A coupla decades back Gradient made dedicated OB subs for both the QUAD ESL (aka "57") and the 63. They did that for a reason: QUAD owners had long been searching for a sub that would "mate with" their dipole ESL’s, to no avail. Non-dipole subs simply do not "mate with" dipole loudspeakers. Why? That information is readily accessible in the literature, including in the writing of Siegfried Linkwitz. I won’t repeat it here; those with the requisite intellectual curiosity will find it on their own. Beside, I have previously done so, and that info has been ignored for reasons at which I can only guess.
The statement "the mate with thing is a non-issue" simply reveals the ignorance (the term used in a non-pejorative spirit) of the person who uttered it in regard to the very real technical problems encountered when attempting to mate a dipole loudspeaker with a non-dipole subwoofer. It is HE who should be ignored. ;-)
The OB/Dipole Sub currently available from the collaborative team of Rythmik’s Brian Ding and GR Research’s Danny Richie is a FAR better product than that of Gradient. Again, the reason that is so may also be learned with very little effort. I’ll give you a hint: The Rythmik Audio/GR Research OB/Dipole Sub is the only sub of it’s kind in the entire history of hi-fi music reproduction, an OB/Dipole sub incorporating servo-feedback woofers. Now THERE’S a mating!
The OB Sub is the first and only sub using dynamic woofers I have found which rivals the bass panels of the Magneplanar Tympani T-IV’a (which I also own) in bass quality. It was those panels Harry Pearson mated with the m/t panel of the Infinity IRS to create his "super" speaker. The IRS includes massive woofer enclosures containing multiple servo-feedback dynamic woofers, yet Harry preferred the bass panels of the Tympani T-IV. I formerly owned the mini-IRS---the RS-1b, which also includes separate enclosures with s-f woofers. The OB/Dipole Sub easily bests the RS-1b woofers. |
@lewinskih01;By jove, I think you have it! 18" woofers have gained favour amongst OB enthusiasts because of their higher max-SPL characteristics in comparison to smaller woofers (and 15" for the same reason). Open baffle woofer design results in lower output relative to sealed and ported---using the same basic woofer (the woofer in the OB Sub is the same as that used in the F12, only electrically optimized for OB usage.), a characteristic cited against them by opponents of OB subs.
That criticism is justified and fair, but there is a solution, one employed by both Rythmik’s Brian Ding in the OB/Dipole Sub, and by Siegfried Linkwitz in his excellent OB/dipole loudspeakers: a dipole cancellation compensation circuit, which provides electronic boosting of the signal sent the woofer(s) at 6dB/octave below 100Hz. Problem solved! Or at least mitigated: even with that circuit, an OB does not produce as much output as a sealed or ported, fed the same amount of amplifier power. You can’t have it all! To get a slight increase in SPL, the 3-woofer OB Sub is offered. And one can of course stack multiple OB subs, using a separate plate amp for each OB Sub H-frame and it’s woofers.
Speaking of subs with 18" woofers: did you notice Rythmik now offers 18" sealed and ported models? Wow! The 15" models already produce a lot of max SPL, I can’t imagine the 18". And with servo-feedback!
Does your friend with the F8’s realize he owns collector items? Brian Ding discontinued the model (and no longer has the 8" woofer manufactured for him), which was popular for mid-bass use. A lot of audiophiles think smaller woofer = "faster" bass, but Ding insists his 12", 15", and 18" woofers are just as fast as the 8". What makes a sub sound "fast" is how quickly the driver stops and returns to "rest" after the signal stops; the Rythmik servo-feedback design provides stop-on-a-dime woofer control and sound quality.
As for OB sub-to-sidewall distance: Rejoice! Due to dipole cancellation on either side of the OB Sub frame (inherent in open baffle design, as described and explained in my earlier post), you may place the OB Sub right against the wall if you wish. Or lay it on the floor---there is no output on either side of the OB frame! As long as the sub fires down the length of the room, you’re good.
As for OB Sub to front wall (behind the Sub, not the listening position) distance: as with all dipoles, a minimum of 3’ is required, more encouraged. Of course, you may try different distances to optimize direct-to-reflected phase correlation and loudspeaker/sub blending, but the continuously-variable phase control (0-180 degrees phase rotation, creating 0-to-16ms delay) makes that unnecessary. But remember: a phase control can only delay the signal, not send it back in time. ;-) |
@lewinskih01: Your question has me confused. After stating "So he's using F12's up to 40Hz", you then ask "Do you happen to know how high he crosses over to the F12G's?" Aren't those the same? Or am I not seeing what you're asking?
You're not differentiating between F12 and F12G, are you? The "G" designation is used in reference to GR Research, the only difference between the two models being the use of a paper cone woofer in the F12G, an aluminum in the F12. Danny prefers paper cone woofers, Rythmik's Brian Ding metal.
Danny uses the OB sub from whatever frequency is required by the loudspeaker it is used with (up to 300Hz), down to as low as it will play, which is into the teens (below 20Hz). In other words, with a low-pass filter on the sub but no high pass. When he adds a pair of F12's, he still uses the OB sub full range, without rolling off the bottom end to "make room" for the F12's.
Le me reiterate that the 40Hz figure I mentioned is the frequency I believe Danny uses the F12 up to when coupled with the OB. I may be mistaken, it could be somewhat higher, though certainly not above 80Hz. |
@ewinskih01: Danny Richie uses a pair of OB subs in the front of his room and a pair of F12G's in the rear (in both his company's listening room and at hi-fi shows), the F12's in phase opposite that of the the OB's. I believe he uses 40Hz as the x/o frequency between OB and F12.
OB subs sound different from sealed and ported for a number of reasons. Not just because of their dipole SPL drop-off with listening distance characteristic, and not just because the woofers don't have an enclosure in which to produce resonances.
First, their dipole design produces a null on either side of the OB frame (for those who don't know, the waves from the front and rear wrap around the frame and meet in the middle of each side. Being in opposite phase, their combined output is zero---the two cancel each other). The result is that the sub---producing no output in the left-to-right plane, typically the room's width---does not energize the room's eigenmodes in that room dimension. Less "room boom"!
Secondly, sealed and ported subs "pressurize" a room; the sub enclosure creates a separation between the interior of the enclosure and the air in the room in which it resides. When the woofer moves outward (in response to a positive signal), the air pressure in the room is increased (compressed); when the woofer moves inward (a negative signal, of course), the room's air pressure is deceased.
OB subs, in contrast, do NOT pressurize a room. The air on both the front and rear of the OB frame is vibrated by the woofer, but the room's air pressure is neither increased nor decreased. How could it be? The air pressure is moved around within the room, but that's all.
Some people like the sound/feeling of the pressurization of the room (Rythmik's Brian Ding, apparently). An OB in the front of the room with a sealed in the rear produces a compromise between the two---the lean/"taut" sound of the OB (optimal for blending with planar loudspeakers), the weight of the sealed. |
@rixthetrick: To read lots of discussions about the GR Research/Rythmik OB/Dipole Sub, head over to the GR Research Forum on AudioCircle. There are threads dedicated to the sub which contain info provided by GRR owner/designer Danny Richie, as well as guys who have built it. Once you have heard an OB woofer, sealed/ported are simply no longer good enough!
Rythmik's Brian Ding does not actively promote the OB Sub, though it is listed amongst the DIY/Custom models (not just the OB, but also sealed and ported subs.). On the Rythmik website, owner/designer Brian provides a LOT of info about the Rythmik line of subs, some of it very technical (Brian has a PHD, and is brilliant). On the website there is also a link to another Forum with a dedicated Rythmik section. Rythmik owners are passionate about their subs! |
Cool @lewinskih01! I chose to go with two woofers per side, in the less-common W-frame (most people go with the H-frame, including the Canadian woodworker who offers GR Research customers a great frame in flat pack form), which Siegfried Linkwitz also chose for the frame of his OB loudspeakers. For that reason I got the 8 ohm version of the GR Research woofer, rather than the 16 ohm.
Why? The Rythmik A370 plate amp puts out maximum power into a 4 ohm load (as do of course almost all solid state amps), but doesn’t like to see an impedance lower than that (few do!). A pair of the 8 ohm woofers are fine (in fact optimal), but three of them present too low an impedance to the amp. For that reason, if using three woofers per amp you MUST use the 16 ohm version. However, two of the 16 ohm---which produce a combined impedance of 8 ohms---doesn’t draw all the power out of the amp of which it is capable. Wasteful, as well as lower in maximum SPL capability.
I have the OB subs 5’ from the wall behind them, which makes sense since my loudspeakers---also dipoles---are the same. I have the two side-by-side, but that’s because I use 180 as the x/o frequency between sub and loudspeaker (unlike a normal sub, the OB plays up to 300Hz. It can therefore be used as a woofer with any loudspeaker whose midrange driver reaches down to 300.). One thing to know about the OB Sub: as it produces a null to either side of the frame, it MUST face the listening position if you want full impact at that location.
Though Rythmik’s Brian Ding was involved in the development of the OB sub (including creating the Dipole Cancellation Compensation Network---6dB an octave below 100Hz---he installs in A370 plate amps destined for OB usage), it is more Danny Richie’s baby. Brian found the OB sub to sound more "lean" than he cares for, without enough "weight". It is that weight that many dipole speaker enthusiasts/owners object to in "normal" subs. Each to his own! |
GR Research has many planar loudspeaker owners (myself included) who have found musical happiness with any one of their subs. Look into the model F-12G, designed in collaboration with Danny Richie of GR Research (hence the "G" in the model designation).
If you are REALLY serious, and are up to a little DIY, the Rythmik/GR Research OB/Dipole Sub is THE sub for use with dipole loudspeakers. Details on the GRR website. |
