Best type of Sub to consider?

ajant---Yes! And that is a very good idea, one which Danny Richie himself has done when showing at RMAF (where the OB/Dipole Sub was voted "Best Bass At The Show" multiple years in the recent past), using the OB’s in the front of the room and F12G’s in the rear. The Rythmik plate amp is available in an XLR version (actually two different XLR models---the XLR2 and XLR3), so you can run a long inter-connect from your pre (or the OB sub’s plate amp) to the F12’s at the back of the room.

The XLR2 allows multiple subs to be connected in "Master/Slave" fashion, but that is recommended only with identical subs, not OB’s with sealed subs. That is because the Master/Slave connection disables some of the Slave’s controls, the Master used to set the operating parameters for both it and the Slave sub. But two subs can be connected without the Master/Slave relationship, the input signal reaching the first sub’s amp merely passed along to a second sub---handy if one’s pre-amp lacks enough outputs for two pair of subs. My pre has both RCA and XLR outputs, two L/R pairs of each, so I can feed OB’s and sealed subs separately.

Your system suggests you would appreciate the sophistication of an OB/Dipole sub. A very unique one is available as a joint venture between GR Research and Rythmik Audio. The sub is not a normal Open Baffle sub, which are already unique enough, but an OB in an H-Frame, superior to a flat baffle because of it’s greater structural stiffness and non-resonance. And of course it’s open baffle design prevents the often boomy sound of even the best sealed subs.

A dipole sub excites the room modes of it’s front and back output, but not those of the room dimension to it’s sides, where there is a dipole null. There are a few OB/Dipole subs available, but the GR Research/Rythmik is unique in that the two (or three) 12" woofers (facing in opposite directions in the H-Frame) are Servo-controlled by the Rythmik plate amp. The amp also contains a 6dB/octave shelving circuit to offset the dipole front-to-back cancellation at very low frequencies.

The sub is offered as a kit only (one kit includes the amp and two---normally, though you can use three---12" woofers). The H-frame into which the kit is installed is available as an easily-assembled flat pack from a couple of wood workers who frequent the AudioCircle GR Research Forum. A pair of kits (for two subs) runs about $1500 shipped, and the flat pack (CNC cut from 1.5" MDF!) about $600. The highest sound quality, though not quantity, sub available.

Kenny, I understand your confusion. The subs Salk Audio offers are the standard Rythmik sealed (either 12" or 15"). Jim Salk installs the same DIY kit you yourself can buy from Rythmik, and installs it in his own larger (4cu.ft. vs Rythmik’s 3cu.ft for the 15"), better braced, beautifully finished enclosure. The OB/Dipole sub is not offered by Salk, and is a completely different animal.

Before getting to the OB/Dipole though, yes, you can try out any of the Rythmik subs (for 30 days I believe, but don’t quote me), paying only for shipping if you send them back. They offer a bunch of different models, both sealed and ported, with 8", 12", 15", and soon, 18" woofers. Also a number of different plate amps, with different power ratings and control features. What they all have in common is the Rythmik patented Direct Servo Feedback design of owner Brian Ding.

The OB/Dipole sub is a joint venture by Rythmik and Danny Richie of GR Research. Danny was already designing OB speakers, and when he learned of the Rythmik design, he envisioned the mating of it with a dipole sub, and contacted Brian. They put their heads together, and co-designed the OB/Dipole sub.

The sub is not available as a ready-built, try-it-before-you-buy-it product, but only as a DIY kit. Don’t let that scare you away---there is a fairly easy way around that. You can see the kit listed on the Rythmik website, on the DIY/Kit page. It consists of the Rythmik A370 plate amp and a pair of 12" Open Baffle woofers, for one channel---two kits required for a stereo pair obviously.

But Brian does not actively promote the OB sub, Danny does. I have suggested to Danny that he make a listing for the OB/Dipole Sub kit on the GR Research site, but he hasn’t gotten around to it yet. You can find information on it buried in the listing for the 12" woofer in the "Drivers" section of his product listings.

But where you really want to go to read about the sub is on the AudioCircle GR Research Forum, where there are several threads discussing the OB/Dipole sub, with pictures posted by those who have made them. It is also there you will find the makers of the H-Frame that the kit is installed in. The frame is offered as a flat pack, and is not much harder to assemble than Ikea furniture. Anyone not wanting to have to do that could have a cabinet maker assemble it in a couple of hours, then paint or veneer the MDF (1.5" thick!) it is made of.

Check it out, it’s really special. The OB/Dipole sub has been incorporated into several full-range speakers, among them The GR Research Super-V (which was awarded "Best Bass at the Show" for several years at RMAF) and Serenity Acoustics Super 7.

Actually jwt, a pair of the OB/Dipole Sub kits is $1500 shipped, and a pair of the H-Frame flat packs is $600 I believe (I got in on the first few sets made at an introductory price). So it’s about $2100 for a pair of the OB/Dipole Subs and really good H-Frames, CNC cut from 1.5" thick MDF! All that’s left is finishing the frames, paint or veneer. Each sub contains a pair of 12" Servo-Feedback controlled woofers facing in opposite directions (they don’t have to be, but doing so creates a couple of benefits), and the Rythmik plate amp with a dipole cancellation compensation shelf to counterbalance the acoustic roll-off inherent in dipole speakers. The amp is available in a couple of different configurations, one being balanced/XLR in and out. One band PEQ is provided, as are high pass and low pass frequency and slope adjustments, three levels of electrical damping, and, most importantly, a 0-15ms Phase Control. Do NOT buy a sub without continuously variable phase adjustment. A 0/180 switch is worthless, and that’s exactly what most subs have. This sub is made specifically for music reproduction, being optimized for sound QUALITY, gladly sacrificing maximum sound quantity to get it. The output of a pair of the OB/Dipole subs is about equal to a single sealed Rythmik. Are you willing to give up 3dB in output to obtain the OB/Dipole sound quality? I was.

In addition to the lack of sealed or ported enclosure resonances, an OB/Dipole sub creates cleaner bass also because it excites only the room mode of the dimension it’s front and back faces. If you fire it down the length of your room, the room modes of the width of the room are NOT engaged---the null created to each side of the sub prevents it. So elegant!

The sub is absolutely and without question the best sub in the world for any and all planar loudspeakers. Not only does it’s Open Baffle design and construction provide the same advantages (and liabilities) as does the non-box design of planar speakers, but it’s dipole acoustical properties and behavior matches that of planars, unlike ANY box sub in the world. The acoustical output of dipoles drops off at only half the rate of boxed speakers; if you balance your speakers and box subs at one listening distance, that balance is different at a different listening distance, and in all other parts of the room. Not so with the OB/Dipole Sub, as it shares with OB and dipole speakers (which is what planars are, of course) the exact same acoustic SPL drop-off with distance rate. Again, elegant!

And I haven’t even brought up the benefits of the Rythmik Direct Servo-Feedback system, designed and patented by Rythmik owner Brian Ding. Not just another servo design, but a new, better one. You think the servo-feedback woofers in the Infinity IRS were clean? Wait until you hear this sub! It’s sound has been described as "stops on a dime". It's the only sub I've found that isn't embarrassed by my Magneplanar Tympani T-IV bass panels. NO overhang, no boom, no bloat. The Rythmik Audio/GR Research OB/Dipole Sub---the only Servo-Feedback OB/Dipole Subwoofer in the world!

Good catch Kenny---your thought had occurred to me after my last post. One point of stating how well the OB/Dipole Sub works with planars is because they (planars) are so notoriously difficult with which to get a sub to blend seamlessly. If a sub will work with a planar, it will have no trouble doing so with any speaker is the logic. But is it true?

The OB/Dipole Sub has been successfully mated with a pro sound high efficiency 15" coax driver on an open baffle (in the Rythmik Super-V loudspeaker)---read reports on the RMAF from a few years ago to see the reaction at the Show to it's bass capabilities, with NEO 10 and NEO 3 planar-magnetics (in the Serenity Acoustics Super 7), with sealed and ported box speakers, with open baffle/cone monitor speakers having either a 5" or 6.5" midrange driver and dome tweeter, with Eminent Technology magnetic-planars, Quad ESL's, horn-loaded high-efficiency direct radiators, and by Ric Schultz in his own EVS speaker design. Ric is one of the Subs biggest fans and proponents.

If a sub sounds extremely clean and non-boomy, with no overhang, no box resonances, and an ability to excite fewer room modes than a box sub, why WOULDN'T it blend well with any loudspeaker you could name? As to working with your loudspeaker to your satisfaction Kenny, you would probably be the first to try! If the Sub sounds at all promising, I would suggest going to the AudioCircle GR Research Forum and reading the threads dedicated to the discussion of the Sub. There you will find not only the opinion of the Sub by those who have bought it, but also pictures of many different builds, some of them quite interesting to look at. In all the discussion of the Sub, I don't believe there is a single instance of disappointment by an owner.

Gradient designed and built an OB/Dipole H-Frame sub for the Quad 63 in the 80's, and REG at TAS loved it. Loudspeaker/crossover design expert Siegfried Linkwitz offers a DIY loudspeaker incorporating an OB/Dipole bass section in a W-Frame, a frame rather flimsy and under-braced in comparison to the very robust H-Frame offered for the GR Research Sub. And there are several other designers catering to the DIY crowd offering Open Baffle subs (not in a W- or H-Frame, but on a flat baffle) for use with OB speakers. Open Baffle subs have long been known to provide a unique, very different sound from "normal" subs, a sound characterized as "lean". As in no boom, no bloat, no overhang, no box resonances, and less excitation of room modes. And the Direct Servo-Feedback design of Rythmik itself is known for IT'S unique sound, one that prompted loudspeaker designer and manufacturer Jim Salk to incorporate it---the product of another speaker designer!---into his top models. It is the combination of the OB/Dipole design combined with the Servo-Feedback woofer control provided by Rythmik that makes the Sub so special. Really special.

Kenny, Danny and Brian worked on the OB/Dipole Sub together, Danny instigating the collaboration. Danny is an Open Baffle enthusiast, Brian not so much. When Brian heard the sub, he has said he found it to sound somewhat "lean", without the weight and fullness one expects from a sub. That leanness is one thing that makes it so special, and to work so well with highly transparent loudspeakers, which themselves sound lean (in comparison to the thick, slightly plump sound of so many box speakers).

In the "regular" Rythmik Sub line-up, Danny had input on only one model---the F12G, the "G" signifying GR Research, Danny’s company. The Rythmik F12 comes in two versions: the standard F12 (with a Rythmik 12" aluminum cone driver), and the aforementioned F12G (with a GR Research 12" paper cone driver). Danny feels the paper cone affords the F12G greater low-level resolution than does the F12’s aluminum cone (due to the lower mass of paper versus aluminum), and a more natural tonal balance (due to the resonant signatures of paper and aluminum). He recommends the F12G for a music-only system, the standard F12 only for use in a system in which it will be played at near maximum output, where the aluminum cone’s greater stiffness will be an advantage.

There are other Rythmik models with cones of paper, but they are budget models, not the top line F15 and F25 (dual 15’s). The difference between the F12 and the F15HP is, as you might expect, the 12" driver versus the 15" (greater cone area of course, but also greater maximum voice coil excursion), plus amplifier power---the F12 having a 370w amp, the F15HP a 600w one. The difference in price between the F12 and F15 is nominal; if I were getting a pair of sealed Rythmiks (which are slightly superior to the ported in terms of group delay and deepest frequency response), I would get a pair of F15HP’s.

In fact, I did! In addition to the OB/Dipoles, of course. But I bought mine as DIY kits, designing my own enclosures, buying the sheets of MDF, and having a cabinet maker cut them into flat packs which I then myself assembled. I made the internal volume of the enclosures 4cu.ft. vs. Rythmik’s 3cu.ft. (for greater efficiency and maximum output), and braced the hell out of them---1.5" Baltic Birch braces every 6", top-to-bottom, side-to-side, and from around the driver on the baffle to the rear panel. I also designed the enclosure as a box-within-a-box, leaving 1/2" between the inner and outer (with "ribs" supporting the inner), filling the 1/2" cavity with sand. Oh, they’re very quiet enclosures, almost non-resonant. And they weigh a ton! What price excellence? ;-)

Great idea, Kenny. Danny comes at subs from a perfectionist audiophile, music-centric point of view. Brian is an unusual sub designer in that his priority is also music reproduction, unlike the home-theater orientation of most sub designers. But GR Research subs are used in music-only systems, Rythmik’s as much in home theater systems as in music ones.

The servo-feedback Rythmiks have a "stop-on-a-dime" cleanness to them that makes ordinary subs sound like they are filling in the empty spaces with "noise"---the drivers don’t stop and come back to rest when the notes stop. Rythmiks have what Peter Moncrieff of IAR calls "inter-transient silence". No matter which Rythmik/GR Research sub model you choose, you will get that sound. When you talk to Danny, tell him Eric sent ya!

What’d I tell ya Kenny! Being a dipole, the OB sub has a null to each side, creating two benefits: First, it loads the depth dimension of the room, but not the width, exciting the longer, further apart nodes rather than the shorter, closer together one’s. Already you have gotten rid of one source of room boom. Second, the side nulls allow the OB sub to be placed right next to your main speakers should you wish to, or right up against a side wall if you have a narrow room. True, it has to be away from the wall behind it (like any dipole), but most speakers sound better there too. And here’s a bonus: the sub can be laid on it’s side and used as a base for a pair Quad ESL’s or other short speakers. That’s just what the Gradient OB/Dipole Sub made for the Quad 63 was. The difference here is that you have the much higher quality GR Research 12’ woofer, and the Rythmik Direct Servo-Feedback system controlling the dual woofers. As I said, a very special sub, one few people have heard but when do are blown away by.

By the way, you can see a pic of the OB/Dipole Sub in the current thread about Virtual Systems.

Hi Bill. No, the only paper cone is the 12. The reason for that is that it is more of a GR Research product than a Rythmik one. The two companies and their owners have a unique working relationship. Brian was already offering the Rythmik products, and that’s what drew Danny to him, specifically with the intent of collaborating on Danny’s idea for the OB/Dipole sub. The sub is really Danny’s baby, and he prefers paper cones. The 12" aluminum cone version is all Brian’s, the paper version being exactly the same (with one exception---read on) but for the cone, which Danny finalized the parameters on. One can buy an F12 with either the paper or aluminum cone, sealed only.

There are two versions of the 12" paper cone woofer: the first is for use in a sealed or ported "normal" sub. The second is one whose parameters have been optimized for Open Baffle or Infinite Baffle use. You cannot use a regular woofer in those two applications, nor an OB/IB woofer sealed or ported. The free air resonant characteristics and other specs are not the same, and the two woofers cannot be used interchangeably.

Kenny, I ordered my H-frames from Jay (Captainhemo on the GR Research AudioCircle Forum) just as you want yours, with flush tops and bottoms. And I put the idea in his head to make the frames with inset grills, to look like speakers from the 60’s (AR’s, etc). He was making them with the grills attached to the front of the side panels, covering them up. If Jay isn’t doing the flush fit anymore, I’ll trade you my tops for your over-hanging ones if you get a pair. I haven’t built mine yet, the two woofers still being in my old W-frames. Jay’s H-frames are great, CNC cut to Danny’s specs from 1.5" thick MDF!

To contact Jay, just register on AudioCircle (or see below)---it takes only a couple of minutes. He’s great to buy from, a real swell guy. If you don’t want to wait for his next run, I would be willing to let you have my pair---I won’t need them for a few months. But I didn’t have my edges rounded over, wanting to do it myself in a very small radius, like only 1/8", also old school. If you want yours veneered, you don’t want the edges rounded---that makes veneering very difficult. Send me a pm if you want, I can give you Jay's email address.