Sand filling a double walled enclosure is a very old idea, going back at least to G.A. Briggs. A sometimes overlooked advantage is that it can be removed for moving the enclosure.
I've wondered about substituting extremely lightweight concrete (can be as low as 20 pounds/cu ft.) for the sand as a damping material.
I've wondered about substituting extremely lightweight concrete (can be as low as 20 pounds/cu ft.) for the sand as a damping material.
Charged posted:
I think of this as "butcher block" tops.
The rub on this material is the orientation of the grain. You have long grain (with the grain) and short grain (across the grain) present in the panels perpendicular to each other. This panel will exhibit different rates of expansion or contraction with moisture changes along each axis. The short grain will move more than the long grain. Yes, it is stable, though not as much so as plywood (with the grain turned in alternate plys) or mdf (which has no grain).
It has and can be done. However it probably would not be among the "best" of methods.
Curmudgeon said:
"perlite" a kind of expanded rock not unlike lightweight (foamed?) concretes has been used for damping enclosures, have a read of this PDF: http://www.ecgcorp.com/avsite/avdocs/papers/Lodengraf_S&V_July2000.pdf
seems to work quite well, although theres no direct comparison with using sand instead. This method seems to have been devoloped where light weight is a key design factor, so isnt really relevant for loudspeaker enclosures where the mass loading effect of the sand would also have benefits- as well as the particle collisions/friction absorbing the energy.
"The idea behind the lots of little pieces is that each of them has a much higher resonance than a single larger piece and the odd shapes and sizes glued to the solid piece breaks up any vibrational modes that would be present."
I understand the idea; it's just that it doesn't correspond with reality, which is that all the small pieces combine to a big panel with a resonant freq somewhat lower than the same thickness panel without the separations between the little pieces.
I understand the idea; it's just that it doesn't correspond with reality, which is that all the small pieces combine to a big panel with a resonant freq somewhat lower than the same thickness panel without the separations between the little pieces.
The spaces between the jigsawwed pieces make the panel flex at different spots not allowing a large primary resonance. If they were regular square pieces a panel would have a number of equal resonances, the number of which would be the same as the number of squares across the panel plus one for the panel itself. By making them of irregular shape and size you are spreading out these 'smaller' resonances and breaking up vibrational modes that solid panel would support.noah katz said:
"The spaces between the jigsawwed pieces make the panel flex at different spots not allowing a large primary resonance."
If that were true, then the circumferential ribs on cones that give a cone more controlled breakup modes would eliminate the driver's primary Fs resonance, which in fact they do not, and cannot.
If that were true, then the circumferential ribs on cones that give a cone more controlled breakup modes would eliminate the driver's primary Fs resonance, which in fact they do not, and cannot.
Thats the idea: More controlled break-up modes! The deal with the cone is the Whole Cone is moving. The ribs break up any modes within the cone not that of the whole cone. You want the cone to move as a perfect piston with no self resonance and the ribs break up resonances caused by cone flexure etc.noah katz said:
In N.Z. a few years ago was a product called Tri-board. Don't know if its still made. I think it was two layers of thin MDF, one each side of a centre layer made of board that looked like pine plane shavings bonded under pressure. It was available in thicknesses up to 50mm. I have no idea how it performed sonically.
jamikl
jamikl
Another product, Pinex flameguard, may be suitable as the centre of the sandwich. Low density fibreboard containing no glues. Cut to std. sheet sizes. 12.5 mm thick. Very soft. Easy to push drawing pins etc into. Supposed to have good sound absorbing qualities. I have wondered about this for awhile.
Too many posts to re-read the thread so please excuse if this has been said before...
Granite and concrete are also composites. Probably why they work so well, no specific resonances for the completed enclosure. Maybe its' time to start using other composite sheet-type materials, like Hexcel sandwich sheets. Not cheap, but available in various combinations and thicknesses from various surplus outlets.
ensen.
Granite and concrete are also composites. Probably why they work so well, no specific resonances for the completed enclosure. Maybe its' time to start using other composite sheet-type materials, like Hexcel sandwich sheets. Not cheap, but available in various combinations and thicknesses from various surplus outlets.
ensen."Thats the idea: More controlled break-up modes! The deal with the cone is the Whole Cone is moving. The ribs break up any modes within the cone not that of the whole cone. You want the cone to move as a perfect piston with no self resonance and the ribs break up resonances caused by cone flexure etc."
We're talking about speaker enclosures, not cones - all vibration modes, including the primary resonance, are undesirable.
We're talking about speaker enclosures, not cones - all vibration modes, including the primary resonance, are undesirable.
...I think it was aerolam - certainly a honeycomb aluminium composite; they use it to build Chiefton tanks. The tweeter, being (I think) the first production metal dome had a really nasty HF (~22KHz) spike, which needed heavy filtration & knackered the sensitivity. This was sorted out by the time they brought out the SL700...
Hi guys this has been a really interesting thread!
I am still taken by the idea of hard foam with a resin skin.
If I understood correctly, for a bass enclosure (below 200Hz, say) it would be good to have a very stiff and light material so that the FS of the cabinet is higher than the frequencies produced by the driver in it.
It seems like some people were suggesting something along the lines of polystyrene or a hard foam of some kind coated with fibre-glass and epoxy could achieve this. The internal skin being corrugated.
Any further thoughts on this? As the rest of the thread was looking more at highly damped heavy enclosures.
Another way of having damping could be (inside to outside) a sheet of something flexible but quite heavy spaced off of an absorptive material then something very ridged. This would absorb a lot of the energy I suspect. There would need to be a good balance between the air gap size and the density of the flexible sheet.
I am still taken by the idea of hard foam with a resin skin.
If I understood correctly, for a bass enclosure (below 200Hz, say) it would be good to have a very stiff and light material so that the FS of the cabinet is higher than the frequencies produced by the driver in it.
It seems like some people were suggesting something along the lines of polystyrene or a hard foam of some kind coated with fibre-glass and epoxy could achieve this. The internal skin being corrugated.
Any further thoughts on this? As the rest of the thread was looking more at highly damped heavy enclosures.
Another way of having damping could be (inside to outside) a sheet of something flexible but quite heavy spaced off of an absorptive material then something very ridged. This would absorb a lot of the energy I suspect. There would need to be a good balance between the air gap size and the density of the flexible sheet.
The reason for the emphasis on damping is that it's not the original flexure that's so bad. Any tendency to continue vibrating after the original stimulus ir removed makes matters much worse; the original signal is no longer masking, and the long duration makes the resonance much more prominent, as the total power over the time is so much greater.
See the cabinet waterfall diagrams in the Stereophile reviews/tests. This is also the reason I tend to be so concerned with speaker HF peaks, and why they are so audible even when rolled off >20db by the crossover. For unpleasantness in drivers, the waterfall is what seems to correlate best for me.
See the cabinet waterfall diagrams in the Stereophile reviews/tests. This is also the reason I tend to be so concerned with speaker HF peaks, and why they are so audible even when rolled off >20db by the crossover. For unpleasantness in drivers, the waterfall is what seems to correlate best for me.
Absolutely, I agree damping is needed, but why not light stiff and damped?
A thin corrugated aluminium honeycomb panel with a latex or silicone skin of however thick for example. Slightly different densities over the panel could also help.
Moving the resonance out of the drivers passband just seems a much better way of doing it.
A thin corrugated aluminium honeycomb panel with a latex or silicone skin of however thick for example. Slightly different densities over the panel could also help.
Moving the resonance out of the drivers passband just seems a much better way of doing it.
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