Scott R. Foster wrote:SoulFood wrote:I'm looking for some acoustic treatment for a home studio, but it has to be very portable, so any kind of acoustic pannels make sense...
Buy or make something light weight that is easy to hang or place to maximize portability. There are significant differences between products as to these attributes. For example the RT424 weighs less than 10 lbs.
With my very limited knowladge in acoustics, as far as I understand, The main difference is that ReadyTraps don't have a membrane. So they absorb higher freqs and could make a room more dead sounding.
Am I correct?
No!
The whole point of my original post here was to explode the myth purported by Glenn that magical qualities arise in "membraned" panels such as the MiniTrap with the result that HF is not absorbed.
As I demonstrated quite clearly - the HF absorption curves of the RT424 [a fabric wrapped 703 panel an analog of which can readily by be made by a DIY user] and the MiniTrap are stunningly similar - in fact in large part, they are precisely the same!
Scott, I think calling it a "myth" that needs to be exploded is a bit harsh and perhaps misses the point of how these materials work with regard to various broadband absorbers *in real world use*. For starters, the effects of kraft paper facing on the fiberglass absorbers is known, and is indeed discussed in some detail on pages 213-215 in Everest's "Master Handbook of Acoustics". To quote Mr. Everest:
"
Figure 9-29 compares the absorption efficiency of R-19 (6 inch) and R-11 (3.5 inch) with the kraft paper backing exposed and with the glass fiber exposed to the incident sound. When the paper is exposed it shields the glass fiber from sound above 500 Hz but has little effect below 500 Hz. The net effect is an absorption peak at 250 Hz (R-19 and 500 Hz (R-11), which may be important in room treatment. With insulation exposed there is essentially perfect absorption above 250 Hz (R-19) or 500 Hz (R-11)."
So . . . unless you wish to also accuse F. Alton Everest of perpetuating a myth, or call him a fraud (both of which you have accused Ethan of
repeatedly over the years), I'd say you'll need to be a little more fair in your accusations.
Further, your assertions that there is no substantive difference between the test results from different ASTM certified labs are not based in reality either . . . unless of course you would also like to call ASTM themselves a fraud. In addition to the graph Ethan posted above, which was originally supplied to us all in the above form by Bob Golds, there is very clear discussion of such differences in section 13 of ASTM's C-423 standards paper (available
here), which also states that you can get the supporting data for the ASTM E.33-05 Committee's round robin tests/research by requesting it from ASTM Headquarters. This is not an unknown fact amongst acoustics professionals -- not by a long stretch. I'd post the document up here, but I don't think it would be kosher to do so, given that these are coprighted documents which ASTM charges a fee to supply -- so it isn't in their or any of our best interests for anyone to do so.
ASTM standards do not cover every single issue that might come into play for certain things. This is particularly true with regard to corner absorption.
So, once again, unless you want to call ASTM, Trevor Cox and Peter D'Antonio (among others) all frauds who are perpetuating myths for commercial or other reasons . . .
Sorry . . . I don't really want to contribute to flame wars either (as you guys know I hate flame wars on forums as a rule, and feel they are highly counterproductive on every level), but I really felt these points needed to be made. Maybe now we can get back to discussing the science of things and perhaps even come up with some answers to the real questions at hand?
Don't be misled by attempts to divert the discussion to uncertainties of low frequency measurement... the original false proposition, and your question are about high frequency - and I assure the % uncertain measurements are miniscule from both labs in these frequency bands [less than 3% on average from 500 to 5,000 Hz for the RAL data - you can see these numbers yourself once I get the final reports posted].
Aside from what I feel is unnecessary aggression and accusations of fraud, etc. in the above statements (highly unproductive, perhaps quite hypocritical, and questionable as to the accuracy of the accusation in this case), it isn't clear to me exactly what you mean by this (i.e., less than 3% variation). Do you mean to say that these labs are both within 3% (at all frequencies in that freq. range) above or below the mean absorption coefficient of the 14 different labs that ASTM tested, as reported in the ASTM round robin tests? If memory serves, the data I've seen did not support this assertion. And, according to that data, RAL is known to report on the high side of the mean, and IBM is known to report on the low side of the mean. That said, I do not have the data to hand at this time. If you have this data, I would love to see it. If I'm factually wrong on this point, I'd be happy to be corrected. (Perhaps it would solve some long-standing arguments!)
Ignoring the lack of any ASTM standards for corners for a moment, without at the very least taking into account this data, it is not really legitimate to use test results from two different ASTM certified labs as a comparison of two different products. Far more accurate to test both actual products in the same lab under the exact same conditions. (I should also point out here, with all due respect, that Eric's quoting of Ethan to point out an apparent conflict in Ethan's statement misses its mark, because the quote was indeed taken out of context, and Eric's interpretation mischaracterizes the meaning of Ethan's statements in that particular article on his website. I can see why Eric might have read it that way, but his characterization in that case is objectively wrong, which is clear when the quoted statement is read in context. I'll be happy to explain further in another post if needs be.)
As to the corner testing issue -- once again, given that there is NO established ASTM standard for corner testing, and the fact that there could very easily be variables in the different rooms (even under ASTM standards) that could make for inconsistencies in corner testing, corner tests are the least accurate with regard to comparing the test results of two different products in two different labs. As one example, ASTM 423 standards do not dictate precise volumes and dimensions for these rooms. ASTM 423 prescriptions for size and shape consist only of what is stated in section 7.3, which reads thusly:
"
7.3 Size and Shape -- The volume of the room shall be no less than 125 m3. It is recommended that the volume be 200 m3 or greater. No two room dimensions shall be equal nor shall the ratio of the lartest to smallest dimension be greater than 2:1. (See 11.12 on calculating room volume.)"
Section 11.12 basically says that room volume must be calculated carefully, taking into account recesses and other irregularities that can make up for more than 1% of the room volume, and also states that, when testing specimens that take up greater than 1% of the room volume, the voume of the test specimen must be excluded fom the room volume.
That's pretty much it. So it seems to me that it ain't "rocket surgery" to figure out the many reasons why this lack specificity could allow for variations that could significantly affect low frequency test results, particularly in corners, even under ASTM standards as they currently exist -- and why it might not be such an easy thing to set up a standard for this across existing ASTM certified labs.
Even ignoring all of this, the only data you are supplying here is the data from corner testing. This clearly shows the peak around 100 Hz that we know is inherent to all corner absorbers (except, apparently, the FBM products, which are clearly utter crap compared to RealTraps and Auralex products from the comparative testing of these products Ethan did at IBM labs). That's all fine and dandy, but what interests me at least as much as (or perhaps even more than) the corner testing data is the data for tests for each of the products using A mounting and comparable E-## mounting I suspect these would be more accurate and usable indicators of the difference between the relative HF absorption and as to whether or not the "myth" of a difference between faced or unfaced rigid fiberglass absorbers is "fraudulent", or at least with regard to any differences in such behaviour in real world use of the products. This is the case especially because neither the MiniTraps nor the Ready Acoustics panels are intended to be used ONLY in corners, and we also know that the absorption peaks in at a different frequency range with these panels (at least the with regard to the MiniTraps, as well as other faced fiberglass absorbers).
This is also one issue I've had with the old arguments put up by you and Eric and a few others (if memory serves) from the Studiotips contingent that the MiniTraps are "peaky", because they can be (and are intended to be) used both ways, which means that using them in combination minimises or eliminates any significant problem of "peaky" absorption curves for these purposes. Unless I've missed something? I mean . . . if you've got problems ~250 Hz and below, put more MiniTraps in the room corners. If you've got problems in the 250-500-700 Hz range, put more MiniTraps on the walls. If you need more HF absorption, use HF MiniTraps (which do not have the facing/membrane, and therefore, according to lab tests done in the same labs under that same conditions, absorb more HF than the standard MiniTrap). Once again . . . it ain't rocket surgery.
Moving on further into the discussion with regard to real world use . . . I think one of the important points with regard to using rigid fiberglass panels with kraft paper or other similar facing material as a scrim, limp mass membrane, or whatever you want to call it (incidentally, F. Alton Everest does indeed refer to these as "membrane absorbers"), is that the facing/scrim/membrane does indeed reflect HF sound. If stand up close and sing into the front of a standard MiniTrap, you will hear the high frequencies reflected back at you, to a very similar degree as you would if you were to sing into a wall made of a plaster, cement or other hard surface . . . though if you listen carefully you'll notice that you do get a slightly different quality of the reflected sound (which I'll discuss further in a moment).
Now, if you turn the that same standard MiniTrap around and sing into the back of the panel (which does NOT have the membrane), you will notice a major difference with regard to the amount of HF sound that is reflected back at you -- this lack of HF reflection is the same on both the front and back surfaces of the HF MiniTrap, which does not have a membrane on either surface. Likewise with a typical DIY 703 or 705 panel (sans facing) wrapped in an acoustically transparent or absorptive fabric.
As I said, I will be interested to see the *full* lab test results (assuming you have also done the testing with E-## mounting standards) for your Ready Acoustics panels. If indeed your panels do show a similar absorption curve to the standard MiniTraps under this test standard, I might wonder if the fabric you are using on your panels is also acting to some degree as a scrim or limp mass membrane? I put that forward as a wild ass speculation only based on Eric's description of the fabric as having a "leathery sheen".
Just to be clear, by the way, I'm not saying any of this stuff to be in any way disparaging with regard to the validity, performance, usefulness, quality, value, etc. of the Ready Acoustics panels. Indeed I think they are quite nifty. To tell you the truth, I remember a number of years ago (before the Ready Acoustics products hit the market) thinking that it would be good to have a product that would allow people who didn't want to go whole hog with the DIY thing a cheaper, easier way to assemble their own rigid fiberglass absorbers that also wouldn't cost an arm and a leg to ship. I came up with a number of ideas, but nothing quite as nifty as the Ready Acoustics product.
Anyhoo . . . to take the conceptual discussion further, my instinct, along with my personal experience in real world use (in my own studio and in others) with the MiniTraps (both with and without the membrane), and experiments using the standard MiniTraps both face in and face out, tells me that there is definitely a difference in the subjective sound of the room (or at the very least at the listening position) between rigid fiberglass absorber panels with the membrane and such panels without the membrane. I've also had direct real world experience comparing the difference between a studio treated with DIY 703 panels (wrapped in fabric, no membrane and no frame) and the same studio treated with roughly the same number of standard MiniTraps (though in the end we used more MiniTraps, which did indeed offer additional improvement that was much needed, particularly in the low frequencies). The difference was not at all insignificant between the LF absorption of the DIY 703 panels and the increased LF absorption of the same number MiniTraps
In fairness, I will also point out that there were other factors that contributed to the difference, such as proper mounting (spaced from the wall) of the MiniTraps versus the various ways the DIY 703 panels were mounted in that room. However, there was still a difference in the amount of LF absorption between just tossing the MiniTraps in the room, unmounted, and having the 703 panels in that room, unmounted and similarly placed. FWIW.
Further, I experimented with treating the small vocal booth in this studio with MicroTraps, Standard MiniTraps, HF MiniTraps and the DIY 703 panels (and for good measure, I'll add that the guy had some FBM or other cheap knockoffs of the LNRDs, which, although they were of a *similar* type of open cell foam, offered noticeably piss poor absorption -- proving yet again that all studio foam is not alike!). This particular room was having the majority of its problems with ringing somewhere in the 200 to 400 Hz range (or possibly a bit lower -- I didn't actually run ETF or R.EQ.W tests on the room), and very little problem with HF ringing (due in part, I suspect, to some angled walls). I found that the MicroTraps (obviously) didn't touch the problem, either mounted in on the walls (with air gap) or across a corner. The DIY 703 panels did a pretty decent job, but the HF MiniTraps did a better job, and the standard MiniTraps did the best job for the low frequency ringing. Overall, I actually preferred the Standard MiniTraps over all in that room, because it left a nice, clear, but controlled presence (without excessive or problematic ringing) in the room for singing. The HF MiniTraps (and the DIY 703 panels) gave an overall deader sound in the room that was subjectively not as nice, either in the room or on recording. We ended up using the HF MiniTraps in the vocal booth anyway, because the standard MiniTraps were more needed in the control room.
What I'm getting at with all this (at long last
) is basically that, even if Scott's assertion that there is no difference (between the standard MiniTraps and the Ready Acoustics panels) in the overall level of absorption for X amount of absorption surface, this doesn't necessarily mean that there isn't a difference in the behaviour of these two devices that can result in a subjective difference at the listening position. (I keep using the term subjective, which may not be exactly the best/most precise term to use here, but I hope my meaning is clear?) I have a couple of explanations and theories (read semi-educated wild-ass guess for the latter term).
The MiniTraps absorb most, if not all, of the high and mid frequencies via the back and side surfaces of the panels, but at the same time allow a certain amount of reflection of the highs and mids off the front of the panel. So, to make a generalised/sweeping statement (subject to the obvious necessary conditions such as having enough of the things and having them properly placed) his allows for control of problematic/repeating/build-up of reflections of those frequencies, but still allows a certain amount of early reflections to reach the listening position. Further, it allows you put more MiniTraps in the room, as needed to control whatever troubles a particular room without preventing some needed reflection/reverb in the high and mid frequencies. I certainly would be less hesitant to substantially cover the walls (e.g., to the degree Ethan has in his home theater room) with panels that allow for the reflection of some highs and mids) than I would be to cover them in the same manner with HF MiniTraps or other unfaced rigid fiberglass absorbers that have an increased absorption in the highs and mids (or, in the words of F.A. Everest, "essentially perfect absorption above 250 Hz (R-19) or 500 Hz (R-11)").
Some theories I have (based on my experience with both the MiniTraps and the 703 panels and on my instinct) are as follows:
I think it's entirely plausible that attaching a membrane to the 705 (as is used the MiniTrap) allows for the whole panel (possibly also affected by the rigidity of the frame) to act in certan ways as a larger/thicker, heavily damped membrane. Given the increased density of the 705 over the 703, this might be more likely to occur (or to a greater degree) with the 705 than with the 703. One of the things that makes me think this is that, if you put your hand on the face of a standard MiniTraps and you sing (or shout) into into it, you can feel the trap itself vibrate (which vibration is very quickly stopped). So perhaps, among other things, this accounts for the difference in LF absorption between the HF MiniTrap (without membrane) and the standard MiniTrap. And, if memory serves, I seem to remember the HF MiniTraps not exibiting the same kind of vibration when I sang or shouted into them.
Another theory I have as that another difference in the reflected sound from the panel WITH the membrane (which I find to be ever so slightly sweeter/clearer, at least in my vocal experiments, than, e.g., the sound that is reflected back from a cement, brick or plaster wall) is that sound waves reflected off a hard surface are reflected 180 degrees out of phase with the direct sound waves, and sound waves that are reflected off a soft surface are reflected exactly in phase with the direct sound, as shown here:
http://www.kettering.edu/~drussell/Demo ... flect.html
In my own studio, I have MiniTraps completely surrounding my drums. I've also noticed that I prefer the sound of my cymbals (in particular) having the membrane side of the MiniTraps facing the direct sound. One of the things I notice is that the top end sounds ever so slightly sweeter to me than with the membrane side facing away from the direct sound.
FWIW.
As I said, the above theories are basically my own wild-ass guesses, and if there is a better scientific explanation regarding what is happening in any of those scenarios, I'm wide open to fair and productive discussion/education on any relavent scientifically based theories/concepts, etc. I put these things out there to (hopefully) add to and/or stimulate meaningful discussion that could be relavent to the questions posed by the original poster and some others in this thread (including SoulFood).
Erm . . . sorry for the preposterously long, windy post. I just had a few things on my mind that I thought might be relevant.
Hehe . . . holy smokes! After a second look I have to say that one was incredibly long . . . even by MY standards!
DOH!
:D 
