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In Reply to: RE: Room Acoustics newbie, hoping for some help from the pros! :) posted by Robo02 on May 06, 2009 at 13:17:02
I don't think those plots you link to are all that impressive.
They show a difference below 40 Hz but it's a very small difference, a little smoothing a few Hz above and below 30 Hz but only by around 1 to 2 dB or so, the before curve is already fairly smooth, and the decay is slightly faster, but they show virtually no difference at all above 40 Hz and most of our problems are above 40 Hz simply because there is little musical content below that. In my view a good product would be showing more effect as frequency rises above 40 Hz because it gets harder to get good results as frequency drops, and because you want the improvement extending over as much of the frequency range below 300-500 Hz as possible. Something that produces a small effect below 40 Hz and nothing above 40 Hz isn't a particularly useful product in my view.
I know a person with Cathedral Panels. He visited my place, was unimpressed with the appearance of my DIY traps, and raved about the Cathedral Panels. Late last year he borrowed my DIY traps to tryh, after I had replaced them with RealTraps, and he ended up buying half of them on the basis of his trial. He felt they produced a bigger improvement than the Cathedral Panels. The DIY traps in question were based on the design of Jon Risch's quick and dirty bass trap and they work out significantly cheaper than the Cathedral Panels.
With any other acoustic treatment product I know of that works into the bass range, what you find is that effectiveness reduces as frequency reduces, simply due to the fact that it gets harder to have an impact on the sound as the length of the wavelength increases. I have never seen plots, other than those in your link, which show effectiveness starting to kick in as frequency drops below 40 Hz. Even RPG who make a product which sounds physically similar in design to the Cathedral Panels, ie a panel with perforations for air flow, show plots for its operation which become less effective as frequency drops.
Sorry but the new plots look as suspect to me as the original plots, and the one person I know who has purchased Cathedral Panels has since found the traditional bass trapping approach significantly more effective than the Cathedral Panels, and cheaper also when the treatments are DIY.
David Aiken
Follow Ups:
I am the person David is referring to in reference to someone who tried his DIY bass traps in conjunction with the Cathedral Sound Panels.
I thought I should chime in to clarify a couple of points. Two of the DIY bass traps in the front wall corners , used in conjunction with 4 Cathedral Sound Panels ( two front and two rear ) did indeed improve bass definition or control . At no stage was any comparison done with and without the Cathedral panels in place. I viewed the presence of the DIY traps as an additive effect providing more control down deeper. The reason I haven't removed the Panels is that they work - I tried living with and without them several times in the past and always preferred them back in position. In fact after living with the DIY traps in place for a while, I eventualy removed them as I was losing too much impact down low. I find I actually enjoy bass that you can feel in your chest as well as hear, and I lost some of this impact with the DIY traps.
The Cathedral Panels appear to work better in the upper bass/mids and provide better focus without being subtractive i.e. no perceived dampening effect on the energy of the music in that area. I believe the guys at the Cable Co. have used all manner of traps in their listening rooms and they appear to have a strong preference towards the Cathedral Panels (whilst still recommending other quality traps) perhaps for this reason. I note all the fuss about measurement but one should carefully listen , simply because a lot of people have acknowledged the panels as making a positive difference. Then find the science to explain what is heard if one has a basic distrust of the design, or change ones testing methodology if the results don't match what is heard.
After reading further about the ASC tube traps and their implementation, I note a range of tube trap sizes is offered and the choice is left to the individual to ' tailor ' the bass control to suit. A larger or smaller tube trap is selected for the corners to achieve this, with the goal not necessarily being perfect measurement, but subjective listening preference. As an experiment, I then went ahead and split the larger rectangular DIY traps into four cylindrical traps, which obviously wouldn't perform as well at the deepest frequencies. On reinserting them into the two front corners and on floor/wall junction at rear, there was a better synergy with the panels without losing the 'bass that you feel ' effect. The full size DIY traps were damping too much deep bass in my case and were obviously performing a function the Cathedral Panels were incapable of. The smaller DIY traps gave a smoother sounding lower bass while preserving impact and bass foundation and were complementary to the Panels. I believe the Panels can be purchased on a home trial basis so there is nothing to lose and in my opinion complementary to other treatments.
Two things about the Cathedral Panels. In my experience:
1. They "kick in" at the frequencies where there are standing waves in the given room. Standing wave frequencies will depend primarily on dimensions of the room. The waterfall plot referenced in the previous posts exhibited standing waves below 40hZ, and so this is where the "after" plot showed improvement. This is called out in the text next to the waterfall plots.
2. They are very good children in the sense that they play well with others. They are complementary with other acoustic treatment products, whether this is traditional absorbing panels and traps, or diffusers, or three other products I find useful: the Shakti Hallographs, Synergistic Research Acoustic ART, and the old RoomLens.
For someone looking for an all out room-tuning, acoustical solution they are not a be-all, end-all product, but because they work on standing waves, and at the deepest bass frequencies, often the most difficult acoustic areas to address and requiring the most and biggest traditional "traps," they are a very good place to start. And if someone is only going to do one thing in a room, or isn't willing/able to fill the room with other types of acoustic treatments, this is a good, domestically acceptable "50% solution" where there is no prospect for going for 100% all out acoustic treatment.
I just think this is a very good and innovative product.
Go back and look at those plots you provided a link for. Where they are having an effect is on a couple of small ridges and valleys in the plots just above and below 30 Hz. Those are very small ridges and valleys in the before plot, nowhere near as extreme as the ridges and valleys shown from 60 to 130 Hz which are also standing wave behaviour and a lot more extreme. The panels did not kick in there.
It's hard to treat low frequency behaviour and it gets easier to treat as frequency increases. Any other product which showed some behaviour at 30 Hz or so like the panels purportedly do in those plots would show greater improvement at 60 Hz and even greater improvement again at 130 Hz but these plots show absolutely minimal change there. That simply doesn't make sense.
And if the panels really do "kick in" at the frequencies where there are standing waves, then they should be kicking in harder on the standing wave behaviour shown at 60 Hz and above than they are at 30 Hz or so. We should be seeing that rising response to the peak at 90 Hz being reduced somewhat and the irregularities above and below it should be smoothed somewhat like the smoothing of the ripples around 30 Hz.
I haven't said the panels do nothing but my feeling is that they certainly don't operate significantly at bass frequencies. They're simply too small to affect frequencies with wavelengths of the length of bass frequencies. I wouldn't be surprised to find they help tame some issues arising in the corner at higher frequencies and help reduce a bit of brightness, and a change that does that at high frequencies can be perceived similarly in some ways to a change which improves bass frequencies. Both can cause a shift in the balance towards the bass and an increase in the warmth of the sound and an easing of brightness, and that can certainly be beneficial in many rooms and systems.
As far as bass frequencies go, however, the change shown in those plots around 30 Hz is insignificant in relation to the sorts of changes shown in plots of bass traps made by ASC. RPG, RealTraps and others, all of which also show much better performance at 100 Hz than they do at lower frequencies whereas the plots for the panels show no real gains above 40 Hz and most of the bass problems in the before plot, and most of the bass problems in our rooms, occur in the region above 40 Hz.
Look for yourself, and compare those plots to the data and plots shown by companies like ASC, RPG, and RealTraps. Those plots you linked to do not show very good results at all, and the fact that they are basically showing results only below 40 Hz with nothing significant above that really does need explaining because that sort of behaviour goes against the behaviour exhibited by every other effective bass treatment product I know of including the RPG panels with similar construction to the Cathedral Panels.
David Aiken
> They're simply too small to affect frequencies with wavelengths of the length of bass frequencies <
Exactly David, and the same can be said of those tiny ART bowl things, and all other too-small "acoustic treatment" products. Not only at bass frequencies where the devices must be large to do anything useful, but even at higher frequencies where sufficient surface coverage is needed. A typical room has 800 square feet or more of mostly reflecting surface, and you need to cover some significant percentage of that to make an audible difference.
What some people fail to understand is that physics is not negotiable. People can wish as hard as they want for a small and WAF-friendly way to improve room acoustics. But it ain't gonna happen. Not now, not ever.
--Ethan
> They "kick in" at the frequencies where there are standing waves in the given room. <
Of course! How foolish of me. It's clear now that they work via magic. How else would they know where to "kick in" and absorb, and where not to absorb? Note that what those graphs claim to show is the result of absorption. Yet their earlier blurbs said they do not work by absorption. These guys really need to get their pitch together and not contradict themselves.
> three other products I find useful: the Shakti Hallographs, Synergistic Research Acoustic ART, and the old RoomLens. <
Yup, I'm sure you find those useful too. :-> )
--Ethan
While it is interesting to know "why" something works, in this hobby we often find out first "that" something works, and only later "why." I am not an engineer and am quite sure I am not going to be the guy that figures out the why of these various alternate approach acoustic products. I am just passing along information provided by the manufacturers, in addition to my own listening experience.
As for size, no doubt for the kind of products you make, Ethan, size matters a lot. All of the products I referred to, and you disparage as "magic," do work. Anyone with ears who is willing to listen can hear that. Obviously they must be working differently than the absorbing type panels you make otherwise they wouldn't work so obviously given their smaller sizes.
I asked the manufacturer once about the size of the Cathedral Panels. I was told that their size is the equivilent of the size of the opening when a standard door is open one inch. The analogy of the effect of the product being similar to the pressure-relieving effect of a door in the corner open one inch works for me.
Have a good weekend.
Well, that's interesting data.
Assume the door is about 6'6" high. An opening 1 inch wide translates to 78 sq in of opening, or 78/144 of a sq ft. An opening 1 sq ft in area provides 1 Sabin of absorption at all frequencies so we're talking about absorption of .5 of a Sabin and the recommended 4 panels translates to a bit over 2 Sabins at all frequencies. 2 Sabins of absorption in a room has little effect. You even get around 5 or 6 Sabins of absorption from a single empty Coke bottle acting as a Helmholtz resonator at its resonant frequency and no one notices a significant difference when there's a single empty Coke bottle in a room. We're talking small amounts of absorption here and small amounts have small effects.
And while the Cathedral Panels may not work by the same mechanism as an ASC Tube Trap or RealTraps Mondo Trap, the effect they have on what is happening in the room is measured in the same way and the results are expressed in the same units so comparing effectiveness in Sabins for all of those products is appropriate. So is comparing frequency response plots and once again I suggest that you compare the plots of the Cathedral Panels with those of the other products. Since those plots are what Cathedral Panels are providing in order to give you information, the comparison with similar plots from other products is appropriate.
The obvious thing, from the Cathedral Panel plots, is that you're not getting that reduction evenly over all frequencies, and not even over all frequencies where standing wave behaviour is occurring. If you were, the effect would also be visible above 40 Hz in the after plot, and it's not.
The other thing we know, from details at RPG's site where they give performance data for their perforated panels, is that the frequency response for their products is not uniform at all frequencies and not only does effectiveness decrease as frequency lowers but the effective bandwidth also depends on the diameter and spacing of the perforations. I think, unless you or someone else can come up with a reasonable explanation of how the Cathedral Panels can work in a different way to the RPG products, that we can assume that the mechanism of operation is similar and RPG are a very respected firm who have done an awful lot of research and development in the acoustic treatment area. Their products have a strong reputation and the reliability of their response plots for their products are well accepted. The first lot of response data for the Cathedral Panels was wrong, and their current plots don't show bass performance of the sort exhibited by any other product. That makes me suspicious of the current plots also, not to mention my reservations based on size.
If you also take a look at Vww's comments about his experience with the Cathedral Panels and with my DIY traps and his subsequent changes to them, I think you'll find that what his experience indicates is that the benefits he noted from the Panels was occurring at frequencies well above 40 Hz, and that he wasn't noticing benefits in the low bass. That's consistent with my supposition that they're actually working at much higher frequencies and that what is occurring is a shift in tonal balance towards one which favours the lower frequencies more and that people are interpreting this as an improvement in bass response when it's actually a taming and reduction of higher frequency problems.
Don't read the claims and accept them at face value without some thought. Look at their plots and compare them to those from other products, look at their statement that a panel is equivalent to a door opening of 1" and translate that into absorption equivalents and then compare that to the absorption data of other products. In particular, compare the data for the RPG perforated panel products to that of the Cathedral Panels because the RPG data is coming from a source with an extremely good reputation and a lot of experience and R&D to back that up, and is also relied on by professionals doing major acoustic products. Think about the differences in what the RPG and Cathedral Panel data show, and how every other product available becomes less effective as frequency drops and seriously wonder how the Cathedral Panels can show a small effect up to 40 Hz and nothing above that. Measure the frequency response of your room and see where the problems are and ask yourself whether a product which shows results below 40 Hz and not above 40 Hz is what you want in order to address those low frequency problems.
If you get an audible improvement from the panels, then fine. As I said, I do think they have an effect but I don't think that effect is occurring at bass frequencies and the comment about the 1" door opening equivalent doesn't change that for me. Their plots are still suspect in my view since there is no explanation for why they only have an effect below 40 Hz and that kind of behaviour simply runs counter to the behaviour of every other bass treatment product around including products with similar construction.
David Aiken
> An opening 1 sq ft in area provides 1 Sabin of absorption at all frequencies so we're talking about absorption of .5 of a Sabin and the recommended 4 panels translates to a bit over 2 Sabins at all frequencies. 2 Sabins of absorption in a room has little effect. <Yes, though 2 sabins is better than 0 sabins, which is what you get from Cathedral panels. There are no unknown principles by which too-small devices can improve room acoustics. Robo's comment that he is not an engineer is typical. The more one understands the science of audio, the less likely they are to fall for this stuff. And the more skilled one is at listening, the better they understand that everyone's hearing is very fragile and what we think we hear is not always valid.
What's really happening is known as placebo effect and expectation bias. If people who think they hear a change in sound from small devices like the Cathedral panels were blindfolded, all of a sudden they would not be able to tell when the devices were present or not in the room. Guaranteed. I'll even put money on it. A lot of money.
--Ethan
[edited to fix a typo]
Edits: 05/09/09
"There are no unknown principles by which too-small devices can improve room acoustics."
Sorry, but we can't know that. If there is an unknown principle, by definition we don't know about it or it wouldn't be unknown. People do make surprising and unexpected discoveries from time to time. Neither you nor I can think of how that could be the case in this situation but neither of us, nor anyone else, can claim categorically that it can not happen. Push me for odds on it happening and I'll come up with a number that's vanishingly small, as close to zero as I can make it, but it will be a finite number, not no chance at all. It has to be a finite number because we can't give that iron-clad guarantee that there is no such principle. We simply don't know what there still is to discover and we are going to be surprised by discoveries from time to time. History teaches that lesson rather well.
I also don't think it's necessarily nothing but placebo effect and explanation bias. I suspect they actually do something which is audible, but at much higher frequencies than the bass. I think they may be producing a slight shift in tonal balance favouring the bottom end or reducing a little top end brightness and people are interpreting that shift as an improvement in the bass when it's actually occurring at the other end of the spectrum. I suspect it's a small shift but we audiophiles tend to be sensitive to small shifts which often seem to have a bigger perceptual effect for us than the actual size of the "physical" shift would indicate. Small things can irritate us and removal or reduction of that small thing can seem like a huge improvement in some cases, not something commensurate with the small change that actually occurred. Of course, if we were actively chasing that change, we may also be psychologically inclined to exaggerate its scale as well, but that inclination need not be the sole determinant of what we hear and it may certainly not result in every such person exaggerating the effect by the same amount.
Certainly, what we think we hear is not correct but that does not mean that our hearing is basically unreliable. Our hearing is basically reliable and we happily rely on it without bothering to check whether or not we're getting it right unless something then happens to make us suspect we've made an error. In my experience we get it right in normal life most of the time, and I've yet to see someone come up with an account of why our hearing should be less reliable when listening to audio than it is under normal conditions. Of course, if one is actively listening to determine whether or not there is a difference and the difference either does not exist or is close to the limits of our hearing then we're going to be more error prone than if the difference is significant in size but that's true of all perception and while we may be more disposed to make a given type of error because of our personal dispositions when there is no difference or only a very small difference, the fact that we're so predisposed does not mean that we're going to get it wrong all the time under those circumstances. Errors definitely can and do occur and I've made a few myself over the years but on balance I think my hearing has been right far more often than it's been wrong. I wouldn't have an audio system and I'd be using a simple boom box to listen to music if I thought my hearing was as fallible as many people claim. There would be no reason to trust that I was getting it right on any of the differences that exist between the sound of a boom box and my system if my hearing was that fallible.
Anyone who invests significantly more in an audio system than the average person does, and probably everyone who posts on this board is in that position, is saying that they hear differences that they're willing to trust their ears on, regardless of whether or not they have test data to back that up. They may be extreme sceptics about cables or certain tweaks or a lot of things and they may not include those things in their systems but they do believe that the choices they do make in assembling their system do result in genuine differences and they trust what they hear regarding those differences. Everyone trusts their ears but some trust them more than others. The differences are often at the margins but people can and do have huge disagreements and disputes about what happens at the margins.
David Aiken
Sure David, there's always the unknown. But even if a new device type is discovered in the future, it still needs to be relatively large to have much affect. This is physics, which is well known. At least the sort of entry-level physics that applies to room acoustics.
--Ethan
Well, we believe size is a given and there are extremely compelling reasons for thinking so. A passive acoustic treatment can only act on the sound which actually falls on it, and the most it can absorb is all of the sound that falls on it. The only way we can get reduce size without compromising performance is by increasing effectiveness and there's always going to be a finite limit to what we can do there. Broadband absorption is the ideal for a couple of reasons to do with both impact on the sound we hear and also the fact that such treatments can be used in any room or space so that makes them a commercially more viable product for manufacture but they can never be more efficient than 1 Sabin of absorption per square foot of surface area. We can get more effective absorption than that from a device like a Helmholtz resonator but then we lose broadband performance and achieve maximum efficiency over an extremely narrow bandwidth of a couple of Hz at most.
And the Cathedral Panels are a passive acoustic treatment in the same way that my RealTrap panels are—they can only work on the sound falling on them. Their area is 11" x 16" which is 182 square inches so at most you could get 1.25 Sabins of absorption from a panel. Using the 1" door opening statement as an indication of how effective they're claimed to be, we're talking around .4 of a Sabin over an unspecified frequency range. If they're actually getting that at the below 40 Hz frequencies indicated by their plots they're doing extremely well but it's quite a trick to do that and have no effect above 40 Hz. That would mean that they aren't broadband in operation and if they're not broadband they're not going to be an effective treatment on their own because if we're going to treat, we need to treat over a wider bandwidth than just up to 40 Hz because modal problems occur over a wider bandwidth than that in every room.
The problem with the claims made for the Cathedral Panels is that if the claims are true and they are effective at controlling standing wave behaviour at frequencies up to 200 Hz, then the plots don't show what's going on because they should show significant benefit above 40 Hz, and if the plots do show what is actually going on, then the claims can't be true because the plots aren't showing significant benefit above 40 Hz even though the untreated room plot is showing standing wave behaviour there, actually more standing wave problems there than below 40 Hz. One assumes they show the best test data they have because you want to present the product in the best light so even if we accept the plots at face value, which I don't, things simply don't add up. The plots are showing something different from the performance claims being made, something that fails to support those claims.
David Aiken
Agreed fully on all points David, especially about the maximum possible benefit being limited to 1.4 sabins due to the small size.
--Ethan
You gotta love this forum. Pages of commentary on how and why something works or doesn't work, primarily between two people neither of whom have listened to the effect of the product being discussed.
Actually I guess it is "products" being discussed, because anything small in the acoustics realm is being dismissed at the same time (or at best given a probability of actually having value that is "vanishingly small, as close to zero as I can make it."). Which means that everyone who has used any of these products and heard a meaningful difference is deluded, including of course anyone else who dares to post.
Ask any carpenter what he thinks of engineers:-)
Now that is off my chest, let me respond to a few specifics:
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..."
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.
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.
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.
> two people neither of whom have listened to the effect of the product being discussed. <
I heard them in the lab room at my company's factory, so I know for certain that the Cathedral panels do not do anything useful.
> everyone who has used any of these products and heard a meaningful difference is deluded <
Deluded is a strong word, and I prefer to say "mistaken." But you're correct - some people think they hear a change even when there was no change. This happens all the time, and anyone who truly understands audio and how we hear knows this.
> 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. <
Even if that were true, which I doubt, the net effect would be improved peaks and nulls and ringing. As David said, "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."
I don't think much more can be said! :-> )
--Ethan
Oh really? Interested to hear all about your listening system in the lab room. I seem to recall seeing some photos posted on your site. If memory serves I saw the test equipment, but no hifi gear. Or are you saying you were listening to a test tone?
If all the people who use the product with music or theater systems like the results, and you listen to a test tone and don't, I will go with the people that listen to music/ theater, which includes me.
And anyway as noted in an earlier post, as I was told that the manufacturer did not feel your testing methodology was correct for this productt so "the manufacturer offered you the opportunity to retest using the appropriate methodology and you declined." I don't believe anyone is saying you did anything wrong in your test, or that the results from the testing methodology you used were in error, only that meaningful testing the Cathedral Panels requires measurement of a sustained tone or noise (to allow the standing waves to build up), rather than a tone/noise burst.
My terminology may be all wrong, but hopefully you get the gist of what I am writing.
Maybe this methodology is unusual in your experience, but this product functions differently from what you are used to.
> this product functions differently from what you are used to. <
Dude, you'd sound less like a shill for this product if you posted your real name and city. If you're unwilling to do that publicly, send me an email from my personal web site and tell me about yourself.
Otherwise you're just repeating the vendor's marketing prose, as if saying it often enough will make the claims true. You've already acknowledged that the related science is over your head. Perhaps you should quit while you're ahead?
Edit: Boy do I feel silly! I just clicked the link for your name and see that you're the sales rep for this product. Wow! So you shill for the product hiding (not very well) who you are, and you admit you have no idea how the product works. Wow, just wow.
--Ethan
Yes, Ethan, like duh, but the (D) next to my posting name means I am a dealer in this industry. Because we sell acoustic products including the Cathedral Panels, ASC, Echobusters, etc., I took your 2 year old critique of the Cathedral product and their documentation seriously and followed the earlier threads and exchanges between you and the manufacturer very carefully. I have been very direct with the manufacturer in this regard and they have been very forthcoming in return. I respect their responsiveness, willingness to acknowledge that the third party that ran the original, since withdrawn waterfall plots, goofed, and they didn't catch it (you did), and their willingness to offer even you, their most vocal critic, the opportunity to retest using a testing methodology that works with their product.
Why don't you address the questions (such as when you say you "heard them in the lab room at my company's factory" are you talking about hearing test tones or music?) instead of getting personal? I can get personal too if you insist.
I love the part too about my needing to quit because I am not an engineer. Hey, at least, unlike you, I have used the products I referred to (Cathedral Panels, Shakti Hallograph, Roomlens, Synergistic Research Acoustic ART, as well as the "conventional" ASC and Echobuster products). At least I admit what I don't understand, instead of insisting that if I don't understand it, it can't work.
Anyone is welcome to share their opinions, but you claim to be an expert, and you beat everyone up with it that has differing opinions (or, sob, who isn't an engineer). Don't you have to have basic experience with the products being discussed to be an expert on them?
So if I am a "shill" because I have actually used the products and like them, what exactly is someone who trashes them unheard because they don't fit your set of comfortable theories?
I don't "beat people up" when they disagree with me, at least not if their disagreement is legitimate. I've learned a lot over the years from people that disagreed with me. But this is not at all like that.
In this case the product is too small to be useful, even if it did work. But it doesn't work, so it's not even minimally effective. Claiming these panels work on "new physics" that defies the large body of current knowledge about room acoustics is sophomoric and disingenuous.
A good example here is Auralex LENRD bass traps. The absorbing material they're made from works well enough, but they're too small to target low bass frequencies. They still improve a room at least a little at higher bass frequencies, which can be easily heard and measured. Versus Cathedral panels that do nothing beyond placebo effect and wishful thinking.
--Ethan
Nobody called it "new physics." Quite the contrary, as was pointed out, the Venturi effect is very old physics. Since the first up when I Google it is Wikipedia, I will post that link below.
I think the only "wishful thinking" here, is your wishing that it didn't work because that would challenge your stuck in cement attitudes.
Assuming that your having avoided the repeated questions regarding your claim to actually have listened to the Cathedral panels means that in fact you did not listen to them, maybe you can stop repeating with emphasis that it doesn't work unless and until you actually have some listening experience with the product in the real world, by which I mean with a music or video system.
And if you want to test it in your lab, at least try the methodology suggested by the manufacturer. Just a thought.
Which leaves us right back with the fact that everyone who has posted on this product after having actually used it, and every reviewer who has actually reviewed this product, liked it.
Since this whole thread started with someone asking for opinions on his room, maybe we can leave it on this note, and suggest that if he is interested, maybe he can test with a money back guaranty - ask a dealer.
I know I am worn down by the whole interchange.
> I know I am worn down by the whole interchange. <
Ya think?
BTW, I did listen to music in the room that day with the Cathedral Panels in place and heard no effect. They don't work. They can't work. Wishing they work will not make it so. Convincing a few people that they work also does not make it so. Some people are convinced they heard an improvement after "demagnetizing" their vinyl LPs. That doesn't make it so either.
Okay, I'm done. :-> )
--Ethan
"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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