Are REL the most Musical Subs?

@phusis: On the Rythmik Audio website designer Brian Ding provides exhaustive technical information on his subs. I believe details on the servo-feedback compensation for voice coil temperature variation and other functions may be found in the site's Technology section. Mr. Ding is not your average hi-fi designer, having a Ph.D. in electrical engineering.

For those who want the OB/Dipole Sub from Rythmik Audio/GR Research but don’t have the tools, experience, and/or interest in building the required OB frame into which the woofers are installed, GR Research has a couple of woodworkers who will make the frame for you. One of them also offers the frame in kit form, pre-cut and ready to assemble, only wood glue and clamps required. And either paint or wood veneer if you want the MDF finished.

The Rythmik servo-feedback system also compensates for the increase in voice coil temperature, which all woofers suffer from, regardless of their excursion capabilities.

Rythmik offers sealed subs with a range of woofer diameters: 8", 12", 15", and 18", and dual opposed/double 15". Rythmik designer/owner Brian Ding states all his subs are equally "fast". Fast is more related to woofer "settling time" (returning to "zero" when the signal stops) than anything else. Of course a poorly-braced enclosure (Tekton anyone?) can make a sub (or speaker) sound "slow". But the major cause of bass overhang is room modes.

@mijostyn: Oh yeah, the Eminent Technology TRW-17 is unique all right. It doesn’t propagate sound waves with a woofer at all!

The dipole cancellation compensation circuit incorporated into the plate amp of the Rythmik Audio/GR Research OB/Dipole Sub does not "compensate for serious flaws". Dipole cancellation is not a flaw, but rather an inherent characteristic of dipole subs and loudspeakers. Arnie Nudell incorporated large "wings" on either side of the midrange/tweeter drivers in the Infinity IRS to prevent dipole cancellation. Siegfried Linkwitz and Danny Richie use either "M" or "H" frames in their OB/Dipole subs, for the same reason. The Rythmik dipole circuit progressively boosts the signal as frequency drops, resulting in flat response to 20Hz.

I’ll say it again: The only people who don’t know how good the Rythmik Audio/GR Research OB/Dipole Subwoofer sounds are those who have not heard it. I’ve owned servo-feedback subs before (in the Infinity RS-1b), but the OB/Dipole Sub is in a completely different class. It sounds very different from my Rythmik F15HP pair, and actually sounds more like the bass panels of my Magneplanar Tympani T-IVa speakers than anything else.

Very, very few @jim2. In regard to the servo-feedback subs of Rythmik Audio it is because RA is a direct sales (to consumers) company, so being able to hear a RA sub before purchase takes some work. The same is true for GR Research, with the additional hurdle of that company offering their subs (and loudspeakers) as DIY kits only.

I’ve posted here on Audiogon about the Rythmik Audio/GR Research servo-feedback/open baffle/dipole sub (the sub is the result of a collaboration between Rythmik’s Brian Ding and GRR’s Danny Richie) on numerous occasions, and the number of Audiogon participants who have heard that extremely unique sub can probably be counted on one hand.

The world of subwoofers can be divided into three categories:

1- The one-of-a-kind Rythmik Audio/GR Research OB/Dipole Sub. The only people who don’t know how different this sub sounds from all others (including the other models from both company’s) are those who have not heard it. That includes almost everyone reading this.

Think about it: servo-feedback control of woofer excursion, dipole propagation (with a plate amp that includes a dipole cancellation compensation circuit), and open baffle sound characteristics. Wow.

2- Another one-of-a-kind sub, the Eminent Technology TWR-17, the world’s only "true" subwoofer. Designed to reproduce only 20Hz down to 1Hz!

3- All other subs.

And like REL subs, many of the Rythmik plate amps provide the ability to be connected to either a low-level source (a pre-amp) or a high-level one (a power amp).