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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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Tweakers' Asylum Tweaks for systems, rooms and Do It Yourself (DIY) help. FAQ. |
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In Reply to: RE: "their size is the equivilent of the size of the opening when a standard door is open one inch." posted by Robo02 on May 11, 2009 at 14:56:27:
"1. Unless the RPG perforated product also uses the Venturi effect, I doubt there is much similarity in the functioning. Venturi, by the way you engineers, has been in use in many other realms for a very long time making things like carburators function and (via a related principal) airplanes fly. Your comment on the RPG panels that "...we can assume that the mechanism of operation is similar" is an unwarranted leap. So is "...the Cathedral Panels are a passive acoustic treatment in the same way that my RealTrap panels are...""
If I remember correctly, RPG say their products use principles of laminar flow. The venturi effect is, I think, a special case of lamninar flow.
"2. You keep reverting to concepts of absorption. My understanding is that the Cathedral Panels do not absorb. They use the Venturi effect to create negative pressure to offset high pressure room nodes caused eg. by standing waves."
The effect of absorption in a room is the reduction of pressure. What gets measured is sound pressure levels and SPL measurements are what produce the plots that you provided the links to. The ability of a product to reduce SPL is measured in Sabins whether that reduction be caused by an pressure escaping to another space through an opening, by venturi effect or laminar flow, or by conversion to heat during passage through an absorbing panel. In all cases what is being measured is SPL change in the treated room and that's what was measured to produce the plots supplied by Cathedral Panels, exactly the same measurement technique as used by all other acoustic treatments regardless of their mechanism of behaviour. If you could not measure the Cathedral Panels in this way, then the plots you provided a link to would not be appropriate.
"3. Since most of what we humans can hear is above 40hz, it makes sense that most of the changes from the introduction of acoustic treatment into a room will be apparent at above 40hz, even if the acoustic product is working primarily on standing waves below 40hz."
In the claims stated in the text associated with your link, the manufacturer of Cathedral Panels claims they are effective in taming standing wave behaviour up to 200 Hz. That's their claim. Their untreated room plot shows a number of standing wave effects, both peaks and troughs at frequencies up to 130 Hz but the only changes that they mention in their comments on the plots, and the only real changes shown in the plot of the treated room, occur below 40 Hz. Further, the standing wave behaviour shown in the plots above 40 Hz is much more significant than that shown below 40 Hz, with much deeper peaks and troughs, and it is not significantly affected by the panels according to their plots, despite the claim that behaviour is tamed up to 200 Hz. Their plots do not support their claim of beneficial effects up to 200 Hz and for any effect above 40 Hz to be audible, it would have to show in the plot. Either the claim is wrong or the plots are wrong. They made the claim and they provided the plots. The plots do not support the claim. Make of that what you will.
"4. It is a good thing to have a product that is particularly effective at very low frequencies. A lot goes wrong at deep bass (standing waves again) and precious few acoustic products have their primary effect at these very low frequencies, especially anything that isn't bigger than a ... cow."
You're right, it would be good if we had such a product but the improvement shown below 40 Hz is actually fairly small, not what I would call "particularly effective" and most of the standing wave behaviour that causes problems occurs above 40 Hz—that's even obvious in the plot they show for the untreated room—so it's even better to have a product that works very well there, where the problems plaguing us are. If the plots showed significant behaviour above 40 Hz, the panels would be an even better product than they are, but the plots don't show that and don't support the manufacturer's claims. You need to consider whether you have to worry about problems below 40 Hz, really only an issue in a room with one or more dimensions greater than 28' which rules out most listening rooms including mine, and ignore what's happening above that or be concerned about problems up to 200 or even 300 or 400 Hz which is where room response tends to smooth out in most of our rooms. The plots provided by Cathedral Panels don't show the panels helping where most of the problems are.
I've said I think they do something and I've explained what I think they do. I have not said they aren't beneficial. What I am saying is that the claims they make about benefits up to 200 Hz are not supported by their plots which only show a benefit, and a small one at that, below 40 Hz. They chose the plots they wished to use to demonstrate the product's effectiveness and they chose the claims they wanted to make. Just compare their plots to their claims and you can see that the plots do not support the claim of benefits up to 200 Hz. Do with that what you like. Certainly try the panels and keep them if they help in your room but if you want to provide evidence that the claim of benefits up to 200 Hz is reliable then you'll need to find some plots showing changes in the room's behaviour which extend up to 200 Hz, two and a bit octaves above 40 Hz.
David Aiken
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Follow Ups
- RE: "their size is the equivilent of the size of the opening when a standard door is open one inch." - David Aiken 23:59:50 05/11/09 (0)
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