thismanysounds - Basement Studio in London UK

Hello all, This is my first post on this forum, but certainly not my first visit! I have the opportunity to build a small recording studio in the basement of an office building. The room was 'built' before, but with no real consideration for isolation. A-weighted transmission loss is about 32dB between live and control (less than 10dB below 80Hz). So essentially we are starting from scratch! Location - London, UK. Dimensions - Appox 9m x 5m x 2.85m Budget - £10-15k for materials. We have a building team, who will be doing the work. Isolation - The goal is to be able to record a live drum kit, without disrupting the office above or the meeting rooms across the corridor. The office is open plan, so 35dB in there will likely be okay. Assuming a drum kit of 110dB that a goal of 75dB transmission loss. A significant amount of noise is impact from the office above, and also some rumble from the underground. I have a feeling we have have to live with that to some extent due to budget/height restrictions. Existing structure - This is in the basement of the building. One wall is external (brick, underground), a second is single brick to a boiler room. The remaining two are simple stud+drywall to a corridor. One corner is curved plasterboard, but this can be removed. We are on the slab, and the ceiling is poured concrete. Sketchup: I have included a sketchup of the existing walls, as well as two possibilities. I will follow up with some questions later. For now, thanks for reading! Colm

Okay, here are some questions: 1) With the rooms built on the concrete slab, at what point will flanking through the floor surpass my efforts to increase wall & ceiling transmission? 2) Newell seems to be a fan of multi-leaf construction with the justification that each layer will reflect at some frequencies, absorb at others, and let sound through at the rest. By having several different constructions, the resonances of each layer are different (more even TL), and the level of extra acoustic treatment is reduced. Looking at Rod's book and this forum, this method seems less popular around here. Is there a particular reason for this (cost / availability of materials, inconsistent results, less accessible, etc)? 3) Common practice seems to include the use of sound locks (sometimes used as booths) between rooms. I believe this is to allow a lower door specification. At what point is this big enough not to be considered a quadruple leaf (reducing TL)? Is this a waste of space in a small studio? 4) At the moment two of the walls are built with brick (one is exterior) and the ceiling is poured concrete. Is it worthwhile to do the remaining two exterior shell walls with sand filled concrete blocks? 5) Does anyone know of TL data available for: Brick-Air-WoodStud-Plasterboard-Plasterboard, ConcreteCeiling-Air-WoodStud-Plasterboard-Plasterboard? At the moment I am allowing 125mm to the stud (to give a comparable air gap to a dual stud wall), is this excessive? 6) HVAC. I am struggling to find much beyond 'don't let HVAC be the weak spot in your construction', and a comparison of ducted and mini-split systems. Please can someone please point me in the direction of some good literature and/or some worked implementations of good systems (including fresh air supply). Thanks in advance

1: I'll let Stuart field that one... I don't know the specific decibel level. I doubt that a concrete floor is going to be your most vulnerable target point though. A concrete slab is supposed to be one of the better "starting points". I've yet to read a thread on the forum, where the walls / ceiling had so much isolation that a good concrete slab was a "problem" (unless we're talking about that crazy 100+ db studio). Have you done any tests to identify exactly how much "rumble from the underground" you're actually getting? I grant that might be a problem, but still, a concrete slab is still one of your better starting points. The impact noise from your ceiling is probably a better focus point to start with, as you can almost certainly do something there. 2: I'm not familiar with Newell, but when you say "multi-leaf" can I assume that you mean 3 or more leaves? I'm assuming that because you said it wasn't popular here, and what's popular here is a 2 leaf system. It's tough to answer when I'm not sure of the exact question (since I don't know the specifics of what Newell has recommended), but I can't help but notice a very real difference in the intended application. You've mentioned multiple layers of construction, intended to control/resonate/dampen specific frequencies, resulting in a room which requires overall less acoustic treatment. These descriptions sound very much like construction focused on absorption plans intended to deal with specific frequency issues. Is it possible it's an apples and oranges comparison? The 2 leaf MSM plan is for isolation and has nothing whatsoever to do with absorption. As described, it almost sounds as though the walls are assumed to each be acting independently, each doing their own thing, then passing on the remainder to the next wall which does it's own thing, but if your describing a series of true walls, that's not really how it works. Each wall can't be assumed to function independently, but rather they work together as a single system, which is why the MSM system is so popular here. In terms of isolation, adding more leaves beyond 2 isn't desirable because the effect is that it actually reduces low frequency isolation. That said... there are applications where more leaves would be fine... isolating exclusively high frequencies for example, but you've mentioned that you want to record drums. That being the case, a 2 layer MSM plan is almost certainly going to be your best bet. Not that there aren't other systems that can achieve good results, but many of them will cost more to achieve comparable results to an MSM system with good room treatment. If you're anything like me, you'd rather spend the money on new gear than on the walls. 3: Would skip the "airlock". Not common practice with the MSM system and just costs space, without any real gains. Put a door in each layer of the MSM system, and there's your airlock without any wasted space. The goal is to make your penetrations the same mass as your wall. Looking at your SKP's, idea 2 seemed a better starting point but it needs some revisions. For example, ditch the airlock and revise the control room so that the back side doesn't get narrower. (you'll often see that shape, but it's the treatments in the room that make that shape and not the hard boundaries of the space.) 4: It doesn't really matter what the walls are made of. Your main goal is to achieve isolation, and if you hit comparable isolation with a different material on the other 2 walls (i.e. cheaper) then there's no harm in doing so that I'm aware of. (just keep the different layers air-tight! Joins between different materials can be a little more challenging) 5: http://johnlsayers.com/Recmanual/Pages/STC%20Chart.htm - This one's older, and doesn't have all the info for different MSM systems, but part way down, it shows insulated timber with one layer gypsum with brick to do about 56 db. There's a more modern version I'm trying to find. Will post if I locate... maybe someone else on the forum knows the link? Little help here? As re: whether that amount of space is excessive, no it's not. If memory serves from reading other threads by knowledgeable people, there is still benefit to making the air gap even larger than that. The drop-off was somewhere around 10 inches if memory serves. 4 inches is a pretty standard number though, and you're above that. 6: Your best bet is to do a search of the forum for HVAC. The issue has definitely come up multiple times. The issue with fresh air supply really just involves being sure to research the device and make SURE that it does that component. I believe there have been mini-split systems that have been used successfully in several studios on the forum. Personally, I'm planning on an "exchange chamber" approach, where I can have a noisier system treating the lobby (outside the MSM boudaries), and then use fans/ducts to take the air into the areas where I want it. That's good for me because I have the space and low funds. I'd go for the multi-zone mini-split systems in a heartbeat if I had the funds, simply because I know they have worked in studios before. I'm still kind of hoping that by the time I build it'll be possible. To start you off, here's a link John gave to a viable system viewtopic.php?f=1&t=15724 Rod's book also has a chapter on HVAC, have you already checked it?

Thanks for your quick reply Johnnie. Just to clear up a few points. 2) It is fairly hard to explain so I have attached a diagram (I hope this is okay). There are several significant (IMO) leafs in the wall. 3) Great, that is better for me. Does anyone want to champion for having an air lock? 4/5) I was thinking that as brick/block is mass'ey which helps with LF transmission, having a solid brick/block exterior leaf would be beneficial. I understand that doubling the mass increases the STC by ~5dB, how does this work in a MSM where the leafs are uneven? Will I get 5dB every time I double the plasterboard side until they are of equal mass (it seems unlikely, but I can hope!)? Will green glue provide any benefit in this situation 6) I could use the boiler room as an exchange chamber, but as it is underground and noisy itself, it doesn't seem as good an idea. I have read Rod's HVAC section, but I don't understand how it all comes together. For example the diagram on Pg130. How is isolation achieved between the mechanical room and the sound room? Where do 'dead vent's' come into play? Similarly, if there is little isolation provided by the ducting, do I need separate systems for each room or can the loop be extended? EDIT: More Googling has given me this: http://forum.studiotips.com/viewtopic.php?t=2144 "Every doubling of mass on the resilient skin gives 3.1-3.3dB". Have I interpreted this correctly?

2: OK! I'm looking at the picture of the design. The first leaf is the brick wall surrounding the design. Next you have layers of various density of insulation material being used to fill the air gap. Then you have the wood framing, on the inside of which are layers of plasterboard which is the second leaf. Then there is more insulation and a fabric front. I think I see the issue... it's important to understand that none of those layers of insulation is a leaf, and when there's several sheets of partictleboard attached together, those all form a contiguous "mass" and represent one leaf. (though I grant I'm uncertain about the effect of that bonded cotton felt... I'd have some concerns that represents it's own gap, and that a further sheet beyond it would function as a 3rd leaf... I'm not sure) At the moment though, I think I'm only seeing 2 leaves. 4: Mass on each of your leaves = good. Yes, block is often successfully used for one of the leaves, however I often see Stuart warning that block/mortar/etc can be porous and to make sure you're sealing them to get your airtight boundary. 5: Re: the web link, Just a quick reminder, that it's not just the mass, but also it's placement and the amount of air gap (air gap is shown on the charts, but not the placement of the mass. You can double your mass but not get the expected results if the wall is not put together correctly. As a great example, look at number 6 on the following page: http://www.stcratings.com/assemblies.html The first example under 6, and the 4th example under 6 have identical amounts of mass, but significantly different isolation. In regards to whether you will get 5db every time you double the particleboard on the inner leaf, leaving the brick wall side alone, I don't believe that is correct. It appears to me that he is referring to doubling BOTH sides, and that by doubling the mass only of the inside portion, that you would have less impact. Example: the link I gave, on number 6 shows a move from 56-59 to 59-60 doubling just one side of the equation, and it goes to 58-63 if both sides are doubled. Yes, green glue has a dampening effect and will aid. 6: Hmmm... I've got the 2nd edition of Rod's book, so page 130 is the start of the chapter with no diagram. I think that you're referring to a diagram on page 141 for me. Isolation between the mechanical room and the sound room comes in a couple of ways... first, by sealing the penetration very tightly. Second, in his mechanical room, the noise components are actually outside the building, and he's talked about the need for canvas duct connectors if metal duct is used to prevent vibration transmission. The Ducting would commonly be lined with absorption and would have silencers at the outflows. Designs for that can be found on the forum, but they basically involve making the air flow around corners so that sound never has a direct path to follow. (with a wide enough path that there's not significant constriction of air creating noise) As for extending the loop, I actually have an outstanding question on that point on my own thread... I'll let you know if I hear.

Thank Johnnie. I think Newell's designs seem great, but a bit untested in these waters, so I am going to keep it simple! Okay, now for a few 'reality check questions'. I have been tracing the first reflections of the studio, and finding it hard to get all the angles to agree. 7) Up to what angle do I need to consider for speaker dispersion? (the speakers are Focal Twin 6BE) 8) With free standing monitors, I believe I need to treat the front wall. According to Genelec the closer to the front wall the better http://www.genelec.com/learning-center/presentations-tutorials/placingloudspeakers/freestanding/. As there is a tradeoff between thickness of absorption and distance from the wall, what should I go for? Now for the BIG questions: 9) With the room being the size it is (4.7x3.8m), the maximum termination gap I can achieve is ~15ms. Am I wasting my time trying to send first reflections to the back of the room? Should I just absorb, absorb, absorb? 10) There is some conflicting view on the forum whether to build the inner leaf with splayed walls, or to build square and then add rfz reflectors (filled for bass trapping). Having a splayed inner leaf will give me some room for ducting, which seems like a good use of space. In my situation, which is preferred? I have attached the modified Idea 2.

Going back to 6) While I understand the importance of caulking and decoupling the ducting between rooms, this still does not satisfy my concerns. Lets say that the ducting has an airborne TL of 10dB between its interior to the exterior. The sound in the 'sound room' is 110dB, and is transferred to the interior of the duct where it is 100dB. It is then free (apart from some absorbtion) to continue along the duct until it is in the machine room. From there it radiates out of the ducting into the machine room, losing 10dB as it goes. This means that there is going to be less than 30dB isolation between the rooms (as far as I understand). Am I thinking about this incorrectly?

Supporting image: Larger: https://dl.dropboxusercontent.com/u/398059/DuctingIsolationQ.jpg

With the room being the size it is (4.7x3.8m), the maximum termination gap I can achieve is ~15ms.

Not really. For RFZ, it's a combination of two things: ITDG plus level. Originally it was 20 ms and -20 dB, but that's hard to do in most rooms and turned out to not be totally necessary. 15 ms and -15 dB works out pretty well for most rooms, and in small rooms you can even relax that to 10 ms and -10 dB without too much harm (although its not ideal). The point is, as long as you are meeting the level criteria, then it doesn't matter so much if you are meeting the time criteria. For example, if you are at -20 dB with your 15ms limit, then you are fine, but if you are only at -5 then you have a big problem!

Am I wasting my time trying to send first reflections to the back of the room? Should I just absorb, absorb, absorb?

That's what the back of the room is for! To "absorb, absorb, absorb". That's why hangers are so well regarded here, or at least very thick insulation with an air gap behind it. If the rear wall is doing its job, then the room actually seems a bit longer, as far as sound waves are concerned, and also the levels coming back to yer ears will be low enough (and hopefully diffuse enough) to not matter.

10) There is some conflicting view on the forum whether to build the inner leaf with splayed walls, or to build square and then add rfz reflectors (filled for bass trapping).

Could you point to any posts about that? Adding reflective surfaces later isn't a good idea in general, unless they are very massive and rigid, but in that case it's the same as just splaying the walls... :) Maybe you are confusing slot walls for "RFZ reflectors"? Not really the same thing....

Having a splayed inner leaf will give me some room for ducting, which seems like a good use of space. In my situation, which is preferred?

Right! The space between the angled section of the side walls can, indeed, be used for HVAC ducting and silencers. That's a smart thing to do, as it makes good use of space. If you leave the inner-leaf rectangular and then add angled surfaces, you waste that space...

Lets say that the ducting has an airborne TL of 10dB between its interior to the exterior. The sound in the 'sound room' is 110dB, and is transferred to the interior of the duct where it is 100dB. It is then free (apart from some absorbtion) to continue along the duct until it is in the machine room. From there it radiates out of the ducting into the machine room, losing 10dB as it goes. This means that there is going to be less than 30dB isolation between the rooms (as far as I understand).

That's why you can't rely on ducting alone to do the job. You need proper silencer boxes to do that. The accomplish several things at once: the sudden change in cross sectional area at the entry and exit points is a major impedance mismatch for sound, which has a really good effect on reducing the intensity of sounds getting through. Then, it provides a path with multiple 90° bends in it for the air, which the sound waves cannot follow, so they are attenuated by the baffles instead. Next, it lengthens the total path considerably, placing more distance between the sound source and the receiver, which also helps. And finally, the lining absorbs even more acoustic energy as the air moves past. The overall effect is a substantial reduction in sound getting through. Also know as "insertion loss". - Stuart -

Thank you Stuart for your responses. That is really good news regarding the ITDG, and definitely good to know before I built it! One of the main proponents of this is John Brandht. This article presents his position well: http://jhbrandt.net/NewsletterArchive/StudioDesignNewsissue2.html Not to sound like a broken record, but regarding loudspeaker dispersion and reflections, when should I stop worrying about reflections. The measurements for my speakers show little loss of energy around 4kHz, even at 60 degrees. Here is the link: http://www.focal.com/en/index.php?controller=attachment&id_attachment=2603 I guess that at >90 degrees the baffle becomes an obstruction (for HF at least), so the level drops enough to not be a concern. Is that it? 90 degrees? HVAC: A ha! Silencer box, that is the term I needed. Back to reading more about ventilation :D

This article presents his position well:

Right. And an important comment in that article (right after he explains why he doesn't recommend splayed walls in most studios), is this: "However, there is a large benefit to angled treatment in an RFZ design.". Yup! :)

Not to sound like a broken record, but regarding loudspeaker dispersion and reflections, when should I stop worrying about reflections.

You probably don't need to go more than about 50° or 60° off axis. Beyond that it is mostly low frequencies, which aren't so much of a problem anyway.

The measurements for my speakers show little loss of energy around 4kHz, even at 60 degrees.

True, but that is the total energy coming from the speaker. It would be more useful to see the plot for each of several frequency bands, and not worry too much about lows. If you ray trace out to 60° off axis, then you are covering the most important issues.

I guess that at >90 degrees the baffle becomes an obstruction

:?: 90° off-axis is PARALLEL to the baffle! If you build your soffits right, then there is no energy radiating form the speaker into the room beyond 90° off-axis. Beyond 90° is behind the baffle, inside the soffit. I noticed that I missed a couple of questions from an earlier post, so I'll try to cover those now:

1) With the rooms built on the concrete slab, at what point will flanking through the floor surpass my efforts to increase wall & ceiling transmission?

Depends on several factors, but by the time you get up to maybe around 65 to 70 dB of isolation, it's really hard to get beyond that at all, without going to extremes. At such high levels of isolation, doors and windows become big issues, needing multiple seals, and HVAC also becomes a big issue: Building silencers for 70 dB insertion loss is a taaallll order.

2) Newell seems to be a fan of multi-leaf construction with the justification that each layer will reflect at some frequencies, absorb at others, and let sound through at the rest.

Yes, but as you may have gathered, not everyone is a fan of his theories, and there's a lot of research that shows common two-leaf MSM isolation walls to be very effective at isolating studios, which is why most studios are built that way these days. I'm not saying that Newell's methods don't work: just that there are other methods that have been demonstrated to work very well, with mountains of laboratory testing to prove it, and well-tested equations to predict and calculate results, and those have shown that 2-leaf MSM walls are very effective down to very low frequencies, while multi-leaf walls are less effective at low frequencies, even though they do better at high frequencies. But high frequency isolation is not an issue anyway: According to simple mass law, ANY wall that isolates well at low frequencies will isolate much better at high frequencies. Also, in most studios it is precisely the low frequencies that are the biggest problems, not the highs, so that's where the efforts should be concentrated. But please don't think I am arguing against what Newell teaches: I'm not. His method also works, as do others. The point is that there are other ways of isolating that use less total materials, less space, are less complicated to build, and isolate just as well, or better. Fully-decoupled 2-leaf MSM is the best of all methods, in the sense that it is the simplest to understand, and calculate, and build, uses the least amount of material, and is the least expensive. For most home-studio builders, those are the things that matter most, especially the "least expensive" part! :) On the other hand, the studio with the best isolation in the world (Galaxy, in Belgium), also happens to be built using the fully-decoupled 2-leaf MSM, so draw your own conclusions from that... :)

By having several different constructions, the resonances of each layer are different (more even TL), and the level of extra acoustic treatment is reduced.

Yes, but like I mentioned above: at the cost of more materials, more complexity, more cost, and less effective low-frequency isolation (all other factors being equal).

Looking at Rod's book and this forum, this method seems less popular around here.

Right! :)

Is there a particular reason for this (cost / availability of materials, inconsistent results, less accessible, etc)?

All of the above, but basically it boils down to simple physics. It works like this: a decoupled 2-leaf wall has a specific resonant frequency that can easily be calculated from the simple equations of resonance for mass-spring-mass systems. At the resonant frequency, it does not isolate at all, but at all other frequencies it isolates very, very well. A simple analogy makes it easy to understand: if you push a child on swing, the swing goes at one single rate, back and forth, no matter how hard or soft you push it. The rate is set by two factors only: the length of the rope, and the weight of the child. If you try to push the swing faster, it refuses! There's no way you can change the speed, no matter how hard you try, unless you force it throughout the entire cycle, with a huge amount of effort. And as soon as you stop forcing it, it instantly goes back to the exact same speed as before. Why? It is a tuned system. It will resonate at only one natural frequency, and it will refuse to resonate at all others. It strongly resists being forced to resonate at any other frequency except its natural resonance. The same principal applies to clock pendulums, bungee jumpers, your car's shock absorbers, and ANY system that consists of a mass attached to a spring. Such as a wall, for example... :) The drywall on each side is the mass, and the air in between is the spring. We don't normally think of air as being "springy", but to a sound wave it sure is! So a two-leaf wall is a tuned Mass-Spring-Mass system (MSM), and will only resonate at one frequency. Even more important, it will actively resist resonating at all other frequencies. So imagine what would happen if you could "tune" the wall so that its resonant frequency is totally outside of the audible spectrum... :shock: Yup. You got it: it isolates across the entire spectrum, and it does so really, really well. It turns out that you can tune a wall such that its resonant frequency is lower than the lower limit. All you have to do is to put enough mass on each side, and make the "spring" springy enough. And it isn't hard to do: you just leave a large air gap between the two leaves. The bigger the air gap, the lower the frequency. The more mass on each leaf, the lower the frequency. This is why a 2-leaf MSM wall is generally considered to be a great method for isolating a room. So some people think "If two is good, then three must be better". Wrong. It turns out that if you add another leaf to the system, so you have an "MSMSM" system ("Mass-Spring-Mass-Spring-Mass"), then the resonant frequency of the entire system goes UP, not down. And it goes up into the audible spectrum again, meaning that such a wall isolates WORSE for low frequencies than a two-leaf wall of the same total mass and thickness. Simple physics proves that, as do numerous laboratory tests. A 3-leaf wall isolates better in the high frequencies (which are not a problem anyway) than the equivalent 2-leaf, but it isolates worse in the low frequencies. Of course, you can add even more mass to a 3-leaf, and make the air gaps even bigger, to compensate, and that works.... but it eats up a lot of extra space, uses a lot of extra materials, costs much more, and is far more complicated to build. That's why most acousticians use 2-leaf MSM walls for isolating studios: it is the lowest cost method of doing so, that uses the least amount of materials and the least amount of space. Once again, it is not the ONLY method for isolating: sometimes you have no choice but to have part of a studio done with a three leaf wall (or even worse, a single leaf wall). But 2-leaf is the cheapest, simplest, least materials, least complex. So my question is: why complicate life when you don't need to? It is complicated enough already! :)

3) Common practice seems to include the use of sound locks (sometimes used as booths) between rooms. I believe this is to allow a lower door specification. At what point is this big enough not to be considered a quadruple leaf (reducing TL)? Is this a waste of space in a small studio?

... at the point where the MSMSMSM resonant frequency can be made lower than the MSM resonant frequency for the far simpler method that Johnnie described: two doors, back-to-back, one in each leaf. In order to do the soundlock, you need large air gaps to force the frequency low enough. And you also need twice the total mass, twice the number of doors, twice the number of hinges, twice the number of seals, twice the number of closers.... :)

4) At the moment two of the walls are built with brick (one is exterior) and the ceiling is poured concrete. Is it worthwhile to do the remaining two exterior shell walls with sand filled concrete blocks?

Yes. The thing with any resonant isolation system is that it has to encompass the entire room. So the mass (surface density) has to be kept more or less even around the entire room. If not, then the part with the lowest mass will have a much higher resonant frequency behind it, and therefore will isolate poorly. so if you have great mass on three sides, the floor and the ceiling, then it makes sense to continue that mass around the other side too, in order to maximize the isolation.

5) Does anyone know of TL data available for: Brick-Air-WoodStud-Plasterboard-Plasterboard, ConcreteCeiling-Air-WoodStud-Plasterboard-Plasterboard?

I assume you mean that the first one is your walls, and the second one is your ceiling? If so, then you can find the answers to your wall question in IR-761, IR-586, IR-693 and IR-832. The answers to your ceiling question, can be found in IR-766, IR-802, and IR-169.

At the moment I am allowing 125mm to the stud (to give a comparable air gap to a dual stud wall), is this excessive?

Probably not excessive, but to be certain you'd first have to know how much isolation you need (in terms of decibels), and what frequencies you need it at.

6) HVAC. I am struggling to find much beyond 'don't let HVAC be the weak spot in your construction', and a comparison of ducted and mini-split systems. Please can someone please point me in the direction of some good literature and/or some worked implementations of good systems (including fresh air supply).

Rod's book has a good chapter on that, to walk you through the basics. And there are many, many threads here on the forum that show how people have built their systems, and the results they have obtained. Use the search feature to find threads that deal with HVAC. The search feature isn't fantastic, and doesn't offer many options, but it can get you on the right path. - Stuart -

Okay, HVAC is seeming a bit clearer. For the moment, I wouldn't mind your thoughts on the following (2d for now) design. The acoustic treatment is still a little sparse, but I am thinking alternating diffusion and absorption for the live room, with corner bass traps (including wall --> ceiling), plus a fully absorbent ceiling. For the control room any free corner will have trapping, and the ceiling will have clouds (to try and keep some impression of height). I am also interested in the diy VPR bass traps LF control, but I need to do some more reading first.

You're not going to soffit mount the speakers?

Johnnie, I am tempted by the benefits, but I don't think I will. Here is my reasoning: - I am a big fan of my Focal Twins, which don't seem particularly suited for flush mounting. - Without spending a lot of money (>£4k), speaker choice seems pretty limited to Genelec's, which aren't my favourite. - In the studios I have worked at (even ones with good flush monitors), most engineers prefer near fields. - It's silly to say, but small speakers flush mounted in small rooms look pretty amateurish. In other news, I may now have the whole 125m2 basement to play with... Designs to follow!

- I am a big fan of my Focal Twins, which don't seem particularly suited for flush mounting

Why not? The Focal Twin 6 is not rear ported or side ported, and does have the necessary adjustments on the rear panel, so I'm not sure why you think it would not be suitable.

- Without spending a lot of money (>£4k), speaker choice seems pretty limited to Genelec's, which aren't my favourite.

A pair of Adam A7Xs or even A8Xs should come it at less than 4k, I would expect, unless they mark them up pretty high where you live.

- In the studios I have worked at (even ones with good flush monitors), most engineers prefer near fields.

Well, I really hate to say this, but I'm not big on following the crowd of what "most engineers" do or don't do. I'm much more interested in getting the absolute best technical characteristics for my room that I can afford, and the only way to do that is to soffit mount the speakers. Even nearfields can be soffit mounted... And curiously enough, there actually isn't any technical definition of what "nearfield" means! Anyone can build any speaker they like, slap a "nearfield" label on it, and nobody can technically say that they are wrong.... :)

- It's silly to say, but small speakers flush mounted in small rooms look pretty amateurish.

Like these ones, for example: I'm not too sure I would consider any of those "amateurish looking"... :) And yes, those are all home studios in small rooms with soffit-mounted small speakers.

In other news, I may now have the whole 125m2 basement to play with...

Now THAT would be cool!! with a space that big, you could do something pretty amazing, provided that the ceiling is high enough. - Stuart -

If I may ask a question related to this thread, but it's for my own edification. Earlier I'd advised thismanysounds that different materials were OK as long as the isolations were comparable. Stuart you'd recommended that it would be beneficial to have those extra walls built the same way so that consistency would be achieved. (thismanysounds... always go with Stuart if there's ever an inconsistency between his advice and mine... I'm an amateur early in the learning process, he's the expert with real practical experience.) I just wanted to ask whether same materials are really important, or is it comparable isolation that's important regardless of material? Or maybe it's just a practical issue and getting sufficient mass to match a sand filled brick wall is just impractical with wood built construction...

Johnnie, I really appreciate that this has stayed in your mind, despite my silence for the last week. The way I read it, it was more that the mass was consistent rather than the absolute material. So here is where I am at the moment: - We now have a much larger area in the basement we can use (~130m2). - There still needs to be access across the basement (see sketchup model). - The extra space should add function, and not just room size. As such a second control/edit room and lounge is desired. - Part of the basement is not submerged, so has thin single pane windows. - The absolute slab to ceiling height is 3.15m, so height efficient construction is desired. Attached is my current design. Here is my reasoning: - Two control rooms share a larger live room. Larger live room makes for better recordings. - One of the control rooms (A) is larger (with better spec). The second (B) is more of an edit room. - Studio A is now a Non-Environment design. I have heard similar rooms before, and enjoyed them. It also makes listening across the room more enjoyable (less of a sweet spot). - Studio B can double up as booth for large sessions, or for overdubs (using the live room) if Studio A is mixing. - This is a project studio, so this seems like a better use of space rather than two isolated live/control studios. - The existing windows/daylight/poor isolation walls are used for corridors and lounge space, rather than blocking them up. Let me know your thoughts! Colm

Actually, scrap that. I have a few questions: HVAC system (see attached photo) - Seeing as I need ducting with silencers for ventilation anyway, it seems logical to go for a ducted air handler system rather than 3x mini splits. Good idea / bad idea? - With silencer boxes, do I need them internally in the rooms (as per the diagram)? I guess the advantage of doing so means that the sound is attenuated before it reaches the shared cavity. - For Control B, will it be better isolation wise to have a separate cool air supply run from the boiler room along the corridor? - What size silencers are needed to achieve the isolation desired? - I have put in a HRV unit to handle the fresh air and to 'push' the air. Is this sufficient, or will I need extra fans for air flow? - The common convention seems to be cool air supply is at floor level (front of CR) and air exhaust is at ceiling level (back of CR). Is there any reason why I would go against this? Flush mounted monitors - Now that the room is a bit bigger, and Stuarts persuasion, I am going for flush mounted speakers. I know that this wall needs to have high mass to work. Does the inner leaf continue behind the speaker creating a box, or does the new massive wall now act as the inner leaf? Low frequency absorption - At what size does it start to make sense to use hangers over other designs? - It seems like: Internal Wall -> VPR absorber (125mm) -> 100mm Rockwool -->Fabric would perform well at LF as well as broadband at a small depth (<250mm). The downside, is that the materials are expensive. If I don't have the space for hangers, what is the best way of achieving Non-Environment absorption?

- Seeing as I need ducting with silencers for ventilation anyway, it seems logical to go for a ducted air handler system rather than 3x mini splits. Good idea / bad idea?

Good idea! For three rooms, yes, definitely worth doing that.

- With silencer boxes, do I need them internally in the rooms (as per the diagram)? I guess the advantage of doing so means that the sound is attenuated before it reaches the shared cavity.

As long as you put them right at the room boundary (inner-leaf), then it doesn't really matter if you put them in the room or in the cavity between the leaves. The advantage of putting them in the wall cavity is that those things are BIG, and take up a lot of space inside the room, so putting them outside makes the room less cluttered and more spacious.

- For Control B, will it be better isolation wise to have a separate cool air supply run from the boiler room along the corridor

?I prefer to always use one duct per room, rather than trying to share a duct between two rooms. The reason is simply that it is very hard to balance the air flow properly between the rooms when you have a shared duct: As you close down the damper for one room, you automatically force higher flow into the other room, like it or not. And the converse also: as you open up the damper to get more flow in one room, you automatically rob the other room of some of its flow. So it's better to run a large central duct plenum with branch ducts and silencers for each room, or to just split them right at the air handler into individual ducts that go to each room, in which case it is easy to have all of the dampers right there, at the air handler, where you can reach them easily for maintenance, repair or replacement.

- What size silencers are needed to achieve the isolation desired?

The cross-sectional area inside the silencer needs to be at least twice that of the duct, and the registers need to be at least as large as the silencer cross-section, or even larger. This is to keep the air flow velocity very low, to reduce air noise, and also to create two "impedance mismatches", where the cross section changes suddenly, which greatly attenuates the sound. Then the number of baffles inside the silencer and the total length of the air path are factors in providing isolation: I have not yet found any way of calculating how much attenuation you get from each baffle (a lot), but there are tables that show how much you get from air path length for different cross-sections (not much). So as a general rule of thumb, I would do one or two baffles for low to medium isolation requirements, three for medium, and four or more for high isolation requirements. The final point is that, since the HVAC duct is basically a huge hole in your isolation wall, the silencer has to be built the same way as the wall: Keep the same surface density on the silencer box at the place where it goes through the wall. Obviously, at the other end of the box you don't need to do that, since you are just connecting to a thin metal thing, but it's easier to just build the box with the same surface density all over.

- I have put in a HRV unit to handle the fresh air and to 'push' the air. Is this sufficient, or will I need extra fans for air flow?

Assuming that your rooms are properly sealed (ie, absolutely and totally air-tight), and that the final static pressure of your complete ducting system is within the specs of the air handler unit, then you probably don't need extra fans. You only have problems when the static pressure is too high for the AHU to handle, which leads to overloading of the fans, inefficient operation, and early failure of the fan motor. Not to mention increased noise...

- The common convention seems to be cool air supply is at floor level (front of CR) and air exhaust is at ceiling level (back of CR). Is there any reason why I would go against this?

Personally, I prefer to do it the other way around: cool air in the back, and exhaust air out the front. Since most of your equipment is usually at the front of the room, it makes sense to have the exhaust above that, extracting it directly, instead of forcing the warm air to flow across the rest of the room to get out. And yes, the general HVAC contractor recommendation is to have the supply coming in down low on the wall, but in most studios that is hard to do, since the silencers are so big that they take up a lot of space, either behind the wall or inside the room. So I generally put the supply registers in the ceiling, and direct the air flow down or sideways from their. Cool air will descend in the room naturally, especially considering that the air flow speeds are very low: the registers are not forcing strong jets of air across the room, but rather gently diffusing air into the room, where it descends towards the floor and is drawn across the room, rising again past the equipment to the return registers, at the top front. At least, that's the way that seems to work for me.

- Now that the room is a bit bigger, and Stuarts persuasion, I am going for flush mounted speakers.

:yahoo: :thu: :!: :-D

I know that this wall needs to have high mass to work. Does the inner leaf continue behind the speaker creating a box, or does the new massive wall now act as the inner leaf?

The inner leaf is actually both! :) Yes, it dies continue behind the speaker. If it did not, then the speaker would be inside the MSM cavity, which would mean that it only had a single leaf isolating it from the other rooms or the outside world. But the front surface of the soffit (technically, the "baffle") also becomes the inner leaf, in the sense that it is now the hard boundary of the room, so that's what you use for your room calculations.

- At what size does it start to make sense to use hangers over other designs?

That's probably a question for John, since he's the expert on hangers, but they have to be pretty big to be effective (like all low-frequency treatment. You should allow for at least a couple of feet depth at the rear of the room.

If I don't have the space for hangers, what is the best way of achieving Non-Environment absorption?

NE and RFZ are very similar in that aspect, so if you don't want to use hangers then I would use large Superchunks in the rear corners plus at least 20cm of absorption across the rest of the rear wall, with air space behind it, and possibly angled forward (larger gap at the top than the bottom). Not sure how you would combine VPR and superchunk though, as they both need to go in the same place, roughly. You might also want to use diffusion in front of the superchunks: perhaps pyramids of various sizes, or polys, or random slats. Or if the room is large enough, maybe even tuned diffusers, such as Skylines, QRDs, or something like that. But the room has to be big enough for that, especially if you want to have a couch at the back: you have to leave enough space between the diffuser and the closest seating position, to avoid hearing the artifacts. - Stuart -

Thanks Stuart, slowly but surely I am getting a grip of this. A/C is not common domestically here, so my starting knowledge is almost none. Silencers I didn't ask this question very clearly, so I am still a little confused. The silencer can be attach on the inside or outside of a leaf, as long as it doesn't couple them. Do I need a silencer for each leaf of the wall? My intuition tells me this is yes, down the same concepts as the drawing I posted earlier in the thread. Rear Wall Bass Traps My GOAL is to achieve good LF control without loosing too much space from back wall. As feared, hangers will need >1m to work, so I am looking at membrane, VPR and helmholtz options. These work well with smaller depths (especially VPRs), but being solid plates will reflect highs back into the room, denying the NE criteria. I would like to have a velocity based trap on front to counter this, hence the VPR - Rockwool idea. The real question is 'Does it work to have a porous absorber in front of a pressure (e.g. membrane) trap?' Side Wall Trapping There is considerable area in the side walls for trapping, but it is shallow. Is this a good spot for hangers? The maximum depth is 700mm, so a porous absorber (with air gap) should get pretty low. Bass Trapping Concepts In the room, there is modal support from about 40Hz, below which it is pressure dominated. As the room will effectively have the same pressure everywhere, does this mean that I cannot do any effective trapping? Does it even matter if the room modes aren't ringing? Flush Wall So that box is going to take up the space I had planned for silencers, which is a pain. Also, the idea of creating a small box (even heavily damped) seems like asking for trouble! How big does it need to be? If if boxed in behind the speaker (with the same mass as the wall), then the speaker would be in the inner leaf. Using passive speakers to removing the cooling requirement, would this work?

Okay, so I had a chat with a distributor of acoustic products which has slightly dented my confidence in my isolation plan. The current plan is to create a dense outer leaf (100mm thick dense concrete block) around the studio area, and then construct stud walls for the studios (100x50mm wood stud, 19mm plasterboard, 19mm plasterboard). A minimum air gap of 250mm between leaves will be maintained. The inner leaf ceiling will be built on the stud walls, with 2x19mm plasterboard, the joist size is to be determined, but will maintain the 250mm air gap. This gives me a MSM frequency of 33Hz between stud walls, and 25Hz between stud and blockwork. This was using Eric Desart's calculator, which I don't think incorporates this lowering due to insulation. Does this need to be less than 20Hz, or lower than 10Hz like a floating floor? The distributor proposed: Block wall - 200mm air - wooden stud - resilient channel - 19mm plasterboard - quiet/green glue - 19mm plasterboard - quiet/green glue - 12.5mm plasterboard. This seems excessive, and very material heavy. Also, I was under the impression that resilient channel was unnecessary with separate stud walls, and would reduce LF performance due to increased stiffness. Is he on to something, or just trying his luck? Also, I am contemplating green glue between the 19mm plasterboard layers. Will this be beneficial with my wall plan?

Do I need a silencer for each leaf of the wall? My intuition tells me this is yes, down the same concepts as the drawing I posted earlier in the thread.

For high isolation, yes, that's the best way to do it.

My GOAL is to achieve good LF control without loosing too much space from back wall.

:) This might sound a bit trite, but "good luck with that"! Not meant to be insulting: just a comment on how hard it is to put a large amount of bass trapping in a small space. You are fighting against the laws of physics there. Yes, VPR's are rumored to accomplish that to a certain extent, but as you point out, the are also reflective for highs and mids. And I'd still like to see some independent laboratory test results on VPRs, to see how they perform under suitably controlled conditions, before committing to them. I guess there must be something out there already on that: I haven't really looked. Also, I'm not sure if you have decided to implement a true RFZ design, but if so you'll still need sufficient absorption on the rear wall to attenuate ALL frequencies enough to meet the criteria. That's hard to do without at least a few inches of absorption.

As feared, hangers will need >1m to work

Not necessarily: you can angle them, and fit them into a smaller space, just not quite as effective. Perhaps 60 cm or so.

The real question is 'Does it work to have a porous absorber in front of a pressure (e.g. membrane) trap?'

I can't think of any reason why that would not work.

There is considerable area in the side walls for trapping, but it is shallow. Is this a good spot for hangers? The maximum depth is 700mm, so a porous absorber (with air gap) should get pretty low.

How much absorption does the room need (total sabins), and what frequencies are you predicting you'll need to cover? Side walls are good candidates for slot walls, except for the first reflection points, of course, where you need thick absorption.

In the room, there is modal support from about 40Hz, below which it is pressure dominated. As the room will effectively have the same pressure everywhere, does this mean that I cannot do any effective trapping?

Not really. The pressure doesn't really remain constant everywhere; it just varies constantly everywhere, like blowing and sucking on a paper bag. So there are still pressure variations in the room at lower frequencies, just that they vary consistently everywhere. Think of it like the speaker cone acting sort of like a piston in a large cylinder, where the room is the cylinder. And since there's no such thing as a perfectly rigid building material, the the entire room also "breathes" to a certain extent along with those pressure changes. Not much, of course, and it depends on the construction, but there can be some movement there. In other words, pressure based traps can still work (eg, panel traps, membrane traps, and even Helmholtz resonators) , and so can velocity based traps; they just aren't very effective.

Does it even matter if the room modes aren't ringing?

How do you prevent a mode from ringing? :) Modes are a fact of life, always present. A mode might be triggered to a greater or lesser extent, by higher or lower levels of sound, but it is always there, potentially. The only way to prevent a mode from ringing is to not play any note at that frequency loud enough to trigger it. Since that's not really an option, all modes can potentially ring. You can't stop them. But what you CAN do, is to damp them, so that the ringing us under control, and consistent with the rest of the room decay.

So that box is going to take up the space I had planned for silencers, which is a pain. Also, the idea of creating a small box (even heavily damped) seems like asking for trouble!

I think you are taking about the speaker soffits here, right? If so, the volume of the box behind the front baffle is irrelevant, acoustically: it isn't even "inside" the room, technically, so it has no effect on the room acoustics. The only thing that matters, is the size of the front baffle, and the angle that it is set to the room. What happens behind that baffle might as well be in a different universe, since it has little effect on the room. However, it does have an effect on the speaker itself, of course: speakers need cooling, as you mention, so that's the key issue here: as long as you have enough ventilation for your speaker, then you'll be fine. The insulation inside the soffit cavity is there for one reason only: damping. It damps any resonance that might be going on inside the cavity. So the size of that cavity isn't too important, as long as it is well damped and provides a suitable ventilation path.

How big does it need to be?

The cavity size doesn't really matter: It's the size of the front baffle that mattes (width and height, margin around speaker, etc.).

If if boxed in behind the speaker (with the same mass as the wall), then the speaker would be in the inner leaf.

That's not an "if": It is a "must"! The speaker MUST be boxed in behind with the same mass as the wall: If you don't do that, then the speaker is emitting serious sound levels into the MSM cavity...

Using passive speakers to removing the cooling requirement,

Passive speaker still need cooling when played at high levels. Maybe not as much as active speakers, but still need some.

The current plan is to create a dense outer leaf (100mm thick dense concrete block) around the studio area, and then construct stud walls for the studios (100x50mm wood stud, 19mm plasterboard, 19mm plasterboard). A minimum air gap of 250mm between leaves will be maintained. The inner leaf ceiling will be built on the stud walls, with 2x19mm plasterboard, the joist size is to be determined, but will maintain the 250mm air gap.

Good plan. Theoretically, that will tune your wall to about 16 Hz, so it will start isolating at around 23 Hz, isolate reasonably from around 32 Hz, and isolate decently above 48 Hz. Isolation should be around 52 dB. That's all theoretical, of course: Assuming you build everything perfectly. Reality might be different, but you should be able to get close to that.

This gives me a MSM frequency of 33Hz between stud walls, and 25Hz between stud and blockwork.

Not sure where you got that! The simplified for of the MSM equation for very massive outer leaves is F0 = 60 / SQRT(m * d) with no internal damping, and F0 = 43 / SQRT(m * d) for fully damped. "m" is around 29 kg/m2 in your case (two layers of 19mm drywall), and "d" is 0.25 meters. With those parameters, F0 = 15.97 Hz. Even if you go with the full version of the equation ( F0 = 43[(m1 + m2)]^.5 / [(m1 x m2 x d)]^.5 ), using more realistic values for the surface density of the concrete, it only changes things by a couple of Hz. Are you sure you plugged in the correct values?

Does this need to be less than 20Hz, or lower than 10Hz like a floating floor?

What is the lowest frequency that you need to isolate? That's the key. Not many people need to isolate all the way down to 20 Hz... You'd only need to do that if your work in the studio involves serious effects work for movies, or something like that, where you are doing earthquakes, canon fire, heavy rumbling, and that type of thing. You'd also need some pretty decent subs to get down to 20 Hz cleanly. Do you need that? If you are just doing typical music, then there's no need to go that low.

The distributor proposed: Block wall - 200mm air - wooden stud - resilient channel - 19mm plasterboard - quiet/green glue - 19mm plasterboard - quiet/green glue - 12.5mm plasterboard.

Either he doesn't understand the purpose of resilient channel, or he does understand it but wants to sell it to you anyway! :) If your inner-leaf is already decoupled (which it is, due to the second stud frame), then there is no point in decoupling it a second time. The 12.5mm plasterboard is also questionable... Why? For what purpose? If he thinks your wall needs that much mass, then why not put at least 16mm drywall on there. 12.5 is not much use.

Also, I was under the impression that resilient channel was unnecessary with separate stud walls, and would reduce LF performance due to increased stiffness. Is he on to something, or just trying his luck?

I vote for "trying his luck"... :)

Also, I am contemplating green glue between the 19mm plasterboard layers. Will this be beneficial with my wall plan?

Yes. It's a proven product, well tested in independent labs, with published results. It works. It will be beneficial, especially for low frequencies, since that is where it helps most. - Stuart -

Okay, lets start with the rough modal calculators (slightly changed dimensions due to similar L & W):

Room Dimensions: Length=4.5 m, Width=4.8 m, Height=2.95 m Room Ratio: 1 : 1.52 : 1.62 R. Walker BBC 1996: - 1.1w / h < l / h < ((4.5w / h) - 4): Fail - l < 3h & w < 3h: Pass - no integer multiple within 5%: Pass Nearest Known Ratio: - "21) Origin unknown: meant for small room" 1 : 1.5 : 1.6 RT60 (IEC/AEC N 12-A standard): 246 ms - ±50ms from 200Hz to 3.5kHz = 196 to 296ms - ±100ms above 3.5kHz = 146 to 346ms - <+300ms at 63hz = 546ms - 300<RT60<600ms RT60 (ITU/EBU Control Room Recommended): 214 ms - ±50ms from 200Hz to 4kHz = 164 to 264ms - <+300ms at 63hz = 514ms - 200<RT60<400ms Absorbtion to achieve ITU RT60: 514 sabins Volume: 63 m^3 Surface Area Total: 96 m^2 (sabins - front wall - carpet) / Left+Right+Rear wall: 31 % (sabins - front wall) / Left+Right+Rear wall: 84 % Schroeder Fc: 109hz Frequency Regions: - No modal boost: 1hz to 38hz - Room Modes dominate: 38hz to 109hz - Diffraction and Diffusion dominate: 109hz to 436hz - Specular reflections and ray accoustics prevail: 436hz to 20000hz Count (35.8-195hz) : Axials=13, Tangentials=55, Obliques=75 Count (35.8-100hz) : Axials=5, Tangentials=7, Obliques=1 Critical Distance (direct = reverberant field): 4.50m

So that is 514 sabins. I hope that is in imperial. So does that mean I need 14.6m3 of perfect absorption? How does that translate to treatment? Seeing as I have a fair bit of width / want to minimise the complexity of the build, I plan on simply absorbing the first reflections (NE style) rather than having a nice termination. The smaller control room will probably in an RFZ vein. In regards to the independence of the test results, Fraunhofer are a very respected in research, and any 'field' results I have seen show good results. The thinner (1mm steel - 50mm basotect) VPR shows 0.8 absorption up to 250 Hz where a porous trap (with >150mm remaining depth) should come into effect. The other option is a membrane absorber, but as they have a higher Q and trickier construction, I am still leaning on the VPR side (despite the cost). Thank you for your response about the modal region, however I was asking about something different (sorry for the poor phrasing on my behalf). My main questions are: -What happens in the time domain below modal reinforcement? - Does the room still resonate or does the replay system limit the transient response? - Do I need to worry about absorption below the modal region (38Hz in my case)? I have attached a screenshot of the MSM calculations.

Soundman2020 wrote:

The current plan is to create a dense outer leaf (100mm thick dense concrete block) around the studio area, and then construct stud walls for the studios (100x50mm wood stud, 19mm plasterboard, 19mm plasterboard). A minimum air gap of 250mm between leaves will be maintained. The inner leaf ceiling will be built on the stud walls, with 2x19mm plasterboard, the joist size is to be determined, but will maintain the 250mm air gap.

Good plan. Theoretically, that will tune your wall to about 16 Hz, so it will start isolating at around 23 Hz, isolate reasonably from around 32 Hz, and isolate decently above 48 Hz. Isolation should be around 52 dB. That's all theoretical, of course: Assuming you build everything perfectly. Reality might be different, but you should be able to get close to that.

Stuart, can I question you on that number? Are you talking STC numbers (a dirty word around here!) or what I could expect once isolating decently (>48Hz)?

Stuart, can I question you on that number? Are you talking STC numbers...

NEVER!!!! Blasphemy! Swearing on the forum! Profanity! Bad bad bad!!!! :) :shock: :!: :lol: 8) That's actually a number produced by a spreadsheet I'm working on that does a lot of things to predict isolation. Assuming my spreadsheet is working OK, that's the number you would see on a Sound Level Meter set to "C" and "Slow". So if your meter reads 102 inside, then it should read 50 outside. I chose C weighting, since it is reasonably representative of how we perceive sound. My spreadsheet should eventually produce an actual TL curve as well, that roughly predicts the overall isolation. It's producing a curve already.... just not very believable.... :) When I have spare time, I do work on that, to see if I can get it to produce more realistic results. As it stands now, the "C" weighting isolation prediction and frequency predictions are fairly reliable, but I wouldn't trust the curve yet (which is why I didn't post it.... :) ). - Stuart -