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Re: I was hoping some technical explanation might appear....

Posted by David Aiken (A) on March 7, 2007 at 14:27:18

In Reply to: Re: I was hoping some technical explanation might appear.... posted by Ethan Winer on March 6, 2007 at 06:44:27:

Ethan,

OK, I can accept those arguments—with a caveat I'll come to—and most especially the one about the number of Sabins absorption required. I think you were a little kind on this point, however. You failed to mention that the preservation of a similar response profile to the original room would require that absorption to have exactly the same absorptive spectrum as the original room. Given the huge variation in absorption 'spectrum' of all the rooms out there in the real world, the likelihood of a passive device being able to mimic all of them is going to be non-existent.

So to the caveat. What if absorption isn't the method used to achieve results with these products? The explanation I read referred to an application of the venturi effect. The venturi effect is based on pressure and relies on a sudden transition between high and low pressure zones caused by a mechanical restriction. What we're seeing in the plots is a reduction in sound pressure levels and that translates into a reduction in variation of air pressure within the room. Venturis don't use absorption to achieve their pressure change .

I can't see how these things could introduce a venturi effect but I really don't know anything about venturis apart from some aquarium applications and having seen smoke from smouldering insulation around the outside of an air conditioning duct being sucked into the air flow within the duct and passed into the building where it eventually caused a fire alert. I'm woefully uninformed about the mechanics and effects of fluid pressure flow.

As I said at the outset, if it does work (something I'm definitely not convinced of) it has to work because it's relying on a different subset of the laws of physics to those used by traditional absorptive devices. If that's the case, then it makes no sense to say it can't work because it doesn't rely on absorption and all the reasoning for why it won't work, based on those laws applying to absorptive techniques, will be invalid because it will be relying on the wrong subset of the laws of physics.

The test of whether something works is whether you can repeatedly demonstrate the claimed results under test conditions. If it can do that, then there will be an explanation which is consistent with the laws of physics. If it can't produce the claimed results, then it doesn't work but one could then waste time arguing over whether or not the reason it doesn't work is that it doesn't comply with the theory underlying the traditional approach or because the purported theory underlying the design doesn't work. An argument can be made for either of those explanations but I would tend to opt for the second rather than the first explanation. You may have a preference for the first.

David Aiken

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