Equivalency of Roxul vs. Auralex

Hello, In doing research of acoustic pannels, I have run into a question regarding the acoustic ratings that each list. For example: Auralex Lenrd Traps 1.24 1.28 1.45 1.39 1.27 1.31 1.35 Roxul RHT80 4” 1.00 0.95 1.06 1.04 1.06 1.08 1.05 Are the specifications for the RHT for a full piece of panneling (2’ X 4’)? Or is it a per square inch, per square foot, etc.? Reason being, the Lenrd traps are 1’ X 2’, whereas, the RHT are 2’ X 4’. In order for me to get the same acoustic equivalency that the Auralex Lenrd Traps offer, do I need to use at least a 2’ X 4’ piece of RHT, or will slightly more than a 1’ X 2’ piece of RHT equate to a Auralex Lenrd pannel? Thank you!!!!!! Fred

Fred, I pitty to say, if I recognize that Auralex measurement (it's always good to give the links), that that Auralex measurement is worthless in this comparison if you intent to use it for corner absorption. And I can hardly imagine that you are going to use the LENRDs as measured in that report. That measurement need urgent update to make it compatible with the common nowadays measurement approach for corner absorbers. While I can understand why it historically is as it is, if Auralex does not substitute that within a reasonable time by another measurement, I call it a wittingly misleading document. This is known for quite some time already. And for me you or anyone can link Auralex to this post. PS: I checked: It's indeed this report: http://www.truesoundcontrol.com/literat ... /lenrd.pdf And I publically start doubting the honest intents of Auralex by not substituting this report, within a reasonable time, and all related/derived numbers used by their distributors. You can find a lot of useful absorption data on Bob Golds page: http://www.bobgolds.com/AbsorptionCoefficients.htm And I DO NOT ALLOW any other producer/supplier to use this post for commercial intents, in whatever direct or indirect manner, even when disguished as (pseudo) educational purpose.

matchless123 wrote:

Are the specifications for the RHT for a full piece of panneling (2’ X 4’)? Or is it a per square inch, per square foot, etc.? Reason being, the Lenrd traps are 1’ X 2’, whereas, the RHT are 2’ X 4’. In order for me to get the same acoustic equivalency that the Auralex Lenrd Traps offer, do I need to use at least a 2’ X 4’ piece of RHT, or will slightly more than a 1’ X 2’ piece of RHT equate to a Auralex Lenrd pannel?

Fred, second part: Both are absorption coefficients. The roxul is a mineral wool panel, likely flat measured on the floor. The LENRDs are measured in a similar manner, but are in fact corner absorbers, which isn't a very logical way to measure them since this measurement does not represent the use of the objects. An absorption coefficient is the absorption expressed in sabins (imperial) or A (metric) per surface unit. It doesn't matter if that are ft2 (imperial) or m2 (metric). One could say it's a percentage, hence 1.00 should be 100%, but that isn't true in fact because the Sabine method allows values higher than 1.00 But that's a complicated business. The higher the value the better. 0.80 in imperial means 0.80 sabin (= 0.8 sft equivalent absorption) per sft of physical covered surface. 0.80 in metric means 0.80 A (= 0.8 m2 equivalent absorption) per m2 physical covered surface. equivalent absorption is sometimes expressed as "open window" where the sound dissapears for 100%. Hence: 0.80 means that the absorption equals 0.8 sft "open window" per sft of covered surface (in imperial - adjust units in m2 for metric). A bit fun and nothing to worry about: The absorption coefficient of an open window is closer to 1.10 than 1.00 which is related to that complicated business I referred to. Hence the notion "open window", rather than "equivalent absorption", is more used as a generic notion to visualize the stuff. .

Fred, > Are the specifications for the RHT for a full piece of panneling (2’ X 4’)? Or is it a per square inch, per square foot, etc.? < Yes, this is exactly the problem with absorption coefficients - it doesn't take into account the size of the absorber. So a small device that might be effective if only it were ten times larger can appear to be "better" than a much larger device that would be a better purchase. What really matters is the total sabins of absorption a bass trap (or other absorber) offers. That is what determines how effective it will be when you put it in a room. Another factor is edge absorption. Depending on how the devices are measured, the one with more edge surface will seem better even if its not, because the absorbing edges are not accounted for when converting from sabins to an absorption coefficient. There's a good explanation of this in my Acoustics FAQ: http://www.ethanwiner.com/acoustics.html See the section The numbers game. --Ethan

Ethan Winer wrote:

There's a good explanation of this in my Acoustics FAQ: http://www.ethanwiner.com/acoustics.html See the section The numbers game. --Ethan

That explenation/section is WRONG. I don't start another discussion in order to get another closed thread. I explained that already before here at John Sayers and on many other spots. And Ethan knows VERY well I should reply to this. I have one HUGE disadvantage: I like physical truth and take people serious. Further I'm out, knowing what could follow.

Eric_Desart wrote:

That explenation/section is WRONG.

As far as I know it's quite correct.

I don't start another discussion in order to get another closed thread.

The reasons threads are locked and deleted is when people are unable to stick to the science. So let's stay focused on the science. Then maybe we'll both learn something useful. --Ethan

Thank you very much for both of your responses. Ethan, I got the info for the Roxul from their website: http://www.roxul.com/graphics/rx-na/can ... 6-2-06.pdf It does not specifically state if it is per inch, per pannel, etc. Thank you!! Fred

Fred, > I got the info for the Roxul from their website ... It does not specifically state if it is per inch, per pannel, etc. < Right, as I explained above, the amount absorbed is not for the full panel but is a proportional amount. In this case a panel 1 foot by 1 foot has the same stated absorption coefficient as a panel 2 feet by four feet, even though the latter really absorbs eight times more. --Ethan

Ethan Winer wrote:

Another factor is edge absorption ... See the section The numbers game.

Apparently my "early Alzheimers" got the better of me again. This was indeed resolved - nearly a year ago! See the last few posts in this thread, starting here: http://www.johnlsayers.com/phpBB2/viewt ... c&start=83 In the final analysis, diffraction accounts for less than 1/5 of the increase in absorption beyond 1.0, and the exposed edges as I describe in my FAQ section The Numbers Game accounts for the rest. Since my FAQ already explains that diffraction does account for some of the increase, this matter is resolved as far as I'm concerned. --Ethan

They're coefficients....they are supposed to be non-dimensional. I haven't looked at the published recommended test methods (I presume that they must be purchased, as that's how ASTM usually works), but something must be wrong if the coefficients are greater than one. Yes, I understand that edge area, and other effects come into play, but there is something inherently wrong with either the definition of the absorbtion coefficient, and or the standard test method (BTW, I did read your page Ethan...). The problem is that having something like an 'absorbtion coefficient' of 1 implies to me that all sound energy at that particular frequency is absorbed. If that were true, one could place the material in a small hole built in a very high isolation partition, and measure the transmission loss. Okay this might work for foam/2D absorbers...but not so well for traps where solid wall backings are required. It appears that absorbtion coefficient is measured by examining the change in reverb time/freq response, and that a coefficient of 1 doesn't really mean that it abosrbs all sound energy at that frequency, but is really more of a reference point. Maybe it would make more sense if absorbtion coefficient was normalized by the trap/absorber volume instead of frontal area. In the end, when you put this stuff in your room it is the volume that makes the difference to your useable space.... Food for thought... Cheers Kris PS: BTW, Ethan, ASTM is not a US organization as stated on your site, it's international....the A in ASTM is really there for historical reasons as it started as a US organization for standardizing the railroad industry. I beleive it became international in the 1930's or so.

Some links Measurement of Sound Absorption Edge Effect Acoustic Test Chambers and Environments

drfrankencopter wrote:

Maybe it would make more sense if absorbtion coefficient was normalized by the trap/absorber volume instead of frontal area. In the end, when you put this stuff in your room it is the volume that makes the difference to your useable space.... Food for thought...

Discrete objects as e.g. traps aren't expressed as absorption coefficients in function of frontal area but as sabins per physical unit. That's how the ASTM Standard RIGHTFULLY defines it.

Kris, > It appears that absorbtion coefficient is measured by examining the change in reverb time/freq response, and that a coefficient of 1 doesn't really mean that it abosrbs all sound energy at that frequency, but is really more of a reference point. < Could be. I always considered 1.0 to be 100 percent, even though the math guys like Eric and Jeff Szymanski are careful to say it's not really a percentage. This is from the first page Eric linked above:

The sound absorption coefficient is the percentage of incident sound energy that, rather than being reflected, is converted to other forms of energy such as heat.

If "percentage" is good enough for National Instruments, it's good enough for me too! > Maybe it would make more sense if absorbtion coefficient was normalized by the trap/absorber volume instead of frontal area. < This is exactly why I have been arguing for years now that sabins is the best way to assess bass traps meant for small rooms. AbsCo is great for ceiling tiles and foam on the walls. > BTW, Ethan, ASTM is not a US organization as stated on your site, it's international....the A in ASTM is really there for historical reasons as it started as a US organization for standardizing the railroad industry. I beleive it became international in the 1930's or so. < Very interesting. As I recall originally (4+ years ago) I said International in my FAQ and someone told me that was wrong so I changed it. Or maybe I'm hallucinating that? I thought ASTM is the American standards organization and ISO is the European equivalent. Or am I hallucinating that too? --Ethan

Ethan Winer wrote:

....This is exactly why I have been arguing for years now that sabins is the best way to assess bass traps meant for small rooms. AbsCo is great for ceiling tiles and foam on the walls......

Are you a comedian? That's just how the Standards are build up as long as they exist. Have you arguing this with the walls? Words .... words .... empty words ..... Diversion ..... diversion ...... diversion .... And No, Auralex has nothing to do with it ... There are SEVERAL threads here and elsewhere where I (and others) tried to get you to respect the Standards. You still don't. Incredible ..... I should write a book about this. I think you just want to keep this thread active by whatever means.

Eric_Desart wrote:

Are you a comedian?

I certainly hope so! I have many posts saved from years ago where I argued several points why ASTM C423 is not very useful for measuring corner bass traps. Most notably, products meant to be mounted in corners should be tested in corners. Likewise, third octave tests that go no lower than 100 Hz are pointless for products that are effective to 50 Hz and even lower. Especially when the fall-off in absorption occurs more rapidly than a third octave test can reliably show. Indeed, below 100 Hz is where the real action is, and that's what separates the men from the boys in bass trapping. I have also pointed out the failings of absorption coefficients in my Numbers Game piece. The related section Measuring Absorption also refers to the advantage of using sabins. > There are SEVERAL threads here and elsewhere where I (and others) tried to get you to respect the Standards. < I don't understand your point. Are you arguing that C423 is all we need, as you used to argue, or are you now agreeing with me that corner testing is more useful as I've seen you state recently elsewhere? > You still don't. Incredible ..... I should write a book about this. I think you just want to keep this thread active by whatever means. < That's what I meant when I said, "threads are locked and deleted when people are unable to stick to the science." Why would I want to keep this or any thread active anyway? What would I have to gain? I would very much like to see the name calling and personal accusations stop! But I can't control what others do, only myself. Other than that, I'm here to learn more just as everyone else is. --Ethan

Reminder for the ones who lost track: The discussion was about:

Eric_Desart wrote:

Ethan Winer wrote:

There's a good explanation of this in my Acoustics FAQ: http://www.ethanwiner.com/acoustics.html See the section The numbers game. --Ethan

That explenation/section is WRONG.

Wich is explained in the two links I provided: And confirmed by the Standard itself and lots of other literature. Lots to be found here in the forum entered by Bob Golds, and substanciated by official measurements I entered here in the forum.

Eric_Desart wrote:

Some links Measurement of Sound Absorption Edge Effect

Links handy/strategically avoided by Ethan Winer too busy explaining that topics get locked by people not sticking to the science, and other non-related and/or incorrect stuff.

Eric_Desart wrote:

Links handy/strategically avoided by Ethan Winer too busy explaining that topics get locked by people not sticking to the science, and other non-related and/or incorrect stuff.

Links handy/strategically avoided by Eric Desart where he admitted he doesn't really know how much of the increase over 1.0 is due to diffraction and how much is due to exposed edges. Yet he argues I'm wrong anyway! :roll: Again, this was settled nearly a year ago. Read this very carefully: Just under 20 percent of the increase is due to diffraction, and all the rest is due to the exposed edges. --Ethan

Sorry, There is and was nothing settled. One does not bargain science. And this is also not, and never was about exposed edges, but your frequency independent linear relationship with the edge surface of these edges, wich is the core of your published stuff. The edge effect relates to edges even in cases with lacking exposed edge surface     (Edit: added)

Ethan Winer wrote:

....Links handy/strategically avoided by Eric Desart where he admitted he doesn't really know how much of the increase over 1.0 is due to diffraction and how much is due to exposed edges. Yet he argues I'm wrong anyway! ....

That remark is so ridiculously much out of context. That remark, within its context, PROVED me a scientist and your use and attitude makes you a disgrace for the same.

Ethan Winer wrote:

If "percentage" is good enough for National Instruments, it's good enough for me too!

If a quote (even out of its complete context) serves your purpose, you use it, no questions asked, side comments made or boundaries drafted. If the much more extensive explanation about the edge effect on the same documents does NOT serve your purpose, even when directly related to the core of the discussion at hand, you ignore it completely as it was never written. That's how you traditionally handle science. And you're too stubborn to admit you lack any formal education to even understand this kind of acoustics. You entered the word "diffraction" on your pages as some kind of addition to cover your ass, after comparable discussions at SOS, where you showed having no idea what the concept was about. For me it doesn't matter what you think or believe. What does matter to me (and clearly not to you), is that you write and publish about stuff you don't know about, don't bother to study or read about, which is at the expense of many others. It is good to explain stuff to people in a simplified, easy comprehensible and accessible manner. However compressing things to their core, making them comprehensible and accessible for many people is an art AND a serious responsibility. Here are 2 options: 1) Explaining things in a simple stylized manner assumes an in-depth understanding by the Author himself. 2) Explaining things in a (pseudo) simplified manner can also be abused to hide that the Author himself doesn't understand what he's talking about. In this discussion clearly option 2) applies for you. I hope people will read between the lines, in their own interest, what really drives you, which has nothing to do with science, nor their interests. People can read that whole thread, you referred to completely, and the thread preceding that one (if remembering correct linked somewhere there, should check) Over and Out.

maybe Keith can come around and punch some lights out here... I've witnessed too much crap between Eric and Ethan to believe they will ever settle. sorry guys, I've got the utmost respect for you, but both of you are acting like kids. (unless a miracle happens and peace returns..) LOCK this please

Ro, I stay out, but maybe you could have done something constructive to solve or help solving such longlasting disputes which affects many, many people. Maybe I'm not the kid/child here.

It seem to me that the whole problem of coefficients above 1.0 arises because the amount of absorber installed into the test chamber does not cover sufficient percentage of the available exposed surface. The standards try to eliminate this by suggesting some minimum square footage of installed area, but perhaps it's not enough. In the end does it matter....I'm not sure, as long as there is an agreed upon (and publically available) standard test method, then I don't really see a problem. I do, however, think that the volume of a trap should be taken into account when considering it's performance. What matters to me as a home owner is 'how much useable floor space do I lose in order to gain some level of acoustic control?' Cheers Kris

From BBC RD 1992-11

The absorption coefficients of different thicknesses of RW2 Rockwool, with the edges enclosed by a chipboard frame, were measured in the ISO-Standard reverberation room at the BBC research department. The results of these measurements are shown in Fig.1

Fig 1 shows absorption coefficients as great as 1.4. No "Edge effect" because the edges are enclosed. Over 20% increase. Andre

Yes, but there are still inside edges...right? Sound can strike the absorber obliquely, and get reflected back through the absorber. I think that really the only way to take out the edge effect is to cover an entire wall (or ceiling or floor). The edges need to be made statistically insignificant compared to the exposed surface. Cheers Kris

Ro wrote:

both of you are acting like kids.

I prefer to address the acoustics stuff and not the personality parts, but I don't follow your logic here so I have to ask. What did I say in this thread that you consider inappropriate or uncalled for? Please start at the first post, and read each post in order. It's not a long thread and it will take you only a few minutes. Then let us know where you think the thread went sour. Thanks. --Ethan

Andre, > Fig 1 shows absorption coefficients as great as 1.4. No "Edge effect" because the edges are enclosed. Over 20% increase. < I have a few problems with your using that to show that diffraction accounts for all of the increase over 1.0 absorption: * The data doesn't show the same absorber tested the same way but without the edges screened off. Since we all know that acoustic data is, let's say, "fragile," without a control test having no screen this proves nothing. * The main increase over 1.0 is at 63 Hz, and we all know labs are not accurate that low. I bet if the same panels were measured a second time with nothing else changed the absorption could have been .90 or .70 or who knows what. That all the other higher frequencies hover around 1.0 proves my point. The paragraph beginning "Fig. 3 shows..." on page 2 confirms this, citing 315 Hz and higher as reliable. * Wood can be an absorber too! Especially at those very low frequencies. And so forth. Andre, here's the crux of it: Do you really believe that in a random incidence measurement, where sound arrives from all angles, that having 50 percent more surface area from exposed edges will have no, or little, affect at all? --Ethan