Need advice on adding subs

$2000 will just cover the cost of the most unique, transparent, unboomy sub of which I am aware: The GR Research/Rythmik Audio OB/Dipole Sub. The catch is that it is not a ready-to-play, factory-finished product. But it's pretty easy to do, if one is sufficiently motivated.

1- You buy the DIY kit from GR Research or Rythmik Audio, the co-designers of the sub. It contains four 12" woofers (a pair for each of two subs) optimized for Open Baffle use by Danny Richie of GR, and a pair of Rythmik's dedicated plate amps (one for each sub, of course) featuring Servo-Feedback control of the woofers, along with a shelving circuit to compensate for the acoustic roll-off endemic to dipole designs. The Rythmik amp also features outstanding controls including adjustable cross-overs (frequencies and slopes), three levels of damping, 1-band PEQ, and, most importantly, a continuously-variable phase control (absolutely mandatory for integrating a sub with speakers. Do NOT buy a sub without it!). The kit is about $1500 including shipping.

2- You buy a pair of Open Baffle H-Frame flat packs from a woodworker who offers them on the GR Research AudioCircle Forum for around $500. Don't worry---I bought from him, he's very honest and trustworthy. The frames are sent unassembled, but are as easy to build as an Ikea bookcase (well, almost). Made of 1.5" MDF (!), they are a truly excellent design, and very non-resonant (unlike the W-frame design of Linkwitz). You then simply paint or veneer the frames to suit your taste and style. See the thread about them on the Forum for details. If this sounds like more than you want to deal with, you could have a cabinet shop assemble and finish them for you.

There was an OB/Dipole sub offered by Gradient in the 80's, for use with the Quad 63 ESL's (reviewed by REG in TAS). This is similar in concept, but much more advanced in execution. Higher quality drivers, with Direct Servo-Feedback (patented by Brian Ding of Rythmik) control of their motion. State of The Art in subwoofers!

cjk---The Rythmik 12" that whart just received is the F12G (G for GR Research) and it has, as he mentioned, a paper cone. The exact same sub is available with an aluminum coned-woofer instead, and that is the plain ol' F12. Danny Richie of GR Research (who designed the paper-coned woofer) feels that paper has a couple of advantages over aluminum: 1- greater resolution and transparency; 2- a more natural timbre and tonality; 3- lower mass and energy storage; and 4- can be crossed over at a higher frequency than can aluminum. Brian Ding of Rythmik Audio (designer of the aluminum-coned version of the woofer) recommends the aluminum-coned F12 for applications where higher volumes will be required (HT, bass heavy material at high SPL). That is because aluminum makes for a stiffer cone, less subject to cone breakup when driven hard. Other than the cone material, the subs are identical. One Rythmik customer (DonH50) just added two more F12's to his system (for a total of four), his speakers being Magnepan MG3A's, and is very pleased with the F12's. If you listen to acoustic music at moderate volumes, or want to x/o at higher than 80Hz, go with the paper. If you listen at high volume to bass heavy material, go aluminum. The difference is subtle, and either will work great with your speakers.

I understand your confusion regarding the Open Baffle nature of the Dipole Sub. I had never heard of the concept and design (though it was not unheard of; the Finnish company Gradient offered an OB/Dipole sub designed and marketed specifically for the Quad 63 speaker a couple of decades back) until I started doing some deep research into subs to mate with perhaps the hardest speaker in the world to add subs to: the original Quad ESL. Open baffle speakers and subs have a cult of enthusiasts who feel that putting a dynamic driver in a sealed or ported box leads to, well, boxy sound! Subs would seem to be a poor application of the OB concept, as the front-to-back cancellation (endemic to OB design) at subwoofer frequencies is a real problem, one leading to loss of output as frequency descends. But OB enthusiasts are guys who find the sound of sealed and ported-box subs too fat, thick, heavy, and boomy. Plus, they "load" the room in a way OB's don't, making the room itself a giant speaker enclosure. More of the room's modes are excited by boxed vs. OB subs, and the result is the "slow" sound of most subs, to use the parlance of the general public!

Cones can be used in free air (rather than in a sealed or ported box), but have to have their electrical and acoustical characteristics tailored specifically for OB use. Danny Richie of GR Research is a long-time designer of drivers, cross-overs, and DIY speakers and subs (including some OB's), and has his driver designs manufactured to his specifications. He offers DIY kits containing those drivers, the x/o component parts, and diagrams for building the open baffle or box within which the speaker or sub parts are installed.

When Danny heard there was a fellow Texas-located designer who had a new patented Servo-Feedback subwoofer design, he envisioned combining it with the OB/Dipole sub design, and contacted Rythmik Audio's Brian Ding in Austin, Texas. The two put their big brains together, and created the world's first and only only Open Baffle/ Dipole Servo-Feedback Subwoofer! By the way, the sub is used in the remarkable $20,000 Serenity Acoustics Super-7 loudspeaker, as well as the GR Research Super-V, recipient of "Best Bass At The Show" award several years running at RMAF. The best bass reproduction available at any price. Not the most output (owing to the nature of it's OB design, and it's "mere" dual 12"-drivers)---for that you want to go with 18" drivers, massive ported enclosures, and class-D pro amps. But for highest sound QUALITY, this is IT!

But the OB/Dipole sub won't be for everyone. It needs to be out in the room (a minimum of 3' from the wall behind it, as with all dipoles), it needs to face you, and it won't have the sound some listeners expect from a sub, one that lets you know there is unquestionably a sub in the system. The OB disappears, it's presence undetectable except that your main speakers now sound like their woofers just gained an octave or more of response at the bottom, the speakers now sounding more transparent, less strained, and playing louder and cleaner. But the standard Rythmik F12 or F12G (or F15, with an aluminum 15" driver, or F25, with dual 15's!) will give you that too, just not with quite the utter transparency of the OB. NO other sub will give you that, but the Rythmik's come closest. They have Brian Ding's Servo-Feedback system for controlling the operation of the woofer, a very high quality driver, amp, and enclosure, and the best controls available in any sub on the market, to integrate the sub seamlessly with any speaker. Sterling Sound in NYC, famous for their world-class LP mastering, has a dozen of them in their monitoring systems. They could buy any subs they choose, and they chose Rythmik.

I understand your trepidation regarding a new-to-you design (open baffle subs), cjk. But consider this: More than a few people consider one particular type of loudspeaker still the best overall of any yet devised: The Planar, one type of OB; Electrostatic, Magnetic-Planar, Ribbon. They have been on the market since the 1950’s, hardly a fad! OB subs are nothing new, but have long presented unique problems for designers and users, and have never become common, remaining a hardcore OB enthusiast cult item. It was Danny Richie’s vision of mating the OB sub principal with Brian Ding’s Rythmik Servo-Feedback design that has allowed the two gentlemen to solve many of the OB Sub’s inherent weaknesses (lack of output, low-frequency dipole cancellation, size), and create the best musical bass reproducer currently available.

Sound quality fanatics, particularly in Asia, have been using Magneplanar Tympani bass panels as woofers since Harry Pearson came up with the idea in the 80’s. The huge Magnetic-Planar drivers provide a quality of bass reproduction unlike that of any cone woofer. If you’ve ever heard a Tympani speaker, you know what I mean. Taut, transparent, with no-overhang or boom. The Tympani’s reproduce the sound of low register piano strings, acoustic bass and cello strings, and bass drum heads like nothing else! I bought a pair of Tympani T-IV’s specifically for use as woofers with my old Quads, finding no boxed sub to blend seamlessly with them, a common opinion amongst Quad owners. The GR Research/Rythmik OB/Dipole Sub has replaced the T-IV’s in my system. It’s that good!

But it’s not appropriate for every listener, system, and/or room. For those people, there is the Rythmik Sub, the next best thing. Call the guys at Sterling Sound and ask them for their opinion of the dozen F15’s in their mastering monitor systems. Brian offers 8", 12", and 15" models in both sealed and ported enclosures. Later this year there will be the new 18" model, at the request of Home Theater aficionados who appreciate the sound QUALITY of Rythmik subs, but want the output of the "monster" subs popular with the HT crowd.