond as quickly as the Vandersteen 8″ drivers to today’s demanding recordings. The 2Wq’s 8″ drivers are designed to handle the content but be “fleet of foot” at the same time. Concerned about where to put them? You need not worry. With the control of both its respective level and the “q” (how loose or tight the low end is) you have the flexibility to place them in a location that fits your living environment and not sacrifice performance. The simple beauty of this product will soon become an addition to your room.

So whether on orchestral music, hard rock or something in between, the Vandersteen 2Wq will exceed your expectations...."
man....and i get acused of being a Vandersteen “ fan boy “....

first your room, long wall odd dimensions math can yield really good sound, as can irregular openings and the natural diffration a truely lived in space can bring..dont sell yourself or the room short...

in truth I have never heard a Rhythmik, but i have read enough bdp24 posts to feel kindred spirit....i will make it a point to go hear them ;-)

any way you can get them both in your room ?

no matter what you do i would download vandertones and invest in good tools (RTA), calibrated mic ( better dealers and all Vandersteen dealers will have these imo essential tools ) so you can see what room is doing....and tweak the setup...

someday, my guess...dunno anything....Richard will put tge 11 band analog EQ into an affordable sub.....

I'll admit that the internal crossovers on many subwoofers leave a lot to be desired, but the best solution is to avoid them altogether and get a preamp or integrated amp that has bass management and room correction built-in, something that's woefully missing from most stereo pre-amps.  

The Anthem STR Pre-Amp is one of the best, though if you're not using balanced connection you could integrate a MiniDSP DDRC-24 for a lot less money.  

For the sake of completeness.....the Rythmik PEQ plate amps (all those not including XLR connections) allow the sub to be fed from either a pre-amp (line level) OR a power amp (speaker level). RCA jacks are provided for line level hook up, binding posts for a high level signal from a power amp. It works the same in that regard as both Vandersteens and REL’s. You can try the sub both ways, and decide for yourself which you prefer. The Rythmiks also have an excellent set of controls, with adjustable phase (not just a 0/180 switch), damping, x/o frequency and slope, and one band of PEQ (parametric equalization, for room modes). None better on the market.

I myself don’t know why anyone would want to add the imperfections of a power amp (they all have them) to those of a pre, but it’s worth a try. The notion that taking the sub signal from the power amp that is feeding the speakers will be of benefit in the effort to make the sub sound "as one" with the speaker strikes me as specious (except perhaps in the case of the Atma-Sphere OTL’s---no output transformers, with their well-known problems doing bass), but I’ve been mistaken before. Heck, I got married once.

For anyone living in or around NYC wanting to hear Rythmik subs, Sterling Sound Mastering has three pair of Rythmik F15’s (15" woofers instead of the F12’s 12") in their rooms. Don’t tell them I sent you. ;-)

I want to repeat my recommendation to use multiple small subs for a much smoother response. See here for an introduction: Good subs will sound better, but the room remains the real elephant in the room. In addition, I would never use subs without some room equalization such as the Antimode 8033. I am overjoyed with mine.

I have always used MK subwoofers. The originators and still right up with the best. Interestingly, they are not mentioned much.

 Vandersteens method of having a capacitor in line to roll off the low frequencies was also done very early in the Dahlquist DLP1 crossover.
In it you could change capacitors/resistors to suit your impedance and roll off frequency. Not sure if anyone else implemented a similar approach.
If you are at all handy with a soldering iron you could pop the top on your amp and install a pair of caps inline on the RCA + inputs. This would roll off your amp at a chosen frequency. Say 80Hz or so. Then your powered subs fed from your pre can  go down from there using their built in crossover. The crossover calculations are available online to determine the size of caps and (resistors) needed.
Vandersteen rolls off the entire frequency band, (via MIT caps in the pair I had) sends it to the subs and then has a boost circuit in the subs power amps to regain what was taken away, while the main speakers are then passively being fed (with roll off intact) thru the subs connections.
Works fine, just a different way.
Nowadays digital processing seems to be the preffered method via devices such as MiniDSP.
I think that bdp24 for has raised points that seal the deal for the Rythmik 12G  over Vandersteen 2wg as to the bass response and appropriate for jazz and fusion jazz (some R&B and little classical) which I listen to mostly. I am a bass player, both contrabass and electric bass (5 string mostly) and I need to hear those low frequencies well and strong. The frequency of low E is aprox 31 Hz and low C on contrabass with C extension (used mostly by classical bass players) is aprox. 33 Hz and low B on 5 string and 6 string basses aprox. 31 Hz, and low A on piano is 27.5 Hz. I need to hear these clearly and with authority therefore 2 Rythmik 12G-SEs should work well for me. This model has the paper cone driver. Looking for dealer in southern California Los Angeles county. Do these ever show up on Audiogon? I need to hear these but almost willing to buy on what I know now from responses here. I am investing in RTA and calibrated mic to help with placement. I now have authority to move sub to space for my basses and keyboard behind listening area in living room and in dining alcove a living room connected area making L shape to living room an extra 80 sq ft to living room. Really looking forward to new subs.
Sorry low E is aprox 41 Hz not 31 Hz as mistake in previous post
It seems like a lot of fuss over what is pretty simple if your room is relatively controllable (if you don't live in an empty shipping container or a large desert tent)…I use 2 older REL subs (Q150e and Q108II) and no DSP, and they are extremely easy to tune to the room…just move them around and tweak the levels (the 108 is downward firing and right behind my left main in a corner created by a gas fireplace, and the more powerful 150 front firing is near the right wall and can be moved around easily…unobstructed and pointed at the sweet spot). Simply use the level settings and "crossover" (my mains only go to 58hz, so that's my starting point to tweak them) pots carefully and you're in there…these RELs cost around 200 bucks each used, and are utterly great things. Also, I think "lowfreqguy" initially simply misstated the 31HZ E thing as he later mentions the "low B" on a bass which IS 31hz…I say restore his points and declare the penalty voided.
Have you considered the Swarm? Multiple subs, single connection, rave reviews. Worth a look or listen...

lowfreqguy, Rythmik sells direct-to-consumers only, but have a deal worked out with speaker maker Ascend Acoustics (who also do direct sales) in San Clemente, CA. Ascend sells the Rythmik subs to partner with their speakers, and I believe demos the subs at their location. Give ’em a call.

I’ve never seen a Rythmik F12G for sale used, a good sign, ay?!

Jadedavid’s passive filter suggestion is a good one, and has been used by perfectionists since the 1950’s. He’s correct about the Dahlquist DQLP-1 incorporating that design---I still have one. I also had capacitors installed on the input jacks of my Bedini 25/25 for rolling of it’s low end for use with old Quads. That method is completely compatible with Rythmik subs.

By the way, the Rythmik F12G is available as a DIY kit, for those wanting to make their own enclosure. Also, Parts Express sells really good sub enclosures the Rythmik kit can be installed in, for the adventurous. 

maybe I misunderstood your point bdp...but the Vandersteen approach preserves the transfer function of the main amplifier which can be heard...Ray Brown Soular energy is an excellent test for continuity....

so glad the OP is working the tools and the room also..

i have a place near San Clemente, so maybe I will pop in and hear the Rhymiks....
I too, have not heard the Rythmiks, but from the standpoint of the laws of physics, it would seem to me that a sub with three eight inch drivers would be a lot quicker than a single 15 inch or even a 12 inch driver. I thought I had read somewhere that three eight inch drivers could equal a sixteen inch driver  in bottom end extension and power.JMO.
Vandersteen sub integration is seamless, when properly set up. My 2w's and 2wq's are heads above any other manufacturer, in my opinion.
The fact that my 2w's are nearing 25+ years old and still function properly is a testament to the design and build quality.

The notion that an 8" woofer will automatically be "quicker" than a 12" or 15" one seems logical, but is actually an over-simplification. The size of the cone is only one factor in a woofer’s performance capability. A woofer’s moving mass vs. it’s motor (magnet) strength is a better way to predict it’s performance capabilities, but again, there is more to it than that simple relationship. The Rythmik website has very technical design information available for those interested (some of it WAAAY over my head. Brian Ding is an engineer with an advanced technical education, having a PhD in the field).

Rythmik offers subs with one or two 8" woofers, but Rythmik designer/owner Brian Ding advises that his 8" woofer is no "faster" than his 12", or 15" and 18" (!), for that matter. But the maximum output capability of the 8" is less than the 12", and the 12" less than the 15", the 15" less than the 18". Three 8" woofers will NOT reproduce to a lower frequency than a single, but will have less low end roll-off as it approaches the lowest frequencies it reproduces, and may therefore sound as if it does. However, three 8" woofers will, of course, have higher maximum output capability than a single. I have heard the Vandersteen subs at Brooks Berdan’s shop (Brooks was one of Richards first dealers), and they are excellent.

tomic601, the Vandersteen sub uses the output of the power amp as it’s signal, rather than a line level signal from a pre-amp. I’m not sure, but Richard may have pioneered that approach. But to repeat, both Rythmik and REL subs offer the exact same facility---it is not exclusive to Vandersteen. The Rythmik PEQ model plate amps provide both a high level input on speaker binding posts (from a power amp, in exactly the same fashion as Vandersteen), as well as a line level input on RCA jacks (from a pre-amp, etc.). There is nothing proprietary about the Vandersteen high level input design; the power amp is connected to the sub via a speaker cable that goes onto the sub’s input binding posts. That high level signal then goes into a circuit that converts the watts into volts (via impedance conversion, I believe). That voltage is then used as the signal for the sub.

My questioning of the logic of the idea is a separate issue, having to do with the wisdom of having the sub’s input signal go through an extra stage of amplification (the power amp) as part of the effort to get the sub to have the same sound characteristics as the speaker the sub is partnered with. The idea is that both the speaker and the sub get their input signal from the same exact source---the power amp, and the sub will therefore be more likely to sound "as one" with the speaker as it would if the sub got it’s signal from a different source---the pre-amp.

sort of
we are mostly on the same page
the Vandersteen “plate amp” is power factor corrected for the exact drivers in the sub  and network  is hand tuned in the anechoic chamber which seems to me a good trade for having a 2nd amp in the system.....
it certainly works on my model 7 in my far, thank God I feel no need for his Model 9 subwoofers.......
oh and Stanley Clarke’s playing on JD Souther Silver Blue ( Black Rose ) will tell you if those 2 amps sing as one 

man what a player.......

@bdp24, this has been an interesting and timely thread. I’m encouraged to read that ESL speakers respond so well with Rythmik subs.

My dedicated music room is pretty much finished sans subwoofer support. I use JansZen’s hybrid Valentina ESL speakers driven by Linear Tube Audio’s ZOTL40 amp and MZ2 preamp, both license David Berning designs. I’m also a vinyl junkie just recently adding the new Technics SL-1200G turntable.

This mix provides a very well balanced and revealing system. Bass with the JansZens is flat to about 30Hz, but I know something is missing and I would classify my bass as super clean, accurate, but polite. I’m not a bass freak, but even David Janszen has told a few of us customers that bass has a ton of ambient information that lives well below what the speakers can produce that only good subwoofers will bring forward. He uses explanations that clip my understand, but in the end he puts it that bass can be great with the right support. A few of us do use subs and I think I’m next. Everyone says use 2 subs. My room is modest size.

My independent research has somewhat narrowed the search to JL Audio and SVS sealed subs and to the servo controlled Rythmik F12G. I have had a 15" Velodyne servo sub in my HT for years and I like what the servo approach does for control. I really like reading what the Rythmik approach does. I also like that the F12G is more affordable than the JL Audio e-series subs. All the other sub brands I’ve researched seem like me-too designs. SVS has stood out simply due to great pricing and amazing customer support. I do know of one friend who uses Vandersteen subs but I know those are priced higher than I care to spend, given that I’m already sold on the idea that I’ll want two.

One nice feature of my LTA amp is it has a pre-amp pass through ability for single ended connections. My amp is between my speakers on a floor rack so bridging interconnects to a couple of subs placed by each speaker should be an easy setup.

Check out HSU ULS-15 MKII
Excellent price, excellent performance!
I am running two in my system and could not be happier.
The "slow' vs "fast" issue regarding subs is especially strange and inaccurate. Bass note "hangover" is generally the room continuing to resonate from low tones (unless damped by rugs, extreme cobweb infestation, bad furniture, or your fat cousin Bob) which is what low tones do, and it should be noted that 15s or 12s or 10s or 8s all respond to bass amp commands similarly (although I like the REL main amp derived method), and when those low notes wind up at your ears it's not due to "speed" at launch as that's just a lazy non technical comprehension catch all.
Best bass driver ever made is the Danley/Eminence designed and built by Eminence LAB12. It's in use by all IMAX and OMNIMAX theaters. Get any subwoofer using a LAB12 and you're set.

One example would be the BK Electronics Monolith Plus. Which also uses a 500 watt MOSFET amplifier. BK used to be the OEM manufacturer for REL. They were responsible for the ST range (Strata, Storm, Stentor, Stadium), which made REL famous worldwide. REL makes Chinese crap now. 

BK has my vote as the ultimate internet direct subwoofer manufacturer. If I had to choose another company, it would be HSU.

As for Vandersteen versus Rythmik, Vandersteen destroys it in every possible way. 
I have a pair of Hsu subs for my office. They are good, but not as good as my Vandersteen 2w's. 
I saw "Dunkirk" at an Imax theater when it first came out and the empty seat next to me rattled (amusingly) with the strangely staged bass under the seats…I've always thought Imax visuals are amazing, and Imax sound shamefully bad. 

I saw one sub designer’s quip: "A fast woofer is a tweeter". Fast in regards to a woofer is not used literally, but to it’s perceived lack of boom. Many factors contribute to boom, mostly the room. But Arnie Nudell didn’t employ servo-feedback woofers in his IRS, RS-1b, and other speakers for marketing reasons, and neither does Brian Ding in his Rythmik subs. Nor does Richard Vandersteen employ feed-forward in his for no good reason.

If you want to see the woofer that hardcore home theater DIY’ers have for years put in their subs, check out the TC Sounds LMS Ultra 5400 18" woofer. When last available (from Parts Express) it was $900-$1000 for just the driver. Insane motor (magnet structure), extremely high excursion (2"!) and SPL capability.

@wolf_garcia Dunkirk sucked. And what does an empty rattling seat have to do with IMAX subwoofers?
Some of the flying bits were well done, but I guess you missed a few points…the empty rattling seat has everything to do with Imax subs as it was an Imax theater hewing to Imax design parameters. The sudden eruption of seat rattling bass tones is more of a distraction than sounding anything like reality, unless bombs explode in your pants from time to time (!). Disconnected bass tone elsewhere during the show isn't part of something other than an Imax theater experience. Movie sound is sort of a joke generally, designed to appeal to people who like bad popcorn and don't mind "sub" standard sound.
FWIW, I picked up a used F12G here on Agon about two years ago and it matches superfluously with my MMGs for the various types of jazz and Steely Dan-ish music I prefer.
I just inserted a B&K EX-442 Sonata into the system to replace my modded Hafler DH-220 (I was curious as to the Hafler's limitations and had nothing to compare it to) and have been very pleasantly surprised.
I thought the system sounded pretty damned good before, but sitting here listening to "Chester and Lester", I couldn't be happier.
The extra juice of the 442 into the Maggies matched with that Rythmik sub produce a wonderful, wonderful sound to my ear. 
I don't care to get into any debate about "fast" subs and whether that's an accurate statement or not, but the adjustability of the Rhythmik (along with the speaker distance setting off my pre/pro) marry that sub and Maggies very, very well.  I get very taut, deep, authoritative and controlled bass out of this match.
Can't speak to the Vandersteen, but I wholeheartedly recommend the Rythmik sub.
I do not have the level of experience as many of the people that have posted above.  However, I decide to post a response because I have used SVS model sb1000 with several sets of speakers, amps, and preamps. I only use one sub. I have been able to adjust the sub in each situation to get the sound I wanted. I have used tube gear (AR, Lamm) and solid state (Pass).  They provide the buyer with a try-out period. Great little sub for a high-end system. 

As another indicator of the sound characteristic of the Rythmik F12G sub, one listener's reaction upon hearing it was that it sounded "leaner" than other subs. To me that's a compliment!

Hartf36 mentioned the Rythmik's adjustability. Brian Ding considers the phase matching of a sub with it's partnering loudspeaker a major priority, and his phase control is the best I've seen. It is a continuously variable rotary knob that allows the close alignment in time of the sub's woofer with the speaker. The sub's position in the room can be selected with the matter of the room's modes (the locations in the room where low frequencies resonate the most---a function of the room's dimensions, causing boom and overhang) as the priority, the phase between the sub and speaker then adjusted via the sub's phase control. Most sub's force one to choose between the two.

When a sub is not precisely aligned with it's speaker, not only is the sound quality of the pairing reduced, so is it's output. With the sub and the speaker slightly out of phase at certain frequencies, their opposing polarities cause a cancellation of combined output at those frequencies. The Rythmik phase control allows the minimization of that phenomenon.

A fair number of the contributors on Rythmik's AVS Forum are Magneplanar speaker owners; the subs are finding favor with that and other planar speaker owners.  

I forgot to mention the speakers I have used with the sb-1000 sub. Magnepan 1.7, YG Carmel, Quad 2805, and YG Kipod 2. The sub blended perfectly with each of these speakers. I should also mention that I listen mostly to classical, especially symphony music. 
I can second the Hsu ULS-15 MkII.  I run a pair and they offer very tight clean bass down to 20hz in my room.  A great value.  I suspect either of the subs you are looking at would be great as well.  In the end what's "best" would only be known after an audition in your room.  That's the tough part--especially with subs. (thinking back to my aching arms after moving the Hsu's all over my room finding the best location!)
If you like Rythmik... you can step it up a notch with a minor price increase from Salk-Sound.
Agree that the room is your biggest issue when trying to reproduce very low frequencies, but having a system that at least has the capacity t do that is also needed.

I have usually had speakers in my main system with pretty good low frequency reproduction. My Vandersteen 4As were the predecessors to the 5s with integral subs - the difference being that the 4s needed separate amps and external crossovers I have also use Vandersteen 2W subs and liked them.

I currently have main speakers that are 3 dB down at 20 hz, which covers just about everything and the replicate realistic 'slam' of a live performance quite well.  I run a pair of Hsu VTF-15 Mk. 2, their current top model, exclusively for bass reinforcement in home theatre use. I don't use them for music, but once did leave them in the loop to do some listening. Run the way I run them, they are 3 dB down at 16 hz.  Is that important? Normally not, but I was listening to digital recordings of European organs with material down to 16 hz (it is important to note that IMHO, you do not hear material that low, rather you feel it).

For the special purpose indicated, the very low bass reinforcement was effective and seamless - I think these particular subs have a very good chance of mating with decent but slightly bass challenged main speakers, and they have considerable adjustability
I certainly agree with wsphon's comments above. But I would also add that with my main speakers, well out into the room, that the Hsu subs have done a great job of recreating deep and tight bass found in many of the recordings (classical and other large scale works) beyond just my organ recordings.  That's what I like about subs in part.  You can optimize your mains for sound stage and the subs for deep bass.  Part of the success of these subs is the huge custom bass trap I made (see my system pics) which really helps bass quality. No bloat.  Just tight and deep with great impact.
I've had many different subs through the years----damn I've spent a LOT of money of them too. All I can SVS SB-4000. I run two of them and really could not be happier. Check them out, you won't be sorry you did.
I have been happy with HSU Subs.....

The Salk subs aolmrd1241 mentioned are really nice. Jim Salk designed and builds incredible enclosures into which he installs a Rythmik 12" or 15" woofer and servo-feedback plate amp. Go to the Salk site just to see what a really well-braced sub enclosure looks like. He then covers the enclosure with rear wood veneers, just beautiful.

Salk also builds the enclosures to Rythmik’s suggested internal volume, which is greater than those used by Rythmik itself. Rythmik uses a 3 cu.ft. enclosure for it’s sealed 15" model (F15), Salk 4 cu.ft. The added cubic foot affords slightly greater efficiency and output. Brian Ding went with 3 cu.ft to keep the enclosure to a size more affordable to ship. The bracing in the Salk enclosures is absolutely insane, the best I’ve ever seen. Check it out!

bracing is good

bracing and constrained layer damping is better

just physics..motion into heat

vs just moving the motion....

Absolutely tomic601. I designed and built my own 4 cu.ft. (internal) enclosures for the Rythmik 15" sub kit, and incorporated Danny Richie’s idea of a "sandbox" (it is viewable on the GR Research website). It is an enclosure within an enclosure, the 1/2" space between them (supported by "ribs") filled with sand. Deader (non-resonant) than a doornail, and very heavy. The inner box has a cross-brace every 6" in all three planes (top-to-bottom, side-to-side, and front-to-back), and the baffle is three layers of MDF (2-1/4" thick). I drew up the plans, and had a local cabinet maker cut the MDF into a flat pack, which I then assembled (glue and clamps) and painted.

I also made some constrained-layer platforms for the tops of my Solid Steel equipment stands, putting a layer of ASC Wall Damp (similar to E-A-R Isodamp) between two of the top shelves. While Maple boards are popular for their pleasing "musical" sound, I prefer no sound from support platforms, same as speaker enclosures.

Why did you not mention Velodyne subwoofers? I would look at a DD 12 Plus. It has both balanced and single ended in/out. It has room and system equalization built in. At around $2,500 it might be too expensive, and that is why you eliminated it.
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Dunkirk. I thought it was just the theater I was in. That monotonous low frequency rarely letup throughout the film. It went on to win the Academy Award for sound?

Velodyne seems to be so busy with their LiDAR sensor development and production that their subwoofer marketing is almost non existent.

There wasn't much on the subwoofer market when I purchased their ULD-18 the first low distortion servo controlled subwoofer whose development has continued to their current products. Velodyne's DD Plus Auto EQ and the flexibility of the visual eight band nine parameter Manual/Preset Room Optimization enables almost limitless adjustability and indistinguishable system integration. 

Back panel connectivity is wide ranging. The remote controllability of polarity is useful on those recordings that reverse polarity from track to track while the six presets and gain are just too much fun.  

I've had my twin Rythmik F12Gs now for close to a month.  I still need to have a friend over to fine tune the phasing, but I'm very close.  These have exceeded my expectations, because playing with other subs never matched very well.  The way concert hall ambience comes forward in large scale orchestral pieces makes my speakers sound twice their price.  Big crescendos with concert bass drums put a smile on my face. My room treatments are also keeping order as intended.  

Electronic bass is never overdone, just supported.  Not overdoing the subs volume is key.  When a truly low note is on the recording, I now hear it, in proper pitch, not as a boom.  Recordings that used to simply boom are now cleaned up.  I couldn't be happier.

Awesome jsm71! The continuously-variable phase control on the Rythmik plate amp makes getting that parameter optimized possible. The 0-180 2-position phase switch found on many subs is a joke!

One old trick for phase adjustment is to temporarily wire your speakers in opposite polarity (switch the positive & negative/red & black leads of your cables), then play a test signal of the 3dB-down point of the chosen crossover frequency between the speaker and sub, and adjust the phase control until the output of the opposite-polarity speaker and sub cancel out each other, creating a zero-sum null. Once the audibility of the test signal has been minimized (it's complete elimination is optimum), switch the speaker cables back to correct-polarity, reversing the plus & negative/red & black speaker cable leads back to normal. 

A phase control is also a joke as it is not constant phase across the subwoofer’s range. For example, at 90° setting shift is 80° at 20Hz, 120° at 40Hz and 150° at 80Hz. Best option is BOTH phase control and 0-180 switch.

Adjusting XO frequency changes the phase.

The wrong way to go about it is to preselect a crossover frequency. It’s been my experience that with the same hardware, the XO frequency is highly room, and to a less extent amp, dependent and picking XO by the numbers is not the way to proceed. Main amplifier choice can necessitate a different XO frequency for the same speakers in the same room.

Adding extra cable and additional connectors to run ’through’ the sub is counter productive. Cable interaction could just as likely negatively impact the entire system.

It my experience, the best way to integrate a sub is add a High Pass to the main amp, drive the sub at line level with a simple high quality Y and adjust the sub to integrate. See for our last XO. The disadvantage of this method is the filter must be matched to the amplifier input impedance. Swapping amps will require a second XO. A distant 2nd best is to use an electronic XO and run the sub wide open. An electronic XO can be a useful tool to find more quickly the sweet spot than soldering capacitors in a passive XO. The main problem with some electronic XO is that the low and high pass frequencies are linked and filter order is usually fixed and steep. A sub with multiple filters and phase controls may allow better integration of frequency, slope and phase.

As far as fast or slow, it is well integrated and not. All to often, the wrong XO frequency is selected and phase is horribly wrong. WAF be damned, sometimes "The sub MUST be placed HERE!!!"

For some background on subs and their operation see
For just setup suggestions see