What I'm going to suggest assumes 2 goals and I'd also guess this would probably be most applicable in an acoustic suspension design.
Goal 1) Prevent sound energy generated by the backwave of a driver from reaching the outer surface of the enclosure and thus radiating into the room.
Goal 2) Prevent sound waves from leaking back through the driver membrane and radiating into the room.
What about building a miniature anechoic chamber inside a fairly rigid and well braced enclosure made from baltic birch, mdf, whatever...? Would that science be scalable to work inside an enclosure at some level? Not suggesting it would be perfect but it may be an additive solution that would enhance the properties of the base material used in constructing the enclosure.
I'm thinking the triangular shapes could be manufactured from a non-exotic material. They'd need to store the sound energy and release it extremely slowly as heat. I think that is the basic principal in the full-sized chambers. Cork? Balsa? I guess you could use something like rigid fiberglass, but making all those--that is getting dangerously close to dollhouse territory.
This might also be like the box inside a box theory, but this inside box could have a vastly larger surface area exposed to the sound energy on the inside. Would that provide any benefit?
Goal 1) Prevent sound energy generated by the backwave of a driver from reaching the outer surface of the enclosure and thus radiating into the room.
Goal 2) Prevent sound waves from leaking back through the driver membrane and radiating into the room.
What about building a miniature anechoic chamber inside a fairly rigid and well braced enclosure made from baltic birch, mdf, whatever...? Would that science be scalable to work inside an enclosure at some level? Not suggesting it would be perfect but it may be an additive solution that would enhance the properties of the base material used in constructing the enclosure.
I'm thinking the triangular shapes could be manufactured from a non-exotic material. They'd need to store the sound energy and release it extremely slowly as heat. I think that is the basic principal in the full-sized chambers. Cork? Balsa? I guess you could use something like rigid fiberglass, but making all those--that is getting dangerously close to dollhouse territory.
This might also be like the box inside a box theory, but this inside box could have a vastly larger surface area exposed to the sound energy on the inside. Would that provide any benefit?
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Re: Re: Re: Re: Carbon fibre.
It not exactly a novel idea - MDF and particle board are of a similar structure. Denser on the outer than the inner. (goes back to the sandwich structure).
Is the intention to build the unit from cedar, then epoxy, or form the material first, then build the unit?
Would it be solid or a cross grain layered? How will the epoxy penetrate the wood, with pressure?
One problem with epoxy on bare wood is that the wood absords the solvent in the epoxy, leaving an unbalanced mix on the surface (one that is lacking in solvent will not cure properly).
If I could be so bold as to recomment another coating that is more stable than epoxy - polyurethane. It will not seperate, and be absorbed into the wood intact, even when thinned.
planet10 said:
It not exactly a novel idea - MDF and particle board are of a similar structure. Denser on the outer than the inner. (goes back to the sandwich structure).
Is the intention to build the unit from cedar, then epoxy, or form the material first, then build the unit?
Would it be solid or a cross grain layered? How will the epoxy penetrate the wood, with pressure?
One problem with epoxy on bare wood is that the wood absords the solvent in the epoxy, leaving an unbalanced mix on the surface (one that is lacking in solvent will not cure properly).
If I could be so bold as to recomment another coating that is more stable than epoxy - polyurethane. It will not seperate, and be absorbed into the wood intact, even when thinned.
liasom said:
Any type of vented speaker wouldn't benefit from total absorption of the back wave, as this is used for bass reinforement. A sealed box should be ok with it, but my own experience with stuffing in sealed boxes (which would be a close second to anechoic ) is that it can make the bass sound muffled. I prefer to cover the insides with rubber-backed commercial carpet. This carpet has good damping properties when adhered to the panels. The difference I hear with this is probably in the higher bass region - above 100Hz.
I can attest to the effectiveness of double walled boxes and horns filled with sand. Having heard, or rather not heard a few, I can tell you that they work great. Very little if any resonance on the outside walls. The same should be true for the inside wall, too. But super heavy and hard to make. Yes indeed.
Very dense marine grade plywood is also another material I've had great success with. Not light either, and not cheap. But very neutral. No box sound.
It would be nice to know how Meyer Sound build their PA boxes. They are extremely well damped. You can thump them or dolly them over rough floors, they don't make a sound. Looks like 3/4" plywood, very dense. One would guess they use very good bracing, too. Whatever it is, it works.
Very dense marine grade plywood is also another material I've had great success with. Not light either, and not cheap. But very neutral. No box sound.
It would be nice to know how Meyer Sound build their PA boxes. They are extremely well damped. You can thump them or dolly them over rough floors, they don't make a sound. Looks like 3/4" plywood, very dense. One would guess they use very good bracing, too. Whatever it is, it works.
MJL21193 said:
I've also heard the muffled sound to varying degrees in stuffed enclosures. That is why I'm thinking to find a way to entirely get rid of stuffing, foam, carpet, etc. in a box shaped sealed enclosure. I have a project in the works requiring small sealed enclosures and am going to try a semi-anechoic idea on a test enclosure. My plan is to make the shapes less deep than those used in the big chambers (see graphic, like on the right side) and to either glue the shapes on only 3 sides--back, bottom, and either left or right or to place them less densely so as to cover about 40%-50% of the interior surface. Probably the latter approach since it might slightly help dampen panel resonances with a bunch of small "braces". I suppose the challenge is to find the right balance. It is so easy to over-dampen an acoustic suspension design. Still investigating to find an appropriate material though.
I figure it's worth a try.
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You might like to try a method that Dave Berriman used in several of his designs - a sandwich (3) of hardboard stuck together with Evostick and with the rough surface towards the drive units. These were very effective.
Talking of whom, does anyone have a copy of Hi Fi News and Record Review with the article on building his floorstander (DB8 I think) circa 1998. I got a mention in the article but made the mistake of lending my copy to a friend and I never got it back.
Talking of whom, does anyone have a copy of Hi Fi News and Record Review with the article on building his floorstander (DB8 I think) circa 1998. I got a mention in the article but made the mistake of lending my copy to a friend and I never got it back.
liasom said:
NOW you have my interest. The idea is taking shape in my head.
A multitude of triangular prisms cut from MDF, glued to the inside panels, in sets of 4. Then a set perpendicular to the first, and so on in a checkerboard pattern.
I wonder how effective it would be? Would certainly strengthen the box panels also.
I have a sealed pair that I'm currently working on that I might try this method. My original plan was to for a constrained layer with the 5/8" MDF on the inside and 1/2" veneered particleboard on the outside with silicone rubber as the adhesive. Then rubber back carpet on the inside to reduce and disperse standing waves.
VERY worth a try.
Thanks.
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