Shed Practice Room

Hi After 3 tries I finally got on the forum! I am in the middle of constructing a practice room in my shed which is a timber clad wooden structure with a cast concrete floor nominally 9 metres x 3.8 metres. I have divided it into two spaces one of which will be the workshop, the other my practice room. I have built an internal separated wall and ceiling from 70mm X 35mm timber which sits on a floating floor of 2 x layers of 17mm plywood on 70mm X 35mm battens on neoprene pads. The gap between the back of the studs and the lining of the outside wall is 40mm nominally. The outside (existing wall) has R2.5 insulation, is lined with Plywood and clad with 20mm Baltic boards. I intend to use the room for practice mostly and some jamming and rehearsal, I want to get the most attenuation from the structure and my budget which is about $5k Aus. The inside dimensions are now 3.6 x 4.2 with 2.3 high walls and the peak of the ceiling 3.7 high. Parallel walls and cathedral ceiling. I wanted to build my room as per John Sayers design but I couldn't work out how to make the design work with a cathedral ceiling. I play bass and percussion. So now the questions. What to use for lining! 2x16mm Fyrecheck, 2x 13mm soundcheck, resilient mounts and furring channel with either of those, resilient channels. Have I made a mistake using 70mm studs, does this mean I can't use the maximum weight acoustic insulation (which is 90mm thick) or maybe i can pack out the studs using resilient mounts or neoprene pads (got some left over from the floor). I'm finding it hard to get comparative information on things like.... will using 15kg/m3 insulation with two layers of 16mm fyrecheck be better than 28kg/m3 insulation and one layer of 13mm soundcheck. Will using resilient mounts and furring channel help by increasing the air gap which I think i made too small (wanted to save on space.....) And finally, on John's site the design for control room windows show one pane of glass on each wall. Is this the same for a structure with an internal and external wall or should I have two panes of glass in the one window on the internal wall. I'm going to post some pictures and hopefully some drawings soon when I work out how..... Thanks in Advance Skabass.

hey there and welcome on board :D

skabass wrote:

floating floor of 2 x layers of 17mm plywood on 70mm X 35mm battens on neoprene pads.

In regards to your room acoustics, this kind of floating floor isn't great unfortunately. What you've built there is basically a big drum head. Like a drum, it'll resonate at a given frequency. The bare concrete floor would have been your best bet. Any chance that ply can come up and be used on the walls?

skabass wrote:

The gap between the back of the studs and the lining of the outside wall is 40mm nominally. The outside (existing wall) has R2.5 insulation, is lined with Plywood and clad with 20mm Baltic boards

just to make sure were on the same page....you're construction at the moment, working from inside to outside goes, plywood of X thickness, stud wall with R2.5 insulation (weight unknown) and 20mm baltic cladding on the outside. Is that right? Are the pictures of stud walls that I'm seeing ones that you have built and are not part of the existing structure? And what is the roof made of? If this is the case then you're in for some bad news as none of that kind of structure will give you the kind of isolation you'll need as...

skabass wrote:

I play bass and percussion. So now the questions.

Bass and percussion. The hardest of the frequencys to isolate, especially if percussion means kick-drum at all :shock: I think the rest of the questions will have to wait until we clear up this first bit, as they're possibly redundant if I'm right about your construction so far. Have a look around the forum for 'two-leaf system', 'bass frequency isolation' etc etc and you'll start to formulate a few ideas about what kind of construction you'll need to make this work properly. I think your budget could be tight, but you may already have a lot of the materials you need if the existing plywood is all 17mm thick. It's just that it sounds to me like these materials are in the wrong places. Again, search around the forum for 'wall construction' and you'll get a better idea. Sorry if that hasn't been the answer you were looking for, but everyone on the forum wants you to end up with the right room for your needs, and it sounds like there's a few hurdles to overcome on this before you keep going. steve

Hi Steve Thanks for your reply, regards the construction, the studs you see are new inside the existing structure and don't touch the outside walls or floor at all.The existing structure is as you have described it. The floor is floating on 80 or so neoprene pads, as per the design on John Sayers website. The floor can't come up, too late for that, can i deaden the floor vibration somehow? The roof has baltic lining boards, insulation (unknown weight) and corrugated iron. Hope that clears up your questions. Thanks Skabass

Hi Skabass, and welcome. Steve is right on with all his comments. Your "floating" floor is a big issue, unless you did all the math correctly. Did you calculate the deflection that each of your rubber pads must attain in order to float? Did you calculate the load that must be placed on the pad in order get that deflection? Did you calculate the mass of the inner-leaf walls and ceilings, plus all of the treatment, equipment, furniture, instruments, and people, to make sure that the total load on the rubber pads will cause them all to deflect to the correct degree when fully loaded? Did you take into account that the walls are high level linear loads, while the floor is lower level area loads? Did you consider the spot loads at some points on the floor, where there might be very heavy furniture or gear? If you did all that correctly, then your floor might be floating, but if you just spread the pads around at random without calculating, then it's pretty much certain that it is not floating. You only need one single pad that is overloaded or underloaded to negate the entire "float". You might want to read this to find out how to float a floor correctly: viewtopic.php?f=2&t=8173

The floor can't come up, too late for that,

Why not? It doesn't look too hard to me. This guy was way more advanced than you when he realized his mistake, and took apart his room to re-do it right: viewtopic.php?f=2&t=17363 It's a matter of perspective: Do you want the room to be usable, with good isolation and good acoustics? If so, then the floor should come out and be done correctly. If not, then you can carry on with your current plan.

can i deaden the floor vibration somehow?

Not really. You could take off all the plywood and fill the cavity with OC-703, which would help to a certain extent to damp the resonance in there... but not very much. And if you did that, then you are half way to dismantling the floor anyway, so it would be cheaper and better to just dismantle it fully. You'd also get back the 12cm of lost ceiling height that you are wasting right now, with that floor in place... :)

What to use for lining! 2x16mm Fyrecheck, 2x 13mm soundcheck, resilient mounts and furring channel with either of those, resilient channels.

If your inner-leaf studs are fully decoupled from the outer leaf, then you do not need resilient support for your drywall at all. Neither RC nor RSIC clips plus hat channel. Those are only used in situations where the studs are not decoupled from the rest of the building. All you need is two layers of plain old 16mm fire-rated drywall, or perhaps one layer of 19mm plywood or OSB plus a layer of 16mm drywall. That has certain advantages, but is a bit more expensive.

Have I made a mistake using 70mm studs, does this mean I can't use the maximum weight acoustic insulation (which is 90mm thick)

Not a problem: Your studs are 70mm but you also have a 40mm gap between the studs and the outer leaf, so your insulation will just stick out 20mm into that gap. That's not a problem at all.

will using 15kg/m3 insulation with two layers of 16mm fyrecheck be better than 28kg/m3 insulation and one layer of 13mm soundcheck.

That's like asking if a fish is better than a bicycle... :) Insulation and mass are two entirely different things. The insulation is not considered to be part of the mass. Insulation acts as the damper on the various types of resonance going on inside the wall cavity (MSM plus all the others). It has to have the correct gas flow resistivity for that application, which varies depending on the type of insulation. If you are using fiberglass insulation then stuff with a density of around 30 kg/m3 will have roughly the right gas flow resistivity. If you are using mineral wool, then you need stuff with a density of around 50 kg/m3 to get the right gas flow resistivity. 15kg/m3 insulation is way too light, so forget that, and 13mm drywall is too thin, so forget that too. You cannot trade off the density of your insulation against the density of the two leaves, as they accomplish entirely different things. The leaves are the mass in the MSM resonant system, and the insulation is the damper: The leaves need to have the right mass to give you the correct MSM resonant frequency that you need for your specific case, and the insulation has to have the right mass to provide the correct gas flow resistivity so that the acoustic damping within the wall is correct. Two very different things. You calculate the density of the drywall according to the MSM resonant frequency that you have chosen for your wall, and the depth of the cavity inside it (distance between the leaves).

Will using resilient mounts and furring channel help by increasing the air gap which I think i made too small (wanted to save on space.....)

Well, that would increase the depth of the cavity, which will help, yes, but you could also compensate with additional mass on the leaves. According to the MSM equations, either increasing air gap or increasing mass will lower the resonant frequency and improve isolation. Personally, I'd go for more mass.

And finally, on John's site the design for control room windows show one pane of glass on each wall. Is this the same for a structure with an internal and external wall or should I have two panes of glass in the one window on the internal wall.

Correct. The thickness of each of those panes must also be calculated so that the surface density matches the surface density of the rest of the wall. Ditto for the doors: each of the two doors must have the same surface density as the leaf it is in (or higher), and the gap between them must be the same as the gap between the leaves of the wall (or greater). The key here is to make sure that there are no "weak points", where either the mass (surface density) or the air gap is too low, as that would allow the MSM resonant frequency to be higher at that point, thus messing up your isolation. And since windows and doors are critical, it's always better to increase both the mass on each of those and also the air gap between them, to compensate for the losses. Windows particularly should have an air gap at least 1.414 times deeper than that of the rest of the wall, or heavier glass (surface density higher than that of the leaves), since for obvious reasons you cannot put insulation between the panes of glass! But there's another issue here. Steve asked this: "you're construction at the moment, working from inside to outside goes, plywood of X thickness, stud wall with R2.5 insulation (weight unknown) and 20mm baltic cladding on the outside. Is that right? " You replied that he is correct. Therefore, you already have a coupled 2-leaf wall, and now you are adding a third leaf! :shock: So you will have to increase the mass yet again, to compensate for the losses due to the third leaf. 3-leaf walls should be avoided in general, as they just mess things up so much, and add to the overall costs and complexity. With a 3-leaf wall, you no longer have one single MSM fundamental resonant frequency, but rather two fundamental resonant frequencies, both of which are higher than what the single one would have been for the equivalent 2-leaf wall. So to compensate for that, you should put twice the mass on the middle leaf and increase your air gaps. You can't do either of those, since your walls are already built, so your only option is to put a lot of extra mass on your final inner-leaf. You can use the 3-leaf equations to figure that out, but I'd guess that three layers of 16mm drywall would probably get close, maybe four layers. Or maybe a layer of 19mm plywood or OSB, plus 2 layers of 16mm drywall. Or perhaps a layer of fiber-cement board would help, if you want to save space. You do have options, but this is going to be more expensive than it could have been if it were done properly, as a 2-leaf system.

The roof has baltic lining boards, insulation (unknown weight) and corrugated iron.

Separated by rafters, joists or trusses in the middle, I imagine? If so, that's a coupled 2-leaf system too, so the same applies as for the walls: you need a lot more mass on the third leaf. Fortunately, you are not too advanced that these things cannot be fixed! What is your isolation goal, in decibels? - Stuart -

skabass wrote:

Hi Steve Thanks for your reply, regards the construction, the studs you see are new inside the existing structure and don't touch the outside walls or floor at all.The existing structure is as you have described it. The floor is floating on 80 or so neoprene pads, as per the design on John Sayers website. The floor can't come up, too late for that, can i deaden the floor vibration somehow? The roof has baltic lining boards, insulation (unknown weight) and corrugated iron. Hope that clears up your questions. Thanks Skabass

yeah, I thought that might be the case with the existing structure. As Stuart has said mate, the best option (especially $'s wise) is to de-construct and start again. I know that sounds painful but you aren't too far along the build to go back a few steps and get it right. You're a bass player, that means your room HAS to isolate well in order to be useful. I can tell you from personal experience that a 3-leaf system is more expensive. I have one in my studio roof (have a look at 'dog and bear studio' in 'other studios' for the gory details) which could have been avoided had I got to the forum when I was at the stage that you are now. It would have also saved me having to hang an extra 2 layers of 16mm fyrcheck (of 4!!) that are on the internal ceiling, buying isolation hangers and probably around $1200 worth of Green Glue :shock: If you've ever hung 16mm ceiling plaster you'll know that the less you have to do the happier you'll be. If you do go for the 3 leaf system then take all of Stuarts advice on it, he really knows his stuff :D And it'd be worth downloading sketchup and doing some plans of what you want to end up with, that way and flaws can be spotted well in advance. cheers, steve

Hi Stuart and Steve This is all great advice, I'll answer the question first on how many dB I want to reduce, well I can't answer that exactly but my aim has never been to have a completely isolated room. Due to the old nature of the existing shed I've never expected recording studio level sound attenuation. Basically for a lot of reasons, I can't start again, the biggest reason is that I can't do much of this work myself so a lot of the cost is in labour and it's much cheaper to add a layer or two to the walls and floor than to dismantle the entire structure and start ripping off linings and re roofing. It's a shame (there are other reasons but lets not go into that). I forgot to mention, I did put insulation under the floor but not high density. Interesting about the 3 leaf system, even if I pulled apart what I've done I still wouldn't be able to make the existing structure work as a single leaf structure, its too old and rickety. So in conclusion I am going to proceed using plywood and two layers of 16mm plasterboard on the walls and ceiling and will add an extra layer to the floor. Should I use something like Impacta mat in between? Got to get back to work now, am also pricing some 48kg/m3 insulation. Thanks Skabass

Hi After 3 tries I finally got on the forum! I am in the middle of constructing a practice room in my shed which is a timber clad wooden structure with a cast concrete floor nominally 9 metres x 3.8 metres. I have divided it into two spaces one of which will be the workshop, the other my practice room. I have built an internal separated wall and ceiling from 70mm X 35mm timber which sits on a floating floor of 2 x layers of 17mm plywood on 70mm X 35mm battens on neoprene pads. The gap between the back of the studs and the lining of the outside wall is 40mm nominally. The outside (existing wall) has R2.5 insulation, is lined with Plywood and clad with 20mm Baltic boards. I intend to

How's this for an idea? Could I get the hole saw out and put a whole lot of holes in the internal lining? Will this turn it into a two leaf structure? Not sure how this will work with the roof as the roofing material is corrugated iron. Cheers Skabass

skabass wrote:

So in conclusion I am going to proceed using plywood and two layers of 16mm plasterboard on the walls and ceiling and will add an extra layer to the floor. Should I use something like Impacta mat in between? Got to get back to work now, am also pricing some 48kg/m3 insulation.

I don't believe another layer on the floor will achieve anything for you, although Stuart might have a more scientific answer to that :D Double check that your existing ceiling structure can take the extra weight you'll be ading as two layers of fyrcheck is a loat of weight. You'l need a suitably qualified builder or enginner for that. I would say to use green glue between your sheets of plaster. I've used it in my construction and it's well worth it. Rob at foam sealant co can help you with GG as well as acoustic caulk. For cavity insulation you want around 30kg/m for fibreglass and 50 kg/m for rockwool. In fibreglass you can go with bradford soundscreen at 24kg/m or fletcher FI32 at 32kg/m.

skabass wrote:

Could I get the hole saw out and put a whole lot of holes in the internal lining? Will this turn it into a two leaf structure?

interesting question :) i'd say possibly, but you'd need to cut a hell of a lot of holes :shock: Stuart will have a much better answer to that.

Thanks Steve The holes in the wall was a good idea, quick cheap and achievable (if it worked) but the problem is the roof… it's only tin and I could cut holes in the roof lining but that would make that leaf corrugated iron, don't know if that is a good thing.. Green glue eh, finally someone who can endorse it personally. They make a lot of claims but I've not seen a lot of expert testimony. It's about $700 to do my shed so it would have to be good. Yes talking to a builder, the 19mm ply will turn those walls into a very stiff structure so I think its ok. Cheers Skabass

I don't believe another layer on the floor will achieve anything for you,

Right! Mass law says that doubling the mass will increase isolation by 6 dB, which isn't very much, and even that is optimistic. In the real world, it's more like 4 to 5 dB. To get a decent increase in isolation, you'd need to increase the mass eight times over... So adding another seven layers of OSB on top of the existing floor would get you an increase of maybe 16 dB or so. Not very exciting, for a floor six inches thick!

Could I get the hole saw out and put a whole lot of holes in the internal lining? Will this turn it into a two leaf structure?

interesting question :) i'd say possibly, but you'd need to cut a hell of a lot of holes

The holes would have to be really large, and the open area would have to be something like 20% at least, to ensure that it doesn't act like a perforated panel resonator (which is a form of Helmholtz resonator).

Green glue eh, finally someone who can endorse it personally. They make a lot of claims but I've not seen a lot of expert testimony.

Check their web site: they have a lot of independent acoustic laboratory tests there, done by Riverbank (one of the best labs in the industry). Very extensive testing, with good results. Their advertising claims are soundly based on those results.

Yes talking to a builder, the 19mm ply will turn those walls into a very stiff structure so I think its ok.

Very stiff in sheer, yes, which is a good thing, but not so stiff in the other two planes. An improvement for sure, and worthwhile. Plus it gives you a 100% nailing surface around the room.... - Stuart -