I agree. Sand is insanely heavy, though, and it has to be bone-dry to avoid problems with wood deterioration over time.
Here's an idea: an array of vertical small-diameter plastic or copper pipes (maybe 1/2" size) filled with sand and glued to narrow grooves on the interior surface of the ply or MDF cabinet. If done right, the pipes would stiffen the cabinet walls while damping them at the same time.
Thanks for the backup information on the Be material that Materion has. I have my first parts from them for a dome tweeter design and it sure would be nice if they could actually produce a diaphragm for the same cost as aluminum but I highly doubt that will happen. The material handling and costs are much higher and so is the processing to produce the foil. From what I am told by Materion the trick to making the foil work to produce a diaphragm requires elevated temperature of the foil while it is shaped. Another thing is that you can not at this time produce a dome that has as much curvature as an aluminum material. For technical reason beyond what I can write here I am told that a shallower profile can match the radiating pattern of a deeper drawn aluminum form.
There are plenty of materials out there to play with ... there will be something that does the job, the trick is to find one that's easily available and not silly in cost. An indicator of how heavy duty one can go are the special mounting pads designed for diesel generator sets in buildings - when it kicks into operation that the constant throbbing of the huge weight doesn't get transmitted any more than necessary through the structure of the building; again, this is just viscoelastic behaviour doing the job.
I don't think it needs to be stiffer, rather that no matter how it may be excited or provoked into making a sound or ringing, that the levels of sound are very benign.
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If you truly wanted to produce a constrained layer material for a speaker cabinet I would use a polyurethane visco-elastic resin system between two layers of whatever wood was desired. It wouldn't be that hard to do but would drive your cost up a significant amount vs just plain wood and sensible reinforcing ribs. Another interesting material I have work with in the past was an energy absorbing urethane that I worked on for Giro Bicycles for a helmet material. Raised the cost of a helmet by about $0.25 and that was enough to kill the program even though the helmets were selling for well over $100.00 each.
If I remember correctly the aerogel materials are made of silica materials and are usually used as insulation materials for high temperatures. I don't think they would have much in the way of a lossy property if put in a constrained layer. The Focal aerogel speakers sound terrible by the way.
Damping is the most important. For a given amount of resistance, the greater the mass the less damping this resistance will offer. Hence lighter is better than massive. the resistance in a CLD panel is a fixed quantity so the lighter the materials on either side the greater the damping effect. this makes MDF a poor choice. Polyurethane boards are the best material that I have found - high stiffness to weight with high internal damping. Damped by CLD using my proprietary elastic Polyurethane composite and the panels are light and dead as can be. High mass just gets you a very heavy cabinet which is just a pain to work with for no advantage except the lowest cost. Mass is cheap actually.
I was thinking more about alumina or carbon aerogel...
didn't know that Focal maid drivers with aerogel ?! I know they have a Be tweeter, some sandwich cones but don't know how they are made...
So the critical issue is the about of epoxy. Damping is due to epoxy, and I have no idea what ratio was used. Basically I just told the artist the volume, hole and enough room for a port of specific length, and desirable material characteristics, a driver for fitting. The idea was "whenever inspiration comes". Came back a few weeks later, it was pretty much done except closing the bottom so we could do some stuffing experiments.
One thing I remember is that he tried to make bubbles in it so that it would mimic real stone, and the color seems to change with age.
Oh! The mic was buried in the sand? That would be interesting.
As for panels, been doing a lot of shopping for small, powered speaker at work. Almost all with 8 or 10 inch woofers are in plastic cabinets. And you can hear it. Not always too noticeable on recorded music, but let someone talk on a mic and you can hear it straight away. Not pretty. But it lets the manufacturers hit a price and weight point.
I don't think they are ("W" cones).
-rather a more typical expansion structural foam that's been formed or milled.
The out-side "skins" is sort of a "spun" glass (..glass fabric and resin milled).
I don't think Audax's is either (where a real aerogel requires super-critical drying). Moreover, their "aerogel" drivers across their line are different in construction and material - particularly with respect to the outer surface/skin that you see when looking at the front of the driver. Not unsurprisingly they also sound different among varying models.
Most that I've heard have the rare quality of both tone and clarity (when properly designed/implemented in a loudspeaker). They are however a bit more damped than thin non-coated paper cones in sound (..generally more "precise" sounding, less "fuzzy" - though a bit less "expansive" as a result).
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..sand and ABS plastic in the right design would be almost ideal. The coupling point for the drivers should be much more rigid material though.
The two sealed cabinets (top and bottom) in this photo of Greg's system are plywood double-box sand-damped with steel plates to couple the drivers to:
Room1
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Pano,
I can't imagine that plaster wouldn't just fall of at some point? I have done a lot of plaster tooling and it just doesn't make much sense to me, plaster is very hard and I would think wouldn't be much better than the aluminum alone. We always added hemp to the plaster to make it stronger, by itself it is very brittle. I would think that if this was something someone want to do why not just bond some neoprene to the inside of the enclosure. Kind of the opposite of what I did for JBL once, we molded over the face of the enclosure with a flexible urethane self skinning foam.
Ps. Get the picture?
I can't imagine that plaster wouldn't just fall of at some point? I have done a lot of plaster tooling and it just doesn't make much sense to me, plaster is very hard and I would think wouldn't be much better than the aluminum alone. We always added hemp to the plaster to make it stronger, by itself it is very brittle. I would think that if this was something someone want to do why not just bond some neoprene to the inside of the enclosure. Kind of the opposite of what I did for JBL once, we molded over the face of the enclosure with a flexible urethane self skinning foam.
Ps. Get the picture?
Hi Pano
I have no idea. I remember reading about it years ago when I read an article about his 6ft. tall Sir Galahad speakers. How he did it, and with what he mixed it to stick I don't know, but I do remember him claiming that it made for the best non-resonant cabinets. Better even than sand-damped walls IIRC. BTW, if you'd like a look at these monstrosities, have a look at this system: John Bamford's system. He's had them for 20 years, so I guess it does keep on sticking.
Deon
I have no idea. I remember reading about it years ago when I read an article about his 6ft. tall Sir Galahad speakers. How he did it, and with what he mixed it to stick I don't know, but I do remember him claiming that it made for the best non-resonant cabinets. Better even than sand-damped walls IIRC. BTW, if you'd like a look at these monstrosities, have a look at this system: John Bamford's system. He's had them for 20 years, so I guess it does keep on sticking.
Deon
Yep, those are monsters!
Kindhorn - in France we call that mixture "Staff". An interesting material.
http://en.wikipedia.org/wiki/Staff_(building_material)
Kindhorn - in France we call that mixture "Staff". An interesting material.
http://en.wikipedia.org/wiki/Staff_(building_material)