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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: Aye, cynical I am posted by Jon Risch on October 22, 2009 at 18:41:46:
Ethan wrote: "The definition of one sabin is a one square foot opening to the outdoors. But a 16-inch diameter tube has only 12.56 square feet!"
Jon wrote: "We both know that there ARE absorption coefficients that go above 1"
But I was talking about sabins, not absorption coefficients! They are related, but are definitely not the same thing. Yes, absorption coefficients can go above 1.0 for reasons both legitimate and illegitimate. But it's physically impossible to have more sabins of absorption than the surface area of a device.
> At your retail website, the data you present shows the mini-traps hung
> on a wall reach an absorption coefficient of 1.86 at 400 Hz, way more
> than 1. Is this then bogus or false too?
As David Aiken explained, when a panel is mounted off the wall, the rear side also absorbs. Absorption by the edges is another reason a flat panel can have an absorption coefficient greater than 1.0. This is why I keep urging you to read my S&V article, because it explains all of these issues in detail.
If I were the king :->) companies selling corner bass traps would list sabins only, and not be allowed to claim absorption coefficients for traps measured in corners. One company I won't name claims an absorption coefficient of 3.0 for one of their bass traps! So I continue to list coefficients on my company's site in self-defense, though that's in addition to listing the sabins.
> You cite an absorption of 3.5 sabins at 63 Hz when your mini-trap in
> the corner, but we don't know that the tube trap was measured this way
This is exactly my point - we don't know! And this is why I wrote yesterday, "... rather than rely on disparate data from disparate sources which simply cannot be compared fairly."
> if the data in Mr. Everest's book were presented in an industry standard
> manner, it should have been with the tube trap laying down on the floor,
> rather than in a corner.
Yes, but it it were measured in an "industry standard manner" the data presented would go no lower than 125 Hz, or possibly 100 Hz. It would also be presented as single values for each standard third-octave band rather than as a continuous line graph.
> My own experiences with actual ASC tube traps, with DIY versions, and
> with simple 2X4 foot fiberglass panels tends to back-up the numerical
> data I am familiar with, and my perception that a simple fiberglass
> panel is just not a bass trap, even if you place it in a corner.
This is why it's not adequate to assess this stuff by ear. The only way to know for sure is by measuring! Trying to judge the effectiveness of bass traps (or almost anything else with audio) by ear alone is fraught with problems. As an over-simplified example, if a room's major resonance is in the key of A, but your test music is in the key of G, bass traps won't seem to do as much as when playing music in the key of A. When you measure using room software as described in my S&V article, the software sweeps through all frequencies so you can see exactly what is happening clearly and with no ambiguity. Versus "I thought I noticed an increased fullness in the mid-bass range" which is vague, and imprecise, and subject to a different impression if you listen again tomorrow or next week.
I assume you weren't at my recent AES workshop in NYC, so I'll summarize one of the most important points made by two of the other panelists. One was James Johnston, chief scientist at DTS (lossy encoding experts), and the other was Poppy Crum, a professor at Johns Hopkins School of Medicine. These two hearing experts spoke for more than half an hour each about the frailty and unreliability of human hearing. They showed with audio examples how we often hear what we want to hear rather than what is real. They explained why we can't discern subtle differences unless the comparisons are very close together (less than a second or two apart), and how easily our ears are fooled generally.
> I believe that I will try to contact Mr. Noxon to further clarify the
> numerical performance of the larger ASC bass traps.
Excellent! Art knows a truckload about this stuff, and his input will only enlighten us all.
> Geocities is closing ALL of their free web site hosting as of Oct. 26th.
Bummer. If you can justify even three bucks per month for a "real" web site, I've had great success with LunarPages.
--Ethan
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Follow Ups
- RE: Aye, cynical I am - Ethan Winer 09:52:23 10/23/09 (2)
- "But it's physically impossible to have more sabins of absorption than the surface area of a device." - David Aiken 13:44:52 10/23/09 (1)
- RE: "But it's physically impossible to have more sabins of absorption than the surface area of a device." - Ethan Winer 06:50:27 10/24/09 (0)
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