[zoltm2001]

Read the following good bits in the planar circle, wonder if there is any more details.

GR Research and Rythmik worked together to create a one-of-a-kind subwoofer system that is uniquely suited for use with Quad Loudspeakers, or any other dipole. It is a pair of 12" woofers mounted in opposing fashion in an Open Baffle W or H-Frame, and powered by the Rythmik A370 Plate Amp fitted with a shelving circuit that counteracts the low-frequency cancellation inherent in such a design. The system benefits from not only the long-acknowledged advantages of Open Baffle speakers in general, but also from the Rythmik Servo System. The Swedish company Gradient offered an OB H-Frame sub for Quad 63's in the 70's and '80's, and built it in dimensions making it suitable to double as stands for the Quads. You can build, or have built for you, frames in any form you want to put the GR/Rythmik OB Servo Sub System into. Details are available on both company's websites.

[kc8apf]

Sounds like Danny's normal 12" sub drivers for OB applications.  He lists them on his website at http://gr-research.com/sw-12-16fr.aspx.  Just above the last picture on the page is a link to plans for a W-frame box using 2 of the 12" drivers.

[bdp24]

Sounds like Danny's normal 12" sub drivers for OB applications.  He lists them on his website at http://gr-research.com/sw-12-16fr.aspx.  Just above the last picture on the page is a link to plans for a W-frame box using 2 of the 12" drivers.

My W-Frames were made from those very plans. And yes, the woofers are Danny's 12" for OB use; the OB woofers (SW-12-16FR) have different specs than the "normal" version (SW-12-04), that version designed for sealed use. Both versions of the woofer are driven by the Rythmik Servo-Feedback A370 Plate Amp, both the woofers and the plate amps optimized for their intended use---OB or sealed.

[Danny Richie]

I have customers using them with all kinds of open baffle speakers from Quads to Maggies, to Sound Labs.

The SW-12-16FR woofers take servo control to open baffle applications. There is nothing else on the market like it.

[zoltm2001]

Greeting Danny, any chance for some photos of the actual thing? I am in particular interested in applications with Quad ESL series from vintage like 57 to the modern siblings like 2905. It would be cool to show the relative position and placement of the OB sub against the main speaker.

Thanks. zoltm.

I have customers using them with all kinds of open baffle speakers from Quads to Maggies, to Sound Labs.

The SW-12-16FR woofers take servo control to open baffle applications. There is nothing else on the market like it.

[zoltm2001]

Danny,

Also, you seems to indicate that servo control is something to be avoid (in the past) for OB application, I sort of understand that servo slow the drivers down and kind of make things worse for OB that require a lot of speed to match up with ultra fast "driver" like electrostat...........

May I know from a technical ground, how this driver together to the plate amp that makes the OB sub a fast enough device to match with OB application. A pointer to some kind of white paper could be a good start. I previously explored OB sub in the linksquitz site but his solution seems to require quite a bit of electronics that steer me away. I ran into this site by accident recently and was pointed to this GR/Rythmik development, I look again and this seems much more manageable, hence the revived interest.

I can roll up sleeves and get my hands dirty someway but need to do some serious homework before hand.

........
The SW-12-16FR woofers take servo control to open baffle applications. There is nothing else on the market like it.

[Danny Richie]

Greeting Danny, any chance for some photos of the actual thing? I am in particular interested in applications with Quad ESL series from vintage like 57 to the modern siblings like 2905. It would be cool to show the relative position and placement of the OB sub against the main speaker.

Thanks. zoltm.

There are a ton of pics out there from customer builds to show coverage of speakers using our OB servo subs.

Placement is not a problem. It is all about distance verses wavelength. The lower the crossover point the further away they can be and the easier it is to dial them in. Then the complete adjustable phase control on the servo amps make is easy to dial them in.

[nickd]

The "servo" system monitors driver position using an extra voice coil on the woofer and a special card in the amplifier. Changes are then applied in the amplifiers feedback loop so the driver position always matches the input signal of the amplifier. Simple, dependable, fast and brilliant solution for really tight, deep tunefull bass up to 200hz. 

[Danny Richie]

Danny,

Also, you seems to indicate that servo control is something to be avoid (in the past) for OB application, I sort of understand that servo slow the drivers down and kind of make things worse for OB that require a lot of speed to match up with ultra fast "driver" like electrostat...........

No. Our servo control system isn't something to be avoided for open baffle applications. Quite the opposite. For a lot of applications it is the only solution. Nothing else can do what these do.

May I know from a technical ground, how this driver together to the plate amp that makes the OB sub a fast enough device to match with OB application.

What makes bass "fast" is the ability to quickly return back to a rest position. And in this regard the servo system is approximately seven times faster than an uncontrolled woofer. 

A pointer to some kind of white paper could be a good start.

Learn all about it: http://www.rythmikaudio.com/technology.html

I previously explored OB sub in the linksquitz site but his solution seems to require quite a bit of electronics that steer me away.

That system really isn't comparable. That is still an uncontrolled system.

I ran into this site by accident recently and was pointed to this GR/Rythmik development, I look again and this seems much more manageable, hence the revived interest.

I can roll up sleeves and get my hands dirty someway but need to do some serious homework before hand.

No problem. When you are ready then I will have what you need.

[Danny Richie]

Here is a pic of a three woofer system in an H frame used with the LSX open baffle line source.



And our open baffle servo subs will play flat to 20Hz and hit a -3db down in the teens.

[zoltm2001]

Hi nick,

Thanks for chiming in, I read somewhere that you have experience with both Rel and Rythmik/GR combo. I m indeed using ONE humble Rel Strata 3, on an extended loan from friend, i.e. free.

Thus far, I could dial it in fairly seemless with ESL 57. It is not hard work. Quite un-expectedly, it is far too hard to blend in with Tannoy 15" Gold, in Rect. York Enclosures. Finally, I sort out the hum issue that prevents me from using the high input. Once I got high input to work, it blends fine with Tannoy.

Recently, acquired the ESL 2905, it does not work as easy with 57 on low level input. High level input hum issue returned and I was hoping high level input could get me blended in with the 2905.

Here is some of my questions,

1. I understand you like the Rythymik solution better than Rel. May I have some ideas on the "why" side?
2. I am talking about 2 channel application, no HT requirement at the moment. Do you use one or two subs?
3. Rel could be have from used market for some silly amount of small money, say a Strata 2 for less than 200 US$, do you think it still justify the path of DIY for the performance gain? Make no mistake, I do have lot of respect on the OB solution mentioned here, in fact, I am quite interested. However, money for sure is an issue, but the TIME for the DIY part is another huge issue, cost of making mistake too.

Look forward to some more interaction.
 

The "servo" system monitors driver position using an extra voice coil on the woofer and a special card in the amplifier. Changes are then applied in the amplifiers feedback loop so the driver position always matches the input signal of the amplifier. Simple, dependable, fast and brilliant solution for really tight, deep tunefull bass up to 200hz. 

[bdp24]

Greeting Danny, any chance for some photos of the actual thing? I am in particular interested in applications with Quad ESL series from vintage like 57 to the modern siblings like 2905. It would be cool to show the relative position and placement of the OB sub against the main speaker.

Thanks. zoltm.

For pics, do a Google Images search for "GR Research OB sub" and "Gr Research Super V". Then go to the GR Research site and look at the SW-16-12FR driver page. There are plans for a W-frame available to look at. After that, look at the discontinued models page and find the Super-V. There are build plans for it also, and the woofer section of the Super-V is an H-frame. When the Google Images search brings up pics of the Super-V, you're looking at an H-frame below the co-ax driver baffle. W and H-frames can be placed on their sides and used as stands for the Quad 57's and 63's, and are a pretty easy build, easier than a sealed enclosure IMO. And the sound is THE best sub match for Electrostatics and Maggies, etc. I went for the OB subs for use with my Quad 57's and Magneplanar Tympani IV's, and the pair of Eminent Technology LFT-8b's that are on their way to me at this very moment. You can also do a search for the Gradient OB sub for Quad 63's. Quad didn't make them, Gradient did, but they were Quad-approved. The Gradient received a very favorable reaction from 63-owners, and both UK and US critics. Some are still in use today, but only because their owners have yet to hear the GR OB! It is far superior to the Gradient.

[nickd]

Zoltm,

The REL's are fine units and far better than most people will ever own. That said, the open baffle bass of the servo subs are a better blend with planars. They move air in the same fashion and with similar speed, they can also play much higher in frequency (up to almost 200Hz). The REL subs are really designed to augment full range loudspeakers (below 50Hz), and help tame room issues.

Danny uses a sealed servo sub when showing at RMAF placed in the back of the room 180 degrees out of phase to add the last bit of "slam" or" room shudder" most folks like me enjoy.

The  only down sides of the OB servo subs is they are NOT compact and they need to be at least 3' out from the back wall to avoid cancellation. If you have the room, they will be a substantial improvement to the Quads.

[SoCalWJS]

Zoltm,

The REL's are fine units and far better than most people will ever own. That said, the open baffle bass of the servo subs are a better blend with planars. They move air in the same fashion and with similar speed, they can also play much higher in frequency (up to almost 200Hz). The REL subs are really designed to augment full range loudspeakers (below 50Hz), and help tame room issues.

Danny uses a sealed servo sub when showing at RMAF placed in the back of the room 180 degrees out of phase to add the last bit of "slam" or" room shudder" most folks like me enjoy.

The  only down sides of the OB servo subs is they are NOT compact and they need to be at least 3' out from the back wall to avoid cancellation. If you have the room, they will be a substantial improvement to the Quads.

OK. Probably a silly question. I'm using the OB Servo sub portion of my Super V's in my "Frankenspeaker" setup. I definitely have a room node centered at around 55 hz. The back of the Super V's are about 40" away from the front wall.

According to the fine folks at THX, bass below 80 Hz is radiated omnidirectionally, so orientation of the drivers is not of great significance (assuming not down firing and the orientation relative to the ground is the same).

Is this really true for paired OB Servos firing in opposite directions? In other words, if I spin the Super V's 45 or 90 degrees, will this change the frequency response at the listening position?

I will try this at some point, just not right now. Santa Ana's are blowing like crazy right now. Power was out for 16 hours yesterday, then 3 and a half this morning. Probably likely to go out again until the winds settle. Also, they're shoehorned into position and rotating them is going to be a B****h.

Figured I'd at least ask first. 

[Danny Richie]

According to the fine folks at THX, bass below 80 Hz is radiated omnidirectionally, so orientation of the drivers is not of great significance (assuming not down firing and the orientation relative to the ground is the same).

Is this really true for paired OB Servos firing in opposite directions? In other words, if I spin the Super V's 45 or 90 degrees, will this change the frequency response at the listening position?

What THX is saying doesn't apply to OB bass. In an open baffle design the output cancels at 90 degrees off axis.

You can also move the speakers out into the room more or play a little with toe in to see what that does for your peak at 55Hz. And of coarse if the crossover to your other speakers is in that area then you can turn the crossover point on the servo amp down further. Or you can use the EQ feature to reduce output in that area.

[SoCalWJS]

What THX is saying doesn't apply to OB bass. In an open baffle design the output cancels at 90 degrees off axis.

You can also move the speakers out into the room more or play a little with toe in to see what that does for your peak at 55Hz. And of coarse if the crossover to your other speakers is in that area then you can turn the crossover point on the servo amp down further. Or you can use the EQ feature to reduce output in that area.

Thanks Danny. I'll start measuring and moving stuff around next week and see what I get. Unfortunately. it's a cancelled node, so I have a bad dropout vs a peak.

I put an absorption panel on the front wall between the speakers and it seems to be helping, but I want to check measurements and confirm that it isn't just my imagination.

[Danny Richie]

Thanks Danny. I'll start measuring and moving stuff around next week and see what I get. Unfortunately. it's a cancelled node, so I have a bad dropout vs a peak.

I put an absorption panel on the front wall between the speakers and it seems to be helping, but I want to check measurements and confirm that it isn't just my imagination.

Ah. And it could well be distance related as a factor of the distance from the front wall. Move them out several feet even if it is impractical just to see if that is it.

[bdp24]

Zoltm,

The REL's are fine units and far better than most people will ever own. That said, the open baffle bass of the servo subs are a better blend with planars. They move air in the same fashion and with similar speed, they can also play much higher in frequency (up to almost 200Hz). The REL subs are really designed to augment full range loudspeakers (below 50Hz), and help tame room issues.

Danny uses a sealed servo sub when showing at RMAF placed in the back of the room 180 degrees out of phase to add the last bit of "slam" or" room shudder" most folks like me enjoy.

The  only down sides of the OB servo subs is they are NOT compact and they need to be at least 3' out from the back wall to avoid cancellation. If you have the room, they will be a substantial improvement to the Quads.

In regards to the size of an H or W-frame, the footprint of the GR OB Sub is only around 14" X 14", smaller than most sealed subs, and much smaller than ported/vented ones, and the height is around 27". And while it is true that OB subs need to be at least 3' from the wall behind them, so too do the Quads, so OB subs don't ask for anything more than your speakers already do.

[Early B.]

And while it is true that OB subs need to be at least 3' from the wall behind them, so too do the Quads, so OB subs don't ask for anything more than your speakers already do.

If you don't have the 3 feet behind the wall, it's not a deal killer. My GR Research OB sub is about a foot from the rear wall due to WAF. One day I moved it several feet away from the walls and I preferred the sound when it was closer to the wall. I'm only running it from about 50Hz and below, though.

[bdp24]

An OB sub can be put right up against a side wall if need be (because of the null on each side of the frame), it's the rear output that needs tending to.