[dayneger]

After needing to step away from audio dreams for a bit, I'm finally planning for how I might make OB work for my context!

Considerations (product requirements in geek speak):

- Fit a single speaker footprint per side
- Full OB top to bottom
- Serious "bottom" capability
- The shorter the better, within reason
- Look fully integrated and simple/streamlined as a design
- Be reasonably mobile as a unit

In the space I have available I'm able to have speakers far enough out for OB to work great when I'm dedicated listening, but need to push back to about 3 feet/1m to the baffle when not (aka, very helpful when amps are on board).  Our patio looks through our living room toward the view in the distance, so height is annoyingly unwelcome (well under 48" preferred).  The design aesthetics I'm not going to (completely) attribute to WAF--we both appreciate designs that we find clean and simple in our environment.  I like to hear both the deepest musical instruments/sounds and the venue itself, so have accepted stereo dual servo subs as a minimum starting point.  The listening room is 17 x 20' with 8' ceilings.

Naturally, all of the above is a reflection of our personal goals and neither implied judgement that what matters to us is better for anyone else, nor implied criticism of other approaches!

[dayneger]

A couple of years ago I appreciated Hobbs' fun with speaker design studies https://www.audiocircle.com/index.php?topic=171691.0 and explored a whole bunch of my own ideas, which I could share later if of interest.

For me a key in all of this is how to disguise and integrate the servo subs.

I'd stumbled across Pass's slot loaded open baffle bass design article (SLOB).  Trying out some ideas based off of that approach, and combining it with the vibration-reducing elegance of dual-opposed drivers seen elsewhere, I then learned I'd essentially rederived Linkwitz's W-shaped work and the ripole subvariant.  So much for unique contribution there. 

[dayneger]

Here's one of my current studies.  Basically, it's an Otica MTM combined with servo subs in a dual-opposed ripole arrangement.  The first images show the MTM plus dual H-frame for scale.

The (huge) amp is just barely integrated, at least as far as I can understand the dimensions of that thing.  The overall height is compressed down as far as I dared, to about 43" as shown (vs 54" for the MTM plus H-frame).  So call it the 43-45" height range.  Assuming stiff construction methods (likely including a bit of fiberglass/carbon fiber reinforcement), the width is around 14.75" at the max and front to back it's currently about 16".  The "wing" angle of 10 degrees and 16" (correct?) are represented as well.

The ripole compression ratio is about 3x, meaning the open area of the port zone is 1/3 of the combined Sd piston area of the 2 drivers... which was claimed to be about ok for high excursion drivers.  The opening could be widened if needed, at the expense of visual integration. 

I don't know how much volume the crossover requires, but I was hoping to stuff it in the cavity in front of the amp.  The drivers would be slid in from behind and the inaccessible screws attached via small through-holes that would then be plugged for airtightness.

This could be constructed mostly or completely out of flatpack elements if the outer surfaces were straightened out.













Feedback is welcome!

[dayneger]

Forgot the top view!

[OrangeAgent]

I will say personally that the visual impact of that is outstanding. While the acoustic aspects of the OB sub stack concept is intriguing, I cant say it gets me excited from a incorporating it into my room point of view.

What is the impact on output from the port design? It reminds me of a big 4th order sub enclosure, where its less of a port and more of a big cavity the subs are playing inside. Would that produce a more peaky response? I would think that the output from the rear would no longer mirror exactly the output from the ported side.

[Tyson]

With OB bass, cancellation happens to the sides of the woofers so you wouldn’t want to stack them facing each other.

[Beerbellydad]

With OB bass, cancellation happens to the sides of the woofers so you wouldn’t want to stack them facing each other.

I think this configuration mimics a ripole sub design - similar to open-baffle dipoles but with a different dispersion pattern. It might be awesome (!)

[Jaytor]

Looks pretty cool. I would block the chamber in front of the sub amp though. That's likely to cause some bad cavity resonances.

[dayneger]

I will say personally that the visual impact of that is outstanding.

Thanks!  Appreciated.  If the concepts work out, I might be able to integrate full OB into our space (crossing fingers here).

I think this configuration mimics a ripole sub design - similar to open-baffle dipoles but with a different dispersion pattern. It might be awesome (!)

You're exactly right!  As briefly noted, I'd first come across Pass's S.L.O.B. article.  https://www.firstwatt.com/pdf/art_slob.pdf  This led me to explore some design concepts based on the H-frames, but with the fronts tapered in to match the upper baffle.  Things were improving but the height was still an issue for my room. 

Recently I tried to tackle the height issue with the dual-opposed driver layout and did some more searching, thus stumbling across the references to Linkwitz and ripole designs.  Here's a nice post from the OB circle with more information, including @Early B. asking about a servo sub implementation! https://www.audiocircle.com/index.php?topic=184135.0 

Reply #13 describes how it's supposed to work, copied from this website I believe:  https://www.modalakustik.de/english-1/the-musikbass/

In theory, more energy out the front, less out the back, and a null on the sides.

I'm just hoping it would perform similarly enough to make things viable!

[dayneger]

Looks pretty cool. I would block the chamber in front of the sub amp though. That's likely to cause some bad cavity resonances.

Good point.  I was hoping to cram the crossover into that space and cover it up with some No Rez.

If someone could give me approximate sizes for the MTM crossover parts I could estimate whether it would fit in that cavity. 

[dayneger]

Perhaps not super helpful for my height goals, I got to wondering what the penalty would be for adding 2 of the woofers per side.

The shortest version I could come up with uses a similar dual-opposed ripole-like arrangement... hoping for the least amount of additional height.  As shown, this is 47-48" high, and that huge plate amp sticks 1.75" out the back.

Could this work?  Would the addition of 2 midbass drivers per side have a useful impact?  Worth adding complexity and 4-5" to the stack height?

[Tyson]

I'll just throw this out here, I think GR is working on a single cabinet design for the NX-Otica already.  Hobbs posted this a little while back:

[dayneger]

Thank you, Tyson!  I don't think I'd have found this otherwise.   

Reference for others, starting with post #13:  https://www.audiocircle.com/index.php?topic=184674.0

I'm sure a lot of people will find that Otica variant attractive!

So, new ingredients to work with here.  The 8" servo sub driver returns to life, or is otherwise reincarnated... very interesting. 

I don't have the driver specs, but grabbing something reasonably representative like a Dayton UM8 has an Sd of 33 sq in, vs 76 for the GR 12" driver, and a similar Xmax.  So basically 100 vs 150 square inches of piston area, and probably around 46-47" tall as shown.  Not bad.  Where does the amp live?

[Danny Richie]

We do currently have a lot of the 8" servo subs in stock for this model.

Hang in there. It is in the works.

[2bigears]

  this looks better all the time. 3 servo drivers per side ?  Great bass there. I'm in. I was thinking the studio but now these kill me. Who wants my go-fund me $$ ,  I'm all in. 

[nlitworld]

I'm still hoping there is an eventual 2x8 sealed box under the Studios like an upgraded Rythmik FM8. For my small room, that be the holy grail of sound quality and convenience using them as sub stands.

[wgraft5]

I'm still hoping there is an eventual 2x8 sealed box under the Studios like an upgraded Rythmik FM8. For my small room, that be the holy grail of sound quality and convenience using them as sub stands.

THIS

Because I'm saving for a pair of FM8's now because it seems to be my best option for now

[nlitworld]

THIS

Because I'm saving for a pair of FM8's now because it seems to be my best option for now

But we all know a GR cabinet will likely be a superior design, and hopefully a slight bit taller than the Rhythmik design. Pop some isolation feet between the two and BAM you got yourself a party.

[Early B.]

this looks better all the time. 3 servo drivers per side ?  Great bass there. I'm in. I was thinking the studio but now these kill me. Who wants my go-fund me $$ ,  I'm all in. 

When the 8" subs were introduced, plans were developed for a 3-servo stand-alone OB cabinet. My friend built his speaker stands from these plans and has a pair of MTM NX-Oticas on top of them. I'm sure the NX-Studios would sound just as good. You'd probably have to spend at least 20 grand to buy better-sounding "floorstanding" speakers. That's why it pays to go DIY.

[Hobbsmeerkat]

When the 8" subs were introduced, plans were developed for a 3-servo stand-alone OB cabinet. My friend built his speaker stands from these plans and has a pair of MTM NX-Oticas on top of them. I'm sure the NX-Studios would sound just as good. You'd probably have to spend at least 20 grand to buy better-sounding "floorstanding" speakers. That's why it pays to go DIY.

Mine sit on a pair of dual opposing 8" servo subs in a U-frame and its a killer combination once dialed in.

Currently they're paired with Danny's original LGK Wedgies.
Similarly great, with a really wide soundstage, but lacks the fuller mid-bass body of the Studios.