Speaker Constructin Materials-Opinion Wanted

[catsomaximus]

Re: Scan-Speak Ultimate Revelation Plans
This has been a great, if not the Best forum, to learn various ideas about speaker construction. Most of the methods I want to use came from the postings and threads in this forum.

I'm planning to build the "Scan-Speak Ultimate Revelation" plan offered by Solen Inc. Canada http://www.solen.ca/ssur.htm They don't specify the type of material to use for construction and dampening of the speaker box. I'm debating the use of the following materials and techniques:

"Cconstrained layer construction" of all box panels: Screwed together, 1" Mediate (recycled, non-formaldehyde) MDF, constrained layer of roofing felt, 3/8" Baltic birch plywood, with strips of solid Birds-eye maple glued to edges to facilitate veneer application and edge rounding.

Glue and screw all joints, internally brace box with Baltic Birch

Dampen and make air-tight inside of each box by applying several coats of liquid Rubber and Epoxy Gluing 1/8" Sound dampening (lead Bitumen, Sound Mat) material found in old luxury cars to the interior of the box.

Filling the cabinet with fibreglass to creates an effective sound sponge.
Flush mounting the drivers with a neoprene gasket made from old tire tube.
The QUESTION: Do these ideas and methods have any positive or negative effect on the performance of the speaker and are they worth the effort?
To accommodate the thicker layered panels (1 1/2"), the outside dimensions of the front baffle and the mounting hole would change from the plan. If I bevelled or rounded the edges would this create any diffraction problems?
I would appreciate any comments and opinions that any one has to offer.
John B. Canada

[sreten]

Hi,

to accomodate the extra thickness of the walls ideally you would make the box deeper.

I'd take a look at the way Tony Gee makes boxes :

http://www.humblehomemadehifi.com/

If you follow his methods I think the bevelled 3/8" ply would look good.

I'll just note epoxy is not the right glue for rubber to damping pad.
Use a good contact adhesive.

Personally I'd just follow the plans as is and add 3/8" ply a la TG.

/sreten.

[catsomaximus]

Thanks for the Reply,
I have looked at Tony Gee's methods, they’re great and I'm just exploring variations on the multi layer theme or "Constrained layer construction" as suggested by Arthur C Ludwig Sr in Panel Vibration Damping Experiments http://www.silcom.com/~aludwig/Louds...Time_alignment

Using different materials in multi-layers seems the way to go. But, what materials, in what order and how connected/fastened?
Arthur C Ludwig Sr suggest some interesting materials, particularly simple house insulation and roof tar paper, which actually are inexpensive technology that can compare to expensive High-tech products and will achieve better or the same result.

What other "Found" or "Recycled" technology that is in use in other applications and technologies (scrap yards, used equipment, pool liners) is available? Quartz Sand, Bitumen, and Rubber are mentioned as effective dampening material. How would a roof shingle (sand bonded to a bituman impregnated paper) coated with some Liquid Rubber, leftover from a roof patching repair, work as a dampening layer?

The various discussions on MDF vs. Plywood vs. Solid wood in Post 34 -"Want to move from MDF to real wood", suggest that a sandwich of birch plywood and MDF might be a viable solution using the strengths of the two materials. Should the plywood or the MDF be on the inside or outside, does it make a difference?

About your two other point: The extra thickness of the box will go the the outside of the box, internal dimensions won't change. You’re right about the glue, I haven' researched the glues that I want use, next step.

[Colin]

I'm not sure what MDF would add to the mix if you were already using birch ply, apart from weight. Birch ply is already layered, so a thicker ply might suffice.

I recently compared a light but stiff cabinet design against a heavyweight (plaster lined) version and thought the lighter cabinet had much less boom. (They weren't like for like, although they shared bass drivers, so maybe boom was a design objective.)

Re damping materials, I read tests somewhere that fibre glass was not particularly good, being reactive and horrible to work with (also beware fibres entering speaker parts). Long fibre wool is usually reckoned to be the best for LF.

Good luck and post the pics when you've done!

[Colin]

You may also find the OneZ speaker project interesting. It's a bookshelf design but discusses vibration control and the benefits of sand-filled panels.

[catsomaximus]

Thanks for the confusion, the OneZ site has a lot to consider.
It's an excellent example of the the light weight design vs the the dense dead cabinet idea. I'm tempted to try the ideas out, but in the next project. For now I will continue to explore the "dense dead cabinet design" idea. After all, the fun is in the journey, not the getting there.
Any comments on the Solen design, drivers, crossover etc. I do appreciate you taking the time to share your ideas and knowledge.
John B.

[Colin]

I can't comment on the Solen design - others here are better qualified for that. I avoid crosssovers wherever possible (I'm slumming it from the fullrange section).

If you go the heavy cabinet route, it's worth incorporating a couple of subtle handholds somewhere around the cabinet. You may want to move them sometime!

[Colin]

PS One reason for mentioning the OneZ site was the use of sand-filled panels. This is supposed to give a very dense cabinet wall and may be worth considering if you are going this route. I believe it's second only to concrete plus you have the effect of the sand grains dissipating energy, as mentioned in the OneZ design.

Another technique I've come across is laminating plasterboard to the inside of the panels, the combined thickness being denser than the same thickness of wood alone.

Good luck.

[critofur]

Two layers with sand in between is much superior to concrete (IMHO).

You don't want just heavy/dense walls, you also want well damped walls. The heavier the wall is, the harder it is to damp. So, as always, there are compromises.

I did an experiment where I build two of the same speakers with the same drivers and crossovers, except, in one cabinet I used 3/4" birch ply instead of 1/2", both with the same internal proprietary damping materials. I made the thicker walled speaker deeper, but the same width, to give equal volume. I expected the thicker walled speaker to sound better, surprisingly (at least, surprising to me at the time) the thinner walled speaker sounded noticeably better.

This was a two way speaker without a subwoofer. For a lower frequency enclosure, different rules apply...

[gainphile]

Dense cabinet sounds good. But what about sound reflection coming out of the paper-thin cone