Yet another plywood dilemma (THT)

[vann]

After a long search for a source of appropriate plywood in my country I'm left with essentially two options.

- Wait even more for something to came up.
- Use 3/4" (18mm) plywood instead of 1/2" (12mm) to build a THT.


I really don't want to wait any more, and the winter is coming...
I'd rather not not work on 15 - 0 Fahrenheit (or even lower sometimes), as my work room doesn't have heating. And I guess this would affect the curing of the glue also. If I don't do it in next month or two at most, I'd have to wait for spring's higher temps.

- So can I use 3/4" plywood if I recalculate the THT box dimensions to allow for the same horn path dimensions while using 50% wider material?

- Another question, since I have some lefover chipboard, can I use it for braces (or at least for some of them)? Otherwise I will have to buy another 8'x4' plywood board and only use up to 1/4 of it (plywood is very expensive here). I don't plan another project anytime soon.




edit: grammar

[Jon Barnhardt]

I've heard of others using 3/4" after recalculating everything. The thing that would scare me would be the added weight to an already heavy sub...

[vann]

Weight will not be of any problem. Workshop is very close to the common room where THT will be located. Even if it ends up really heavy, there are always friends eager to help in return of few beers...

But I'd really like to hear if there are any obvious (or not so much so) pitfalls to using 3/4" ply.

[LelandCrooks]

Just having to refigure the layout because of the extra width. The path widths are critical.

[vann]

Thanks.

How about using particleboard (chipboard) for some of the braces? I've got quite some leftovers of it, veneered on both sides. Or just bite the bullet and buy third 8'x4' plywood board (and only use up to 1/4 of it)?

[DJPhatman]

DO NOT USE CHIPBOARD!

7-12mm ply is fine for braces. If you use 9mm or less width, you should use dados on all the panels where the brace will attach.

You need to call around to custom cabinet makers, and ask them who they get their premium plywood from, before you use 3/4" (18mm). Maybe they will even let you pillage their waste bin for suitable brace scraps.

[vann]

I kinda guessed that answer (about chipboard).

So one more full 8'x4' ply board it is than...
If I may ask (just curious), I guess it's because particleboard's (chipboard) inferiority in vertical strength? And/or the overall thickness of it?


I've been at several local cabinet makers. Any 12mm (1/2") ply I sow had very slender veneer kind of ply as sides. I think I've red somewhere that that kind of ply is no good for loudspeaker usage.
Anyway, If I have to use 18mm (3/4") ply... Should I also use 18mm (3/4") ply for braces too?
Or it's better to use even that veneered 12mm or slimmer ply for braces?

[jcmbowman]

it's better to use even that veneered 12mm or slimmer ply for braces?

that's your answer.

[jjohnson]

've been at several local cabinet makers. Any 12mm (1/2") ply I sow had very slender veneer kind of ply as sides. I think I've red somewhere that that kind of ply is no good for loudspeaker usage.
Anyway, If I have to use 18mm (3/4") ply... Should I also use 18mm (3/4") ply for braces too?
Or it's better to use even that veneered 12mm or slimmer ply for braces?

I would think that since the braces are glued on edge the veneered faces wouldn't matter. I know that you don't want to fasten to the veneered side but the edge should be fine.

[el_ingeniero]

If you were to dado/rabbet every joint, would this allow using the thin veneer ply?

[jcmbowman]

since the braces are glued on edge the veneered faces wouldn't matter. I know that you don't want to fasten to the veneered side but the edge should be fine.

+1

[Rick Lee]

I don't want to start an argument but chipboard (or OSB as we call it here in the states) is fine for bracing. It used to be inferior to plywood but the stuff you get now is plenty strong and durable. Supposedly the puncture strength isn't the same as plywood but the vertical strength is the same. Laminated I-beams anyone?

If you do use chipboard for braces don't use anything thicker than 1/2" or else it's way overkill.

Chipboard isn't fun to work with though so I would use the thin veneered stuff (on edge only!). Much nicer looking.

[DJPhatman]

If you read the OPs post

Thanks.

How about using particleboard (chipboard) for some of the braces? I've got quite some leftovers of it, veneered on both sides. Or just bite the bullet and buy third 8'x4' plywood board (and only use up to 1/4 of it)?

That is chipboard, also called particle board, not OSB, or Oriented Strand Board. I don't recommend using either for anything, because the dust from both, when cutting, is quite toxic. Particle board has only slightly more strength than laminated cardboard. It is only used because it is made from the sawdust of any wood species, thus is very inexpensive to make. Grind down all the sawdust, mix in some glue, pour in in a form, add high pressure, and viola, make cheap furniture, shelves, most anything normally made of wood, slap a decal (paper printed to look like wood grain) and your average consumer doesn't know the difference.

[Rune Bivrin]

If you read the OPs post

Thanks.

How about using particleboard (chipboard) for some of the braces? I've got quite some leftovers of it, veneered on both sides. Or just bite the bullet and buy third 8'x4' plywood board (and only use up to 1/4 of it)?

That is chipboard, also called particle board, not OSB, or Oriented Strand Board. I don't recommend using either for anything, because the dust from both, when cutting, is quite toxic. Particle board has only slightly more strength than laminated cardboard. It is only used because it is made from the sawdust of any wood species, thus is very inexpensive to make. Grind down all the sawdust, mix in some glue, pour in in a form, add high pressure, and viola, make cheap furniture, shelves, most anything normally made of wood, slap a decal (paper printed to look like wood grain) and your average consumer doesn't know the difference.

Have you actually considered how much a shelf full of plates, or a complete encyclopedia weighs?

Particle board is absolutely strong enough for bracing. Where particle board differs from plywood in use is primarily in how it deals with impact and how well screws hold. The weight difference is notable of course, but for a few braces in a largely stationary speaker I wouldn't worry about it.

Yes, there are some issues with dust, but I wouldn't call it toxic. It's same issues as with any fine dust. If you worry about that in the quantities resulting from the occasional speaker build you should take up fly fishing instead .

[DJPhatman]

I'm not getting into a pissing match with you, Rune. I am only giving advice on what I have experience with. It is up to the individual reading all the advice given, and making their own decision.