Control Room Construction

I do not lean towards the use of tuned traps, that would only be a last resort if I had a pesky frequency I could not deal with otherwise........ And no - the installation of a helmholtz trap does not make a 3rd leaf..... A tuned trap set right against a wall (as is typical for good reason) DOES - but due to their small relative size in comparison to the total surface area of the 2nd leaf - the effect (if any) is so small as to be almost non-existant. Rod

Hi Stuart, Thanks the reply. And my apologies for our heated argument in the other post... I haven't had much sleep lately!

Apology accepted! No problem. Glad to see that you are back in learning mode now! (Like me!)

Rod was saying in a previous post that he does this sometimes... that is, constructs a false wall to place acoustic treatment behind.

Yes, but his "wall" is just a piece of acoustic cloth stretch across a frame. It isn't really a "wall" at all. It just looks like one, but it has practically no mass, and no effect on sound. Sound just goes right through, as thought it was not even there. Visually, it looks like a wall, but acoustically it is transparent.

AFAIK

AFAIK means "As far As I Know". Abbreviation.

My guess is that placing slats on the front of a breathable false wall, such as above, will only reflect higher frequencies.

It will also create a slot resonator, which will absorb certain frequencies. The ones it is tuned to. See below...

Many of the materials I have read conclude that broadband bass traps are more efficient in the long run... as peak and nulls occur at all frequencies... not just at room resonances.

I wasn't talking about room resonance: I was talking about the tuned resonators that you show in your drawing. If you put wooden slats over a sealed airspace, you have created a slot resonator, whether you intended to do that or not! It's a type of Helomhotlz resonator, and it will be tuned to a certain frequency, or range of frequencies, depending on how it is built. If the slats are parallel to the wall, then it will be tuned to one specific frequency band. If the slats are angled away from the wall, then it will be more broadband, covering a wider range of frequencies. The center frequency is governed by things like the depth of the wood slats, the size of the slots between the slats, the depth of the cavity behind the slats, etc. If you have several slats with different dimensions, then you can treat several bands at once with one resonator. So what you are doing by placing slats in front of your hangers is to combine a tuned bass trap (the hangers) with a tuned resonator (the slots and slats). That's why I said you would be compromising both of them. The slot resonator will be tuned to one frequency or band of frequencies (by the dimensions of the slats, gaps, cavity, etc.), so the loudest sound inside the cavity will be that frequency band. The hangers will be tuned to another frequency or band of frequencies (surface density of the panels, etc). The frequency band that the hangers is tuned to will not be the same as the band that the slots are tuned to, so neither of the two treatments will be efficient. I think they will both work, but they just won't work efficiently. At least, that's the way I see it. I might be wrong on that. - Stuart -

I was talking about the tuned resonators that you show in your drawing.

Are you referring to the acoustic hangers... or the slotted false wall?

So what you are doing by placing slats in front of your hangers is to combine a tuned bass trap (the hangers) with a tuned resonator (the slots and slats).

I can't remember me saying that the acoustic hangers were tuned.

The slot resonator will be tuned to one frequency or band of frequencies (by the dimensions of the slats, gaps, cavity, etc.), so the loudest sound inside the cavity will be that frequency band. The hangers will be tuned to another frequency or band of frequencies (surface density of the panels, etc). The frequency band that the hangers is tuned to will not be the same as the band that the slots are tuned to, so neither of the two treatments will be efficient. I think they will both work, but they just won't work efficiently.

The concept is similar to a Membrane Absorber... additional treatments can be placed behind the membrane to broaden the Q of the trap. Thus, if the hangers are not tuned, I don't think these would deduct from the traps effectiveness. Alternatively, one could stuff the whole thing with glass wool... as is common with membrane absorbers.

If you have several slats with different dimensions, then you can treat several bands at once with one resonator.

The idea is to splay the false, slotted walls, much like the image below: Any additional treatment placed in between the false wall and MSM system is to broaden the Q.

The idea is to splay the false, slotted walls, much like the image below:

Those are not "false, slotted walls"! They are the inner leaf of a MAM system, just like you suggested when you first posted that image. If you wanted to install false walls, or slot resonators (I don't see how you can have one wall that is both "false" and "slotted" at the same time!), then they would go WITHIN the room that is defined by those walls on your diagram.

Are you referring to the acoustic hangers... or the slotted false wall?

They are both tuned. And that is not a false wall: if it is a slotted wall, then it isn't false. If it is a false wall, then it isn't slotted. Two different concepts. A false wall does NOTHING to the acoustics at all. It is totally transparent to sound, and has no effect on it (or to be more accurate, the minuscule effect that it does have is irrelevant). A slotted wall, by definition has an effect on sound, therefore it is not a false wall.

I can't remember me saying that the acoustic hangers were tuned.

You didn't have to say it! It goes without saying. They are tuned, whether you want them to be or not! How do you make hangers? You take a piece of wood (or other similar material), and wrap it in insulation. The wood will have a resonant frequency. Hence, the hanger is tuned. It may be a very broad, low level resonance (wide Q), or it may be a very narrow, sharp peak, but it WILL be resonant. A hanger works because it vibrates. If it did not vibrate, it would not work very well. It vibrates best at its resonant frequency, hence it is tuned. - Stuart -

Those are not "false, slotted walls"!

Yes. They are. I posted the image again ONLY to illustrate the intended CID. NOT to show the entire design of the room.

And that is not a false wall: if it is a slotted wall, then it isn't false. If it is a false wall, then it isn't slotted. Two different concepts. A false wall does NOTHING to the acoustics at all. It is totally transparent to sound, and has no effect on it (or to be more accurate, the minuscule effect that it does have is irrelevant). A slotted wall, by definition has an effect on sound, therefore it is not a false wall.

Fine. I'll call it a slotted wall then... if that makes you happy.... It really doesn't matter what you call it. Refer to it as a banana if you want... the concept behind my idea is what I was trying to get at... NOT the name.

You didn't have to say it! It goes without saying. They are tuned, whether you want them to be or not! How do you make hangers? You take a piece of wood (or other similar material), and wrap it in insulation. The wood will have a resonant frequency. Hence, the hanger is tuned. It may be a very broad, low level resonance (wide Q), or it may be a very narrow, sharp peak, but it WILL be resonant. A hanger works because it vibrates. If it did not vibrate, it would not work very well. It vibrates best at its resonant frequency, hence it is tuned.

Stuart, obviously everything has a resonant frequency... BUT In relation to acoustics... An absorber with a wide Q, and thus a wide frequency response, is called broadband. An absorber with a narrow Q, and thus a narrow frequency response, is called tuned... because it is tuned to a specific frequency (or small range of frequencies). You will find this in ANY acoustics educational material. Rod:

I do not lean towards the use of tuned traps, that would only be a last resort if I had a pesky frequency I could not deal with otherwise........

So, if what you saying is correct.... does that mean that Rod doesn't use any traps!?!? Haha...

Fine. I'll call it a slotted wall then... if that makes you happy.... It really doesn't matter what you call it.

Actually, it absolutely DOES matter what you call it! That seems to be a big part of your troubles here: you keep referring to the same things with different names, different things with the same name, switching names, using the wrong names, then you expect the rest of us to know what YOU meant when you said it! Either that is a slotted wall, or it is a false wall. It cannot be both. It's like saying you have an opaque transparent window. Accuracy is paramount. Even in using the right words.

Refer to it as a banana if you want... the concept behind my idea is what I was trying to get at... NOT the name.

It looks like you didn't get enough sleep again! :) Well, we already get the concept you are trying to put forth, and we keep on commenting on it. But the issue seems to be that you don't like the comments, and you want things to work in ways that they don't actually work, so you keep on trying to present the same concept wearing different disguises, hoping that maybe one of the disguises will hide the underlying issues enough that nobody notices! You seem to think that your concept actually will work, if only you spray-paint it the right color and decorate it with pretty beads and a smoke-screen! Sorry, but I'm just calling it the way I see it.

In relation to acoustics... An absorber with a wide Q, and thus a wide frequency response, is called broadband. An absorber with a narrow Q, and thus a narrow frequency response, is called tuned... because it is tuned to a specific frequency (or small range of frequencies). You will find this in ANY acoustics educational material.

I said something to the contrary? You can waffle all you want about frequency ranges, but the fact remains: your hangers work as BASS traps because they are TUNED to BASS frequencies. Period. That's what they are designed to do: resonate at bass frequencies. How else do you think the could absorb bass, if they are not tuned to bass? And your slots will work as mid range HELMHOLTZ resonators, because that's what they are, and the frequencies they are tuned to are MID range. Period. So, if you stick a BASS trap in a cavity where MID RANGE frequencies predominate (such as the interior of a Helmholtz resonator, for example) then there just won't be much BASS in there for your BASS traps to absorb, now will there? Sure, there will be SOME bass in there, but since it is a Helmholtz resonator, then most of the bass stays outside, and what stays INSIDE really, really well will be the mid range frequencies that your slot resonator is tuned to. Period. If you want an analogy in terms of light, you are basically saying that you want to put up a blue filter at the front, and then a red filter behind it: That won't work, because the BLUE filter only lets in BLUE light. There won't be any RED light left for the red filter to work on! I can't put it much clearer than that.

Rod: I do not lean towards the use of tuned traps, that would only be a last resort if I had a pesky frequency I could not deal with otherwise........

So, if what you saying is correct.... does that mean that Rod doesn't use any traps!?!? Haha...

Huh? How did you get to that conclusion from anything I said? I can't say that I've seen Rod promoting the use of bass hangers inside Helmholtz resonators, which is what YOU want to do! I said nothing at all about what Rod can or cannot do: Nothing I said would lead anyone with an understanding of acoustics to say that you cannot use traps to treat a studio! What I said is that if you do what you suggested, placing tuned bass hangers in a cavity that is tuned to a higher frequency, neither of the two will work efficiently. Unless you tune them both to the same frequency range, then you just CANNOT get the effect that you think you can get. On the other hand, if you DID manage to tune them both the the same frequency, then you'd probably get spectacular absorption at that frequency. but of course, that isn't what you are talking about. What you are talking about is putting BASS traps inside a MID-RANGE trap, and wanting them both to work efficiently. It ain't gonna happen. Both will work to some extent, but neither will work efficiently. Rod does NOT mount his bass traps behind slot resonators (AFAIK!), which is what you want to do. He mounts them behind false walls, which is something totally different. Like I said before, a false wall is for aesthetics only: it has no effect on acoustics, which is why Rod's bass traps actually do work at peak efficiency, they way he designed them to work. If he were to seal them up behind a sheetrock wall, they would still work to a certain extent, but much less efficiently, simply because they are no longer exposed to the full sound field inside the room: they are in a difference acoustic space now. All that they can work on is what is left of the sound after it gets through the sheetrock. The exact same situation occurs in your case: you are placing your bass hangers in an acoustic space which does not "see" the full sound field of the room, since it is tuned to only a certain range. You cannot beat the laws of physics. You seem determined to prove that you can use the same space with multiple treatments on it to treat multiple things at once, and the simple truth is that it CAN work under some circumstances, but NOT the ones you have presented so far. If you do not believe me, then just do a real physical test, in a real lab. Build one of your devices in an actual acoustic lab, and measure the results. - Stuart -

There seems to be too much of a communication barrier between us, Stuart. Thus, I think it may be better to just place this thread in the cupboard. We don't understand each other. I think I'm going to stick to educating myself via books/reports for a little while... get up to scratch on a few things. Although I have already done a lot of reading... I think I may have missed something. Thanks for trying to help Stuart. :) Andy

If you want an analogy in terms of light, you are basically saying that you want to put up a blue filter at the front, and then a red filter behind it: That won't work, because the BLUE filter only lets in BLUE light. There won't be any RED light left for the red filter to work on!

Stuart, A final thought... From the information I have read, I don't think you can use the light analogy for all frequencies. This can apply mainly to high frequencies, where ray acoustics apply. However, physicists say that this approach does not work when considering lower frequencies, as they're characteristics are quite different. So, using your analogy, low and high frequencies are completely different 'types' of lights. Also, it is common to place a reflective surface on the face of a bass trap... in order to reflect high frequencies. Just because the reflective surface effects high frequencies (in your words, a 'blue' filter), does not mean that the materials behind the thin reflective material will not effect low frequencies (in your words, the 'red' filter). In fact, this is the basis on which a Membrane Absorber works. Just a thought... :D

Andy, in all sincerity, the communication problem doesn't come from my side. Communication is what I do for a living, most of the time. I think I've explained things about as clearly as is humanly possible, albeit perhaps not with Rod's diplomacy and tact. Those never were my strong points. Regarding your comments on the light vs. sound analogy, it stands as an analogy, which is what it was intended to be. I guess you didn't notice the post where I explained that your confusion about rays and waves is simply a matter of scale, not a matter of inherent differences. Sound waves behave as sound waves at all frequencies. The mathematical equations that you use to describe the behavior of sounds hold true at all frequencies, from sub-sonic to dog-whistle. You do not need different equations to describe how the wave from a bass guitar moves, as compared to the wave from an electric guitar, or from a violin. The equations hold true for all sound waves. The reason why you can use rays to describe propagation at higher frequencies is simply due to scale. The much shorter wavelengths at high frequencies make it easier for us, as humans, in our normal scale of things, to pretend that they are rays. But they are still sound waves, and still behave as such. If you place an object that is small IN RELATION TO THE WAVELENGTH in the path of a high frequency wave, then that wave will bend around the object as though it were not there, in the exact same manner as a longer wave bends around a larger object. So while a high frequency will bend around something the size of a matchbox or smaller, a low frequency needs something the size of an 18-wheeler to get the same effect. That's the difference. You are look at scales with differences of three orders of magnitude, but waves behave the same at both ends of the spectrum. All that changes is the scale. Bass waves do not behave inherently different than treble waves do: they just behave on a scale that is a thousand times bigger, so you can THINK of them acting differently, since YOUR scale as a person leads you to do that. But the waves don't care about your perception of their size: they still behave the same. If you want to take things to extremes, a recent paper in Science magazine (I think it was Science: I may be wrong) mentioned that "sound" waves have now been detected with wavelengths of hundreds of lightyears, moving through interstellar gas where supernovas have exploded, and these waves are behaving in exactly the same way as the note from a flute. The only difference is that you'd need something the size of an entire galaxy to refract those waves, whereas you can refract the wave from your flute with your shoe. So, once again, thinking about higher frequency waves as rays, is simply a matter of mental convenience, making it easier to visualize how they behave in an spaces whose dimensions are very large in comparison to the wavelengths, such as a human-sized room. You can think of them as rays, but they are still waves, and still behave as waves. The only difference is scale. Scale up your point of view and your objects by a factor of one thousand, and kick drum waves behave exactly like piccolo harmonics do at normal room scales. Getting back to the point: I just cannot comprehend what it is about the situation with your multi-purpose, tuned-trap-within-a-tuned-trap that you are having trouble grasping. It is not hard to visualize. It is not hard to understand that bass traps act on bass frequencies because they are tuned to bass frequencies. even though you don't seem to agree, and want to argue about Q and bandwidth, the fact remains that bass traps are called bass traps because they are tuned to bass frequencies in order to trap bass. It is also not hard to understand that slot resonators are in fact just another form of Helmholtz resonators, and that the air inside the cavity will resonate in the frequency band to which the resonator is tuned. It is not hard to understand that, at the scale you show, the slots will be tuned in the mid range, well outside the frequency of the bass hangers. So it is also not hard to to understand that the hangers will be exposed mostly to frequencies which they cannot absorb, and will be exposed very little to frequencies that they can absorb.

Also, it is common to place a reflective surface on the face of a bass trap... in order to reflect high frequencies.

Usually, simply wrapping the insulation in plastic is plenty good enough for that. And I beg to differ that it is "common practice". It is only done when it is needed. If the room is bright enough already, then it won't be done simply because "it is commonly done". As Rod has explained to you endlessly, he normally covers his bass traps with acoustic cloth, which is of course acoustically transparent, not reflective at all.

Just because the reflective surface effects high frequencies (in your words, a 'blue' filter), does not mean that the materials behind the thin reflective material will not effect low frequencies

I would hardly consider large solid wooden slats to be "thin reflective material"!!!

In fact, this is the basis on which a Membrane Absorber works.

Then I guess they must have changed the principle for membrane absorbers since I last checked: I've yet to see one built like a slot resonator!

I guess you didn't notice the post where I explained that your confusion about rays and waves is simply a matter of scale, not a matter of inherent differences.

Confusion? What confusion? I am only going by what I have read in books far more highly esteemed, than your opinions. Well, you try and tell that to F. Alton Everest, or even a Physicist. See if you can convince them.... This is essentially what you saying... "Oh yeah, all frequencies are the same... Gamma-rays, X-rays, Ultraviolet light, visible radiation, microwaves, and radio waves are all the same... Just because the have different frequencies, and different wavelengths, doesn't meant they are any different." Ok, Stuart, well how about you try and take an X-Ray with Microwaves? Or how about you try and see some radio waves? Maybe use gamma-rays as radio waves? Why not?... They are all the same? Right? Radiation is the same... as the difference, just like sound 'waves', is in the frequency, and thus the wavelength. Of course, you can say, "Well, microwave radiation is just ultraviolet radiation, at a lower frequency, and with a longer wavelength." OF COURSE IT IS! But BECAUSE of that lower frequency, and longer wavelength, it reacts differently to ultraviolet radiation. So to reiterate, yes, there is a scale, but the scale determines it's characteristics... THUS there are major differences throughout the scale.

Andy, in all sincerity, the communication problem doesn't come from my side.

Well, this shows how much you know about communication. Communication is a two-way street Stuart. I've been to Rwanda a few times... but I didn't go around saying, "Oh no, they don't speak my language, so they have a problem." - And I'm sure the Rwandans didn't think, "Oh no, he doesn't speak my language, so he has a problem" The fact is, communication is about finding an equilibrium, where both parties come away better-off then before. I didn't go around trying to prove that the Rwandans don't speak English, and vice versa. The fact that you've replied in such a lengthy and defensive manner, proves that all you are concerned about is being 'right'. You can try and convince me about frequencies being "all the same"... "just at different ends of the scale" ... etc. But in all honesty, I think I'll stick to what F. Alton Everest says on the subject. So tell me, Stuart, who should I believe... Some who has, and has been: - BSc in EE, Oregon State; EE Stanford - Professor, Oregon State and Hong Kong Baptist Universities - 25 years film production - 15 years consulting in acoustics - 4 years in wartime research in undersea acoustics - Published over 20 books on audio and acoustics - Emeritus Member of the Acoustical Society - A Life Member of the IEEE - A Life Fellow of Society of Motion Picture and Television Engineers - Member of Audio Engineering Society - Co-Founder and Past President of American Scientific Affiliation This ^ person spent his entire life writing articles and books in an effort to assist learning on a large range of subjects. Or... should I believe: - A translator. Who's interest is obviously not assisting learning, but proving himself right. Even though I may be wrong, this is not the point... but in any case, I feel I will learn more, and in a better clarified condition, from F. Alton Everest..

There certainly is truth in the old saying: "You can lead a horse to water, but you cannot make it drink". I'm not quite sure how you managed to get electromagnetic waves confused with sound waves, but I guess that says a lot, in and of itself! Wow. Like I said, Andy, I'm not about to get into a long and pointless pissing match with someone who refuses to learn, and only wants to promotes his own "paper", part of which is plagiarized anyway. So fine, carry on thinking whatever you want to think, and I'll simply suggest what I have suggested several times before that you should do, with your weird and wonderful ground-breaking acoustic designs: test them, then post the results. Go to a lab, build your treatment, test it, then post the results. That, in itself, would be fascinating. Another saying comes to mind: "There are none so blind as those who refuse to see". So please do have fun with your plagiarized delusional manner of mangling both the physics of sound and the meaning of words, but don't expect further responses from me: I have far better things to do with my time than to try to teach someone who refuses to learn. I'm sure you'll probably post a few more comments on this thread, trying to pretend that your understanding of acoustics is perfect, and that everybody else is wrong, and trying to defend your plagiarized "paper" as being perfectly fine and acceptable, but nobody here is buying that anyway, and after maybe two or three additional posts you'll realize the error of your ways and stop posting uneducated drivel, and go back to studying real acoustics so you can learn how sound actually works in real life, rather than in your imagination. At least, I hope that's how it works out. I won't be bothering to try to teach you any more, since you seem to be unteachable. - Stuart -

I'm not quite sure how you managed to get electromagnetic waves confused with sound waves

HAHA! Three posts ago you were relating acoustics to light... which ARE visible electromagnetic waves. Hence, another reason why I don't listen to you... I was using it as an ANALOGY... just like you did. BUT.. you don't understand that visible light is only a small fraction of the EM spectrum. And in that spectrum, there is range that goes from radio waves (low frequency, long wavelength) right up to gamma-rays (high frequency, short wavelength). So the fact that you were talking previously about 'light' filters... means that you were talking about a specific frequency range, and a specific range of wavelengths... in the small spectrum of visible radiation. Here's what you said in your post about 'light':

If you want an analogy in terms of light, you are basically saying that you want to put up a blue filter at the front, and then a red filter behind it: That won't work, because the BLUE filter only lets in BLUE light. There won't be any RED light left for the red filter to work on!

That's correct. But... Radio waves, microwaves, ultraviolet waves, x-rays, and gamma-ray waves WILL go through both filters... as they have no regard for the wavelengths/frequencies of visible radiations. If they did, we would be able to see radio waves, microwaves, etc. In other words... a radio wave doesn't give a bucket of frogs for your 'red' or 'blue' filters. It will go straight through it. Thus, this proves my point... Different wavelenghts, different frequencies... behave differently... They do in the EM spectrum, and they do in the frequency spectrum... If they did not... why would physicists use wave and ray acoustics?? You can blabber on all day about 'scales' - but the fact is, they are at that point of the scale for a reason, and thus we must see them as such. The reason they named, radio waves.. radio waves, is for a reason...

part of which is plagiarized anyway

If my paper is plagiarized, then everything you have said is also plagiarized... because obviously you read it at one stage from a book. (or did you? perhaps you just made all this up? ... it would certainly make more sense.) Getting information from various sources... then writing it in your own words... is NOT plagiarism. Likewise, in the cases that I may not have used strictly my own words... you are legally allowed to reproduce 10% of any book, article or material. Besides, I posted that DRAFT about a month or so ago... it was a collection of ideas and references from other sources... I hadn't even started properly laying it out yet. I have changed pretty much everything (aside from diagrams) since. So don't get so bitchy mate. I think it's hilarious that you ignored essentially everything I addressed in my last post. Just shows you don't know what your talking about... And for the record.. if I wasn't keen on learning... would I be here? Would I have posted this? Would I be writing this reply? Would I have responded to Rod? Don't think so.

"legally allowed to reproduce 10% of any book, article or material." http://www.copyright.com.au/info%20shee ... cences.pdf This is an International issue, with digital conversion being part of the mix. As I understand it, the law sides with the Nation of origin. Just something to think on while you two figure out another way to take this sideshow up to another level.

Haha, cheers man. Yeah, i think the rules change again. Because it's an educational paper (as part of an assessment), and will most likely never see the light of day. As I said previously, we should definitely place this thread on the shelf. It has most certainly done the rounds.

Hey guys, Have been reading through MHoA again.. and found a very interesting sentence.

Unused spaces above control room ceilings and between inner walls and outer shells are often used for trap space.

Master Handbook of Acoustics, Chapter: Absorption of Sound, Page: 205 Now Rod has already pointed out that when Everest speaks of an outer shell, he is in essence speaking of an MSM system. However, Everest also mentions in this sentence an 'inner wall', moreover, that bass traps can be placed between the outer wall (MSM) and the inner wall (?). It has also been pointed out that a false wall would not attribute another leaf to the system... however I imagine it would be a significant error not mentioning that it is in fact a false wall of which he speaks... and not, for example, a stud wall. For, if he is talking about another stud wall... then this would present another leaf to the system... Unless of course, Everest assumes that the reader knows that when he speaks of a wall inside an MSM system, he naturally means a false wall?? Any thoughts guys? Cheers, Andy