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Old 4th September 2011, 04:24 PM   #1
vann is offline vann  Macedonia
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Default Plywood dilemma

I'm (finally) about to start building a pair of G Chang cabinets to use with a pair of FE207e drivers. After reading through much of cabinet materials discussions and heeding Scott and Dave's advice, I've decided to go with plywood.
Problem is that in my country there's not much choice of quality plywood. I tried to source a baltic birch but it's just not possible (short of importing it form Scandinavia )

After visiting almost every lumber yard in 100km range, the choice is:
1. 15mm beech plywood, 11 sheets of wood, looks very nice, quality and straight, without any visible voids at edges, quite expensive (around 70USD per 8'x4' sheet, and I'm only stating the price because I want to cry when I see ppl in US say that they can easily find 18mm baltic birch for around 50USD per sheet)
2. 18mm plywood which salesman says is mahogany, 7 sheets of wood, considerably cheaper but it just doesn't have the quality look of that 15mm beech plywood.


The design requires 18mm material (3/4 inch) but Dave suggested that lesser size could be used with sufficient bracing. So my dilemma is which plywood to use, 15mm beech or 18mm of the cheaper plywood?

I think I'm going to choose the 15mm beech and allow for more bracing but I'd still like to hear other opinions before I go to that lumber yard tomorrow.
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Old 4th September 2011, 04:32 PM   #2
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Is it beech or Birch plywood? Birch ply is so much denser than normal ply that 15mm could be stronger than the normal 18mm.
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Old 4th September 2011, 04:42 PM   #3
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I think your choice will be OK. I would also have no problem using the 18mm mahogany material-which sounds like a marine-grade plywood- for a speaker project.
Here in Canada, most of the commonly-available plywood is very low quality, with plastic filler and voids (empty spaces) in the interior layers. That stuff is what we need to avoid for speaker projects.
BTW, in Canada the 'baltic Birch' plywood seems to usually be offered in 5 x 5 ft sheets, so your price (@ 4x8) may not be so different.
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Old 4th September 2011, 05:02 PM   #4
vann is offline vann  Macedonia
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It's beech, not birch...

And about that 18mm plywood, the salesman says it's mahogany, but I seriously doubt it since it's like 33% cheaper than the beech (which is also just 15mm wide). I always thought that mahogany is quite expensive wood? It looks solid, but not as quality looking as the beech plywood, just 7 layers of wood etc

I think I remember somebody said in some cabinet material discussion thread at the Construction Tips subforum, that he used beech plywood, and perceived it as nice and live sounding...
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Old 4th September 2011, 05:13 PM   #5
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Beech in Europe is not the same as Beech in the Americas. It is much closer to our maple. Mahogany plywood here is often Philippine Mahogany. It is not a real Mahogany only has a similar color and is used for floor underlayment as it is so cheap and rough. (Maple is stronger than birch and costs more.)

There are three common kinds of birch plywood here. The Finnish birch plywood is the best, Russian birch is not quite as good and the 18 mm may be 17 to 19 mm. Chinese birch made using Russian timber is quite inexpensive and very much lighter and deflects more. Russian birch is most often used for kitchen cabinets at 12 mm thickness and last year was in short supply.

$70 for a 4' x 8' sheet of solid maple plywood is a bargain. So the beech should be a good choice. If you can find 9 mm thickness you might just double up thicknesses. I do sometimes get 3mm birch for bending and laminating. It is called aircraft plywood as it is close to what used to be used to build biplanes.

One issue is what type of plywood core is used. Cross laminated plys is the expected norm, but there is also solid core. That is where the core is made up of smaller solid pieces and only the face is veneer. It is fine for furniture but would not perform the same in a loudspeaker enclosure.
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Old 4th September 2011, 05:26 PM   #6
vann is offline vann  Macedonia
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Quote:
Originally Posted by simon7000 View Post
Beech in Europe is not the same as Beech in the Americas. It is much closer to our maple...

...Cross laminated plys is the expected norm, but there is also solid core. That is where the core is made up of smaller solid pieces and only the face is veneer. It is fine for furniture but would not perform the same in a loudspeaker enclosure.
So some of those thick layers in the cheap 18mm "mahogany" could be solid core pieces? Sounds logical, being quite cheaper...

Can I guess that the 11 thin layers in 15mm beech plywood are cross laminated plys? In any case this appears as better choice.
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Old 4th September 2011, 05:30 PM   #7
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Quote:
Originally Posted by vann View Post
So some of those thick layers in the cheap 18mm "mahogany" could be solid core pieces? Sounds logical, being quite cheaper...

Can I guess that the 11 thin layers in 15mm beech plywood are cross laminated plys? In any case this appears as better choice.
Solid core has only face veneer the rest is blocks.

I suspect the beech is a superior plywood to even some of the birch plywood and at a reasonable price!
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Old 4th September 2011, 05:55 PM   #8
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see if you can find a woodworker/ cabinet maker somewhere who makes custom furniture for others or for himself. They may know of a suplier that sells to trades people and not the general public. The plywood at the lumberyards here is not good. There are a couple of places here that sell wood to pros and hobiest. I had to look hard for them. here is a link to one of them for your information, notice they have 6 types of mahogany

https://kjpselecthardwoods.com/index.html

good luck finding wood
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Old 4th September 2011, 07:03 PM   #9
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Don't cry about the prices. A 4x8' 18mm birchply sheet costs ~$170 in Sweden. That's quite pricey...
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Old 4th September 2011, 09:19 PM   #10
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Without seeing them, i would tend towards the 11-ply 15mm (with more bracing in the cabinet) over the 7-ply 18mm. The plys count. 15mm/11ply is the same as the Baltic Birch we use. Given that your sheet is 4x8 and ours 5x5, your price is comprable to what we pay (and we buy wholesale, and sometimes a lift as a time). 4x8 is also much more convienient than 5x5 in your build. When we look at a build with panels in excess of 60" we are faced with a price on the order of $120 per 4x8 sheet.

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