GR Research Open Baffle Dipole Subwoofers

[marcl]

HEAVY!  

The amps came today. I was tracking UPS and ALMOST got to the door in time so I wouldn’t have to pick the box up off the sidewalk. 34lbs … probably 90% transformers.

I was concerned at first that maybe they shipped the wrong version because the instructions said “sealed version” but I called Danny and he said they always send the same instructions, but the servo version has a little circuit board added to the back with the shelving circuit.

The cardboard boxes are real sturdy so very likely I’ll spray paint them black, cut a hole for the servo wires and just use them sitting behind the speakers since they say you should keep the amp within 3ft.

[ttocs]

May 20, 2024 12:00:57 GMT -5 marcl said:

HEAVY!  

The amps came today. I was tracking UPS and ALMOST got to the door in time so I wouldn’t have to pick the box up off the sidewalk. 34lbs … probably 90% transformers.

I was concerned at first that maybe they shipped the wrong version because the instructions said “sealed version” but I called Danny and he said they always send the same instructions, but the servo version has a little circuit board added to the back with the shelving circuit.

The cardboard boxes are real sturdy so very likely I’ll spray paint them black, cut a hole for the servo wires and just use them sitting behind the speakers since they say you should keep the amp within 3ft.

View AttachmentView Attachment

Cool!

Are all the settings on this amp analog? . . . so no DSP?

[marcl]

May 20, 2024 12:15:58 GMT -5 ttocs said:

May 20, 2024 12:00:57 GMT -5 marcl said:

HEAVY!  

The amps came today. I was tracking UPS and ALMOST got to the door in time so I wouldn’t have to pick the box up off the sidewalk. 34lbs … probably 90% transformers.

I was concerned at first that maybe they shipped the wrong version because the instructions said “sealed version” but I called Danny and he said they always send the same instructions, but the servo version has a little circuit board added to the back with the shelving circuit.

The cardboard boxes are real sturdy so very likely I’ll spray paint them black, cut a hole for the servo wires and just use them sitting behind the speakers since they say you should keep the amp within 3ft.

View AttachmentView Attachment

Cool!

Are all the settings on this amp analog? . . . so no DSP?

ASP only ... switches and knobs.  The shelving circuit that they add for open baffle just compensates for the OB extension loss and it's the same circuit whether you have one, two or three drivers.

[marcl]

Next steps ...

Shipping of the servo amps was delayed a few weeks because the folks at Rythmik Audio were away on a business trip. But this hasn't delayed the build because as it happened, my month old grand nephew had his open heart surgery moved up sooner than expected and so his dad was unable to spend the time to build the enclosures for me. Well little Leonardo is all recovered and home safe, and Harry should have some time soon to build the enclosures.

But in the meantime, I can still do some testing. Like ... I can prop up one of the 12" drivers and put a mic a couple inches away, and drive it with a regular amp and the servo amp and see what the shelving circuit does. I can use the servo amp and try various switch positions for the extension filters and servo damping. After all ... the drivers will not be in a box, and NO baffle is not that different from open baffle. None of this will give me data that correlates to how the finished open baffle subs will ultimately perform or sound, but it will let me see how the options reflect in measurements. Like, do I see a really big difference in impulse response with the three servo damping settings.

So hopefully sometime this week ...

[marcl]

Well, the cabinets are not done yet.  But I decided it would be interesting to do some measurements with the servo amp and one speaker.  So I rigged this up today and I learned a lot ... all good!

I played around with PEQ, Bass Extension filter, Crossover, and Servo Damping settings.  I was kind of surprised that a single driver sitting loosely in a cardboard box would respond so low.  It's just sitting in a hole with the styrofoam packing material holding up the heavy magnet inside the box.  A couple shelves sitting on the box to stabilize it, and the end of the box open.

With the settings in the photo above, here's what the frequency response looks like with hi, mid and low damping (pink, yellow, blue respectively).  Less damping results in a little bit more output at the very low end.  Very slight difference with the impulse response.   With the servo coil disconnected (not shown here) there is a much bigger difference from no Servo to Hi Servo, than there is with respect to the Mid and Low at least up to 10ms.


So that's about all the testing I can do before I get them built.  But I am encouraged that with three drivers per sub and two subs across the front of the room, I should easily get down to 17Hz.

[klinemj]

I saw your post with the sub control details and thought "looks like my Rythmik instructions", and...it is! Same amp I have in my F25.

Mark

[marcl]

May 27, 2024 15:17:37 GMT -5 klinemj said:

I saw your post with the sub control details and thought "looks like my Rythmik instructions", and...it is! Same amp I have in my F25.

Mark

Yes the amp is the Rythmik 370PEQ modified by them for open baffle use.

[klinemj]

May 27, 2024 16:04:23 GMT -5 marcl said:

May 27, 2024 15:17:37 GMT -5 klinemj said:

I saw your post with the sub control details and thought "looks like my Rythmik instructions", and...it is! Same amp I have in my F25.

Mark

Yes the amp is the Rythmik 370PEQ modified by them for open baffle use.

Mine is currently back with them for the 2nd time. I plan to make sure it has better surge protection this time. Great sound, but...

At least Brian is good to work with.

Mark

[leonski]

Very comprehensive control setup for the amp. Building the speakers is just the beginning.

With this amp, you have an incredible number of combinations. A setup which works best, might

not even be the most obvious way to go...

I would mess with all the settings before measuring ANYthing. Measuring is one thing, but associating

what you measure with what you hear is quite another.

[leonski]

May 27, 2024 17:06:02 GMT -5 klinemj said:

May 27, 2024 16:04:23 GMT -5 marcl said:

Yes the amp is the Rythmik 370PEQ modified by them for open baffle use.

Mine is currently back with them for the 2nd time. I plan to make sure it has better surge protection this time. Great sound, but...

At least Brian is good to work with.

Mark

Depending where you live, you might be able to use MOV type protection.

But for no prisoners and no compromises?   Maybe the 'Brick Wall' conditioner....

An isolation transformer for some applications?   

Maybe even a whole-house solution IF local conditions warrant....

[marcl]

Quick update .... looks like the cabinets should be done within two weeks. Then painting, assembly and LOTS of testing. I'm hoping for moderate weather so I can do some free-field tests outside. Here are the final drawings that I modified slightly from GR Research plans. Hope everything fits!


I asked Harry to drill the holes in the baffle so I could use bolts instead of wood screws.  Easier to drill before assembly.

GR recommends lining all the internal surfaces with their No Rez product, which seems to be an asphalt layer with an inch of foam on top.  Has anyone used this product?  I kind of think the foam does nothing at bass frequencies.  And while the asphalt will have some deadening properties ... with these dimensions and thick MDF walls I find it hard to believe there will be any resonances.  But I may experiment with butyl rubber or mass loaded vinyl ... or Dynamat.

[leonski]

WOOD SCREWS? presumably to secure drivers? NO WAY would I do that. Probably not even T-Nuts, given access to BOTH sides of the driver / baffle.....

And YES, for sure, the Automotive End of audio will have already come up some materials which are useful for taming cabinet resonances......

I would go NUTS on this.

For example....one of several....I would make use of a ROUTED joint. On the side view? The main baffle would be 1 1/2" longer with 2x 3/4" slots cut
for it to sit into......OR the 2 piece ends could be made as 3 piece with the outers being as drawn and the inners being 2-piece. You could than skip router....

Several other opportunities for similar construction.....I'm a personal Big Fan of Pocket Screws...... I built a 30 cubic foot box for ALL my BBQ stuff using
that technique and it is rock solid. I can stand a 220lb friend up IN the box and roll it around with him in it......Various other features NOT germain to speaker
enclosures

[marcl]

Jul 21, 2024 18:08:21 GMT -5 leonski said:

WOOD SCREWS? presumably to secure drivers? NO WAY would I do that. Probably not even T-Nuts, given access to BOTH sides of the driver / baffle.....

And YES, for sure, the Automotive End of audio will have already come up some materials which are useful for taming cabinet resonances......

I would go NUTS on this.

For example....one of several....I would make use of a ROUTED joint. On the side view? The main baffle would be 1 1/2" longer with 2x 3/4" slots cut
for it to sit into......OR the 2 piece ends could be made as 3 piece with the outers being as drawn and the inners being 2-piece. You could than skip router....

Several other opportunities for similar construction.....I'm a personal Big Fan of Pocket Screws...... I built a 30 cubic foot box for ALL my BBQ stuff using
that technique and it is rock solid. I can stand a 220lb friend up IN the box and roll it around with him in it......Various other features NOT germain to speaker
enclosures

No wood screws for sure!  The speakers came with them but no way.   I think #10 hex bolts and nuts will be the way to go since I'm having him drill the holes in the baffle before assembly.

The cabinets could come in at 80lbs each if my MDF calculation is correct.  Then 20lbs each for drivers ... 140lbs per box assembled!

Looks like I'll pick them up Aug 3 

[marcl]

Here's the plan for the new Open Baffle Dipole Subs and a modified approach to using my Dynamic Woofer Modules.   This eliminates miniDSP from the design and uses two Rolls MX401 like mixers to combine signals with level and panning control.   In this approach I'm letting the left and right Fronts play their respective sub content only to the left and right subs, but I have the option to mix them to both subs.  I also am starting with the Fronts crossed to the subs at 50Hz but I ordered crossover modules for 60 and 80 so I will be experimenting to see where the OB subs best integrate with the Magnepan 3.7/DWM bass.  And finally, rather than driving both voice coils with separate amps in the DWMs for left, right and center content, I'm mixing them with another Rolls MX401 and driving one voice coil in each DWM from the Crown amp.



p.s. For those not familiar with my setup, the DWM is a Magnepan bass module 20"x22" that plays from 50-300Hz.  Feeding it the left and right Front signals allows them to fill in some cancellations in the bass response due to room resonances.  They also augment the CCR Center speaker by playing bass from 200Hz down to the center bass management crossover point which is currently 60Hz.  

[marcl]

So while waiting for the sub cabinets to be finished, and for some final components to arrive, I was sitting in my "padded cell" .... inside the box - and nearly asleep listening to some Atmos music - thinking outside the box.   I came up with an alternate connection scheme using exactly the same components as my original plan, but arranged differently.

Here's my original Plan


And here is the new Plan B


So what is different?

• In Plan A the Center channel is Small. It goes through a crossover that sends >200Hz to the CCR and <200Hz to the two DWM panels.  I then cross it to Bass Management around 60Hz.
• In Plan B the Center channel is Large.  It goes through a crossover that sends >200Hz to the CCR.  <200Hz goes to a mixer that combines the Lo Center output with the L/R Front outputs.  The combined L/R + C Lo then go to the active crossover which sends <50Hz to the subs.  L/R +C >50Hz  (C only 50-200) are split to the 3.7 and DWM L/R fronts.
• As before, the L/R Lo outputs of the crossover combine with the Center Sub LFE output and go to the subs.  I have the option to run these signals mono to both subs, or to send L/R to their respective subs and LFE to both.

Why might Plan B be better?  Because everything below 200Hz for the Center channel goes to the L/R 3.7/DWM speakers.  This, as opposed the Center 50-200Hz going only to the L/R DWMs.  I think the imaging and quality of the sound for the Center below 200Hz will be enhanced, and will have the benefit of higher power from the L/R 3.7 + DWM amplifiers.

I'll think about it some more, but I think it will be better!

p.s.  ttocs  ... keep me honest ... I think there will be a problem after I run Dirac 

[ttocs]

Aug 9, 2024 15:21:43 GMT -5 marcl said:

So while waiting for the sub cabinets to be finished, and for some final components to arrive, I was sitting in my "padded cell" .... inside the box - and nearly asleep listening to some Atmos music - thinking outside the box.   I came up with an alternate connection scheme using exactly the same components as my original plan, but arranged differently.

Here's my original Plan
View Attachment

And here is the new Plan B
View Attachment

So what is different?

• In Plan A the Center channel is Small. It goes through a crossover that sends >200Hz to the CCR and <200Hz to the two DWM panels.  I then cross it to Bass Management around 60Hz.
• In Plan B the Center channel is Large.  It goes through a crossover that sends >200Hz to the CCR.  <200Hz goes to a mixer that combines the Lo Center output with the L/R Front outputs.  The combined L/R + C Lo then go to the active crossover which sends <50Hz to the subs.  L/R +C >50Hz  (C only 50-200) are split to the 3.7 and DWM L/R fronts.
• As before, the L/R Lo outputs of the crossover combine with the Center Sub LFE output and go to the subs.  I have the option to run these signals mono to both subs, or to send L/R to their respective subs and LFE to both.

Why might Plan B be better?  Because everything below 200Hz for the Center channel goes to the L/R 3.7/DWM speakers.  This, as opposed the Center 50-200Hz going only to the L/R DWMs.  I think the imaging and quality of the sound for the Center below 200Hz will be enhanced, and will have the benefit of higher power from the L/R 3.7 + DWM amplifiers.

I'll think about it some more, but I think it will be better!

p.s.  ttocs  ... keep me honest ... I think there will be a problem after I run Dirac  ;)

And I thought you were on the path of simplicicicicity!

Boiling it down, Plan B is adding the L&R from 50-200Hz as additional Center Channel duties, correct? If so, this would effectively create a larger expanse of Center, correct?
How do you account for the timing when spreading the Center Channel out wider into additional speakers? Are there delays in the chain somewhere?

[marcl]

Aug 9, 2024 16:09:37 GMT -5 ttocs said:

Aug 9, 2024 15:21:43 GMT -5 marcl said:

So while waiting for the sub cabinets to be finished, and for some final components to arrive, I was sitting in my "padded cell" .... inside the box - and nearly asleep listening to some Atmos music - thinking outside the box.   I came up with an alternate connection scheme using exactly the same components as my original plan, but arranged differently.

Here's my original Plan
View Attachment

And here is the new Plan B
View Attachment

So what is different?

• In Plan A the Center channel is Small. It goes through a crossover that sends >200Hz to the CCR and <200Hz to the two DWM panels.  I then cross it to Bass Management around 60Hz.
• In Plan B the Center channel is Large.  It goes through a crossover that sends >200Hz to the CCR.  <200Hz goes to a mixer that combines the Lo Center output with the L/R Front outputs.  The combined L/R + C Lo then go to the active crossover which sends <50Hz to the subs.  L/R +C >50Hz  (C only 50-200) are split to the 3.7 and DWM L/R fronts.
• As before, the L/R Lo outputs of the crossover combine with the Center Sub LFE output and go to the subs.  I have the option to run these signals mono to both subs, or to send L/R to their respective subs and LFE to both.

Why might Plan B be better?  Because everything below 200Hz for the Center channel goes to the L/R 3.7/DWM speakers.  This, as opposed the Center 50-200Hz going only to the L/R DWMs.  I think the imaging and quality of the sound for the Center below 200Hz will be enhanced, and will have the benefit of higher power from the L/R 3.7 + DWM amplifiers.

I'll think about it some more, but I think it will be better!

p.s.  ttocs  ... keep me honest ... I think there will be a problem after I run Dirac 

And I thought you were on the path of simplicicicicity!

Boiling it down, Plan B is adding the L&R from 50-200Hz as additional Center Channel duties, correct? If so, this would effectively create a larger expanse of Center, correct?
How do you account for the timing when spreading the Center Channel out wider into additional speakers? Are there delays in the chain somewhere?

This is not topologically more complex though.  It uses all the same parts as the original plan, but incorporates the Center farther upstream so its low end 50-200 goes to the 3.7s as well as the DWMs, instead of just the DWMs.   The 3.7 image is slightly wider than the DWM image alone, so below 200Hz the Center image may be wider.

It's all analog ... no delays.  BUT .... I can't yet get my head around the fact that in this scenario, when Dirac sweeps the center it will play through the CCR, both 3.7s, both DWMs and both subs.  It will correct the Center frequency full range 16-20k and impulse response based on that.  So what will Dirac think the distance is, if there are 7 speakers playing, separated by a couple feet here or there?  And when it corrects the output of all those speakers based on the center sweep ... then it corrects the L/R 3.7/DWM pairs separately ... will those corrections step on each other?

[leonski]

Only ONE way to tell.....and that's just run the experiment.

Do you have a scope / mic to measure impulse response?

[marcl]

Aug 10, 2024 16:01:13 GMT -5 leonski said:

Only ONE way to tell.....and that's just run the experiment.

Do you have a scope / mic to measure impulse response?

REW measures impulse response. I’ll be able to see what’s going on. Also I’ll see if there are any anomalies in the frequency response when it all plays together. It will be an interesting experiment but if it doesn’t work I just revert to Plan A which I know will work.

Hopefully tomorrow or Monday 😄

[leonski]

I must disagree! With all due respect! 'if it doesn't work I just revert to Plan A'.........This is a fine time to innovate or simply experiment.......

When I installed my Maggies? Simple pair and later a sub......But ME? I couldnt' follow the directions so I tried them ALL FOUR ways.

Pole piece forward or back? Tweeter 'in' or 'out'...... So? IMO, 'revert' to Plan A is a non-starter. In my speaker foolings and

without any measurements? Installed an artsy absorber on the side opposite. Reflection tames. Than the orientation experiments.

The only thing not messed with was speaker to amp connections... As it turned out? Some setups last only minutes. Others last

for hours or even days. When I got to my final tests, I ended up by doing a fine tune and leaving it......Little bits of toe? Wall spacing

to desired included angle?

I'll bet you get on to something. Maybe unexpected or without warning from any of the people who know this approach and may have

known?

I have a few ideas, but based on maybe......philosophy? So we can maybe talk later......

cheers.....