Build a ..

[humlan57]

I´m on my way to build a couple of "Spawn of Frugel-Horn--Sachiko style"
I have noticed birch veneer shuld be the best material to build with...
But I thinking of use 28mm rod glued massive oak or beech, on all visuable sides, and 18mm form plywood in all other places.., this way it must be much more stable..
What do you people here in the forum think of my/our material choice?

I don´t know if form plywood is right word in english, but it´s the kind of plywood which is used to pour concrete in...

humlan/Sweden

[Jim Shearer]

I don't know about the plywood used for concrete forms in Sweden, but the stuff I see here in the USA is nothing I would ever consider for building speakers. Full of voids, warped, yuck!

Cheers, Jim

[humlan57]

Originally Posted by Jim Shearer

I don't know about the plywood used for concrete forms in Sweden, but the stuff I see here in the USA is nothing I would ever consider for building speakers. Full of voids, warped, yuck!

Cheers, Jim

Then I can assure you, it´s not the same thing we use over here
Plywood we call "form plywood" is same construction as common veneer, but glued with more stable glue, and coated so that anything can attaches to it, not even paint.. It´s so stable, it can stand in water 20 years without changes a bit.., and it´s rock-hard and a lot more stable then common veneer.

I think you mean construction plywood, or maybe OSB.., which is junk plywood, mostly used for non visable constructions. And pour concrete, must meen you can´t use them, more then one time.., "form plywood" you can use, over and over again

Link: Formplywood - Skivmaterial - Moelven

You can chose english.., as you can see, we have a lot of plywood/veneer to choise between...

humlan.

[humlan57]

Same site/URL translated with Google: Google Translate

humlan.

[planet10]

What you are looking for in a plywood is stiffness (primary) & lightness. You want as many plys as possible, and no voids. A less stiff glue between plys should give better damping as you get a greater impedance mismatch across each boundary.

dave

[humlan57]

Originally Posted by planet10

What you are looking for in a plywood is stiffness (primary) & lightness. You want as many plys as possible, and no voids. A less stiff glue between plys should give better damping as you get a greater impedance mismatch across each boundary.

dave

Exactly, and the shape plywood (form plywood) is very stiff... But why lightness.., not understand what you meen by that... is it minimum kg/m²? If, then shape plywood (spruce) is lighter then birch plywood.
Can you explain in other words, what I achieves with light plywood. Is it that the resonans point for the cabinet will be placed higher in the frequens curb?
What do you tink about Lauan Meranti plywood then?

humlan.

[chrisb]

Originally Posted by humlan57

Exactly, and the shape plywood (form plywood) is very stiff... But why lightness.., not understand what you meen by that... is it minimum kg/m²? If, then shape plywood (spruce) is lighter then birch plywood.
Can you explain in other words, what I achieves with light plywood. Is it that the resonans point for the cabinet will be placed higher in the frequens curb?
What do you tink about Lauan Meranti plywood then?

humlan.

I think the point Dave may have been trying make was that the plywood should be lighter than say, MDF or particle board.


Of course not all plywood is created equal, even when using the same veneer species for the cross bands - as I've certainly seen with the Chinese vs Baltic Birch we've had in our shop.

The Luan or Meranti plywood available here is generally much lower ply count than the BB ( 7 vs 13 for 3/4" ), and while it can vary surprisingly in density, is riddled with internal voids, frequently delaminates and is not as stiff. Suitable for cabinet carcasses and shipping crates, but I'd avoid it for speaker enclosures.

[kmaier]

Its been box building week.... bought two sheets of baltic birch, one in 12mm and one in 18mm. Very nice stuff in general, but there are some plugs to work around and I have found some small voids while cutting as well. The main issue for me is that the outer ply veneer is quite thin which increases the difficulty is doing mitered corners. All in all, certainly much better plywood to build enclosures with.

Regards, KM

[humlan57]

Ok.., so stiffness has first priority, and low weight 2:nd.., or as I think, doesn´t matter that much...
Shape plywood is much stiffer than common birch plywood, so I think I will use that.., or maybe body plywood..

This is hard.., "your" plywood, is not exactly the same as we have in Sweden, so compairing is confusing.. :-)

humlan.