The walls are 40cm thick rammed earth (Pisé – a traditional construction technique in my area of France). But one of the 4 walls is stone (40cm thick
That should get you pretty good isolation. The weak points will be the ceiling, doors, windows and HVAC, probably.
Budget is 13,000€ and I’ll be doing everything myself.
You have about 30m2 of floor area, so that works out to roughly €430 / m2. Probably OK (although studios almost always end up costing more than you ever imagined they would!
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I would like to get 50db of reduction, any more would be icing on the cake.
That's a reasonable goal. Doable.
One essential element is to use the barn door opening to allow in light.
I mentioned this before, and Glenn did too: a pair of sliding glass doors, back to back, would do what you want. With Glenn's idea of lockable sliding barn doors on the outside, for security. There are different "standard" sizes for glass sliders: get the biggest ones you can afford, and get them with laminated glass. Even better is acoustic laminated glass, if you can find a source for that where you live.
I suspect that the 30db reduction between the future studio and the bedroom is a good indication of what I would achieve if I simply closed and insulated the barn door opening and and the ceiling.
Right! So you only need to go 100 times better...
I kid you not! dB is a logarithmic scale, which basically measures the difference between two levels. A difference of 10 dB means 10 times more intensity. An increase of 20 dB (going from 30 to 50) means 10 x 10 = 100 times the intensity. So you need to block about 100 times more energy than your current bedroom wall is blocking. That sounds like a really big amount, and it is, but it is achievable in your situation. If you needed to get to 60 dB, that would be an increase of 30 dB, so 10 x 10 x 10 = 1000 times the intensity... probably not achievable, unless you also have ten times the budget!
The pisé/stone walls are a great starting place, but it needs to be closed. For the barn door opening, I’ll use a commercial sliding glass door.
A single glass door of they type you can typically buy in a "Home Depot" type store, with ordinary glass in it, will give you a total of about 25 dB isolation. Maybe 29 if it is really good. You would need two such doors, in parallel ("back to back") to get the isolation you need. And they would need to have better glass than then typical 5mm or 6mm window glass. A pair of sliding glass doors, back-to-back, with laminated glass in them, and a good separation between them, can get to the level you want. But when you buy them, do pay careful attention to getting doors that have really good seals around the sliders! That's critical to getting high isolation.
And for the upper part of the opening, I’ll build a wood structure with OSB 3 and 15cm of wood fiber insulation panels.
Here again you will need two such walls (one for each sliding glass door). Inner leaf and outer leaf. You will also need more than just a single layer of OSB on your two leaves. You need to get a lot of mass on those walls. I'd suggest at least this: Start with a layer of 19mm OSB nailed to the studs, then put a layer of 16mm drywall over that using Green Glue in between those two. Do that for each of the two walls, to create a proper two-leaf MSM system, like this;
What is MSM? How does it work?I’ll create a false ceiling, by hanging metal rails from the roof joists and attach OSB 3 panels.
Here too, that alone won't get you to 50 dB of isolation. You'll need to add more mass to that. A single layer of 12mm thick OSB will only get you maybe 25 dB of isolation. Here too I would suggest doing the same as for the walls: a layer of 19mm OSB on your new metal ceiling joists, then at least one layer of 16mm drywall on that, with GreenGlue in between. Even better would be two layers of drywall. You'll need to ensure that the supporting structure is strong enough to take all that weight safely.
I’ll build a wood inner structure completely decoupled from the walls and ceiling
I’ll leave about 5cm between the studs and the pisé wall (pisé absolutely needs to breathe, and I figure this is convenient for sound isolation as well).
General rule of thumb; In order to get the MSM resonant frequency low enough, you should have a minimum air gap of about 4" (10cm) between the inner leaf surface and the outer leaf surface. More is better. So, assuming that you are using 2x4 studs, which are about 9cm deep usually, and you leave a gap of 5cm between the studs and the outer-leaf wall, that would give you a 14 cm air gap. That's good. If you can spare even more space, then leaving a 10cm gap between studs and wall would give you nearly 20cm
of air gap (about 8"). That's excellent! Of course, that reduces the floor area of the completed room, so do take that into account as well!
Between the studs I’ll have 15cm of wood fiber insulation panels.
Do check on the acoustic properties of that insulation first! The normal recommendation for studio isolation is either mineral wool or fiberglass wool insulation. If you use mineral wool, then you would need a density of about 50-60 kg/m3, and if you are using fiberglass it would need to be 35-45 kg/m3. Each type of insulation is different. In fact, it's not really the density that matters, but rather a property called "Gas Flow Resistivity" (GFR). That's a measure of acoustic impedance, and that's what matters most. I'm not aware of any acoustic research on wood fiber insulation, so I have no idea what the correct density would be, in order to get the right GFR. You can't just use any old insulation and hope it will work. It has to have properties that are acoustically useful. For example, polystyrene insulation has very good thermal properties, but is totally useless acoustically, so you will never find it used in studios.
The floor will be insulated with rigid wood fiber panels, and probably OSB on top.
Probably not a good idea. The bare concrete floor is an excellent surface, acoustically. If you want to make it look nicer, you could stain or polish the concrete, or use laminate flooring with an acoustic underlay... which is also good if you want to have a floor that looks nice and also feel nice to walk on, softer than concrete. But putting an OSB layer on top of joists with an air gap under it, will create a resonant chamber. Usually not a good idea for a studio floor! (There are ways of doing that, but it needs careful design).
Double flow CMV for air exchange. The in/out vents will each have a baffle box.
For heat/cooling a mini-split heat pump. (In France you can buy these from a hardware store and install them yourself, you just need a specialist to check the seals and insert the liquid refrigerant.)
As Glenn said: definitely get the specialist in to do the refrigerant! I have installed and even repaired mini-split systems myself, but I'll always call in the expert to do the checking and filling.
Are there other easy/cheap sound reduction additions that would be worth my while that I haven’t thought of?
Yes! A product called "GreenGlue", made by the "Green Glue Company". It isn't glue! (despite the name). You can't use it to stick your drywall to something. You just spread it between the layers of drywall, and hang the drywall in the normal way (nails or screws). It's a visco-elastic damping compound that does good stuff, and greatly increases the isolation. Here's an article I did on it:
The truth about Green Gluethe ceiling is a normal MAM construction. But given that the outer leaf is still mostly protected from the elements by the porous roof, would it be wise to add insulation on top of the false ceiling?
Always! The insulation in an MSM (MAM) wall or ceiling is a critical part o the system. It provides the acosutic damping in the cavity, which is very necessary. Completely filling the air cavity but without compressing the insulation, is the best option. That gives the highest isolation. But for really deep cavities, that can be expensive. In that case, as Glenn mentioned, filling it at least half way is an alternative, as long it is at least 10cm (4") thick. And the right type!
How could I make airtight seals between the tongue and groove panels of OSB? And then between the OSB panels and the pisé walls?
Caulk. Any type of bathroom/kitchen caulk will do, as long as it remains soft and flexible even after it has fully cured. Personally, I recommend Sika 11FC, as that does a good job at a reasonable price, and seems to be available in most countries around the world. Sealing EVERYTHING is the key to good isolation. Even a tiny gap or crack that you didn't notice can have a strong negative effect on your isolation. Be very careful with your sealing!
When doubling drywall, each layer needs to be sealed with drywall mud and ideally the seams need to be staggered, correct?
Right. You can sometimes substitute caulk for mud-and-tape: it's faster to apply, and give a better seal.
My carpenter who’s helping with the framing tells me that I can’t attach drywall directly to the wood studs because the wood will warp and cause problems in the drywall. This doesn’t seem right to me - any thoughts?
I have NEVER heard of that before! Attaching drywall to wood studs is very, very VERY common. It's the way houses are built in the USA. And offices. And shops. And schools. And churches. The only reason I can think for studs to warp, is if they were not properly dried before being installed. Good quality studs should not warp after they are bought. They might already be a bit warped when you buy them (if they are low quality), but running them through a thicknesser or power plane can fix that, if it is too pronounced.
But in any case, as Glenn already said, the best idea is to put a layer of OSB, MDF or plywood on the studs first, then put your drywall on top of that, The OSB greatly increases the structural integrity of the wall, and it also means you have a nailing surface all around your room. Without that, you can't nail into drywall just anywhere: you can only nail where there is a stud. But if you have a nice thick layer of OSB on the studs (eg 19mm), then you can nail anywhere you want, without needing to find a stud.
I could conceivably build the doors with a significant air gap between them. If I built the 25cm or 50cm apart, would I actually be gaining sound reduction? What would be the ideal distance?
Yes! There's an equation for calculating that. The size of the "air gap" (distance between the two leaves of the wall) affects the resonant frequency of the wall system. Bigger gap = lower frequency, which also implies better isolation. Of course, there's an optimal distance beyond which you don't get any more benefit. 25cm would likely already be very good, assuming that you also have enough mass in the glass (thick laminated glass, rather than ordinary window glass). More mass = better isolation.
Also, would an acoustic curtain be a helpful addition between the two doors?
Maybe it might help a little tiny bit, but not enough to be worth the cost and hassle. It would be helpful at frequencies that don't need help, and not helpful at frequencies that do need it. Just use suitable thick insulation around the perimeter of the cavity between the doors.
And I realize the seals on these doors are the most important/difficult part. Is it pointless to try for more insulation, doubling drywall, or adding green glue, etc. in other parts of the construction, knowing that the double sliding glass door will get whatever isolation it gets, and can’t be improved? In other words, is sound isolation only as good as the weakest link?
It's definitely not pointless, no! But rather than reduce isolation in the rest of the room, work on increasing it for the doors!
Does anyone have any experience with the self installed mini split heat pumps? I’ve heard mixed reviews, but I figure that if it’s just for a 30m2 room and not the whole house, it might be a good option. The whole thing is about 1500€
It's not hard to do. I've done it, many times. As long as you follow the manufacturer's instructions, it's not a big deal. Mini-splits are great, but do make sure you get the right capacity for your room in your climate! For example, a 24,000 btu/hr unit might do fine for a studio located in a moderate climate where the humidity is low and temperatures don't go much over 26°C or so or much below 5°C, but would be totally inadequate for the exact same studio located in an area with high humidity where the outside temperatures are regularly over 35°C, or below -15°C. Another case: the same unit might do fine for a home hobby studio, which just has two or three people in it at a time and mostly with acoustic instruments, but do terribly for the same studio in the same climate with twenty people inside, and stacks of high-powered electric gear (big amps, stacks of speaker, lots of outboard gear, etc.).
Best advice: do the calculations to make sure the unit you are thinking of is right for you.
- Stuart -