[David Platt]

MDF is the best for creating acoustical energy in any room

*sigh*

Yet another person posting a reply to a query that was ten years old!
(The original request was posted back in 2004).


What a stupid statement. VERY few musical instruments use MDF, (when was
the last time you saw a Piano made from MDF?) and even many good speaker
boxes use plywood rather than MDF.
In any case the sound from a speaker should come from the cone, not the
box, and apart from it's obvious drawbacks, concrete is far better than
MDF for speakers, so MDF can hardly be "best" for anything.

Acceptable, perhaps.

No, it can not be said like that. It is not a rigid material, so it becomes
very much a matter of how the box is braced. The "best material" is quite
likely to be a composite structure.

Example: Briggs "Loudspeakers" has as an example of a good construction
concept a corner bass reflex box built of bricks and mortar with a 12"
loudspeaker mounted on a plywood panel for ease of fitting. It is many ears
ago I borrowed the book from Duelund and read it, but I tend to think that
Briggs expressed preference for bricks and mortar over concrete.

I'd put it this way: MDF is one of the better compromise materials
that's easily available to the speaker home-builder. It's got good
dimensional stability, it's not difficult to work with homeowner-grade
tools, it glues and screws together easily, it's easy to paint or
veneer, it's strong enough to be routed for a speaker-flange recess,
and (unlike some common plywood) it won't have hidden voids or
loosely-glued sublayers which could buzz at embarrassing moments.
It's available in convenient-sized sheets from your local homebuilding
store... easier to find and afford than void-free Baltic birch
marine-grade plywood (another favorite).

On the down side: it wears out tool-steel saw blades quickly (use
carbide!), it's heavy, it's not all that rigid (you're right, good
bracing is very important), and it can crumble at the corners if
struck. And, of course, Stradivarius didn't ever mill any of his
better violins out of it :-)

I put together a big floor-standing system a couple of decades ago,
made mostly out of MDF - still very happy with the results. I did do
a bunch of internal bracing, made the front baffle out of two sheets
glued together (with some damping between the layers), and damped the
whole interior of the box with an elastomer paste. The resulting box
is quite acoustically "dead"... but man, is it ever *heavy*!

I was tempted to try a more exotic composite design... thin walls of
something stiff, with an interposing layer of a gridded plastic
stiffener (e.g. fluorescent-light diffuser) filled with fine sand for
damping. I decided that discretion was the better part of valor,
though... putting something like that together for a fairly complex
cabinet shape was beyond my skill-and-equipment set.

I do remember seeing a picture of Ray Dolby's listening room years
ago. Five huge exponential horn systems (three in front, and two in
back) built into the building structure, composed of masonry of some
sort (I can't recall whether it was brick-and-mortar, or cinderblock
filled with sand). I think he used a whole rack full of Flame Linear
400 amps to power the drivers.

I'm sure that was a system that you didn't *need* to turn up to 11!