Actually, a composite (such as a layer of concrete between two sheets of MDF, or technically just MDF or plywood) panel resonates at a single frequency that is determined by its combined moment of inertia, size, and composite stiffness. You can use laminate theory if the composite is complex enough, but the end result is that any given quasi-uniform panel (i.e., may be different in different directions, but not in different areas) will have only a single resonant frequency. And for that matter, it will have only a single equivalent damping characteristic.
It isn't that different layers will attempt to resonate at different frequencies, with some damping out others, but rather that constrained layer damping is just a practical way to get a high damping material in the composite mix.
I did simplify things just a bit, since a highly elastic internal damping layer might cause the panel to actually act as two different panels that are loosely coupled, and it is possible to construct that panel so that the outer layers have different natural frequencies. However that is only possible with very elastic center layers, such as a sheet of rubber or thick non-hardening adhesive. When talking about something stiff like concrete that doesn't apply.
It isn't that different layers will attempt to resonate at different frequencies, with some damping out others, but rather that constrained layer damping is just a practical way to get a high damping material in the composite mix.
I did simplify things just a bit, since a highly elastic internal damping layer might cause the panel to actually act as two different panels that are loosely coupled, and it is possible to construct that panel so that the outer layers have different natural frequencies. However that is only possible with very elastic center layers, such as a sheet of rubber or thick non-hardening adhesive. When talking about something stiff like concrete that doesn't apply.
If I may. I agree that marble may resonat too much.
But on the subject of working with or using rock as speaker material, I have myself thought of wether perhaps 'Slate' could be a viable solution.
It is harder than sandstone yet softer than stone(rock). Slightly simplified mud/sand->sandstone->shale->slate->rock....
The mdf of the earth, as it has somewhat muddy ancestors. And then it usually comes with a neat deep black finish.
But on the subject of working with or using rock as speaker material, I have myself thought of wether perhaps 'Slate' could be a viable solution.
It is harder than sandstone yet softer than stone(rock). Slightly simplified mud/sand->sandstone->shale->slate->rock....
The mdf of the earth, as it has somewhat muddy ancestors. And then it usually comes with a neat deep black finish.
tmblack said:
I love the sphericals, saw them in an audio mag add when Susan Parker designed them. Susan told me she went to southern Europe to find a marble produce for a reasonable fix.
Price depends on the type of Marble,on size also.
The most beautifull white marble comes from Italy, it saves a bunch to buy marble there.
Traditional marble users are in the deseized business, tomb stones and the like.
I had a couple marble front plates for amplifiers made to size by one.(engraved too, go figure)
A more economic solution is looking for a company that specialises in stone materials, many are able to saw the stuff to size for you. They sell in all sizes, deliver material for kitchen sinks, dinner tables.
Black Belgium hardstone is a nice material too, i think.
Price difference when buying directly in Belgium is staggering, as with white Italian marble.
Hi,
Marble is hard to work so maybe synthetic marble and
use it with moulds. Spherical enclosures for bass are not
found commercially very often. The Ferguson Hill Horns have
spherical subs and US Enclosure used to do a 24inch sub with
NHT driver that was still grumbling down at 15-18hz. Line it with barium filled plastic and have a suspended centre core to absorb
reflections and some way of supporting the thing on the floor so
it does not roll onto the driver and happiness might be yours !
Also consider lightweight concrete as a substance to work. Locally in OZ Cemlite or Cemlite HE look interesting IMHO!
regards
AnthonyPT
Marble is hard to work so maybe synthetic marble and
use it with moulds. Spherical enclosures for bass are not
found commercially very often. The Ferguson Hill Horns have
spherical subs and US Enclosure used to do a 24inch sub with
NHT driver that was still grumbling down at 15-18hz. Line it with barium filled plastic and have a suspended centre core to absorb
reflections and some way of supporting the thing on the floor so
it does not roll onto the driver and happiness might be yours !
Also consider lightweight concrete as a substance to work. Locally in OZ Cemlite or Cemlite HE look interesting IMHO!
regards
AnthonyPT
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