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In Reply to: RE: Aye, cynical I am posted by Ethan Winer on October 21, 2009 at 07:29:51
Ethan wrote:
"I didn't link to my company's site, I linked to my personal site. Just as you link constantly to your personal site."
A: OK, you are correct on this, I saw the link to www.ethanwiner.com, and thought it was a link to a subset of your retail site. I also thought that www.ethanwiner.com had links to the retail site. I was wrong about that, and I apologize for the misunderstanding.
However, your comment that: " You delete my posts because you don't like what I have to say about the science of acoustics. " is wrong, it was a misunderstanding, which I do regret, for the simple reason that it does give the impression that I was somehow after you personally.
I am completely in agreement that science should be the basis for acoustic absorbing devices, but as Mark Twain once said: "There are lies, damn lies, and statistics." Science too can be slanted or manipulated to present one POV or another in a more positive light, simply by the omission of certain information, or the failure to disclose all of the conditions of a measurement or experiment.
Ethan wrote:
"Jon, that's a lie and you know it. If you can find one place where I said tube traps are worthless, I'll send you $1,000."
Later he wrote:
"We measured two 4-foot high by 20-inch tube traps in the certified reverb room at IBM's lab, and the tube trap had 4.70 sabins of absorption. Now, compare that to your claimed anonymous source of 14.9 sabins for a 20-inch tube only 3 feet high, and you'll see why I call BS."
So you didn't come out and say the words that you thought the tube trap was worthless. But in this very post, you make claims that first, the data I posted was BS, and 2nd, that the absorption of a 20" tube trap is only 4.7 sabins. Isn't that, in effect saying that the tube trap is worthless compared to a panel? Especially since you claim much more than that for one of your 2 foot by 4 foot panels?
Let's look at YOUR claim in a little more detail.
1st, the data I posted in the first section of my post, was, as I clearly stated, from "The Master Handbook of Acoustics", 3rd Ed. by F. Alton Everest, on page 413. As I noted, this data is not the same as the data shown at the ASC website, as it is shown for an entire 3 foot trap, as opposed to the data at the ASC site, which shows the absorption in Sabins on a linear foot basis. Thus, the data at the ASC site would have to be multiplyed by 3 for a 3 foot trap, 4 for a 4 foot trap, etc.
The data in the "The Master Handbook of Acoustics" is not identical to that at the ASC site, even after this multiplication has been performed, thus my belief it is a third party measurement.
I do not know for sure that it is third party data, but in order to dismiss this data, you would have to essentially be dismissing Mr. Everest and his book. While some folks might be inclined to go along with your hand-waving attempts to dismiss me, I think they would have to think twice before doing so with regard to Mr. Everest.
I also note that the data for the 20" cylinder trap is the same as the data for the 16" trap, I went with the same data for the 20" tube trap, so I wouldn't be using the ASC data. I don't think that is an unreasonable assumption, or an unreasonable extrapolation of one set of data to another. It also happens to jibe closely with a set of data for the ASC traps I got off of an acoustics forum some years ago, but that particular site is no longer available.
In any case, you do not cite what frequency this 4.7 sabins represents.
If it is 63 Hz, I thought that you just said that no labs were certified for such measurements?
This would be poor performance in the low bass, if true. But it doesn't jibe with what we DO know about the tube traps, if we just stop and think one minute.
If we allow that the data in the "The Master Handbook of Acoustics" is even close to correct, then how could the 20" trap have so many less sabins of absorption than the 16" trap? Mr. Everest says that the 16" trap has 14.9 sabins at 63 Hz. You say that at some unidentified frequency, a four foot high 20" diameter trap is only 4.7 sabins.
Let's look at another aspect of the 20" trap. Even if it had only a 1" thickness of high density fiberglass in it's cylindrical shell of absorbing material, then via it's circumference and a height of 3 feet, this amounts to a surface area of 15.7 square feet. The surface area of one side of a 2 by 4 foot panel of fiberglass is only 8 square feet.
A four foot tall 20" diameter tube trap has 20.94 sq. ft of surface area.
Not like the tube trap is lacking for sheer material, so the 4.7 sabins is sounding pretty unbelievably small at this point.
Ethan wrote:
"I won't say you lied about the data you posted, but it's clear you do not understand how acoustic products are measured."
A: I'm not calling you a liar, but you must be stupid? Isn't that cute.
I understand perfectly well how the acoustics products are typically measured, but more importantly, I know how they are actually used, and what the results will be in a room.
I intended to cover some of this in my other posts on bass traps, and will.
But wait, Ethan wrote:
"So I'm pretty sure I'm not the one lacking credibility here."
Well, so much for acting like a gentleman and talking about science and acoustics from Ethan. He plays the authority card, and wants us all to know how many articles he has written.
I am not exactly a back-woods hick when it comes to acoustics. I earn my living designing and voicing pro loudspeaker systems. One of the more recent projects I headed was the Peavey Versarray 212 and 112 modular line array systems. The Versarray 112 recently won an award from Live Sound International magazine
See:
http://www.prosoundweb.com/article/the_envelope_please_meet_the_winners_of_the_2009_readers_choice_best_produc/P2/
I designed the very well regarded Versarray 118 and 218 subwoofers, and the 218 utilizes the patented UniVent air exchange vent cooling system, US patent #6,549,637, my invention. It is a unique and fundamentally new way to utilize a vented cabinet to cool the speakers, as well as to linearize the speaker.
So I am not exactly a klutz when it comes to acoustics either.
So far, you have one undocumented, private number that you have thrown out as your proof.
As near as I can tell, there is no data currently given on Tube Traps at your web site either. I recall that you used to have such data, but then, you probably don't want to talk about that either.
I think that folks will just have to keep in mind that I do not sell or make any monetary gain from acoustic absorbing devices, nor does the company I work for. On the other hand, you DO sell acoustic absorbing devices, and have a particular POV to defend, as well as a vested interest in trying to show up competing products. The ASC tube trap is a competitor, and sales of these devices, or DIY builds of them, WILL directly impact your products sales.
I am not going to continue a "back-and-forth" with you on this subject, I think that it will lead no where, and be counter-productive.
I will continue with my series of posts on bass traps versus simple wall panels, and call a spade a spade. I hadn't intended to directly mention you, your products, or your company in those posts, and still don't.
However, if you continue to attack me, or keep posting very questionable "data", then I may be forced to respond to some of those particular instances, if nothing else, to keep the real truth from being obscured or covered up by a smoke screen.
Good day,
Jon Risch
Follow Ups:
> OK, you are correct on this, I saw the link to www.ethanwiner.com,
> and thought it was a link to a subset of your retail site. I also
> thought that www.ethanwiner.com had links to the retail site. I was
> wrong about that, and I apologize for the misunderstanding.
Okay, thanks Jon, I'm glad that's straightened out. It's still a bit exasperating to me, because we discussed this by email at least a year ago.
> I am completely in agreement that science should be the basis for
> acoustic absorbing devices, but as Mark Twain once said: "There are
> lies, damn lies, and statistics." Science too can be slanted or
> manipulated to present one POV or another in a more positive light,
> simply by the omission of certain information, or the failure to
> disclose all of the conditions of a measurement or experiment.
Yes, but if you think I did that, or I think you did that, then we can have a calm discussion and either prove or disprove the validity of what is claimed by talking it through. As you know, I've done an awful lot of testing, both in a real acoustics lab (six times), and in my company's "lab" room (dozens of times) using ETF and REW software to assess comparative differences as described in my S&V article linked previously.
> So you didn't come out and say the words that you thought the tube
> trap was worthless.
Yes, I never said that, or anything like that, so again it's exasperating to be accused of something I did not do. I like tube traps! I really do. I don't think the smaller ones are as good as a thick 2x4 flat panel, but at 20 inches in diameter tube traps are excellent.
> But in this very post, you make claims that first, the data I posted
> was BS, and 2nd, that the absorption of a 20" tube trap is only 4.7
> sabins. Isn't that, in effect saying that the tube trap is worthless
> compared to a panel? Especially since you claim much more than that
> for one of your 2 foot by 4 foot panels?
I thought I made it clear that I was talking about 63 Hz only. I know I stated that no US lab I'm aware of is certified to measure that low, and people should take with a grain of salt both your data and mine. But for now let's overlook that labs are not certified that low, or are even repeatable that low, since all we have is what was reported.
When mounted straddling a corner, my company's MiniTraps measured just under 3-1/2 sabins at 63 Hz. This is for 2 by 4 foot panels placed in the best locations possible. Looking at the tube trap sabins graph in Everest's book (page 487 for the popular 4th edition), it is claimed that a 16-inch diameter tube trap has about 15 sabins of absorption at 63 Hz. 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! So even if 1-inch thick 703 rigid fiberglass could absorb 100 percent at 63 Hz, which we all know it cannot, the highest value theoretically possible is 12.56 sabins:
(16 x 3.41 x 36) / 144 = 12.56
My best guess is that data was for five or more tube traps, and they were not measured in corners. The standard ASTM C-423 lab test demands at least 60 square feet of surface area placed flat on the floor for valid and certified results. So if the data in Everest's book was measured in a lab, it's likely the numbers are for the entire batch of traps rather than only one.
Maybe you can email Art Noxon and ask him to chime in? I'd like to know more about that data too.
> in order to dismiss this data, you would have to essentially be
> dismissing Mr. Everest and his book.
That doesn't make sense. Are you suggesting that 1) Alton Everest is infallible, or 2) even if he's a crackerjack acoustics expert, it's impossible for him to ever make a mistake? Further, I wouldn't be surprised if Alton didn't even write that section. Other sections involving commercial products were written by the product creators, such as the section on ETF written by Doug Plumb. Regardless, I doubt this is fraud or incompetence, just failure to state the test conditions clearly enough.
> So I am not exactly a klutz when it comes to acoustics either.
Okay great, so now we can both stop insulting each other. :-> )
But for god's sake Jon, please stop deleting my posts. Okay? Whatever your true motive, deleting countering opinions just makes you look insecure.
> there is no data currently given on Tube Traps at your web site
> either. I recall that you used to have such data, but then, you
> probably don't want to talk about that either.
Again with the insults. I took that down a few years ago out of respect for Art Noxon. Art is a terrific guy and he makes a great product, and I didn't think my comparison was fair. I had compared products that cost the same, rather than were the same size. So this pitted one of my full-sized MiniTraps against one of his small diameter quarter-rounds.
> I think that folks will just have to keep in mind that I do not
> sell or make any monetary gain from acoustic absorbing devices ...
> sales of these devices, or DIY builds of them, WILL directly
> impact your products sales.
Of course, but that doesn't mean I'm wrong or lying. I'm sure I explained this to you in the past when I told you the difference between my personal and business sites:
Even though I sell acoustic products, I feel so strongly about the importance of acoustic treatment that I continue to host and update my Acoustics FAQ and give out free DIY advice in several dozen forums every day. I would much rather someone buy from a competitor, or make their own treatment, than do without.
> I will continue with my series of posts on bass traps versus simple wall panels, and call a spade a spade.
Jon, I really wish you would do some testing of your own rather than rely on disparate data from disparate sources which simply cannot be compared fairly. Here's the link again to my S&V article that explains all of the issues:
Alternative Test Methods for Acoustic Treatment Products
I would love for you to compare various panels and tubes, capped and not capped, filled and not filled, and report the data here. Heck, if you do some valid tests, I'll give you some space on my personal web site since you mentioned you plan to drop your site soon.
--Ethan
Ethan,
Thank you for a reasoned reply.
I just have one comment, and one correction.
First, regarding:
"When mounted straddling a corner, my company's MiniTraps measured just under 3-1/2 sabins at 63 Hz. This is for 2 by 4 foot panels placed in the best locations possible. Looking at the tube trap sabins graph in Everest's book (page 487 for the popular 4th edition), it is claimed that a 16-inch diameter tube trap has about 15 sabins of absorption at 63 Hz. 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! So even if 1-inch thick 703 rigid fiberglass could absorb 100 percent at 63 Hz, which we all know it cannot, the highest value theoretically possible is 12.56 sabins...."
A: We both know that there ARE absorption coefficients that go above 1, this happens all the time, and it can either be due to measurement 'artifacts', or other acoustic absorbing actions, such as diaphragmatic sheets or barriers included in the absorbing device, or a combination of the two. The tube trap does indeed include such a diaphragm, in the form of a perforated metal barrier in the earlier retail traps, and later on, in the form of a limp plastic sheet which seems to have minute perforations in it. I know this because of being present when some traps were dissected by an interested party (who sought my advice on how to effectively put them back together without having "broken them"). Thus a tube trap can achieve an absorption coefficient greater than 1, and indeed, the data at their web site shows this, with the absorption coefficient reaching greater than 1.4 at middle bass frequencies.
Data at ASC's site shows a 20" trap reaching an absorption coefficient of 0.94 at 63 Hz. Using the surface area I calculate for a 4 foot tall 20" diameter trap of 20.94 sq. ft., this would equate to 19.68 sabins, for a single trap.
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? You apparently use that same greater than 1 absorption coefficient data to calculate the Sabins to reach 14.88 at 400 Hz.
There doesn't seem to be any disclaimer, or "correction" to an absorption coefficient of just 1.
You cite an absorption of 3.5 sabins at 63 Hz when your mini-trap in in the corner, but we don't know that the tube trap was measured this way, in fact, 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.
Nowhere in my edition of "The Master Handbook of Acoustics" does it say that the measurement represents more than one tube trap, or a corner measurement.
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. Yes, it does SOMETHING, especially when you compare it to nothing, but it is not doing the same thing as what I consider a bass trap to be doing for the control of the lower bass room modes, and the smoothing and defining of the bass musical notes.
So I believe that I will try to contact Mr. Noxon to further clarify the numerical performance of the larger ASC bass traps. While I am satisfied with the numbers I have seen, I wouldn't mind getting further reinforcement of that data.
Finally, regarding my website, Geocities is closing ALL of their free web site hosting as of Oct. 26th. For some reason, I was remembering it as this Friday, which is only the 23rd. I want to re-locate my site to another (free) host, but just haven't had the time yet. Maybe this week end, if I get the time.
Jon Risch
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
This is only true for some devices.
Everest quotes research showing that a single Coke bottle absorbs 5.9 Sabins at 185 Hz. Of course that's a Helmholtz resonater with a very narrow absorption bandwidth but a single Coke bottle doesn't have a surface area equivalent to 5.9 sq ft or more.
Mechanism obviously plays a part in how much some devices can absorb. Porous absorbers like panel traps do seem to be limited to a theoretical maximum absorption equal to their surface area in square feet but pressure absorbers are also absorbing by another mechanism. I have no knowledge of any data for the efficacy of absorption via a process of pressure equalisation but I do think it is possible that a tube trap may absorb more Sabins than it's surface area, at least over that part of it's operating range where it is working as both a pressure and a porous absorber.
David Aiken
Good point David. In the case of a Helmholtz resonator, the turbulence at the mouth is very high. At least I think turbulence is the right word. I'm not a physicist, I only pretend to be one on the Internet.
So the net effect is sort of like a horn loudspeaker, where the horn is an impedance transformer. Or like a megaphone that "passively amplifies" (there's an oxymoron for you) by restricting the frequency response.
--Ethan
possibly out of place but also possibly of relevance to panels.
When I was first starting to read up on acoustics and get interested in DIY stuff in my room, I was working in the health and safety area and being asked for info about noise and hearing related stuff. I was sent a test report for a workstation panel system, vertical panels mounted on a frame that supported a desk surface on either side of the panel with the panel acting as a workstation divider. The absorption coefficients measured for the panel were well in excess of 1.0.
I couldn't figure this out but then, rereading the report again, I noticed that the panel had been placed somewhere in the middle of the test room and the penny started to drop. I forget the panel size but I had calculated the area by multiplying height by width. In the location in which the panel was measured, the panel had 2 sides exposed to sound, not one. The actual surface area "collecting" sound was twice the area I had calculated. Using that total area the absorption coefficients came back into line with what I had expected. I phoned the company producing the panels and spoke to one of their people who said that was what was going on.
So, while a tube trap will have surface area as Jon has calculated because the other side of the fibreglass is sealed inside the trap, a panel spaced away from the wall is actually going to have a larger surface area than indicated by height and width alone because both sides are effectively exposed if the panel is spaced away from the wall by spacers that don't block sound access to the space behind the panel.
So I just think it's worth commenting that the issue of what constitutes surface area is going to be a little different for a sealed tube trap than it is for a panel with both sides exposed, even if the exposure to the rear side is only a relatively narrow gap. I would expect a panel with a one sided surface area equivalent to the exterior surface area of a tube trap, both using the same thickness of the same material, to measure slightly better than the tube trap *IGNORING BENEFITS FROM THE PRESSURE TRAP MECHANISM OF THE TUBE TRAP* (ie considering only absorption from the material used) due to the fact that both sides are exposed.
The amount of extra benefit gained by the panel as a result of absorption of sound impinging on the second side is going to depend on placement and I have no idea how much it adds but I definitely think it will add something. Of course it isn't going to extend the lower frequency of the panel's operating range but I expect a panel with both sides exposed is going to be more effective than expected and absorption coefficients significantly above 1.0 are going to be possible. If I remember correctly, the coefficients I was concerned about with the workstation panel I mentioned were around 1.6 in the vocal frequency range which was, of course, the frequency range of concern in an office setting.
David Aiken
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