| Plywood and engineered wood 101 [message #40635 is a reply to message #40633] |
Thu, 13 March 2003 19:37   |
BillEpstein
Messages: 886
Registered: May 2009
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Illuminati (2nd Degree) |
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There are so many types and constructions of sheet goods, but here are a few generalities:
Plywood is cabinet or lumber yard grade but both are industry graded like this,
A)Perfect knot free
B) Some small tight knots
C) Loose knots that can are filled (footballs)
D) Loose knots and other imperfections not filled
Lumberyard plywood is usually B-C, one side B, the other, C. Made from Pine or Spruce. The problem with it for speakers is that the inner plies can be C and D with loose knots and voids from those knots that rattle when they vibrate (play music). And the voids can telegraph through the veneer you apply. And, the footballs can come loose and ruin the finish and sound. Footballs are those oblong, hence football shaped fillers in the C face.
This is why at the lower price point MDF is king. But MDF is heavy. And it rings. But it machines and veneers beautifully. This is why MDF is used in so many, including the finest, speakers: price. And so the makers try to convince you that it sounds better. BULLSHIT!!!
Cabinet grade, A-A or A-B properly braced Baltic Birch should be and is the material of choice.
No voids, no filler footballs and 11 or 13 plies of wonderful Birch, a true hardwood.
It's lighter, stronger, more resistant to edge damage and veneers well. And it's almost as dimensionally stable as MDF. And it resonates at different freqs than MDF. Holds screws better, too.
But it's expensive and isn't on Home Depot's shelves.
Now, if you want to use lumberyard plywood, and lot's of good speakers have been built from it, drive by Lowe's and Home Depot, wave and head on into your independent lumberyard. Their B-C plywood will be better than the "big box" stuff and just a few dollars a sheet more. Or don't buy it and go on to the next yard. They will also have iron-on edge banding to hide the edge plies. Or you can paint.
Can't wait to see pix of the speakers you build.
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