[HAL]

captainhemo also has modular H-Frame OB sub cabinets for flat packs as well.  You can build up 1x12 OB servo modules as time goes on.  They are held together by dowels, so can be taken apart and more added easily but very stable.  I use those for both my speaker systems as they are easier to move around.   You can start with a single 1x12 per side with a servo amp, then add 1x12 modules as time goes on and budget permits.

He is making shipping one more pair of 1x12's flat packs now to take my 2x12's to 3x12's as needed.  He also has the flat packs in stock.

[jesphoto]

Can the 2 1x12 be driven by a single amp?  Thanks

[Tyson]

Can the 2 1x12 be driven by a single amp?  Thanks

It can but it'll be mono bass instead of stereo bass.  Which is less of a problem if you're running the subs only to 70 or 80 hz.  But it IS a problem if you are running it above 100hz.

[mlundy57]

However, the long wire runs can cause issues with the servo control. Danny recommends not having the amp any further from the driver than the wiring that comes on the amp will allow.

[mlundy57]

The dual H-Frames are 16"W x 15"D x 30"H. With the MTMs on top the total height is 54".

You can't pare down the size of the cabinet. They are as small as they can be. Each 12" driver is in a 13" square space. This allows just enough room to mount the driver without touching the sides anywhere. The walls of the cabinet are 1-1/2" thick and the baffle is at least 3/4" thick. They need to be this stout to be sturdy enough for the forces the drivers put on the cabinet. You can reduce the height a couple inches by using a W frame instead of an H frame. However, the W frame is not as well braced and the drivers are more difficult to mount.

The depth of the cabinet is a trade off between low bass output and cavity resonances near the crossover point to the midrange drivers. The cabinet was originally designed to cross over to the mids around 200Hz. The NX-Otica MTMs cross around 100Hz. Since the subs don't have to play up as high, you can make them a little deeper which will give you a little more output on the bottom. For best visuals, I'd recommend making the cabinet depth match the base of the MTMs.

Although you can't make the cabinets physically smaller, you can make them visually smaller by making them lighter in color and or with vertical grain patterns. The darker they are, the more imposing they will look.

Because the subs cross to the mids around 100Hz, they need to be physically very close to the MTM monitors. Directly underneath with the front baffle of the monitor flush with the front of the sub gives the best performance.

Here are some links to some show reports from the Lone Star Audiofest talking about my MTM monitors/dual servo subs:

From the 2019 LSAF

Part-time Audiophile  https://parttimeaudiophile.com/2019/06/05/uilleam-audio-lone-star-audio-fest-2019/

Positive Feedback  https://positive-feedback.com/show-reports/lone-star-audio-fest-2019/  (in the Uilleam Audio room reviewed on page 3)

LSAF 2018

https://positive-feedback.com/show-reports/lone-star-audio-fest-2018/     (in the Uilleam Audio room)

LSAF 2017

https://positive-feedback.com/show-reports/lone-star-audio-fest-2017/  (in the Speakers by Mike room)

My earlier recommendation for the X-Statiks with a single sealed servo sub was based on your $2k budget. If you are willing to spend the money, I wholeheartedly agree with all the recommendations that if you want the best performance you can get in a room the size of yours, these speakers are the way to go.

Mike

[dayneger]

- Tyson, nice example of how adding some volume can make something feel smaller!

- Hobbsmeerkat, those stands are cool... anyone know why the 8" version isn't offered any more?  Also curious how that configuration works.  Is the stand open to the back (or actually, the side)?

- How long of a wire run are the servo amps limited to?  I couldn't find anything on the GR or Rythmik sites.  Those are pretty big units to try to hide on the speaker itself, especially the A370PEQ class.

- Speaking of finding things, I also couldn't find the NX-Otica MTM dimensions despite best intentions searching here.  A drawing or file would be great if you have one.

- Could someone give me the dimensions of the 12" driver outer and inner bezel (outer diameter and inner diameter before rubber/spider start)?  Or has anyone made 3D CAD files of the drivers?

- Mike, great links and craftsmanship. Beautiful!  I'm currently considering less traditional materials like cast concrete... about which I know next to nothing, but it could be a fun learning project.  If the housings fail as subs I'll have made some fancy garden planters.

[mlundy57]

The open baffle version on the 8" servo sub drivers weren't very popular so Danny quit carrying them. Rythmik sells 8" servo sub drivers for sealed enclosures. They are sold either separately or as a dual mid-bass driver module. The finished mid-bass modules have the drivers facing forward.

The factory wiring for the A370 series amps is about 24" long. The amps are normally put in separate boxes and sit on the floor either behind or next to the speaker.

I'm not sure of the exact dimensions of the inner and outer bevel for the 12" servo sub drivers but the cabinet plans have an 11" diameter through hole with a 12-9/16" outer diameter with a 3/4" deep rabbet for recessed mounting.

The MTM monitors are about 24"H, 8-3/4"W at the front, 15"W at the back, and 16"D.

Concrete cabinets? I thought you wanted less bulk 

[dayneger]

Thanks, Mike! That's a challenge about the amps... in my living room, in order for the rig to be far enough from the front wall I'd need to be able to walk behind the speakers and not kill myself on an amp box.  Hmmm.  In the acoustical domain of the human brain the time latency of a few feet of electrical cable should be irrelevant, so I'm curious what the deal is.

I also appreciate your trying to help me out with the MTM dimensions. 

At the same time--Danny--is it too much to ask for you to update your new site with the basics of the products you're selling?  A year ago the excuse was that the new site was coming.  Now it's here and a DIY-inclined person still can't find much.  Scraping Audiocircle is neither efficient nor sufficient.

Concrete cabinets? I thought you wanted less bulk 

As a matter of fact, I do want less bulk.  And I think it should be possible.  In my opinion, gluing flat panels of MDF together isn't necessarily an advantaged choice for containing high pressure radiative sound waves in a non-resonant fashion, much less doing so in a compact visual footprint.  That's my take and I'm sticking with it... unless of course my other ideas bomb.

I've mostly been sketching on paper in odd moments between busy work and family moments, but I did quickly model up one of the many potential directions I'm considering for what could be called the sub chamber(s).  As shown, this has 1" thick walls of countertop or similar/better grade concrete.  Naturally there'd be stabilizing feet and the mid/tweeter section above it.  It's just a simple version to study proportions, 15" outer tube diameter and the aforementioned 14" deep.  It's not the right driver, I downloaded it from a kind individual on GrabCAD. Building a mold for one of these would take some doing for a concrete newbie, but once figured out it should be pretty easy to make the second sub section.

I have other ideas with separate front/back shells that in effect sandwich the driver--meaning, conceivably as low as 13.5" outer diameter--as well as deaggregating each individual sub zone as its own tubularish volume with a modular stacking potential to go 1-2 high as a FR speaker or 2-4 as separate sub towers, probably at the cost of some height efficiency.  Ah, if only this fun play were my actual occupation.

Assuming that it's stiff enough etc, are there any acoustic reasons why the fundamental geometry of this direction would run into problems?

[corndog71]

My dual subs weigh about 88 pounds each.  MDF. 

I can’t imagine what concrete would weigh. 

[jn316]

At the same time--Danny--is it too much to ask for you to update your new site with the basics of the products you're selling?  A year ago the excuse was that the new site was coming.  Now it's here and a DIY-inclined person still can't find much.  Scraping Audiocircle is neither efficient nor sufficient.

Yes, in the ideal world that would be the case, but Danny is working 14-16 hour days to take care of his customers already. You might want to cut him some slack here.
Concerning the things you were looking for, I too had to search for them and didn't have that hard of a time searching GR's forum and finding them. Yes, it took a little time, and is not efficient, but the reality of the past year is that a lot of things have not been efficient.
With that said, many of us are here to help and you have been the recipient of that. You have some interesting ideas and we are trying our best to answer your questions.
Also, Danny almost always picks up the phone when I call him and patiently answers my questions. That is a great option too that is very efficient from a customer perspective.

[dayneger]

How much they'd weigh is a fair question!  According to the CAD system, the image above would have 112 pounds of concrete, or 1.5x 80 lb bags at $5-20 per bag depending upon the quality chosen.  Add in, what, 20 lbs per driver and another 10 for stabilizing feet and you land at 160 lbs (73 kg) each as sub towers.  Then put the mid/tweeter section on top:  170-180 lbs per side as a complete speaker.

Fortunately, the expected manufacturing plant (aka my garage ) is only one step up from the living room level.

My perspective is that even the MDF dual subs plus mid/tweeter section (about 100 lbs total as a complete speaker) have already exceeded the inflection point where carrying them around alone would be difficult and/or dangerous to my health--I still could, but it'd be a risk every time. If I proceed with the duals I'd be expecting to integrate wheels into the stabilizing elements, or slider pads under the feet at the minimum.  Semi-freed from the tyranny of gravity, lots of non-resonant dead mass usually becomes our acoustic friend, right?  Please do correct me if I'm on the wrong track here, but these speakers seem to fall into the category where we want to hear just the drivers and not have what they're mounted to singing along.

jn316, thank you, I do understand your point and don't doubt that Danny's extremely busy.  As someone who wishes GR Research well (and have since 2003 when I joined AC), I also feel it's fair to suggest that populating and controlling the site is something he could/should address to build his business faster while lowering the total admin load on himself.  For example, hire an audio-interested computer science student for 10-20 hours a week to do exactly that; or see if back office work could be streamlined; or whatever.

Thanks for the helpful comments thus far!  Any idea whether the tubed/oval-style implementation would perform equivalently (enough) to the regular H-frame?

[corndog71]

Before buying the h-frame flat packs I looked at similar designs.  My first GR sub is kit 2 sealed sub.  I wanted to do something different so I built my sub as a tube.  It was a fun and challenging build and is still in use today.  But the more I thought about doing some similar as an open baffle the more I realized it was very impractical.  I wouldn’t be able to integrate a speaker on top or at least not easily.  I think it would look amazing if one were to build triple subs this way.

[mlundy57]

How much they'd weigh is a fair question!  According to the CAD system, the image above would have 112 pounds of concrete, or 1.5x 80 lb bags at $5-20 per bag depending upon the quality chosen.  Add in, what, 20 lbs per driver and another 10 for stabilizing feet and you land at 160 lbs (73 kg) each as sub towers.  Then put the mid/tweeter section on top:  170-180 lbs per side as a complete speaker.

Fortunately, the expected manufacturing plant (aka my garage ) is only one step up from the living room level.

My perspective is that even the MDF dual subs plus mid/tweeter section (about 100 lbs total as a complete speaker) have already exceeded the inflection point where carrying them around alone would be difficult and/or dangerous to my health--I still could, but it'd be a risk every time. If I proceed with the duals I'd be expecting to integrate wheels into the stabilizing elements, or slider pads under the feet at the minimum.  Semi-freed from the tyranny of gravity, lots of non-resonant dead mass usually becomes our acoustic friend, right?  Please do correct me if I'm on the wrong track here, but these speakers seem to fall into the category where we want to hear just the drivers and not have what they're mounted to singing along.

jn316, thank you, I do understand your point and don't doubt that Danny's extremely busy.  As someone who wishes GR Research well (and have since 2003 when I joined AC), I also feel it's fair to suggest that populating and controlling the site is something he could/should address to build his business faster while lowering the total admin load on himself.  For example, hire an audio-interested computer science student for 10-20 hours a week to do exactly that; or see if back office work could be streamlined; or whatever.

Thanks for the helpful comments thus far!  Any idea whether the tubed/oval-style implementation would perform equivalently (enough) to the regular H-frame?

That's an interesting idea. Very modern looking. You'll probably have to build it to see how it sounds. Just be sure the cavities are deep enough for the proper delay between the front and back waves wrapping around the cabinet and creating cancellation effects that would diminish the low end output.

I use a hand truck to move my subs any distance. For setting up I put magic sliders under the cabinets to make them easy to move around then remove them once I have the final placement.

[corndog71]

AC member, PDR, made a unique version that turned out well.

[dayneger]

Mike, for reference/scale, the image I uploaded before has 12" drivers more or less centered--actually, they probably need to be moved forward a touch if the middle of the cone should be centered--and they're 14" front to back like regular H-frames.

corndog71, thanks for sharing PDR's work.  It's always impressive to see the care, attention and skill others invest in their creations!  If the rounded top worked there, it's a good sign.

And since you asked I went ahead and made a few additional models for you... but why show up for the game with only 3 when you could have 4?   The big guy has about 240 lbs of concrete as shown. 
 Crazily enough, that's only a $20 bill's worth of Sakrete 5000.





I have lots of ideas for variants of this--without the dividers in the middle, side lofting, front and back shells that are possibly smaller in diameter, etc.  I'll model an Otica-MTM with the dual OB if someone could post a drawing.

[Early B.]

Consider some creative ways to integrate the amps into your designs.

[Hobbsmeerkat]

Consider some creative ways to integrate the amps into your designs.

This!

Lately weve seen some doubles being made the height of triples, but the bottom portion hides the plate amp, and can easily be segmented & filled with sand to balance out the weight being shifted upwards, esp when the drivers are forwarded facing.

[dayneger]

Yes, those amps are some pretty serious bricks, aren't they?  And all of the inputs and controls are plate amp style. 

Maybe what I should do is make further subwoofer exploration a separate post.

[dayneger]

So, now that I've theoretically wiped out my budget just getting to 100-200 Hz , I'd like to keep exploring the OB frequency ranges to understand them better.

What happens across the mids?

From my initial post:

...I'm frankly finding it hard to fully understand exactly which factors lead to which results across the frequency spectrum; which are unique to dipole implementations; and which combination could work best for my context.
...
A few examples across the frequency range, without intending to imply that any approaches are inherently superior:

1.  Only >1200 Hz (at the minimum due to Neo3):  NX Studio.  Not positioned as an OB speaker per se, but claimed to have a fair amount of "OB goodness".  Closed bass/mid-bass, requires some kind of sub.

2.  Only mids:  Statement IIs, Travelers, etc. from Jim Holtz/Curt Campbell collaboration.  Also not positioned as OB, mid opens to back via a 6" tube, claimed to add air and soundstage depth.  Closed tweeter, ported bass depending on model.

3.  Only bass through lower mids, 32-575 Hz:  Spatial M3/5 Sapphires.  Fully OB-mounted 15" driver on flat baffle, closed sapphire tweeter covers 575 and up.  Considered OB.

4. Only bass 20-180/250 Hz is OB, rest is "non-boxy" closed speaker implementations (Gallo, modified KEF), as seen in Vic's entertainingly informative blog:  https://trans-fi.com/diy-speaker-blog. Holy dual 18's per side.   

What are the pros/cons of fully OB through the vocal range?

#4 above has achieved good results both fully OB and completely closed, #3 is OB only to 575 Hz and closed above, #2 has the mids "quasi transmission line/open back/di-pole design or whatever terminology you want to hang on them" (quoted from speakerdesignworks), and the NX-Studios are open starting from wherever Danny crossed the Neo3 on up.

[Peter J]

Dayneger,  a couple of things to consider.

 The amps are "plate style"  because they were designed as plate amps. For many sub configurations that works and is the easiest, most economical path. I'll bet they could be configured in some other form but I suspect the potential market determines that. It's a small part of a small market. From the perspective of product marketing only, I'd venture adding a boxed variant wouldn't increase sales much if at all, but would increase cost of production and also double inventory requirements.

Concerning concrete as you casting medium. I'm no acoustic engineer, but experience tells me concrete, especially with the size of aggregate in typical sack mix, rings. Tap a concrete stepping stone not in contact with the earth with a hammer..."tink"!. Tap the same mass made from MDF or plywood and..."thud". I'm guessing  at the effect of such a structure on sound reproduction, but there would be reasons to think resonance would be a factor to contend with.

If one is making a mold anyway, I suspect something like casting resin, perhaps epoxy or acrylic, might be a better bet. Perhaps  adding something to a custom cement mix would help to mitigate. Perlite, rubber chips, smaller aggregate, etc.. Hypertufa comes to mind, but I question whether adding organic matter would be prudent.

Anyway, some food for thought.