Hi doogyscoot
The well tried and documented construction method of double (wooden) wall, cavity filled with dry sand, always works very well.
Sand is massive and it is very dissipative too.
To optimize this construction in terms of acoustic impedance matching, the innermost walls may be dressed with cork or balsa
Water, like any other Newtonian liquid, is (practically) incompressible and therefore non-dissipative. It does not posses a high density, therefore is not very massive. The acoustic attenuation is quite low. In my opinion , it is not a good candidate for sound deadening material.
Regards
George
The well tried and documented construction method of double (wooden) wall, cavity filled with dry sand, always works very well.
Sand is massive and it is very dissipative too.
To optimize this construction in terms of acoustic impedance matching, the innermost walls may be dressed with cork or balsa
Water, like any other Newtonian liquid, is (practically) incompressible and therefore non-dissipative. It does not posses a high density, therefore is not very massive. The acoustic attenuation is quite low. In my opinion , it is not a good candidate for sound deadening material.
Regards
George
I've not read this whole post, but I have a lot of experince here.
Water is very low damping, not a great material in this application. There are polyurethane elastomers with a lot of water like properties that are very well damped. Add some micro-ballons and it would be very well damped, low cost, reasonbaly easy to work with, and its what I use.
Water is very low damping, not a great material in this application. There are polyurethane elastomers with a lot of water like properties that are very well damped. Add some micro-ballons and it would be very well damped, low cost, reasonbaly easy to work with, and its what I use.
Is anyone still interested in this thread? Oh well here goes my first post.
Back to basics - The amount of energy a speaker puts out into a room is equal to the amount of energy put into the enclosure. Since the enclosure is usualy smaller than the room
the energy density in the enclosure is much higher than that in the room.
Concrete or brick is one of the means to provide very stiff enclosures that due to their mass simply do not vibrate and therefore do not exicte the air. ie the energy inside the enclosure doesn't come out.
So what happens to it. It just excites the air inside the enclosure and is able to excite the cone producing distortion.
The other approach is to absorb the energy (or much of it) before it excites the enclosure walls. Water may work, never tried it. If you have a stiff cabinet then layering the insides with absorbent materials will absorb the energy before it hits the walls. Here are some of the things I have tried.
30mm cured silicon
big bubble wrap (needs to be glued well)
LDF (they make pin up boards with it. Not expensive)
Cork
In a good speaker you need to do both, stiff unyeilding walls and absorbing the energy within the enclosure.
Back to basics - The amount of energy a speaker puts out into a room is equal to the amount of energy put into the enclosure. Since the enclosure is usualy smaller than the room
the energy density in the enclosure is much higher than that in the room.Concrete or brick is one of the means to provide very stiff enclosures that due to their mass simply do not vibrate and therefore do not exicte the air. ie the energy inside the enclosure doesn't come out.
So what happens to it. It just excites the air inside the enclosure and is able to excite the cone producing distortion.The other approach is to absorb the energy (or much of it) before it excites the enclosure walls. Water may work, never tried it. If you have a stiff cabinet then layering the insides with absorbent materials will absorb the energy before it hits the walls. Here are some of the things I have tried.
30mm cured silicon
big bubble wrap (needs to be glued well)
LDF (they make pin up boards with it. Not expensive)
Cork
In a good speaker you need to do both, stiff unyeilding walls and absorbing the energy within the enclosure.
pheonix358 said:
Your first sentence is entirely incorrect, although your last sentence is reasonable. Its hard to see how you get from one to the other. The speaker is designed to couple well to the air in the room, but it does not couple very well to the enclosure. So one mode of sound radiation is much more efficient than the other and the energy ratio is something like 100:1.
Damping in the enclosure is a very important aspect. Probably more so that rigidity.
How about "nanogels" or "aerogels"?
I was watching one of those home building shows the other day and they were making walls with translucent polycabonate panels filled with nanogel. That brought to mind this thread. =)
Nanogel is strange stuff, the lightest solid made. But it might just work as well or better than sand, as it is sort of sand with lots of air. And very tightly interlocked, I think. Much, much ligher than sand.
Couldn't find much info on the sound deadening qualities, mostly thermal properties, tho many documents say its acoustic properties are good, especially below 500Hz.
I was watching one of those home building shows the other day and they were making walls with translucent polycabonate panels filled with nanogel. That brought to mind this thread. =)
Nanogel is strange stuff, the lightest solid made. But it might just work as well or better than sand, as it is sort of sand with lots of air. And very tightly interlocked, I think. Much, much ligher than sand.
Couldn't find much info on the sound deadening qualities, mostly thermal properties, tho many documents say its acoustic properties are good, especially below 500Hz.
OK, I'll stick my neck out.
How about an enclosure with a vacuum in it?
Obviously the speaker cone would have to cope with the preload as a result of atmospheric pressure. An unfortunate 1600 lbs in the case of a 12 inch but a mere 45 for a 2 inch. Mass and compliance seem to be the principal engineering obstacles, combined with maintaining the air seal.
Or maybe some way of utilising vacuum chambers to isolate the interior from the exterior. A vacuum flask leaks heat, but it's good enough to be useful.
w
How about an enclosure with a vacuum in it?
Obviously the speaker cone would have to cope with the preload as a result of atmospheric pressure. An unfortunate 1600 lbs in the case of a 12 inch but a mere 45 for a 2 inch. Mass and compliance seem to be the principal engineering obstacles, combined with maintaining the air seal.
Or maybe some way of utilising vacuum chambers to isolate the interior from the exterior. A vacuum flask leaks heat, but it's good enough to be useful.
w
Thanks for continuing this thread guys, it is still something I'm investigating and the nanogels thing sounds like it could be worth a punt. I've been trying to read through speaker building 201 to clear up some patches in my understanding of the basics before I start hassling people but will be back on to pick up this thread soon.
ta Doug.
ta Doug.
"Gedlee - Your first sentence is entirely incorrect, although your last sentence is reasonable. Its hard to see how you get from one to the other. The speaker is designed to couple well to the air in the room, but it does not couple very well to the enclosure. So one mode of sound radiation is much more efficient than the other and the energy ratio is something like 100:1."
I have to disagree. Laws of energy come into play. Every force has an eaual and opposite force. Consider a the difference in loudness between speakers playing in a small room vs a large room. Now consider the inside of the speaker as a small room. There is a great deal of energy in a speaker enclosure and that needs to be dealt with. Perhaps you could provide more information why you think this is not so.
I have to disagree. Laws of energy come into play. Every force has an eaual and opposite force. Consider a the difference in loudness between speakers playing in a small room vs a large room. Now consider the inside of the speaker as a small room. There is a great deal of energy in a speaker enclosure and that needs to be dealt with. Perhaps you could provide more information why you think this is not so.
"OK, I'll stick my neck out. How about an enclosure with a vacuum in it?"
1. The air pressure outside the enclosure would push the cone in all the way to it's mechanical limits and it would not function.
2. The enclosure and drivers would have to be airtight over time.
Ever watched "air crash investigation" when there is a sudden hole in the cabin causind sudden decompression? That is how your cone would feel, sucked into the box. May be fun to try though
1. The air pressure outside the enclosure would push the cone in all the way to it's mechanical limits and it would not function.
2. The enclosure and drivers would have to be airtight over time.
Ever watched "air crash investigation" when there is a sudden hole in the cabin causind sudden decompression? That is how your cone would feel, sucked into the box. May be fun to try though
As the discussion has shifted away from water and more into what would be a good absorbing material and how to measure it's performance,
I was thinking along the lines of what has already been discussed and what has already been used in speaker enclosures.
How about sponge? Natural sponge? It is compressible and the very structure of the material would allow the air waves to enter the sponge mass, deflect and meet and negate each other to a large extent. At least that is how I guess it would work.
But I think we need to separate two different issues on enclosure vibration in general.
There is the matter of rear radiation from the cones that need to be managed against forming standing waves.
There is the matter of mechanical vibration emanating from the driver's rim to the front baffle to the rest of the enclosure.
I have seen several approaches to solve the second problem, like using concrete or any high mass material in generous amounts building a 200lb enclosure.
The first issue is generaly solved by laminating the inner walls of the enclosure with non reflecting material and adding wool or similar material inside the enclosure to absorb the energy of the standing waves.
But perhaps it is possible to just avoid the standing waves by careful design of the enclosure itself. Perhaps avoiding parallel walls?
I was thinking along the lines of what has already been discussed and what has already been used in speaker enclosures.
How about sponge? Natural sponge? It is compressible and the very structure of the material would allow the air waves to enter the sponge mass, deflect and meet and negate each other to a large extent. At least that is how I guess it would work.
But I think we need to separate two different issues on enclosure vibration in general.
There is the matter of rear radiation from the cones that need to be managed against forming standing waves.
There is the matter of mechanical vibration emanating from the driver's rim to the front baffle to the rest of the enclosure.
I have seen several approaches to solve the second problem, like using concrete or any high mass material in generous amounts building a 200lb enclosure.
The first issue is generaly solved by laminating the inner walls of the enclosure with non reflecting material and adding wool or similar material inside the enclosure to absorb the energy of the standing waves.
But perhaps it is possible to just avoid the standing waves by careful design of the enclosure itself. Perhaps avoiding parallel walls?
I have made small plywood/silicone/plywood sandwich cabs before.
To my ears it made the cabinet inert using a "tap" test.
I haven't worked towards testing efficacy using a piezo transducer yet.
In the Speaker Builder 5/96 issue the article: The Opposite Moduli (OM) Speaker Cabinet - featured experiments with amalgams mixtures.
Using mixes of differing Young's modulus instead of a singular substance converts sounds to heat more effectively.
I mix clean fine sand and Rosco FlexBond.
Extremely inexpensive as acoustic dampening.
To my ears it made the cabinet inert using a "tap" test.
I haven't worked towards testing efficacy using a piezo transducer yet.
In the Speaker Builder 5/96 issue the article: The Opposite Moduli (OM) Speaker Cabinet - featured experiments with amalgams mixtures.
Using mixes of differing Young's modulus instead of a singular substance converts sounds to heat more effectively.
I mix clean fine sand and Rosco FlexBond.
Extremely inexpensive as acoustic dampening.
I vote for snow over water.. Snow is an excellent sound dampener, ever stood outside and listened how everything sounds different after a big snowfall? Not sure how practical it would be in a speaker cab though, you'd have to keep them cabs real cool Lead would be an excellent choice, but the weight penalty is quite high... Mercury might work?
I've heard of a new drywall brand but can't remember the name, that is designed for sound deadening in buildings etc.. I think it's supposed to be like 1 sheet of it is like the same as if you put up 5 or more?, something like that.. That could be a good substance to try for sandwiching into a loudspeaker cab.. This might be the stuff, not sure though http://www.quietsolution.com/html/quietrock.html
Dave
Lead would be an excellent choice, but the weight penalty is quite high... Mercury might work?I've heard of a new drywall brand but can't remember the name, that is designed for sound deadening in buildings etc.. I think it's supposed to be like 1 sheet of it is like the same as if you put up 5 or more?, something like that.. That could be a good substance to try for sandwiching into a loudspeaker cab.. This might be the stuff, not sure though http://www.quietsolution.com/html/quietrock.html
Dave
Sandwitching a wave diffusing material between two sheets of plywood would render that material useless.
The effect of silicone, rubber, sand or whatever between these two sheets of plywood is supposed to be to absorb - by mass differential - the waves formed inside the cabinet that found their way through whatever material is applied on the inside walls to the plywood and on their way to resonate the outside wall and more importantly the edges and corners.
I would opt for the simple option of controlling inside standing waves, making walls not parallel to each other as much as possible and trimming the corners so that they become spherical.
The effect of silicone, rubber, sand or whatever between these two sheets of plywood is supposed to be to absorb - by mass differential - the waves formed inside the cabinet that found their way through whatever material is applied on the inside walls to the plywood and on their way to resonate the outside wall and more importantly the edges and corners.
I would opt for the simple option of controlling inside standing waves, making walls not parallel to each other as much as possible and trimming the corners so that they become spherical.
HK26147 said:
I am afraid you misread my statement and in retrospect, I might have been unclear.
The phrase you quoted refers to sound diffusing lamination, see snow
to the inside of the enclosure.My second phrase
refers to the solution you describe, like silicon sandwitched inside the plywood sheets.
I know that what you are doing works. I have already done half that: Firmly glued a 0.5" rubber sheet to the inside of the enclosure on all walls.
My point is that although complex concepts that work are nice to study and enjoy, we should investigate further for simpler solutions.
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