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In Reply to: RE: Granite is posted by unclestu52 on October 29, 2007 at 19:50:48
a
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coral? The point is that according to the laws of thermodynamics, energy can not be destroyed or created. The best you can do is to transmute it it into some other more benign frequency.
Granite has been always been brighter sounding in my experience, although I like it for certain purposes because it is dimensionally very stable. As others have noted, you must couple the granite slab with a much more compliant footer in order to obtain the best tonal balance. In my opinion, that means you have to go to a much more complex suspension/shelf system.
For many, that is fine, but I prefer a simpler system. I've had my fill of air bladders, sand boxes, lead shot and the like. I've gone back to a solid wood spruce shelf with cone feet and, you know, in my system, it outperforms roller bearings of all sorts, carbon fiber shelving, slate and granite slabs, MDF shelving, exotic hardwoods, sand boxes, air bladder sytems and the like. I had one combination of special cones sitting on a CF shelf sitting on CF cones which may have sounded marginally better, but the cost was astronomical in comparison to simply using plain Jane spruce with no coned feet at all.
Of course, YMMV.
Stu
I am sure I used coral sand, but please bear in mind that even with the sand box, I was not happy with the results. I even put the sandboxes and granite on a Sound Anchor stand. Even that was surpassed by a Reference Mana stand with its upward and downward spikes.
I have not had good luck with wood either as I find it dulls transients. I have tried maple, butcher block, and walnut with and without tiptoes underneath or the rubber and cork feet from Mapleshade. The best of these that I have found is one that Walker made for under his Velocitor. The only satisfying isolation that I have found is the Halcyonic active isolation platform, but it is just too expensive.
Auditioning Speakers
Rap your knuckles on the speaker cabinet. If it sounds like you are rapping against a piece of granite, this means the cabinet is well damped from vibrating on its own (the inside of the cabinet contains wool, fiberglass, sometimes lead or sand to dampen vibrations of the cabinet). If rapping your knuckles against the cabinet results in a drum-like sound, called resonance, the cabinet may not be well damped. Resonance can add artifacts to the sound (the vibrating cabinet acts like a speaker itself). Click here to listen to a wav file that was recorded when rapping on a speaker that has excellent damping (the speakers shown on the left).
The idea is to move the resonant frequency above the critical midrange bandwidth. That being said, examine the philosophy of the critically acclaimed Harbeth speakers. They use a simple 9 mm birch type ply without bracing for their cabinets which actually rings quite a bit. They claim that the resonant frequency is part of the design, but is high enough to be situated outside the critical mid band.
Most so called 'non resonant' cabinets are simply well braced, some with a double wall construction which usually raises the frequency either well above or well below audibility. They still resonate, hence the ability of devices like the Tekna Sonic to 'work'. As a matter of fact, that's why even cones work on speaker cabinets.
The 'rap' test is more a measure of cabinet bracing and strength of construction. The idea is not to eliminate resonance, which is impossible, but to control it and to transform it into a more benign form.
Stu
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Generally, it s regarded as the range where the human ear is most sensitive and you can examine the loudness curves to get the approximate frequency ranges. Bear in mind, individual sensitivities will vary, but similarly, as with setting crossover points for a tweeter, most designers try to either move the resonant points beyond the mid range bandwidth. Most opt for lower frequency bandwidths, but there are speakers with granite cabinets, aluminum cabinets, even steel cabinets, but, of course, resonance is not only determined by material, but also by size and other details of assembly.
Stu
> Click here to listen to a wav file that was recorded when rapping on a speaker that has excellent damping (the speakers shown on the left). <
I would REALLY like to "click here", but there is no here here.
Oz
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