[Nelson26]

What can i use to deaden sound inside my speaker?
or do i even need sound deadening materials?

[sbrtoy]

You need to provide some more info for an informed answer...is it commercial or DIY? Cabinet size and material? Bracing? Drivers and tuning?

[Danny Richie]

If you are looking to do away with that hollow ring of the enclosure then laying in something that is heavy and non-resonant is the ticket. Industrial vinyl floor tiles are cheap and work pretty well.

A secondary and thinner enclosure within the enclosure with an open space between them filled with sand works really great too and doesn't cost much.

Plenty of bracing is also a really good idea.

Be sure you allow for the air space that any of that takes up.

After that you will still need to add material to absorb standing waves in the box. This can be felt, open cell foam, fiberglass insolation, or poly fill.

This stuff will slow down the air flow in the box and make the woofer see the air space as slightly bigger, so you need to allow for that as well.

[Duke]

Nelson26, in general you want the inside of a sealed box to be acoustically quite absorptive but with a vented box you don't want to overdo the stuffing material as that can kill the bass.

If you're building a sealed box then I'd suggest using about 1/2 pound per cubic foot of Polyfill, avaliable at fabric stores.   

If you're building a vented box, stuff about half of the box with 1/2 pound per cubic foot Polyfill and leave the other half of the box unstuffed.  Keep the stuffing away from the port(s) - in other words if the port is in the top rear of the cabinet, stuff the bottom half but leave the top half unstuffed. 

As an alternative, with a reflex enclosure glue empty cardboard egg cartons to the inside surfaces wherever you can, and use little or no stuffing.  You want the egg-holding side out so that the sound bouncing around inside the cabinet sees a highly diffusive surface when it hits an interior wall.  Gorilla glue works good for this.  You can also glue convoluted foam to the interior walls, but I suggest only on one of each pair of opposing walls (like do one side wall, the back wall, and the top).  Acousstic fiberglass is an alternative, but it's nasty nasty stuff that I wouldn't wish on anybody.

My preference for dealing with panel resonances is bracing and/or contrained layer damping.  The latter is where you glue large squares or rectangles of plywood to the inside surfaces using a glue that stays soft.  I think there are some types of Liquid Nails that have this property, but I use a water-based glue that I buy in quantity.  If you ask at the paint department at Home Depot for a glue that stays soft they can probably help you.

Feel free to call or e-mail me if you'd like, and best of luck with your project.

Duke LeJeune
audiokinesis at yahoo dot com
208-852-2610

[S Clark]

Nelson,
Carpet padding and linoleum squares layered has been recommended.  Also, fiberglass insulation works well, but handle it with gloves and spray the outer edges with hair spray or spray enamel to stabilize it so that microscopic fibers don't exit the port.

[Russell Dawkins]

I read of an unusual approach the other day - this fellow makes his own felt by buying old, worn, but real thick wool sweaters from a second hand clothing store.
Then he washes them in hot water and tumble dries them - more than once if necessary to make them shrink as much as possible.

By this time they resemble (in fact are) coarse felt and quite a good sound absorber. He then does what Duke suggested with convoluted foam, and stapled the pieces to one of each pair of opposing inside surfaces.