Subwoofer Decision

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. 

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.

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!

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 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.

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.

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. 

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. ;-)

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.