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From: rcd@opus.UUCP (Dick Dunn)
Newsgroups: net.audio
Subject: Re: Homebrew speakers (using plywood)
Message-ID: <937@opus.UUCP>
Date: Wed, 7-Nov-84 03:26:37 EST
Article-I.D.: opus.937
Posted: Wed Nov  7 03:26:37 1984
Date-Received: Sat, 10-Nov-84 03:03:55 EST
References: <557@asgb.UUCP> <55100059@trsvax.UUCP>
Organization: NBI,Inc, Boulder CO
Lines: 32

> All the books I ever read advised against plywood and recommended particle
> board.  There is nothing wrong with plywood as such, but with age it
> can internally delaminate and cause buzzes and rattles.  Particle
> board may be harder to work with, but it will stay dead.

I've got two references which say that plywood is preferred, for these
reasons:

	Plywood is much stiffer (and somewhat stronger) than particle
	board of corresponding thickness.  This matters in larger
	and/or sealed enclosures, as particle board will tend to vibrate
	more and color the sound.  This can be fixed somewhat by adding
	bracing, but that alters the inside shape and volume of the
	enclosure...

	It's almost impossible to make particle board hold a screw well.
	It DOES matter that a speaker enclosure be strong and sturdy; the
	time-honored technique of gluing and screwing is the best way to
	get there.

BUT...the parent article is partly right--there ARE some problems with
plywood.  Some plywood is poorly glued.  Don't buy shop plywood and you'll
have a better chance of avoiding this one.  A more likely problem is that
the plywood may have voids (from knotholes, etc) in the interior
laminations--which gives you funny little air pockets covered by thin
sheets of wood.  There may also be loose bits of wood in these voids.
The solution is simple:  Use good plywood--A/B at least, and marine grade
if there's any concern over moisture.  Ask someone who understands plywood
grading and such to explain what you're getting.
-- 
Dick Dunn	{hao,ucbvax,allegra}!nbires!rcd		(303)444-5710 x3086
   ...Never attribute to malice what can be adequately explained by stupidity.