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Today, most mainstream speaker manufacturers strive for a 'dead' sound from their speaker cabinets. They want the speaker box to interact as little as possible with the speaker itself, and they use a number of techniques to accomplish this. If building speaker cabinets yourself, you can use these ideas too: start with some beefy, high-grade 3/4 inch plywood and use internal bracing in the seams of the speaker cabinet whenever possible (some speaker designers actually use two layers of plywood for the front of the speaker to cut down on resonances further).
To cut down on internal standing waves, some speakers have no parallel walls. A cheaper and easier way to deal with standing waves is with internal sound absorption (usually in the form of 1 to 2 inch thick fiberglass batting on the inside back and sides of the speaker box for ported designs and poly-fill material to stuff the box if it's a sealed design).
*If you REALLY want dead speaker enclosures there's always concrete.
I've built a number of speaker cabinets, and one of the things I learned is that the old theory about wood density only applies if that's the sound your looking for. It always baffled me(no pun intended)why someone would build a cabinet out of dense material and then fill it with soft material. I have a woking band and between considering the quality of sound and the benefits of portability, nothing beats Virola plywood. It's probably the lightest, softest plywood you can buy, yet is still very durable , even on the road.
This method of deadening the resonant frequencies only decreases the amount of frequencies the enclosure is capable of reproducing. If you want an enclosure that sounds awesome without any colourations from the enclosure itself then try an OB or Open baffle speaker which leaves the sound nice and pure at the cost of lowered bass response.
An open baffle is simply a piece of wod with a driver stuck in it. The dimensions of the wooden baffle may or may not be of any consequence as long as there is something thre to increase the bass reporduction if that's what you want.
There are several thousand different types of open baffle speaker configurations including dipole. There is a new speaker plan found at www.decware.com This speaker uses an empty cavity of air that excited by the driver by vibrating air across the opening and creatind a small amount of bass. Just enough to make the speaker listenable.
3/4 inch MDF is the standard for speaker building, not plywood. It has the best dampening characteristics of all readily available building materials. It is more expensive than plywood, but sounds better and is easier to work with. Finishing techniques for MDF speakers are widely available on the net.
|Jennifer Mathes, Ph.D.|