Ceiling as a broadband/bass absorber approach.

I'm thinking of stuffing rockwool between the floor joists in my basement for the the acoustic benefits since I have a such a low ceiling (6'6'). I already have a layer of 1/2" drywall screwed to the subfloor between the joists. Would I get some decent amount of isolation doing it this way compared to not having rockwool stuffed in it?

Due to lack of response I'll take that as a no. I thought since it was absorptive that it would make a noticeable difference in isolation since the sound would have to travel through 6" of it.

Well, I'm not surprised you didn't get any replies! You didn't exactly provide a lot of information to go on! But in general, yes, absorption on/in your ceiling is a good thing. It might be a good thing, depending on other aspects of your room, and depending on what you are trying to achieve with that room, and depending on how it sounds right now. Without knowing anything abut that, all that anyone can say is that usually it is useful. Your question is something akin to asking "Is it a good idea to put salt on my food?" The answer depends on so many things that all one can say is "Usually, people do put salt on their food". The above is a polite way of reminding you that if you want meaningful answers to your questions, then it would help if you asked meaningful questions. - Stuart -

Yea I guess I could give a bit more info :D I'm building a recording studio in my basement. The bedrooms are on the second floor of the house and the kitchen is on top of the tracking room on the main floor. I'm interested in treating the tracking room this way. I would like to have the whole ceiling as dead as possible so I don't get any nasty reflections for when I'm tracking and also get some extra bass trapping. I want to stuff 6" of rockwool in between the joists (the floor joists are 7" deep) to achieve this. I want to do this if I can get a decent amount of isolation out of it as well so I don't drive my roommates too crazy haha. It doesn't have to be completely sound proof and it's ok if there's a bit of lows leaking up. I'm wondering from anybody's experience on here if there's a noticeable difference in sound isolation with rockwool stuffed in between the floor joists and covered in fabric to the floor above compared to not having anything in between them.

I'm wondering from anybody's experience on here if there's a noticeable difference in sound isolation with rockwool stuffed in between the floor joists and covered in fabric to the floor above compared to not having anything in between them.

Nope. Rockwool is not meant to isolate sound. It doesn't do that very well at all. You seem to be confusing the concepts of "isolation" and "acoustic treatment". They are two totally different animals. Not even the same species! In order to isolate, you need mass and density and stiffness. That isn't rock wool. Rock wool is a great ABSORBER, but a lousy ISOLATOR. It might sound counter intuitive, and you are thinking that if it ABSORBS sound then it must also STOP sound from going through, but that simply is not the case. Think of a bath sponge: It measures maybe two inches by four inches, and it is a great water absorber. Nothing better for mopping up water. But I don't think you'd consider using that sponge to plug a two inch by four inch hole in your bath tub, where all the water is leaking out! Same principle with sound. rock wool is great for "mopping up" sound, but lousy at stopping it. You don't want to try using rock wool to stop sound getting through your ceiling, for the same reason you don't want to use sponges to build a dam! It won't work. In order to stop sound, you need the same kind of stuff that you use to stop water. What do the use to build dams? Yep: Concrete. ie. solid, massive, dense stuff. Mass stops water, and it also stops sound. Now, I'm not saying that you need concrete in your ceiling (it would work very well though!), but you do need mass. Sheetrock (also called drywall, gypsum board, etc.) is also massive and dense. And cheap! So if you need to block sound going up through your ceiling, then you can attache a couple of layers of sheetrock to the sub-floor above you, up there between the joists. Do it carefully, cut the sheetrock to the exact shape so that it is a tight fit, and seal it around the edges with caulk. Hold it in place with cleats, as caulk is not strong enough to keep it from falling out. But STOP! BEFORE you so that, you need to make SURE that you can do it safely. Attaching two or three layers of sheetrock is going to add a lot of mass to the floor above you. That's the hole idea! You need to add mass. But you also need to get a structural engineer to check what you are planning to do BEFORE you do it. Your joists might not be able to take that extra weight, and it would be very sad to have a great sound-isolating ceiling up there, but then have it all come down on your head. Get a qualified structural engineer to tell if you can do this. Do NOT do it until he gives the go-ahead. And don't just listen to a buddy who helped build a house once: get a qualified structural engineer to look at your joists and floor, and tell you (in writing) if you can hang a few hundred extra kilograms of sheetrock under it. But STOP! You are not done yet. That mass will help, but it isn't enough. If you are going to be tracking things like drums and bass and electric guitars, then you also need to put something called "resilient channel" across underneath your joists, and then attach a couple MORE layers of sheetrock underneath that: The structural engineer needs to consider the weight of that too. Plus the 6 inches of rock wool that goes up in the gap, between the joists. Plus the ADDITIONAL six inches of rockwool that you now need to attach BELOW the last layer of sheetrock, which is your acoustic TREATMENT. The other six inches (above the sheetrock, between the joists) is part of your isolation, but it is not part of your bass trapping or treatment. That rockwool is up there to act as an acoustic damper in the resonant cavity between your new sheetrock ceiling, and the pieces of sheetrock that you attached to the sub-floor above you. That rockwool is part of the mass-spring-mass isolation barrier that you just built above your room, but it is not part of the the acoustic treatment that you need to build inside your room. You need another layer or rockwool for that. I hope I helped you to understand the difference between "isolation" and "treatment". They are two very different things. If all you want is "treatment", to give you a dead ceiling for your tracking room, then fine, just stuff some rockwool up there, and it will work quite well. But it will do nothing at all to isolate your room. You will still hear people walking on that floor, and dropping things, and talking, and the radio and TV. And they will certainly hear your drums and guitars and singers! Sound goes both ways: if you can hear them, then they can hear you. You cannot have a one-way sound barrier, any more than you can have a one-way sponge! So, if what you want is "isolation" between the two areas, such that sound cannot get through, then you need mass plus a rockwool-filled-air-gap plus more mass to do it. Treatment is not isolation. Isolation is not treatment. Rockwool in the joists can be part of the isolation, or it can be part of the treatment, but it cannot be both. (Yeah, guys, I know! That isn't strictly 100% accurate, but please don't jump on me!! I'm just trying to give the guy the general picture...) - Stuart -

Hi Stuart I must disagree i the isolation vs absorbation thing. We all knpw that energy cant be used up, it can only be converted. I the case of a porous absorber the acoustic energy is converted into heat. So how can come noise to the other side of a wall amde of porous absorbers which is converted before? The frequency range of isolation of a pure absorberwall is related to the absoberthickness, and the absorbation characteristics of the material. that`s my view of the problem. but nobody wants to have a 10m thick wall :wink: cheers Mika

mika wrote:

but nobody wants to have a 10m thick wall :wink:

That is it in a nutshell. Andre

I must disagree i the isolation vs absorbation thing.

So why did you bother putting sheetrock on your walls then? Why not just hang fiberglass across the room, from ceiling to floor and wall to wall, if that will do the job of isolation? Sorry, but you are wrong. Absorption is a very inefficient way of isolating sound, due to the wavelengths and energies involved. Mass or vacuum are the only ways of preventing sound getting from "A" to "B" efficiently, and six inches of rockwool or fiberglass has neither. If you do not believe me, then place a six-inch thick piece of rockwool in front of your speaker while it is pumping out 120 dB of pink noise, and see how well it blocks the sound.... All it will do is attenuate the highs a bit, but the lows will come right on through, as loud as ever.

We all knpw that energy cant be used up, it can only be converted.

Then again, it can be reflected back to where it came from, which is what mass does.

I the case of a porous absorber the acoustic energy is converted into heat.

Very inefficiently, and also selectively. A bit better at high frequencies, not so at mids and lows (depends on the material, of course).

The frequency range of isolation of a pure absorberwall is related to the absoberthickness, and the absorbation characteristics of the material. that`s my view of the problem. but nobody wants to have a 10m thick wall

Actually, if you wanted to do it with full wavelength absorption alone, for the entire spectrum, it would need to be more like 17 meters thick, and even then there are no guarantees... Thanks, but I think I'll stick to an inch or so of sheetrock, rahter than seventeen meters of rockwool... In any event, six inches of rock wool is not going to to much to ISOLATE the sound going up through that floor. It won't add much useful mass to the floor, and it wont add another leaf, which is what the question was actually about. - Stuart -

Be it that this may be off topic, but I feel it necessary to address your attitude Stuart. I've only been on this forum a short time, but in the time I have been here, all I've ever seen from your posts is negativity and a know-it-all attitude. Telling someone that they're perspective on a topic is 'wrong' doesn't help anyone, and makes you seem like a real jack ass - in my point of view. The purpose of this forum (and any forum) is to LEARN. It's not a contest of knowledge, and it is CERTAINLY not to prove each other right or wrong. Acoustics is an extremely interchangeable subject, and approaches must change wether we are talking, for example, large or small room acoustics, rays/waves, etc. Again, if you simply want to revel in your abundance of 'correct' knowledge, I suggest you write a book. You can call it: "The Right Way for Acoustic Treatment". But for the sake of creating an inviting and 'learner-friendly' environment on this forum, I suggest you have a think about your approach to answering questions. Nothing personal. Andy

Tell you what, Andy, if you see me say something that is acoustically incorrect, or give somebody downright bad advice, then feel free to correct me, and add a link to a research paper that proves your point: Otherwise, I think I'll just treat your comment with the contempt it deserves: If you don't like my attitude, nobody is forcing you to read my posts. feel free to ignore them. - Stuart -

I'm not talking about information being incorrect or correct. And yes, I do think - 'no, your wrong' - is bad advice. For some strange reason you seem to bring everything back to isolation. Here is my opinion... Firstly, not everyone is as concerned as you may be about isolation. In my instance, I live out in the bush, so the only reason I would be overly concerned about isolation, is if the kangaroos start to complain. Secondly, your perspective on isolation is centered around a single approach, and does not taylor to all circumstances, all budgets, all rooms, and mainly, all intents. Acoustics is a varying subject... why do you think they ask posters on this forum to provide so many details? Thirdly, isolation and absorption are more closely related than you think. The waves that introduce the need for effective isolation when transmitted, are the same waves that excite room resonances when reflected. There are no 'isolation waves' or 'absorption waves' that target specifically either of the two. You can however divide isolation/absorption between wave and ray acoustics. Better yet, dividing between the four frequency regions plotted by F. Alton Everest provides a more detailed approach. Physicists treat waves and rays as to completely different subjects, and the reason behind this is the huge variation of wavelengths. Waves from around 21 Hz - 100 Hz are between 16 m and 3.4 m in length. (This is defined as Region B by F. Alton Everest. Region A is below 21 Hz, however there is little modal support that low, so this region is rarely considered.) The application of wave acoustics is needed in this region. Frequencies from around 100 - 400 Hz are between 3.4 m to 86 cm in length and are known by F. Alton Everest as Region C. This region acts as a 'transitional zone', where wavelengths are too short for wave acoustics, yet too long for ray acoustics. Rays from around 400 Hz to 20 kHz are between 86 cm to 1.8 cm in length. This is known as Region D, where the application of ray acoustics is needed. It's obviously apparent that a range of 16 - 3.4 m is huge, when compared to a 86 - 1.8 cm range. This is why we must have a different acoustic stance for each of the 4 frequency regions. Methods for absorbing the energy of frequencies will change throughout the four frequency regions, however (for example) a 100 Hz wave will NOT be exempt from the wave approach, just because it may be transmitted, reflected, or absorbed when it meets a surface. The goal of both isolation and absorption is to reduce the energy of offending frequencies. Yes, absorptions goal may be to prevent the excite of room resonances, and yes, isolations goal may be to prevent unwanted sound from getting out, and in to, the studio, but when we consider the 4 frequency regions, both aspects require similar treatment. Thus, I think you will find that broadband solutions can be formed that combat both areas. I in no way mean to offend you Stuart, I just think you should be a little more open is all. Cheers, Andy

Just read this in Philip Newell's "Recording Studio Design":

The main means by which we achieve the necessary sound isolation in recording rooms is by reflexion, because absorption, as a means of isolation, is rather disastrously inefficient.

Page 75, Second Edition. Thought it might be of interest. Andy

The main means by which we achieve the necessary sound isolation in recording rooms is by reflexion, because absorption, as a means of isolation, is rather disastrously inefficient.

Thank you for backing down and confirming my point: Isolation is achieved by reflection, keeping the sound IN the room, since trying to isolate using absorption is, as you correctly quote, "disastrously inefficient". The converse also follows: Trying to accomplish absorption using materials that are designed to isolate, would be just as "disastrously inefficient". Ie, as I said, absorption and isolation are two entirely different things: Materials used for acoustic absorption treatment are pretty useless for isolation, and materials used for isolation are pretty useless for absorption. Isolation is best accomplish be reflecting the sound back into the room using stiff massive solid materials, and treatment is best accomplished using large volumes of open-cell fiberous materials which has good gas flow resistance in the useful range for our kind of sound waves. Using either one to do the job o the other is pointless.

Firstly, not everyone is as concerned as you may be about isolation. In my instance, I live out in the bush, so the only reason I would be overly concerned about isolation, is if the kangaroos start to complain.

Unless, of course, it rains, or the wind blows, or an aircraft flies overhead, or someone arrives in a vehicle...

Secondly, your perspective on isolation is centered around a single approach, and does not taylor to all circumstances, all budgets, all rooms, and mainly, all intents. Acoustics is a varying subject...

Well, if you have a better way of achieving isolation in the average home studio than MAM or mass on a reasonable budget, then please do go ahead and and explain it to us! Sure, a couple of sheets of lead plate would be spectacular, but that is still mass, and hardly attainable on the average budget for a home studio.

The waves that introduce the need for effective isolation when transmitted, are the same waves that excite room resonances when reflected. There are no 'isolation waves' or 'absorption waves' that target specifically either of the two.

Somehow, I don't recall claiming anything like what you suggest! Whatever made you think that? I repeat, isolation is best accomplished using rigid, massive surfaces. Absorption does not and cannot do the job efficiently. It has nothing at all to do with your imaginary 'isolation waves' and 'absorption waves'. It is totally related to to the manner in which sound waves react when they encounter a different medium. If the medium is solid, rigid, massive and large in comparison to the wavelength, then the wave is reflected back: isolation. If the medium is open-cell, "fluffy" and has the right gas flow characteristics, SOME of the energy in the wave is converted into heat as the fibers vibrate. The rest of the energy carries on through: Absorption. Two entirely different principles. Just like I said. Of course, refraction can also come into play to some extent, depending on the differing characteristics at the interface, but the basic principle of isolation is "bounce the wave back", and the basic principle of absorption is "capture the energy and convert it to heat".

You can however divide isolation/absorption between wave and ray acoustics.

Well, I'm sure you could if you wanted to, but it would not change the PRINCIPLES used to isolate and absorb. You simply CANNOT absorb a wave very well with a solid, rigid, massive object that is large in comparison to the wavelength, and you simply CANNOT reflect a wave with open-cell fierbous materials, where the cells/fibers are tiny in relation to the wavelength. It just does not work. The principles hold true, regardless of the frequency. Yes, some materials absorb better or worse at some frequencies, and other materials reflect better or worse at other frequencies. But taht does not change the fact that it is the PRINCIPLE that we are talking about here, not the degree.

Methods for absorbing the energy of frequencies will change throughout the four frequency regions, however (for example) a 100 Hz wave will NOT be exempt from the wave approach, just because it may be transmitted, reflected, or absorbed when it meets a surface.

No, the method won't necessarily change: The SCALE might change, but the PRINCIPLE remains: If you want to absorb a wave, a good wave to do that is to get it to make something else vibrate, and absorb the vibration in that "something" by conveting it to heat. Huge hangers designed to work at 40 Hz and fluffy fiberglass or acoustic foam designed to work at 4 kHz. both work on the same principle. The SCALE is different, but the basic PRINCIPLE is the same: you absorb the energy by getting it to make something else vibrate, and convert the energy to heat. Ditto with isolation: The only difference is scale. You need a rock cliff face to effectively reflect a 0.4 Hz. wave, but you can effectively reflect a 40 kHz with a sheet of paper. The PRINCIPLE does not change. The SCALE changes. Solid, rigid, massive in relation to the wavelength.

The goal of both isolation and absorption is to reduce the energy of offending frequencies

Ummmm.... no it isn't. That only applies to absorption. The goal of isolation is to REFLECT the wave back where it came from. And reflecting something does not reduce its energy appreciably. Isolation works by NOT letting the energy escape, by keeping it where it is: Absorption does the exact opposite: it attempts to NOT keep the energy where it is, and instead to convert it to another form.

but when we consider the 4 frequency regions, both aspects require similar treatment.

No they don't: they require different treatments, because they are based on different principles. All that changes across the spectrum is the scale.

Thus, I think you will find that broadband solutions can be formed that combat both areas.

OK, so why don't you show us your design for such a broadband solution that both absorbs and isolates the same frequency band? Post your design here for a broadband acoustic absorption trap that is also an efficient isolator for the same band, and is made from one single material. Please feel free to show your design and calculations here (without plagiarizing the work of other people, of course) for an efficient broadband absorber that covers the range from, say, 20 Hz to 1 kHz, and also acts as an effective reflector for the same frequencies. It would be something simple, something that I can use instead of building a normal wall in my studio, something that fits in more or less the same space as a normal wall plus treatment, and costs more or less the same to build. Something that I can erect in place of the wall that will both isolate my room, and also provide good absorption across that range, using only one type of material. You made the claim, so please do provide the design that proves your claim is valid. I would be fascinated to see such a design, as I'm sure many other posters here also would. It would save lots of time, money and hassles for us folks who erroneously think that absorbing sound and reflecting it are two different concepts, requiring two different materials.

I in no way mean to offend you Stuart,

So you normally call people "jackass with a negative know-it-all attitude" without meaning to offend them? I'd hate to see what you call people when you really DO plan to offend them! - Stuart -

better way of achieving isolation in the average home studio than MAM or mass on a reasonable budget

You just proved my statement entirely. Your approach is singular. For an average home studio, on a reasonable budget.

Well, you certainly do want fiberglass or mineral wool in the air gap between your leaves, but the purpose of that insulation is NOT bass trapping! Bass trapping is something entirely different. The purpose of the insulation is to damp the resonance of the cavity. It is part of the spring in your MSM system. It isn't meant to be part of room acoustics, and is only part of the room isolation. Two different things.

Philip Newell applies the same mass-spring-mass, or shell-air-shell principle... but he, like myself, does not chiefly assign the structure to isolation, and this is my point. Newell calls the outer shell or leaf, the isolation wall, and he builds the 1st mass and spring in the same manner as you would, however he relates it ALL to acoustic treatment as well... there is no way that the MSM system can be purely for isolation, it's not physically possible. Wave acoustics states that waves will travel through the first mass, and therefore the rooms resonances will be defined by the outer shell or leaf. Yet you are determined that the MSM system is purely for isolation, and has nothing to do with acoustic treatment. As you said early, 'you appear to be confusing the two subjects.' --- is Philip Newell also confusing the two subjects? Do you realize that the MSM system forms a type of Membrane Absorber? Which is a form of bass trapping? Look up the meaning of a Membrane Absorber, and it will almost exactly define the MSM system. My point, Stuart, is that the MSM system, the two-leaf system, the 2-shell system, what ever you want to call it, effects the acoustics of the room just as much as it does the isolation.

Bass trapping is part of the room treatment, not the room isolation, and goes inside the room (in the corners), or is done with hanger in / above the rear area, but not inside the walls. The two-leaf wall is for isolating your room, not treating it. Treatment goes on the inside, and is a separate concept.

Again, I completely disagree. The outer shell IS the room, and ANYTHING inside the inner shell, is inside the room, therefore effects the frequency response of the room. The inner shell is constructed inside the outer shell. I have never ever heard of any one who constructed an outer shell over an existing shell.

It has nothing at all to do with your imaginary 'isolation waves' and 'absorption waves'

They are not "my" imaginary waves. It seems, however, that they are yours. Because you seem to think that the acoustics will not be effected at all by the MSM system.

isolation is best accomplished using rigid, massive surfaces.

Thats what you say now... And this is what you said before...

If you really want to spend all the money to build 12-inch thick solid high density reinforced concrete walls, then you can get decent isolation. But if you don't want to waste your money, you can just build an MSM wall and get decent isolation for much less expense.

And again...

get MUCH better transmission loss using MSM for MUCH less total mass.

I thought you said isolation was best achieved through reflection? Not absorption?

You simply CANNOT absorb a wave very well with a solid, rigid, massive object that is large in comparison to the wavelength, and you simply CANNOT reflect a wave with open-cell fierbous materials, where the cells/fibers are tiny in relation to the wavelength. It just does not work.

Ok... thanks for letting me know. Although I think I may have understood this already... Cheers, Andy

You just proved my statement entirely. Your approach is singular. For an average home studio, on a reasonable budget.

Well, that actually is what this forum is about, last time I checked. But I'll humor you, and ask you for the same thing, for ANY studio on ANY budget. Show us a better way of isolating a recording studio other than by using the principles mentioned on these pages, and that designers such as Rod, Andre, John, etc. have used successfully in countless studios around the world. I'm sure they would love to learn about your better method. "Better", or course, meaning that it either gets the same isolation more cost effectively, or gets better isolation for the same price. Go ahead, and propose your design methodology (not based on MAM or mass law) for achieving better results than MAM at the same price point, or the same results at a better price point. I read your paper, and found nothing to hint that you have such a method, so I'd like to see what you propose.

there is no way that the MSM system can be purely for isolation, it's not physically possible.

Why not? What law of physics prevents an MSM structure from effectively isolating a room?

Wave acoustics states that waves will travel through the first mass, and therefore the rooms resonances will be defined by the outer shell or leaf.

Wrong again! Room acoustics are defined by the inner solid, massive, reflective boundary, which is the inner leaf. Anything that gets through that and is reflected off a SECOND boundary (the outer leaf) will be greatly reduced in amplitude, and have a much lower incidence on the room acoustics. Such a wave will have been attenuated by passing through the inner leaf TWICE, (once on the way out, and again on the way back) and thus being affected twice by the double impedance mismatch, and twice by the barrier itself, and twice by the cavity, and twice by the absorption in the cavity. In any event, the MSM wall acts as a single unit. At the low frequencies where it is subject to mass law or stiffness law, the wavelengths are huge compared to the thickness of the wall: the waves "see" it as a single resonant object.

Yet you are determined that the MSM system is purely for isolation, and has nothing to do with acoustic treatment.

Well, it certain does reflect as much sound as possible back in to the room, so I guess you could call that "acoustic treatment" if you wanted to! But clearly that is not what you are talking about. If I understand you correctly, what you are claiming is that the insulation inside a well built MAM wall acts as a highly effective broadband bass trap. Tell you what, seeing that are determined to prove your point, post some real results from real independent lab tests that demonstrate what you claim is true. All you'd need to do is to show the frequency response of a room built with an excellent MAM wall, first without any insulation in the wall, and then with the entire cavity stuff full of mineral wool. If you are correct, then the second graph will show an appreciable flattening in the response curve and waterfall plots at the bass end of the spectrum, with an accompanying substantial decrease in RT60 times for all bass frequencies. If you are wrong the second graph will either show no appreciable change, or it will show an increase in bass mode peaks and valleys, and an increase in RT60 times at the low end. So, since you are making the claim, please do show the data for actual physical tests from reputable acoustic labs, as outlined above.

Do you realize that the MSM system forms a type of Membrane Absorber? Which is a form of bass trapping?

And the resonant frequency of such a wall would be what? How about if you do the math, and demonstrate your point.

My point, Stuart, is that the MSM system, the two-leaf system, the 2-shell system, what ever you want to call it, effects the acoustics of the room just as much as it does the isolation.

The only effect that it has, is that it attempts to keep as much sound as possible INSIDE the room, by reflecting it at the hard boundary, which of course has the effect of making a really terrible acoustic space, that then needs treatment INSIDE the boundary.

I completely disagree. The outer shell IS the room,

Once again, how about if you show us data to support your claim? Such as results from lab tests or research papers which demonstrate that the modes that are excited at the low end are those corresponding only to the dimensions of the outer leaf. Just post some graphs and results taken from lab tests, proving that the room ratios should be measured from the outer leaf, not the inner leaf.

The inner shell is constructed inside the outer shell. I have never ever heard of any one who constructed an outer shell over an existing shell

. And your point is? What on earth does construction sequence have to do with acoustics? Do you think the sounds waves really care which wall you built first?

Because you seem to think that the acoustics will not be effected at all by the MSM system.

Wrong. Room acoustics WILL be affected: the room will be MUCH WORSE acoustically for having a MAM wall around it, than it would be if it had, for example, a cardboard wall around it, or a rubber wall around it.

Quote: " isolation is best accomplished using rigid, massive surfaces." Thats what you say now... And this is what you said before... Quote: "If you really want to spend all the money to build 12-inch thick solid high density reinforced concrete walls, then you can get decent isolation. But if you don't want to waste your money, you can just build an MSM wall and get decent isolation for much less expense." And again... Quote: "get MUCH better transmission loss using MSM for MUCH less total mass." I thought you said isolation was best achieved through reflection? Not absorption?

Ummmm. Yep! That's exactly what I said in all three cases. Isolation is best achieved through reflection, which is what an MSM wall does, and also what a concrete wall does, and also what a lead sheet wall does. The difference is that the MSM wall accomplishes it at lower mass and lower cost. I thought I made that clear. You seem to be under the mistaken impression that the isolation in an MSM wall absorbs the sound, and that is what makes it work. Wrong. An MSM wall will work without any insulation in the cavity. It just won't work as well. The purpose of the insulation is not to absorb sound: the purpose of the insulation is to damp the cavity: it puts a bigger shock absorber on the "spring". The air acts a reasonably good damped spring anyway (due to its stiffness), but the insulation improves the damping. It is not there to absorb the sound on the way out: it is there to damp the cavity. After all, a couple of inches of mineral wool will have pretty much no effect on blocking the passage of sound waves. Andy, I'm not about to get into a pissing match with you about how acoustics works, since you clearly have problems understanding the basics (like I said: I read your paper). It makes no sense to try to explain to you how an MSM wall works, since you want to insist that the principles on which it is based do not actually work. All that I can suggest to you is that you should go searching for the real-world proof that I outlined for you above, since that data would show you whether you are correct of not. Just find "before" and "after" graphs for a really good MSM wall that show how it acts as an effective bass trap, greatly flattening the response curves and waterfall plots, and reducing RT60, after the insulation is installed in the cavity. Also, provide data from real-world studios which clearly demonstrates your claim that it is the outer shell of the building that governs the low frequency modal response, not the inner leaf of the room. Do that, and I might get your attention. I'm sure you'd get John's attention, and Andre's attention, and Rod's attention too! By the way, it seems that you already attracted Rod's attention. I don't know if you noticed, but Rod Gervais has a question for you on the thread you started about your studio. You might want to answer it: viewtopic.php?f=2&t=11522 - Stuart - (edited for spelling errors)

Anything that gets through that and is reflected off a SECOND boundary (the outer leaf) will be greatly reduced in amplitude, and have a much lower incidence on the room acoustics.

Last time I checked... That is EXACTLY what absorption is!!!!!!!

which clearly demonstrates your claim that it is the outer shell of the building that governs the low frequency modal response

You may be surprised Stuart, but I don't magically create my own information. Almost every word I have said (aside from the part about your being a jack ass) is from a book written by someone who I imagine has been in the business a little longer than you. So I figure I will take they're advice, over yours.

since you clearly have problems understanding the basics,

Clearly not... you are the one who thinks a 16 m wave will reflect of 2 cm of sheetrock!!!!!!! Low frequency modal response governed by outer shell = F. Alton Everest MSM System utilized as a bass trap, as well as for isolation purposes = Philip Newell & David Miles Huber Do I really need to cite all of my references?? I suggest you consider the source of one's knowledge, before accusing it. Your not trying to prove me wrong... Your trying to prove F. Alton Everest, Philip Newell, Heinrich Kuttruff, etc wrong. But hey, I'm sure you know more than them...

andihopkins wrote:

Low frequency modal response governed by outer shell = F. Alton Everest

Andy, when Everest speaks of the Outer shell - he is speaking of the ENTIRE outer shell - which consists of both the inner and outer walls. It is those 2 walls together that create the outer shell - and they can only be measured (in terms of isolation) together. The inner shell he refers to is the innermost surface of the wall system - which it is critical to the acoustic qualities of the room - and this is independent of the shell as a whole. Rod

I just want that magic building material Staurt was talking about.

Clearly not... you are the one who thinks a 16 m wave will reflect of 2 cm of sheetrock!!!!!!!

Ummmm.... it seems that you STILL have not grasped the concept of the MSM wall. The ENTIRE WALL acts together as a SYSTEM to reflect sound back into the room, not the individual components. And yes, you actually can build a very effective MSM wall using NOTHING but a few panels of 2cm sheetrock and a few studs. No concrete blocks required. As numerous folks here who actually have built studies already will confirm. Maybe this will help you get your head around the concept: Turn your proposed construction around, put the concrete block leaf on the inside, and the sheetrock leaf on the outside. Is the total TL of that wall now different? According to you, it must now be a TERRIBLE wall, since you now have the leaf that deals with high frequencies on the OUTSIDE of the wall, and the leaf that deals with low frequencies in now on the INSIDE. According to you, the insulation in the wall will no longer works as bass trapping, since it is not exposed to bass frequencies any more, as the inner concrete wall blocks those.... Do you see the problem you create for yourself? In effect, you are saying that the wall acts in a different manner for sound going one way through it, than for sound going the other way through. According to you, such a wall would be the acoustic equivalent of a diode! It would have a different effect on sound, depending on which way the sound goes through it! So, if Rod were to test one of the studios he has designed and built, according to you he would find that the TL for a kick drum played 1m inside the studio wall would be different from the TL for the exact same kick drum played 1m outside the studio wall... According to you, the "bass trap" effect in the wall would only work form the inside going out, not from the outside going in since the bass waves would never see the bass trap, so the TL would be different. It would have to be different, if your theory is correct. Are you seriously suggesting that Rod would find such a difference? How much difference should he expect? 5 dB less TL going out to in? 10 dB? 15 dB? Since you apparently have a theory, you should be able to predict this difference, then Rod can get someone to measure it for him at one of the studios, and we can see if you are right or not. So please go ahead and predict the approximate difference that we can expect in transmission loss for sound passing in each direction through the wall. - Stuart -

andihopkins wrote:

You may be surprised Stuart, but I don't magically create my own information. Almost every word I have said (aside from the part about your being a jack ass) is from a book written by someone who I imagine has been in the business a little longer than you. So I figure I will take they're advice, over yours.

Well, there's the thing, isn't it? I agree with Rod: You may have read the books, but somehow the information didn't survive intact, on its journey from page to neurons... The problem is not with the advice they imparted on the pages they wrote: The problem is with the way you understood it. Which one of the most respected experts of the day, Rod Gervais, is trying to help you understand (in his rather more eloquent style than mine!) You should actually feel quite honored: I don't recall seeing Rod spend so much time and effort with one person on this forum, trying to re-educate them, in years!

I suggest you consider the source of one's knowledge, before accusing it.

Oh, I don't question the sources! Not in the least! What I question is your interpretation thereof. And I cite as the source of my knowledge on this issue: Rod Gervais, and more specifically his book "Home Recording Studio - Build it like the pros".

Your not trying to prove me wrong...

That's hardly necessary! You do a great job of that, all by yourself, without my help! :)

Your trying to prove F. Alton Everest, Philip Newell, Heinrich Kuttruff, etc wrong. But hey, I'm sure you know more than them...

No, but I do seem to at least understand what they wrote... I'm not trying to prove them wrong, since I agree with them in general. What I am attempting to prove wrong is your grasp of what they said. - Stuart -

stuntbutt wrote:

I just want that magic building material Staurt was talking about.

What "magic material" would that be? I don't recall mentioning any such material. - Stuart -

Post your design here for a broadband acoustic absorption trap that is also an efficient isolator for the same band, and is made from one single material. Please feel free to show your design and calculations here (without plagiarizing the work of other people, of course) for an efficient broadband absorber that covers the range from, say, 20 Hz to 1 kHz, and also acts as an effective reflector for the same frequencies. It would be something simple, something that I can use instead of building a normal wall in my studio, something that fits in more or less the same space as a normal wall plus treatment, and costs more or less the same to build. Something that I can erect in place of the wall that will both isolate my room, and also provide good absorption across that range, using only one type of material.

Just being silly :D

Ahh! Ok Gotcha!!!! :) :wink: If you find some, I'll take a truckload, please!