Drum set and a brick wall - reducing noise with a PARTIAL barrier/panel

[spitzer]

To rob aylestone and witzendoz in particular:

I realise some of my replies to you have been blunt and seem harsh (even if you didn't feel that way I still wanted to say this, because it might look different to a 3rd party). That was all on purpose. I might have said this even earlier, but I simply want to be clear and straightforward and just plain sort it out to minimise the misunderstandings multiplying over time. We've already noticed sort of the thing where it's getting confusing like witzendoz said: someone mentioned something and then someone else thought I was considering doing that.

Also I again want to stress that to me, this is not a debate and what I mean by that is that my intention is not to prove this or prove that. For example the cardboard box thing I keep bringing up is not supposed to be this or that in itself, it is part of the process of figuring out "well if I do this and it works like that, probably the same principles apply to..." You know? I do accept alternate theories and I certainly always accept the truth. What I do NOT mean by that is that "I'm always right." Please. Please understand this. No, I can be wrong about a lot of things. If that is the case, I really wish you would point that out specifically and explain what is wrong.

There's also the loss of focus effect in ignoring "correct" sentiments and instead pointing out something else (usually small and beside the point) that's "incorrect". Saying I misused the term "flanking" and that I don't understand the detailed mechanics of how wall plugs work while at the same time not acknowledging at all that the cardboard box barrier worked is an example of this loss of focus. As far as I can tell, so far no one has refuted that it did in fact work. That is so much more interesting than anything else being discussed at that point that it's not even funny. Do you think it did really work? Do you think it was an illusion of some sort? How do you explain why it worked the way it did? Should I have specifically pointed out that because that worked, I think a larger device of similar construction would also work in a similar fashion? To me, it was obvious that this small-scale experiment is linked to my plans for the wall or large panel, and not just some random thing I decided to post here to confuse people. Why would I do that?

To me there is this odd disconnect: The site is called Home recording, which to me does not suggest academic, esoteric, difficult stuff. On the contrary, I think the default assumption should be that people have NOT read 700 page books on mechanics, aerodynamics and material technology. Who records at home? Probably an amateur musician. Are they likely to invest the time and money and have the knowledge and skills to build a top of the line professional level recording studio? Are they likely to even try to do that?

 

[rob aylestone]

Spitzer - I'm not intending to make any real points apart from my inability to work out what you want to do. I shouldn't perhaps have mentioned the drum screen, but the point is that barriers close to your drums make them louder, and quieter the other side. In realise that you have some kind of desire for something to happen, but I just don't know what the end game is? We're responding to responses to responses now as the journey has got more complex. I really did think at some point you were filling the cavity in one of the ideas you had with rock wool, then there was a post saying something was better than rock wool, hence my thought you had rock wool in the design somewhere. Basically, we're answering your thoughts chronologically but the weight of our comments is very low, because everything is generic, nothing specific. We have no plan to consult, just an artistic impression. Maybe it's time for you to come up with a design, and we can look, possibly calculate and comment. I'd really suggest though, that you consider my comment regarding the distance from the drums - this is critical. Too close and you will find the drums very difficult to work with, but too distant and it will sound just like your plaster wall. That, I'm certain of. Quite interesting watching the ebb and flow though.

 

[spitzer]

Rob, the basic concept has not changed. A quick recap: I already have 2x4's, chipboard, blockboard, beadboard, felt, old carpets, polyurethane panels, wall plugs, screws, nails, and probably something I forget -- everything I need to build something. Right? I also live a walking distance away from a hardware store (several stores, actually) and can relatively easily get whatever additional materials I need. But the idea is to use what I have and not spend the equivalent of several hundreds of euros, dollars or sterling on something I don't really need. One point I made when I revised the original post is crucial: to me, failure IS an option. If you missed that previously, don't miss it now. If whatever I build turns out horribly wrong, I will simply dismantle it and try something else. Although I would like to say I can not possibly imagine how anything I decide to do would turn out to be harmful in any way. Maybe it'll have no effect at all? So what?

Rob, I want you to understand that the drums are presently close to the concrete wall. They have been for more than 10 years.

Can we agree that there is a difference in whether the (reflective) wall next to the drums is concrete, or wood paneling? To eliminate any confusion,
wood paneling looks like this:

Plaster concrete looks like this:



Can we?

Can we even agree that these surfaces have very different reflective properties?

I can provide you with a plan, but to me that's almost "thinking in reverse". There are things I need to know BEFORE I make an actual detailed plan, and that is precisely why I have been spending hours upon hours of reading about stuff in addition to asking questions here. The reason I'm asking you about the properties of certain materials, for instance, is that I need that information to make the proper plan. I suppose you follow? I put it the way I did on purpose -- I described the dimensions, surface material and not much else. I can fill the panel with old rags and sawdust, or I can leave it completely hollow. That's two plans. Which one would you go with?

Would providing you with a (what would be very large) set of different plans with drawings for each actually make anything easier? Are you unable mentally to work with a drawing that only describes something as "absorbent" and not specifically "rockwool" or "styrofoam" or "felt"? That is what I don't understand. That's almost the only variable there is! (there is something else, I'm trying to think of something specifically concerning the corner but I do NOT want to bring one bit of more confusion to this right now.)

 

[mjbphotos]

Back to my comment a while back - polyurethane FOAM insulation I have heard of, not polyurethane blocks as you previously mentioned. Great thermal insulator. Not SOUND.

Go ahead and spend your effort using what you've got, instead of arguing with every single person who has tried to suggest things here. Tell us how it comes out.

 

[mixsit]

...Rob, I want you to understand that the drums are presently close to the concrete wall. They have been for more than 10 years.

Can we agree that there is a difference in whether the (reflective) wall next to the drums is concrete, or wood paneling? To eliminate any confusion,
wood paneling looks like this:

..

Umm, if that is what it looks like- paneling with shallow groove (recesses) milled in it...?
Then, no not much at all.
See this, tables for recess depths and widths.
Razorblade Science | Primacoustic
Take the effective freq / per depth left 1" depth column. Double that 3-1.4KHz freq for 1/2" depth, double again for 1/4" deep etc.. Yes a little lower than for 'trowel marks but.. :>)
The width table is even worse (spread freq limits are even higher.

Are we still saying this is a brick wall.. w/ the cement covering..?

 

[spitzer]

Just to make sure... you are saying that there's no difference between wood and concrete? A room in a wood cabin sounds the same as a concrete walled basement or garage? Or a cathedral with hard stone walls?

 

[spitzer]

Most recently I was again looking at this chart, before I came back to check this thread: Coefficient Chart . I was most interested in the enormous differences I saw between "Plaster (gypsum or lime, on masonry)" and 10 mm plywood.

Back to my comment a while back - polyurethane FOAM insulation I have heard of, not polyurethane blocks as you previously mentioned. Great thermal insulator. Not SOUND.

I just used some PU foam a couple of hours ago. It's used to plug leaks (holes, seams) and such, and sticks to almost every imaginable material. At least that's what the can says. The blocks, or sheets... I have read they are also effective in reducing sound, but I don't know the underlying mechanism. The density figures I have found for PU suggest it could work as an absorbent. So do the figures for both EPS and XPS by the way. XPS is denser and stiffer than EPS, but it's thermal conductivity is slightly higher. It's the same chemical, but the manufacturing process is different. With a spray canister of the stuff... who knows what the "manufacturing process" is like there? I wouldn't say without doing considerable research that (yes, I am now talking about the "liquid" foam) it is not an effective this or that, because the structure differs at a microscopic level. Let's say you spray it somewhere, let it dry... do you at that point know its molecular structure? I suppose you could take a dry piece, cut it in half and put it under a microscope. If I had to guess, I would guess it would be different from both EPS and XPS as made on manufacturing line.

Go ahead and spend your effort using what you've got, instead of arguing with every single person who has tried to suggest things here. Tell us how it comes out.

I'm sorry to say I don't understand. You have been one of the few who have actually made at least one reasonable and practical suggestion and I don't recall there being any misunderstanding between us. On the contrary, I felt we were on the same page in that you didn't seem to have trouble interpreting the circumstance quite correctly without me providing millimetre-level plans. I completely missed one of your posts (you apparently suggested a bass trap early on) for whatever reason, but did we at some point argue about something??? I most certainly haven't said "no, not a bass trap". I wouldn't say that, as that's something I've been interested in for years. The space is small enough that when playing together with a bass player, there are significant problems with hearing what's going on (which does not happen with a regular guitar, even in baritone tunings). I always ask the bass player to turn the treble and high mids up a LOT, otherwise it sounds more or less like a lawnmower to me. I suspect that is at least in part due to 1. a corner and 2. standing waves. During one jam session a while ago, the bassist had sneakily kept on just turning the volume up and what happened was that I stomped on my kick pedal and couldn't hear it at all. That was the strangest feeling.

Yes, it seems I'll just have to go ahead because the conflicting information will never end.

Here is my finalised plan: I will burn all of the beadboard in the fireplace, bash the plaster with one of the 2x4's to create a harmonious diffuse surface, then hammer some 9 inch nails in it for no reason, duct tape random sized chunks of styrofoam on the wall, throw a bunch of old rags over them and expect it to function as an absorbing diffusor/reflector that causes a 35 dB reduction in SPL on both sides of the wall. I'm so super absolutely sure that this will work because I'm always right and other people just don't get it. You will never hear of me again because this concept will make me a billionaire and all the cool cars and hot girls will make me totally forget about this forum.

 

[mixsit]

Just to make sure... you are saying that there's no difference between wood and concrete? A room in a wood cabin sounds the same as a concrete walled basement or garage? Or a cathedral with hard stone walls?

No of course hard wood and cement won't sound exactly the same. But 1st, what's with this basement' vs wood cabin' or cathedral stuff. That's about hugely different spaces, and where these differences -in totally different reflections, sizes etc are in play.

You are doing 'a room, where you are proposing to change one small portion of it!

Rob, I'm thinking of doing a slatted/diffusing wood surface front what comes to the "planks" in the diagram. Also, correct me if I'm wrong but I expect that any kind of wood surface will produce substantially different echoes compared to a concrete wall since wood is softer and porous. Concrete is just REALLY hard and the reflections are harsh. Especially apparent in comparing e.g. a crash cymbal on the side of the wall (diagram left) and another one on the open side. The one right next to the wall is instantly reflected right back into your ears, the other one sounds much more pleasant because it's surrounded by much more air space. So this part of it is actually just changing the timbre of what's being reflected. I chose a wood surface (instead of let's say just covering the wall with very thick carpet) exactly to preserve, aka reflect, the high frequencies but taming them a little bit. ...[snip]

...and the link (and my post) is obviously about diffusion ..to help you follow your stated intent.

 

[rob aylestone]

In terms of the 'sound' then I'm convinced that there are two things to how a solid surface reacts to sound. The density thing seems to be one important factor, and the other the smoothness of the surface. A newly plastered surface here with a decent polished and smooth plaster finish over brickwork sounded different to the same surface with a two coats of emulsion paint. I cannot pin it down scientifically, but the paint surface, thin though it is does act as a diffuser at the HF end, deadening the reflections a little up top. However in one of my two studios that I have been refinishing I have used 18mm MDF on two of the walls, over the existing plasterboard inner room within the room. This hardened up the sound to the point where it sounded like the plaster finish in the other room. I can only imagine it's the density and again the very smooth surface compared with the paint.

I think that you're quite right with fibrous wood - diffusion, but if the actual timber is dense and perhaps sealed on the outside with stain or varnish, then I reckon it's a pretty solid reflector and poor absorber. What also might happen is that transmission through it could be high. I'm thinking about when you knock with your knuckles on a panel between the stud work - it's a membrane that can move. Not a lot, but standing on the other side you can hear a knuckle tap quite easily. This could perhaps be mopped up with something inside.

I really think you're going to have to build the darn thing and see/hear what happens? I still reckon that having the drum kit in it's old position and sticking the panel in between the kit and the original wall will make the kit much louder. Inverse square law proving itself.

I've been working inside a Cold War concrete underground bunker, and I wish I could have recorded down there. Concrete, 3ft thick, with a rough cast sprayed concrete/air top layer. 100m long tunnels - all right angle bends and because of a historic fire - no doors left at all. RT60 of maybe 10 seconds, perhaps even more.

 

[spitzer]

No of course hard wood and cement won't sound exactly the same. But 1st, what's with this basement' vs wood cabin' or cathedral stuff. That's about hugely different spaces, and where these differences -in totally different reflections, sizes etc are in play.

You are doing 'a room, where you are proposing to change one small portion of it!

...and the link (and my post) is obviously about diffusion ..to help you follow your stated intent.

Okay, okay. That's why I asked, because I was very confused about what you said and thought part of what you were trying to say was missing or something. What I read was (simplified) "can we agree that wood and concrete are totally different?" and you saying "no". That was again one moment where I felt this is hopeless. I was, seriously, astounded that anyone would say that.

It's paramount here that we can to a significant extent agree on this matter, as the entire wood thing is the centre of what I'm doing.

The surface is by nature diffuse, which I theorised would help with the one problem that is fast, direct and HARSH reflections from the concrete. But the point of the wood is not diffusion, the point is that wood is wood, and concrete is concrete. It's about weight, it's about density, it's about absorption, all that stuff.

BTW, have you visioned the ENTIRE space being otherwise concrete walled and completely empty??? And then a tiny bit of wood in one corner? Again something that needs to be clarified.

 

[spitzer]

In terms of the 'sound' then I'm convinced that there are two things to how a solid surface reacts to sound. The density thing seems to be one important factor, and the other the smoothness of the surface. A newly plastered surface here with a decent polished and smooth plaster finish over brickwork sounded different to the same surface with a two coats of emulsion paint. I cannot pin it down scientifically, but the paint surface, thin though it is does act as a diffuser at the HF end, deadening the reflections a little up top. However in one of my two studios that I have been refinishing I have used 18mm MDF on two of the walls, over the existing plasterboard inner room within the room. This hardened up the sound to the point where it sounded like the plaster finish in the other room. I can only imagine it's the density and again the very smooth surface compared with the paint.

MDF is an engineered wood product. Its density is similar or higher than a number of hard hardwoods, such as birch or maple. It's also often covered with melamine, which is smooth and incredibly dense.

I think that you're quite right with fibrous wood - diffusion, but if the actual timber is dense and perhaps sealed on the outside with stain or varnish, then I reckon it's a pretty solid reflector and poor absorber. What also might happen is that transmission through it could be high. I'm thinking about when you knock with your knuckles on a panel between the stud work - it's a membrane that can move. Not a lot, but standing on the other side you can hear a knuckle tap quite easily. This could perhaps be mopped up with something inside.

Perhaps. I reckon that soft and thin dry timber will not reflect sound waves below 500 Hz. But what I reckon is of little importance, no?

 

[mixsit]

Okay, okay. That's why I asked, because I was very confused about what you said and thought part of what you were trying to say was missing or something. What I read was (simplified) "can we agree that wood and concrete are totally different?" and you saying "no". That was again one moment where I felt this is hopeless. I was, seriously, astounded that anyone would say that.

It's paramount here that we can to a significant extent agree on this matter, as the entire wood thing is the centre of what I'm doing.

The surface is by nature diffuse, which I theorised would help with the one problem that is fast, direct and HARSH reflections from the concrete. But the point of the wood is not diffusion, the point is that wood is wood, and concrete is concrete. It's about weight, it's about density, it's about absorption, all that stuff.

BTW, have you visioned the ENTIRE space being otherwise concrete walled and completely empty??? And then a tiny bit of wood in one corner? Again something that needs to be clarified.

Last one first, I got that there is perhaps one 'cement/brick wall(?), and your 'panel will cover only part of it.(?)

On the wood vs cement -of similar stiffness- I'd presume there are slight differences between the content of what they reflect, or the small amount they attenuate -mostly in the high frequencies.

If they are allowed to vibrate in response to low frequencies- then there can be some low freq attenuation. (See the limp designed-to-vibrate type of thin solid panel bass absorbers. The name escapes me right now :>)
But diffusion means depth variations -typically preferably random.

 

[spitzer]

Last one first, I got that there is perhaps one 'cement/brick wall(?), and your 'panel will cover only part of it.(?)

On the wood vs cement -of similar stiffness- I'd presume there are slight differences between the content of what they reflect, or the small amount they attenuate -mostly in the high frequencies.

If they are allowed to vibrate in response to low frequencies- then there can be some low freq attenuation. (See the limp designed-to-vibrate type of thin solid panel bass absorbers. The name escapes me right now :>)
But diffusion means depth variations -typically preferably random.

I have zero time right now but I see wood and cement "of similar stiffness" as an impossible end result here, and in general almost only in theory. I'm talking about WOOD-wood, not glue laminate or something similar which is an engineered wood product, not "wood". I wouldn't even refer to melamine coated chipboard as "wood" in this context. Suitably for the topic, how about one of my drums? The shells are made of wood. Laminated hardwood. They're extremely thin (hardly more than five millimeters), they are round, yet they are incredibly strong. A 100 kg tub of lard can stand on the bass drum and it won't break. They (bass drums) are commonly used to support other drums and other heavy stuff attached to it with steel rods or rods. It (or the other drums) won't bend, break, or change shape... ever. My set is over 30 years old and is in perfect condition.

Back to the wall. The current surface is lime plaster on brick. Since I have already specified beadboard countless times, maybe you could shift your focus on that a little bit. For anyone else following, beadboard is thin, usually unfinished, tongue and groove planks made out of softwood or very soft hardwood depending on application. Most commonly pine, spruce and so on.

I again refer to this chart which contains absorption coefficients for a bunch of different materials: Coefficient Chart . Read it.

Oh yeah. Theoretically none of the walls are just hard anything, since each of them has things attached to them. The wall I'm talking about though is the one with the largest surface area (about 9 m2) of only the plaster on brick.

 

[rob aylestone]

You know, that asking people for help then ordering them around is a bit rude? You're starting to get angry with people who pop in to help, and haven't been machine gunned earlier in the thread and gone away. I'd love to see why you have a 100Kg tub of lard sitting on your kick drum shell. Great picture - perhaps you could stand next to it so we can understand what you mean? Honestly though, you are starting to get ratty - repeated emphasis with repetition and bold text sounds angry in print. Picking about engineered wood products rather then "wood" is just unnecessary degenerative descriptive emphasis - the kind the university professors try to counsel their students against using. Frankly, the only constant is people just quite surprised with some of the things you say. I think your entire concept is seriously flawed because you cannot describe what you actually want? You make a statement, people try to work out what you want, and post. You then slap them about a bit for being too stupid to understand you. As it has now happened over and over again, maybe you should start to understand that we simply don't get it, despite your vague explanations of purpose. I guess you want to use beadboard because you have it to hand. So just make the damn thing and stop the analysis and prove your ideas will work and make you happy. Many respondents believe the entire thing is pointless and lacking common sense, let alone any real science. You have the coefficient chart, so you read it and draw your own conclusions. We simply have no hard information on what result you require, because you avoid direct questions, and seem to refuse sensible solutions based on our understanding of your imagined requirement that we simply do not get.

So going back a few pages - I've concluded you are just playing with us, changing your tack whenever we get close, and moving gateposts to match your new version of the question.

I've put up with your rudeness to me, I'm used to dealing with petulance in my job, but now you're just getting unpleasant. I'm out. I'll watch with interest, but I don't like the bitchyness. If you know, then do. if you really want help, be nice. You're the one wanting response - why shoot the messengers every single time. Re-read your post above. There are so many snappy and bitchy retorts to people trying to help, it stinks.

 

[spitzer]

I never realised typing emphasized text was rude, bitchy, or anything else negative that you described. I still think what you're experiencing is misunderstandings, it doesn't matter by whom.

And when I said I have zero time, I meant that I have other things to do and I have to go.

So I'll address the rest later.

 

[mixsit]

I have zero time right now but I see wood and cement "of similar stiffness" as an impossible end result here, and in general almost only in theory. I'm talking about WOOD-wood, not glue laminate or something similar which is an engineered wood product, not "wood". I wouldn't even refer to melamine coated chipboard as "wood" in this context. Suitably for the topic, how about one of my drums? The shells are made of wood. Laminated hardwood. They're extremely thin (hardly more than five millimeters), they are round, yet they are incredibly strong. A 100 kg tub of lard can stand on the bass drum and it won't break. They (bass drums) are commonly used to support other drums and other heavy stuff attached to it with steel rods or rods. It (or the other drums) won't bend, break, or change shape... ever. My set is over 30 years old and is in perfect condition.

Back to the wall. The current surface is lime plaster on brick. Since I have already specified beadboard countless times, maybe you could shift your focus on that a little bit. For anyone else following, beadboard is thin, usually unfinished, tongue and groove planks made out of softwood or very soft hardwood depending on application. Most commonly pine, spruce and so on.

I again refer to this chart which contains absorption coefficients for a bunch of different materials: Coefficient Chart . Read it.

Oh yeah. Theoretically none of the walls are just hard anything, since each of them has things attached to them. The wall I'm talking about though is the one with the largest surface area (about 9 m2) of only the plaster on brick.

You read it.
See where your 'concrete on the top freqs varies with painted or not, and Wood parquet on concrete or joists varies in the lows because of flex in the mounting, but.. acts like 'concrete up top?

I don't know if you're being thick' about understanding this stuff, or just not trying to understand tossing all the unrelated crap in, or what.

I came back around here- because I thought you would come around to some science. These are the basics.

 

[witzendoz]

You know, that asking people for help then ordering them around is a bit rude? You're starting to get angry with people who pop in to help, and haven't been machine gunned earlier in the thread and gone away. I'd love to see why you have a 100Kg tub of lard sitting on your kick drum shell. Great picture - perhaps you could stand next to it so we can understand what you mean? Honestly though, you are starting to get ratty - repeated emphasis with repetition and bold text sounds angry in print. Picking about engineered wood products rather then "wood" is just unnecessary degenerative descriptive emphasis - the kind the university professors try to counsel their students against using. Frankly, the only constant is people just quite surprised with some of the things you say. I think your entire concept is seriously flawed because you cannot describe what you actually want? You make a statement, people try to work out what you want, and post. You then slap them about a bit for being too stupid to understand you. As it has now happened over and over again, maybe you should start to understand that we simply don't get it, despite your vague explanations of purpose. I guess you want to use beadboard because you have it to hand. So just make the damn thing and stop the analysis and prove your ideas will work and make you happy. Many respondents believe the entire thing is pointless and lacking common sense, let alone any real science. You have the coefficient chart, so you read it and draw your own conclusions. We simply have no hard information on what result you require, because you avoid direct questions, and seem to refuse sensible solutions based on our understanding of your imagined requirement that we simply do not get.

So going back a few pages - I've concluded you are just playing with us, changing your tack whenever we get close, and moving gateposts to match your new version of the question.

I've put up with your rudeness to me, I'm used to dealing with petulance in my job, but now you're just getting unpleasant. I'm out. I'll watch with interest, but I don't like the bitchyness. If you know, then do. if you really want help, be nice. You're the one wanting response - why shoot the messengers every single time. Re-read your post above. There are so many snappy and bitchy retorts to people trying to help, it stinks.

I agree, everything I've suggested has been dismissed with a know it all attitude, if the original poster has already made up their mind why ask. Even the original question has changed around so much no one knows what they are answering. Known solutions (to whichever problem we are supposed to be addressing) have been dismissed with frequency readings and cardboard box reduction theories.

I have been trying to help but have given up. I suppose reading books and the subject for over 40 years and having built 4 studios I just don't know what I'm doing, you know we are only trying to help but I feel we are having the piss taken now.

Alan.

 

[spitzer]

You are not the only ones who are frustrated, I assure you. That's why I went away for a couple of days. And was extremely disappointed to come back and see myself being ridiculed and misrepresented once again. What purpose does calling me "thick" serve?

Assuming you want to help, what do you need? How can I help you help me?

 

[spitzer]

You read it.
See where your 'concrete on the top freqs varies with painted or not, and Wood parquet on concrete or joists varies in the lows because of flex in the mounting, but.. acts like 'concrete up top?

I don't know if you're being thick' about understanding this stuff, or just not trying to understand tossing all the unrelated crap in, or what.

I came back around here- because I thought you would come around to some science. These are the basics.

Who's painting what? Where's the parquet? You seem to be purely messing with me now.

The only point of interest, and the only reason I referred to that chart - TWICE - was that it says right there that the absorption coefficient of lime plaster on masonry is 0.01 at 125 Hz. Which, in practice, means it doesn't absorb it at all. Correct me if I'm wrong. The absorption coefficient of every thickness of plywood listed with different sized airgaps, is 0.15 or more, which is over 10 times that of lime plaster on masonry. Correct me if I'm wrong. The absorption coefficients are hugely different across the entire frequency spectrum. Correct me if I'm wrong. So, based on that data, for example 3 mm plywood paneling would absorb sound completely differently than lime plaster on masonry. Correct me if I'm wrong.

Each time you correct me, if you do, please shortly explain why I'm wrong.

Thank you.

 

[mjbphotos]

Absorption of 0.15 still sucks - that's barely anything. 1" Roxul or OC 703 do that - but at least they absorb better at higher frequencies.