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?
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?
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
Maybe a Matrix (like B&W speakers) with the foam covered with copper could work well???
D
F=MA
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
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
Re: F=MA
That's why I'm laminating the foam between two very thin sheets of metal. It's easy stuff to work with if you've got the tools - for small boxes, all you really need is a big square piece of wood and a hammer with the end covered by duct tape.
By laminating the foam between two layers of metal, I think I can greatly reduce vibration - in addition to the greater mass, the metal will vibrate much differently, and because all the layers are stuck to each other, I presume that very little will actually reverberate at all.
I was intending to use 1/2" or 3/8" foam with aluminum flashing to make a TL - they don't need to be quite so thick as other designs. However, for smaller boxes, two 3/8" layers of foam and three 3/8" layers of aluminum should eliminate vibration almost entirely.
I'm not so sure if this makes sense for smaller box-style speakers, but for large TLs, it makes construction a snap. All you need is two pieces of metal bent at the correct intervals (the metal layers), and some pieces of foam cut to the correct sizes (which is really easy with a $10 homemade hot-wire cutter.)
Assembly is also much easier. Bending metal is amazingly simple if you have access to a machine called a bend-brake, and even thin metal can result in an amazing degree of rigidity if bent and riveted.
Foam, however, is the easiest to work with of all. Just use epoxy to hold it together, and cutting a huge sheet of foam into a complex shape takes only seconds with a hot-wire cutter.
joe carrow said:
That's why I'm laminating the foam between two very thin sheets of metal. It's easy stuff to work with if you've got the tools - for small boxes, all you really need is a big square piece of wood and a hammer with the end covered by duct tape.
By laminating the foam between two layers of metal, I think I can greatly reduce vibration - in addition to the greater mass, the metal will vibrate much differently, and because all the layers are stuck to each other, I presume that very little will actually reverberate at all.
I was intending to use 1/2" or 3/8" foam with aluminum flashing to make a TL - they don't need to be quite so thick as other designs. However, for smaller boxes, two 3/8" layers of foam and three 3/8" layers of aluminum should eliminate vibration almost entirely.
I'm not so sure if this makes sense for smaller box-style speakers, but for large TLs, it makes construction a snap. All you need is two pieces of metal bent at the correct intervals (the metal layers), and some pieces of foam cut to the correct sizes (which is really easy with a $10 homemade hot-wire cutter.)
Assembly is also much easier. Bending metal is amazingly simple if you have access to a machine called a bend-brake, and even thin metal can result in an amazing degree of rigidity if bent and riveted.
Foam, however, is the easiest to work with of all. Just use epoxy to hold it together, and cutting a huge sheet of foam into a complex shape takes only seconds with a hot-wire cutter.
454Casull said:
It's a bit different. Extruded polystyrene usually has a composition of lots of tiny little styrofoam balls stuck together - it's usually used as packaging. Expanded polystyrene is the stuff used to insulate houses - it has a much more regular consistency, and is much tougher.
I have suggested this material in the past for speaker enclosures but in order for it to work it must be very rigid in addition to it's deadness.
This is best accomplished with a very strong skinning material on both sides of the foam and the foam will work best if it is thick. Like at least 1 inch or more. The thicker wall give it more rigidity when bonded to the skins. Fiberglass and epoxy resin would work the best for a reasonable price but I assume Aluminum would work rather well if it was thick enough and totally bonded to the foam.
Copper is a soft metal and very expensive. Would look great but would be very expensive in thick enough sheets. Copper might also be a greater bonding problem. However, sheets of brass may work and is more rigid than copper.
The edge bonding are as important to the cabinet as the walls so methods of strong corner bondings should be well thought out.
Another method that might work really well is to make an inner and outer skin of bent reinforced sheet metal and then pour expanding type foam into the cavity. This stuff also bonds like glue to the skins but you would have to invistigate how well it bonds to metal.
This is best accomplished with a very strong skinning material on both sides of the foam and the foam will work best if it is thick. Like at least 1 inch or more. The thicker wall give it more rigidity when bonded to the skins. Fiberglass and epoxy resin would work the best for a reasonable price but I assume Aluminum would work rather well if it was thick enough and totally bonded to the foam.
Copper is a soft metal and very expensive. Would look great but would be very expensive in thick enough sheets. Copper might also be a greater bonding problem. However, sheets of brass may work and is more rigid than copper.
The edge bonding are as important to the cabinet as the walls so methods of strong corner bondings should be well thought out.
Another method that might work really well is to make an inner and outer skin of bent reinforced sheet metal and then pour expanding type foam into the cavity. This stuff also bonds like glue to the skins but you would have to invistigate how well it bonds to metal.
This kind of foam that I mentioned in my above post is heavier and more dense than the rigid foam board. I used it several years ago when in college as I had a work study job at the local museum helping to build exhibits.
It might be more like the polyisosynuride type of building foam panels (probably didn't spell that right). It is more of a structural foam because it is much stronger and more dense. It is two parts that mix together and then watch out. It foams up big time and fills all gaps.
It also might have been a type of polyeurathane expanding foam.
It might be more like the polyisosynuride type of building foam panels (probably didn't spell that right). It is more of a structural foam because it is much stronger and more dense. It is two parts that mix together and then watch out. It foams up big time and fills all gaps.
It also might have been a type of polyeurathane expanding foam.
Hezz said:
This stuff might be what you're talking about.
http://www.cockeyed.com/inside/foam/foam.html
You can get it in various densities here:
http://www.shopmaninc.com/foam.html
I wonder how well a cast polyurethane foam speaker would work? The 16-lb. stuff should be plenty dense.
This is how they make refrigerators. An outer shell. Fit all the plumbing and what nots. Put in the liner, and fill the gap with expanding foam.
Tapping on the door and sides of my fridge, doesn't indicate it would be a good baffle. It needs to be stiffened up a bit.
I think there would be too much flex for air-suspension or sealed type enclosure. A BR, maybe, as there is not the same pressure variation.
Transmission lines maybe. My tubes don't vibrate at all on the pipe, can't say if flat panels in a TL are the same.
Aperiodic. Should be ok if the baffle is stiff enough.
Worth looking into.
Regards,
Geoff
Tapping on the door and sides of my fridge, doesn't indicate it would be a good baffle. It needs to be stiffened up a bit.
I think there would be too much flex for air-suspension or sealed type enclosure. A BR, maybe, as there is not the same pressure variation.
Transmission lines maybe. My tubes don't vibrate at all on the pipe, can't say if flat panels in a TL are the same.
Aperiodic. Should be ok if the baffle is stiff enough.
Worth looking into.
Regards,
Geoff
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