9ply Golden Virola ply from HD (1 Viewer)

[Vince Bray]

Found at HD today some very clean, A-A plywood called golden virola. It's 9 ply, very low voids, although some small ones, but looking at the 2'x4' cut up pieces, it is very low void for off-the-shelf plywood. Also with 9 plys, the voids are small where present. This seems very comparable to paraply, but the grain is much more attractive.
I found some info on MOE, but it doesn't specify what thickness, or whether it was plywood that was spec'd. Does anyone know how this compares to marine ply? What species is marine ply?
This would seem much easier to laminate, since smooth on both sides, and the info I found reports that it glues very well.
Thanks!

 

[Ben Cannon]

Why not laminate MDF instead? MDF is inherantly uniform all across, and has far better damping charisterics than any plywood. Not just in speakers, but in general acoustic construction; I find it to be very useful.

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Ben Cannon
Dream With Your Eyes Wide Open, Inc.
"Every man dies, not every man really lives" --Mel Gibson, "Braveheart"

 

[AjayM]

Andrew
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[Julian Data]

I highly agree with Dan too.
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[Hank Frankenberg]

"It probably applies just as well for regular speakers also..."
No, it doesn't, as Dan said, and others who know their cabinetry will tell us (ThomasW, where are you?). Plywood will resonate at higher frequencies than are encountered in subwoofers. MDF is better for mains cabinets IMHO.
This 9-ply virola sounds interesting. What's the price?
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"Do you expect me to talk?"
"No Mr. Bond, I expect you to die!"
[Edited last by Hank Frankenberg on August 08, 2001 at 07:38 AM]

 

[Jack Gilvey]

I think Hank hit it on the head. Very different applications.
I'm going to look for that stuff.

 

[Vince Bray]

$38 a sheet. Now I'm trying to find trim wood of this species and no luck so far....
Check it out.. it seems like decent wood!
Vince

 

[Pete Mazz]

Virola is actually a trade name for some species of cheaper mahoghany. Phillipine mahog is one that's fairly common, as are some of the newly found "rainforest" species. At 9 ply it sounds pretty good, as standard for this kind of board is 7, but the apple ply and baltic birch are 13 ply (for 3/4" panel). Marine ply gets its rigdity and strength from the massive amount of resins used to make it waterproof.
Pete
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[Pete Mazz]

Virola is actually a trade name for some species of cheaper mahoghany. Phillipine mahog is one that's fairly common, as are some of the newly found "rainforest" species. At 9 ply it sounds pretty good, as standard for this kind of board is 7, but the apple ply and baltic birch are 13 ply (for 3/4" panel). Marine ply gets its rigidity and strength from the massive amount of resins used to make it waterproof.
Pete
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[Vince Bray]

The mahogany thing makes sense, because I found a web site that talks about the wood, where it comes from and how it's harvested. It's called Batai in the Phillipines according to this doc and is a 'favored plantation species' there. The grain on the sheets is very attractive, with a large oval pinkish pattern. I think it would look good with clear poly and some grill cloth with some texture and a tan color, something like burlap or a heavy but open weave...
I'm not saying this is the equivilant of marine in strength (esp since i've never seen / worked with marine ply) but from what i've heard, it is a cheaper alternative with some favorable qualities. I am very happy with it as compared directly to mdf (which i have worked with a good deal)
I have a bandpass cylinder with mdf end/mid caps where the top is extensively braced to the inner partition, which, in turn is braced to the bottom, and (while very good) it still has some resonance issues above what I expected. The bottom line (as I have gleened from many comments on the subject on this board by those more knowledgeable than myself.. but it makes perfect sense...) is that bracing has to work alot harder to overcome a fundamental resonance of the material. The panel might vibrate three times more in amplitude at resonance than at other frequencies. Just as a woofer goes nuts at resonance, so must a panel.
So that's the plan.. maybe i can get it together enough to post some pics of construction. That will be awhile, though, as passive radiators aren't expected to ship for about two weeks...
Vince

 

[Pete Mazz]

If you're going to stain the piece, and are looking for a deep, rich burgundy tone, try MinWax Red Mahoghany stain. A couple of coats of stain will give a very nice tone and has been a long time favorite of many shops.
Pete
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[Vince Bray]

Thanks for the tip.
I'm not sure if I want a color, or just the natural wood. I'm going to look at the pieces I've got ( I had HD cut it into 2x4 pieces) and see what would work. Because of the large box - well relatively large at ~22" cube, I thought the light color would seem less imposing. The red, however, would match my mains better, which are mahogany stained deep red-brown.
Vince

 

[Ben Cannon]

Ah, I meant to add "begin silly question" tags to my post, but it didn't work (html filtering here?

Anyway, if it's for a sub, it all makes sense now.
Though I still think a combination of 3/4" MDF, 1/8" lead, and 3/4" MDF (repeat optional, and rather heavy) is very hard to beat. Or make any drum-like noises at all
It has been my expierence that for bracing to work well, it needs to be very, very massive. Think B&W's matrixing. When I brace, I often use single or double 3/4" MDF with ~4" holes cut in with a drill press
The end result is one very massive speaker however.
Best!
Ben.
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Ben Cannon
Dream With Your Eyes Wide Open, Inc.
"Every man dies, not every man really lives" --Mel Gibson, "Braveheart"

 

[Jack Gilvey]

Here's a relevant quote from Greg Monfort from a while ago:

For good mechanical efficiency, and therefore good electrical to acoustic conversion, a rigid cab is required. For a rigid cab to be acoustically inert WRT the driver's BW requires that its Fs must be either above/below it.
MDF has a low Fs Vs no-void ply's much higher Fs. The MDF also has a low MOE (modulus of elasticity, a measure of 'stiffness') Vs an equal thickness no-void ply, so is much less rigid. Since MDF requires mucho bracing just to match an unbraced ply cab of equal thickness, it can never be as efficient as a braced ply cab without additional mass to 'help' stiffen it.
Since stiffening increases the cab's Fs, it takes very little to raise a ply cab well beyond a sub's BW, ergo there's nothing to excite it. Acoustically, it's 'dead', even though it may ring like a bell if given the 'knuckle' test. You want an excellent sub cab, make it out of metal. So all you metal fabricators out there......
The MDF cab OTOH, winds up in a loop. Increase the stiffness to raise its Fs, and the added mass lowers it, so you add more stiffness, mass, etc...... Ultimately, you wind up with the equivalent of a concrete cab weight wise that's somewhat larger than the no-void ply to get the Fs below the sub's BW, if you want it acoustically 'dead'.
Between being lazy and having a bad back, 3/4" no-void ply braced with a few 2x2s is a no-brainer for me.