SEOS / Dayton 2 way

[gedlee]

CLD (constrained layer damping) between 2 MDF sheets. The middle layer of non hardening glue is put under strain/stretch as the cabinet vibrates out and inwards and is "stopped" by the stiffer MDF sheets.

It is important to understand that CLD works well because the center layer is put into shear by the bending vibrations of the panels and damping is much more effective in shear. Under simple compression (strain) the center layer will add very little damping.

 

[JShadzi]

I would try an avoid a gap between the two cabinets as this would be a major diffraction point, which is why I suggested a rubber sheet.

Recessed rubber feet in the bottom of the cabinet would avoid that issue and would be easy to do with a Jasper circle jig.

 

[nonobaddog]

I'm not sure where you'd source the foam in Canada. The best source I've found is here in the US and is actually local to me. He imports it from Germany.

Hi, I am also in Rochester, MN. Where is the source for the reticulated foam?

 

[Adhoc1]

It is important to understand that CLD works well because the center layer is put into shear by the bending vibrations of the panels and damping is much more effective in shear. Under simple compression (strain) the center layer will add very little damping.

Thanks, “shear” is a better word than “strain”, I suppose (language barrier there, as English is not my native language).

JShadzi, how small diameter can you cut with the Jasper jig? Recessed solid rubber pucks need to be very small area wise for any probable speaker weight. If they should function well as vibration dampers down to say, 20 Hz, about 7 mm deflection is needed for 90 % / 20 dB isolation. A rubber sheeting the same size as the foot print of the speaker will not offer anything isolation wise, might avoid some rattling between two hard uneven surfaces, that’s about it. A more specialized elastomer like Sylomer from Getzner, a rather soft closed cell polyuretan, often ends up at around diameter 35 mm or so for “common speaker weights” and at the same time give some good isolation.

For solid rubber and wanted isolation frequency wise, check out the diagrams here: http://www.tme.eu/se/Document/fb716885927a5b9b8a7f6be51b7da173/DVA-EN.pdf (These dampers are 55 Shore, so they are softer than a usual rubber sheet of about 70 Shore, but harder than a common rubber band of about 40 Shore.)

 

[JShadzi]

@adhoc1 jasper goes done to 1", Forsner but would go to any size below that...

Regardless even with a 1" recess you could still use a 7mm foot, that's elementary.


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[Adhoc1]

I must have written something unclear. To reach good isolation (decoupling) down to 20 Hz, say -90% / -20dB, with a semihard rubber of 55 Shore, 7 mm of deflection is needed. (Compression if one so like, even if compression is not the right word as an elastomer cannot be compressed, only bulge out with a weight on top of it).

If you check the type DVA.4 in the link http://www.tme.eu/se/Document/fb716885927a5b9b8a7f6be51b7da173/DVA-EN.pdf , article no 412751, it has a diameter of 20 mm x height 30 mm (how thick is the speaker bottom for that kind of recess?). It needs 38 N per 1 mm deflection. For 7 mm deflection and 4 feet used on the speaker, one in each corner, 7 x 38 x 4 = 1064 N would be needed on top of those vibration dampers. Is it probable that the speaker weighs 1064 / 9,8 = 108 kg / 239 lbs? If substantially less, the worse the isolation (decoupling) will be and the more vibrations of frequencies also higher than 20 Hz from the cabinet will be transmitted to the room structure.

(Some of those vibration dampers in your Mcmaster link are good stuff, while I would see those Peavy rubber feet as a waste of money other than protect the floor from scratches. So, check your speaker weight, think about what your goal is, go to manufacturers technical data / diagrams and make your choice. If there is no hard data published for the stuff, my recommendation is easy: Don't by it.)

 

[Mindsource]

I will likely fire up the Sorbothane calculator and see if I can source the right size/duro from Amazon. Otherwise I will just call Sorbothane, they have great customer service. Right now I am grappling with how to cover the front baffle in speaker cloth, because the drivers are so ugly/don't pair up well. But I can't figure out a way because I need to be able to access the screws for removal/repair.

I'll probably have to just cover the woofer/waveguide by stretching fabric over the backside of the baffle for the woofer, and over the waveguide/behind the baffle for the SEOS. Oh well it's my first build.

Then there is the issue of the screws, if I am rounding over the edges, but the only place to screw the front baffle is the edge of the perpendicular side panel behind it, then I will be screwing into the round over. Not ideal. Only way around it that I can think of is double thick panels, I'm not crazy about that idea.

I wanted to double check, and Dr. Geddes I was hoping for your input here, Should I build for a lower box Q because heat inside the box raises it?

Thanks everyone for the input. Thanks ad-hoc I appreciate what you had to say about CLD materials. I guess I will look into a different visco-elastic layer. Hopefully I can choose and get one sooner than later because I'm hoping to get the ball rolling on cutting real soon.

Shawn

 

[AllenB]

then I will be screwing into the round over.

Can't you drill a pilot hole from the back, then use a small spade bit from the front to counterbore a surface for the bolt head (with a flat washer), then back fill with a removable putty?

 

[Mindsource]

That's probably exactly what I'll do. I'm not sure if I'll use a putty though. I'm hoping to veneer the baffle and I think the putty will look worse than a screw head.

Still wish I could think of a way to just wrap the whole front baffle in fabric, and still be able to remove it.

 

[Adhoc1]

You could counter sink strong neodymium magnet into the baffle and then add veener over the baffle. If you have a thin and light weight frame for the fabric with some iron washers glued to it, you would have a removable cloth frame without any screews and also access to the drivers.

 

[Mindsource]

Only thing that comes to mind with that is diffraction. I realize we're probably splitting hairs here, but hell I've probably lost enough hair learning how to build this thing, what's a few more?

 

[Mindsource]

I also don't know how to attach fabric to a thin frame.

 

[gedlee]

I wanted to double check, and Dr. Geddes I was hoping for your input here, Should I build for a lower box Q because heat inside the box raises it?

Shawn

I don't think that issue would be significant. I'd just ignore it.

I would not use a framed baffle grill as the diffraction would be immense. If you mounted the drivers from the back then you could just glue down the baffle grill.

 

[Mindsource]

Thanks, Then I think I know how I'm going to do this. I'll report back just before I'm about to bring it to the lab.

 

[JShadzi]

I also don't know how to attach fabric to a thin frame.

3M 77 spray adhesive

 

[gedlee]

Not 77, its too weak, use Spray 90, it holds better.

 

[JShadzi]

Not 77, its too weak, use Spray 90, it holds better.

Haha, wow @gedlee, I certainly can't win in this thread for loosing! 😛

I've been using 77 and 90 for 30 years, to attach speaker grill cloth, I can definitively say your statement is patently wrong.

@mindsource if you need anything from me you know how to contact me, I'll be unsubbing from this thead.

Cheers!

 

[gedlee]

So you are saying that 3M's wrong. They claim exactly what I was stating. And, having used both myself for decades the 90 is clearly the stronger bond.

 

[Mindsource]

Adhoc, where did you buy Terostat 930 from? And what thickness of it is ideal for CLD? Say I can't find it in Canada, what's the next best option?

Thanks
Shawn

 

[gedlee]

The best CLD material glue that I have found is a two part shore A polyurethane from Innovative Polymers. Slower setting time is beneficial. Mix this with 3M micro-balloons for a very highly damped never hardening glue that is ideal for CLD. Just beware that it is pretty pricey.