Foam speakers - would they work?

[Spasticteapot]

Of all the materials I can think of, extruded polystyrene (not the bubbly stuff - it's very regular) is the most acoustically dead materials I can think of. You can whack people with it, hit it with sticks, whatever - no noise is produced.

So, why not build a speaker out of it?

I have nearly zero woodworking ability - I've already stated as much. However, I think that the combination of a thin metal skin (likely copper) with some reinforcing elements (likely steel) and a layer of 3/8" foam, as shown below:
http://www.foamfly.com/help.php?section=what

This would then be stuffed as normal.

I'm hoping that this combination will work well. I'm a reasonably skilled metalworker, and being able to build light, simple, and cheap speaker boxes out of attractive materials would make my life very, very easy indeed. (For example, using this technique, I could rivet together a straight tapered-quarter-wave-pipe in under an hour.)

Another option is to sandwich a sheet of foam between two very thin sheets of copper. This might work even better - I'm not really sure. I theorize that by using a spray adheisive to attach the layers together, I can get the desirable properties of thick metal in a speaker (low reasonance, almost no effect on sound) without requiring a forklift to properly position it.

Any comments?

[phase_accurate]

A very light sturdy combination is a laminate of this one and epoxy-resin/glassfibre on both sides. I have seen boat hulls built that way.

Regards

Charles

[Dag]

Nice idea!

A sandwich with Al-foam-Al would be very light and stiff.

D

[Spasticteapot]

Originally posted by Dag
Nice idea!

A sandwich with Al-foam-Al would be very light and stiff.

D

Aluminum is nice, and cheap, too. However, I'm a fan of copper - it's very pretty, and very soft. (Also, it's much easier to work with than aluminum - that stuff you just can't solder to!)

[Dag]

You are right, aluminum is not easy to work with. But I think aluminum is much better than copper for a speaker because it is much stiffer. Stainless might work too but it is also difficult to work with and it is maybe too hard and resonant.
Maybe a Matrix (like B&W speakers) with the foam covered with copper could work well???

D

[Spasticteapot]

Originally posted by Dag
You are right, aluminum is not easy to work with. But I think aluminum is much better than copper for a speaker because it is much stiffer. Stainless might work too but it is also difficult to work with and it is maybe too hard and resonant.
Maybe a Matrix (like B&W speakers) with the foam covered with copper could work well???

D

I'm not sure. A lot of stiffness would be obtained from the laminated materials. Regardless, if I go for a foam sandwich, I can use aluminum on the inside anyway.

[joe carrow]

Hey, it's an interesting idea- I've explored something similar in the past.



The largest problem I found was that the box was so light that it was actually moved in opposition to the cone motion. The walls were 1/2" thick foam-core with aluminum L-brace reinforcement on the inside along the edges.

If you make a cabinet that weighs 1/10th as much as a normal cabinet, then it's going to move 10 times as much. There's an obvious solution- have two woofers arranged as a bipole.

If you do this, I think the way to get the best performance will be to have walls at least 3 times thicker than you would build out of wood. You save weight, but you need extra volume. Consider this- you could lay a normal speaker cabinet on its side and stand on it without breaking it. You might cringe a little, but you could probably stand on it without bending or cracking anything. What do think you need to do to get that kind of strength out of foam?

Cool idea. I hope you do more with it

[SY]

Every once in a while, it takes one of the old farts to mention KEF and Leak, who have done this commercially.

[owen]

Not for the box though...

You could use a thin skin of 4mm ply inside and out. That would be pretty tough


Owen

[angsuman]

Yeah this is a great idea. Everytime I walk by a large foam cooler I think about using it as a speaker box, perhaps with thin plywood reinforcing the outside and inside, for those of us who are afraid of metal.