Garden drum studio strategy

Hi all I'm planning a garden drum practice studio project. I'd be very grateful for an initial steer on my outline plans. I'm at research stage really - just thinking about materials. This project is for me to practice and teach drums in a residential garden, so I need to achieve good results. I have described my thoughts below as succinctly as possible. I've built a similar 'room within a room' before, but last time the outer leaf was a pre-existing garage. This time I am building both rooms from scratch, and to circumvent planning requirements (and significantly reduce costs) I am planning to use boards instead of brick/concrete block. So, a summary plan (without dimensions or detailed spec as yet) is as follows: 1. Install a level concrete floor pad, size approx 6m x 5m, with appropriate foundations. Not sure yet about damp proof course. Both frames will be built on the concrete pad.  2. Build an outer frame using 2x4 battening, with a pent roof. The outside of the frame will be covered with 18mm OSB, and all of the OSB will be painted using rubberised paint to waterproof the exterior. 3. On the inside of the outer frame I will fix 18mm chipboard, and will have 2 layers. The outer frame will therefore have 3 layers of 18mm boarding (including ceiling), all sealed with acoustic caulk. 4. Next I will build an inner frame using 2x4 battening, leaving a gap of approx 50cm between the outer frame inside walls and inner frame. I will cover the inside of the inner frame with 18mm plasterboard. This will be 3 layers thick, and made airtight with acoustic caulk.  Is there anything I could think of doing differently for a similar budget, that may give me better results than the above? Very broad question as I haven't specified doors and ventilation, etc, but at the moment I'm just scoping primary materials for this project. Any guidance appreciated! I have no more than £4k available for the entire project. The concrete pad and excavations for this will take about £1k of that for starters I think. I already have foam tiles for the interior and some bass traps. Cheers James

What you describe is a 3-leaf system! :shock: You won't get good isolation for drums like that. 3-leaf is always worse than the equivalent 2-leaf, all other factors being equal. Your slab is great: That's a good start. Your 2x4 framing for the outer leaf is also fine. But you want all of your layers of mass on only ONE side of that frame, never on both sides. So just put 2 or 3 layers of OSB on the outside, taking care to stagger the joints and seal each layer air-tight. I'd also consider adding some type of siding rather than just paint. That won't look too good, and might not perform as well as you are hoping in wet weather. You do seem to be adding a lot of mass to your leaves! That's good, for sure, but do you need that much? How many decibels of isolation are you looking for? You mentioned the walls, but not the roof: what's the plan up there?

Any guidance appreciated! I have no more than £4k available for the entire project.

That might not be enough, depending on how big you want the room to be. Your HVAC system alone will eat up a sizable chunk of that, and 18mm OSB / drywall are not cheap. From what I've heard, building from the ground up in the UK costs around £ 500 per square meter, give or take a bit. so 4k is not going to get you a very big space, realistically. What size will the room be? - Stuart -

Thanks for the reply Stuart The build is 2 leaves but apologies if I've not explained this very well. There are two frames; leaf 1 is on the inner side of frame 1, and leaf 2 is on the outer side of frame 2. With 6 layers of board in total, I felt it may be a little bit heavy; hence 2 frames. Would mounting both leaves off one frame be a good option to reduce costs - perhaps hanging the inner frame off RC? I'll also fill one of the frames with rockwool. The ceiling will have the same approach as the walls, except that it will be a pent design. Hanging 3 layers of plasterboard from the inside makes me a little nervous - again, views appreciated - the rationale is just to maximise mass. I'm a drummer and felt the more pass of each leaf the better. The ventilation and heating will be quite primitive - I'm not expecting to spend too much on this - but admittedly I haven't given it a great deal of thought yet. The completed booth will give me internal space of very roughly 3.4m x 4.6m x 2m(h) I will be sourcing doors off eBay - just solid, heavy doors that I can also reinforce if I need to. I'm also planning a window in one of the walls. Not sure of the size (approx 100cm x 150cm), but again I was going to try and source 2x second hand matching double glazed windows and install them opposite each other in the frame(s); so each double glazed unit is a leaf. James

There are two frames; leaf 1 is on the inner side of frame 1, and leaf 2 is on the outer side of frame 2. With 6 layers of board in total,

That's different from what your first post said, so maybe there's some other type of misunderstanding here. Here's where the three leaves are located in your original post:

2. Build an outer frame using 2x4 battening ... The outside of the frame will be covered with 18mm OSB,

That is leaf number 1: One layer of OSB on the outside of the first frame.

3. On the inside of the outer frame I will fix 18mm chipboard, and will have 2 layers.

That is leaf number two: 2 layers of chipboard on the other side of the first frame.

4. Next I will build an inner frame using 2x4 battening, .... I will cover the inside of the inner frame with 18mm plasterboard. This will be 3 layers thick,

That is leaf number three. Three layers of drywall on the inside of the second frame. So that certainly is 3 leaves, and therefore isolation for low frequencies would be worse than if you used the same materials to have just two leaves. Isolation in a 3-leaf system is always worse than for a two leaf system of the same total mass and thickness.

Would mounting both leaves off one frame be a good option to reduce costs -

That would be a fully coupled 2-leaf system with a very small air cavity. Not very good isolation there either, I'm afraid.

perhaps hanging the inner frame off RC?

That would decouple the inner-leaf, yes, but the air cavity would still be relatively small, and you need a large one. The MSM resonant frequency of the wall is governed by two factors only: the total mass (which you have plenty of), and the size of the air cavity between the leaves. With a single-framed wall, the air cavity is very thin, so the resonant frequency is very high, and thus the wall does not isolate well. There's also the issue of how much mass of drywall you can put on RC. I'm pretty sure you can hang three layers of 15mm drywall, but I don't think you'd be able to hang three layers of 18mm.

I'll also fill one of the frames with rockwool.

You'll have to fill both of them if you want good isolation! And the gap between them, too, for maximum isolation. The insulation acts as damping on the various types of internal resonances going on between the leaf surfaces inside the cavity. The more you can damp that, the better your isolation is. Insulation also changes the way air dissipates heat (adiabatic/isothermal), and lengthens the path length that sound "sees", so it's a good idea to fill the entire cavity, if you need very high levels of isolation.

Hanging 3 layers of plasterboard from the inside makes me a little nervous - again, views appreciated

Then build your ceiling "inside out", with the drywall on top of the joists, instead of underneath them. Much safer, and also acoustically better, in many ways. A bit harder to build, but worth the effort.

the rationale is just to maximise mass.

:thu: absolutely!

I'm a drummer and felt the more pass of each leaf the better.

I guess you meant "mass" not "pass", and yes, that's definitely a good thing. Mass is good, when used correctly. More mass is better! But it's better to actually do the math, rather than guess, to be sure that you have enough, and also that you don't have too much. I mean, too much would be a good thing, acoustically, but not so good for your wallet. The math might reveal that you don't need so many layers on each leaf... but that also depends on how much isolation you need (how many decibels) :)

The ventilation and heating will be quite primitive - I'm not expecting to spend too much on this - but admittedly I haven't given it a great deal of thought yet.

That's actually very common. Many studio builders don't give it much thought, until they are well advanced with the build, then realize what a big mistake that was... :) Think of it this way: each of your leaves will be sealed absolutely air tight: totally hermetic. Meaning (obviously!) that no air at all can get in or out. People have this annoying habit: we breathe! With each breath, we take in a bunch of oxygen, and expel a bunch of CO2 (and other things). In a small room, playing drums hard, you'll be sucking down a lot of oxygen and pumping out a lot of CO2. You'll also be exhaling moisture, and sweating (more moisture), and to put it delicately, you might be producing various other chemicals that make the air unpleasant, fast. You need oxygen to live. You can't live long in a room which is saturated with CO2 and has no O2... In other words, you HAVE to bring in fresh air, and exhaust the stale air, and you have to do it at a rate that replaces all of the air in the room every few minutes. A good rule of thumb is to figure 6 to 8 "room changes per hour". So you have to do the math, figuring out the volume of the room, multiplying that by 8, to get how many cubic meters of air you need to pump through the room every hour. People don't normally think of that in a typical bedroom, living room, TV room, or whatever, because houses are NOT sealed air-tight: there's plenty of ways that fresh air can get in, and stale air can get. No special treatment needed. But your room will be double-sealed, with two perfectly hermetic leaves... Then there's heat: You will have multiple layers of very thick thermal insulation, and huge amounts of thermal mass. Any heat generated inside that room ain't goin' nowhere! It will stay right there, stuck inside the room, since it cannot get out like it would in a typical bedroom, lounge, etc. So heating won't be what you need: cooling is what you need. You might need heating when you first enter the room after it has been empty for a long time, but it won't be long before the temperature rises in there, with you hammering away heavily on the drums, with the lights on, and probably some electronic (heat-producing) gear in there with you... The human body puts out several hundred watts of heat when it is working hard (such as playing the drums), and that heats up the room. And lastly, there's the issue of humidity: as I mentioned above, you exhale moisture with each breath, and you also sweat, which evaporates to keep you cool. The hotter the room gets, and the harder you play, the more you sweat, meaning that you are pumping a lot of water into the air, thus raising the relative humidity. High humidity is bad for instruments, bad for some types of microphones, and conducive to mold, fungus and other nasties. So your HVAC system needs to do four rather important things: 1) It needs to bring in fresh air with good oxygen, so you can stay alive. 2) It needs to remove the stale air with the high levels of CO2 so you can stay alive. 3) It needs to remove the excess heat you generate from your own body, from your lights, and from your equipment. 4) it needs to remove the excess humidity from the air, so your room stays livable, mold free, and healthy, and your drums and condenser mics stay tuned and in good shape. There's a couple of ways you can build your HVAC system, so you should start looking into that now. (And start doing the math, too! :) )

The completed booth will give me internal space of very roughly 3.4m x 4.6m x 2m(h)

Good! There's the basis for some of the math: That's about 32 cubic meters, times 8 room changes per hour is 250, so you need to move 250 cubic meters per hour of air through your room. That's about 4 cubic meters per minute, but some systems are still rated in cubic feet per minute, so you need to know that too: about 140 CFM (cubic feet per minute). Some systems are also rated in liters per minute, which would be 4200 in your case, or liters per second, which would be about 70.

I will be sourcing doors off eBay - just solid, heavy doors that I can also reinforce if I need to.

That's a good plan. Or you could build them yourself. But don't forget the seals! Each door needs at least two (preferably three) complete, independent perimeter seals (both sides, top and bottom, no breaks or gaps). One good source for those is Zero International, but there are other options too.

I was going to try and source 2x second hand matching double glazed windows and install them opposite each other in the frame(s); so each double glazed unit is a leaf.

Actually, a double-glazed unit is already TWO leaves, so a pair of those would be a FOUR leaf system, which is even worse than a three-leaf system for low frequency isolation. So that would not be a good plan, especially if they are identical units: if that's the case, then the coincidence dip for both of them would also line up perfectly, potentially creating another isolation "hole" in the upper mid frequencies. What you should do, is to put a single pane of thick laminated glass in each leaf. One pane in the outer leaf, and one in the inner leaf. The thickness that you need depends on how the rest of the wall is built. What you are looking to do here is to choose glass that has the same surface density as the leaf it is in. Glass is roughly three times as dense as drywall, so it only needs to be about one third as thick to get the same surface density. So if your inner-leaf is three layers of 18mm drywall, then the glass in that leaf would need to be 18mm thick. I'd recommend 9mm+9mm laminated glass for that leaf, if you do figure that you need three layers of drywall. You could also go for something asymmetric there if you wanted, such as 10mm+8mm, or even 6mm+12mm, but I wouldn't go thinner than 6mm. And make sure that the interlayer (the thin plastic sheet that bonds the two layers of glass together, usually made from some form of PVB plastic) is proper acoustic interlayer. But before you decide on how many layers of drywall on each leaf, and how big the air gap needs to be, you first need to come up with the number that defines how much isolation you need. That number is simply decibels. It's the difference between how loud you are inside the studio when you are playing your drums loudly (in decibels), and how quite that needs to be on the outside (also in decibels). Both of those are easy to measure with a simple hand-held sound level meter, so you should borrow or buy one of those and do some tests to figure out how much isolation you need. Everything else depends on that. - Stuart -

Thanks Stuart, really appreciate the reply and the good advice. I will refine my plans and work out my requirements more scientifically, and look properly at the ventilation issue :oops: As you pointed out, I clearly described a 3 leaf system in my original post - haven't a clue what my brain did there! I hadn't written what I had visualised. One question; you mentioned insulating both frames which I can understand, but you also mentioned filling the gap in between. Isn't this better to leave as an unfilled air space in a M-S-M wall? If I do fill the air gap, doesn't it make it one leaf?

you also mentioned filling the gap in between. Isn't this better to leave as an unfilled air space in a M-S-M wall?

The entire zone inside the wall between the two leaves is the air gap, regardless of whether or not there is any insulation in there. After all, insulation is mostly air anyway... :) So even if you fill the entire cavity with insulation, it is still technically an "air gap", and still considered as such by the equations. However, the equations in that case do take the insulation into account since it acts as damping, thus reducing internal resonance and therefore driving down the MSM resonant frequency and improving isolation: The equations account for it by changing one of the constants, which effectively makes the air gap seem 1.414 times bigger, if the gap is completely filled. If it is NOT completely filled, then that number should be reduced again, closer to the original constant, since not all of the cavity is having that effect. In other words, 0% insulation means that the constant is multiplied by one, and a fully filled cavity means that the constant is multiplied by 1.414. Anything in between means a smaller constant, somewhere between 1 and 1.414

If I do fill the air gap, doesn't it make it one leaf?

No, as long as you use the correct density of insulation, and that you only "place it" in place, without "cramming it" into place. Just enough to fill the cavity, and no more. Insulation is very, very resilient (provided that you don't compress it) so it won't create flanking paths across the cavity (provided that you don't compress it). Did I mention that you have to be careful to not compress it? :) And as I mentioned, you also have to be careful to use the correct density. Some people think that using insulation with very high density must be better (using faulty logic: "If some is good then more must be better"), but high density insulation is much more rigid (less resilient). So not only does the higher density reduce the damping effect and reduce isolation, it also increases the changes that the insulation will "bridge" the gap mechanically, thus creating a flanking path. In fact, even if you did manage to create flanking paths across the cavity, it still would not really make the wall back into a one-leaf wall. Rather, it would be a coupled two-leaf wall, which is still a lousy isolator, or course, but not quite as bad as a true single leaf wall. If you want to get into the detailed explanations and the math of all this stuff, with the various types of leaves, attachments, damping and coupling, then this is still one of the best papers for getting your head around it: https://app.box.com/shared/jcaoavdc8g That's a really old paper, from way back in 1973, but the principles laid out in it are excellent, and still absolutely true today.

I will refine my plans and work out my requirements more scientifically, and look properly at the ventilation issue

Smart move! :thu: It would also be great if you design your studio in SketchUp, and post the design here, so we can take a look at it and make suggestions on how to improve it. - Stuart -

Sorry, another quick question: metal stud work will work out cheaper and be much easier for me to work with in erecting my studio. Any strong views? I was looking at this stuff - http://www.buildingmaterials.co.uk/metal-stud.html Cheers James

Metal studs actually have a slight advantage over wood studs for isolation. There's not a huge difference, but it is measurable, so you could do that. But to take into account the structural requirements: if you need very high levels of isolation, then hanging 3 layers of 16mm drywall for the ceiling might be a problem on metal studs, if you have to span a large distance. - Stuart -

Actually if a metal type of product is to be used in an overhead situation, it will be a thicker gauge of metal. You have to use a screw that will pre-drill the pilot since the metal is designed for structural situations as opposed to a typical light weight metal stud that you can bend with a hammer. But the overhead configuration may get tricky, as Stuart mentioned, and a truss layout might have to be used or structural decoupling hangers.