Building rehearsal / mixroom

Hi! Lurking around on the forums for quite a while now, and now the day has come to ask for help ;) The situation: Me and my band are renting a room of (H x W x D) 2,93m x 5,18m x 9.58m on the groundfloor from a building contractor inside a 2-store building. More people/companies rent a room over there. We are going to setup our rehearsal room in there as well as a small mixroom. Several steps are needed to make it an enjoyable space :) Starting with the first step: Sound isolation Explanation of the current room: We mostly rehearsal at evenings when the building is practically abandoned, nevertheless the need of good ( at least better then current) sound isolation is needed. Mixing will also happen during daytime as evenings. In our room, a stair lead to a room located at the upper floor. We've decided, together with the renter, that we will create a small corridoor leading to the stairs as well as our rehearsal room for privacy reasons. No-one likes interrupted rehearsals ^^ Furthermore, we will create a room within a room for better isolation. In the picture below you can see the global floorplan as far as we've come up with so far, the room within the room is not drawn in yet. First problem we need to tackle is ''Wall A''. The wall is made of a sort of sheet, consisting of a 2 small metal layers with foam in between. Isolation is rubbish, almost as little as a thick curtain. We're thinking of putting up at least 2 layers of gipsum board against that wall ( directly mounted on the surface) with a sheet of rockwool facing to the inside of the room. Making the wall heavier will hopefully increase the isolation. Furthermore, we plan on having the dividing wall between the corridoor of the stair and the rehearsal room to be a single stud wall, 2 plies of gypsum on the stairs side, rockwool between the studs. All remaining walls facing the rehearsal room will have a sheet of rockwool. For the inside room we will also build a single stud wall, of course reverse build as the dividing wall of the corridoor. It will be like this : 2 plies of gipsum -studs with rockwool - 10cm airgap - studs with rockwool - 2 plies of gipsum Are we on the right track here? Thanx in advance, Marlon.

Marlon, You're on the right track with the double wall construction. Don't forget the ceilings. TIP: If you can get cheap fluffy attic insulation for your wall cavities you will be better off financially. Tests show negligible difference in transmission loss between heavier compressed fiberglass /rock wool and the lighter building insulation. For Wall A... room in a room here?? if so, it would be better to remove the junk that's currently on the studs, fill with fluffy insulation and then build your new iso wall 10cm in front of this. -- if wall A needs more mass, you can either add the gypsum board to the other side (other property) OR cut pieces of gypsum board to go between the studs inside the wall. - You can 'toenail' them in place and then caulk the edges. Now the rock wool covered walls don't do much for the isolation but if you want that wall dead sounding.. fine. You are probably better off using a checker board pattern with the rock wool than full coverage. (better economy) You will get almost the same absorption with half the rock wool checker boarded compared to full coverage. understand? Cheers, John

Hey John, thanks for the reply :) Quick question for the double walls: Insulation also in the airgap or leave it open and just put insulation between the studs of the walls? Have read both options are possible. I think my first post isn't typed clear enough by me :( ( english is not my native laguage ;) ) Wall A is a self supporting dividing wall made of large sheets of 125cm wide, 10cm deep -( thin layer of metal of 1mm - insulation - metal layer of 1mm), no studs are used for this wall. It cannot be removed or altered itself unfortunately. Acoustically, the wall is practically invisible, sound passsed right through it, from high to low frequencies. We've started to add mass to that wall, using the wall itself to support the added mass. Works very well so far. All gaps will be caulked and we'll continue to add at least 2 more layers, starting with a fibre board layer and on top of that a gipsum layer. Of course caulking every gap. The room in a room I described is for bith the rehearsal as the mixroom. That's why the isolation is already drawn in the picture, the outerwalls acts as the outerwall for the room in a room. Hev made a quick sketch to illustrate that idea more :)

Marlon, You can fill the wall cavities & air space completely with fluffy, but not with rock wool. I see, so the partition is made with 'refrigerator' panels. - I don't think code would pass your modifications & I think that it might possibly be dangerous. Just be careful, ok? 2 layers of 15mm gypsum board gets really, really heavy and can break a leg (or a neck) if it comes off the top of the wall. I have a client that has the same problem wanting to use these surplus refrigerator panels. They offer nothing acoustically or structurally. They are real good for refrigerators! haha! You need the structure to support the gypsum board and this gives you the STC figures that you want. It's not just about mass. Rigidity, damping, resonance, all play important parts. Cheers, John

hehe, no we're not planning on gypsum head butting as a new hobby ;) Unfortunately, these panels are a given fact as in: they're there and cannot be removed. So what's the best solution in this case? Erect a new studwall next to or attached to the panelwall to offer the support to hold all the new gypsum layers and insulation? Will this not cause a triple leaf effect? Just out of curiosity: A very stiff wall, without studs but with a very large mass and well sealed will still work? Are studs are there for stiffness and support only, or do the studs themselves also have a isolation value?

The thin transparent refrigerator panel wall will not come much into play as a 'leaf', IMHO. Sometimes compromises must be made. I wouldn't worry too much about that. Studs are there for stiffness and support - in this manner they affect the transmission loss. Here is my suggestion if it is possible; Build a 2 X 4 frame wall, attach 2 layers of gypsum board to it and tilt it up or move it right up next to the refrigerator panels. At this point you can attach it to the ceiling joists, side walls and shoot it into the floor. - I don't know your room construction so I'm just giving general info/suggestions. -- Basically, you will be building an inside-out wall so that the gypsum will be facing the refrigerator panels. THEN, build another 2 X 4 frame wall starting 2 to 4 inches from the inside-out wall frame for the interior wall of your room(s). Before you put gypsum board on the inside of this new wall, you'll need to do all wiring and HVAC openings, and then install cheap insulation (as thick as possible) between the studs in both walls. I didn't mention that this interior wall will need to be built as a 'load bearing' wall to support a ceiling... The devil is in the details and this is not all of them. :wink: This can give you up to STC67 depending on your attention to construction details. Cheers, John

Thnx again, I like the suggestions you did for the ''refrigerator'' wall A, seems like a good solution to tackle the problems of that wall :) The inner walls will take a little whole before we get to them, first the outer walls need to be done ofcourse ;)

You also need to decouple the walls between your CR and LR. Right now your model shows the side walls running through what should be the air gap, joining the two rooms. You need to break that connection. - Stuart -

Yes, that's correct :) The last file was a quick draft. Will start on a decent sketchup version once all dimensions are more clear. Basically, it will be a compromise between the live room to be as large as possible and the mix room having as good as possible ratios. For the mixroom the ceiling height and divide wall between the liveroom and mixroom will be the 2 factors to ''play'' with. Update, We took a good look at wall C, and it's build as a stud wall with 1 layer of gipsum on each side. not good. We start to remove the gipsum on our side of the wall and add extra layers of gipsum between the studs.

Quick question: The original ceiling above the room will need to be beefed up to improve isolation. Does the entire original ceiling need to be treated or will only the parts above the mix and rehearsal room ( the rooms within the room) be enough? I think the first option will be needed, but maybe I'm wrong?

Yup. All of the parts of the ceiling that are part of the outer-leaf will need beefing up. You need to treat everything the same, or you will create "weak spots"- - Stuart -

I meant the entire part above mix / live room, excluding the corridoor. Really need to start explain myself more clearer. Have attached a picture to show what I mean. The red area only needs beefing up, or also the part above the hallway/corridoor with the stairs in it?

Marlon, Only the red areas. yes. The stairway, etc are outside your double wall system.

Ok, cool :)

Wall A is done, and we've started building the dividing outerwall between the stairway corridoor and the liveroom and mixroom. Need some advice on the beam which sticks out at wall D ( see attached picture ) It's stick out 19cm into the room. Question is what should I do with the inner leaf of the mixroom. Build it entirely in front of the beam, with that creating a larger airgap between the inner and outer leaf (picture a) or build the wall around it and use the extra space for extra basstrapping (picture b) , but having a cornered backwall. Both pictures are roughly drawn btw, real walls will have proper dimensions. Picture APicture B

Either will work. But if it were me, I'd go with "A". It gives you greater depth in your air gap (improved isolation), the construction is much easier (and cheaper!), and you won't have that strange shape in the rear corner, which might do strange stuff acoustically. My $0.02 - Stuart -

I'm with Stuart. :D Cheers, John

Ok, thanks for the advice ;) Keep the shortest distance of that wall at at least 5 cm of the beam or can we get away with a shorter distance between wall and beam? Measuring from wall frame to the beam. We're still thinking of using an inside out wall or a regular wall. Higher isolation values are preferable. Inside out wall would mean an inside out ceiling construction too I think, haven't found out yet how to combine an inside out wall with a regular ceiling if possible at all.

2cm from the beam is fine. The inside-out wall will not have the isolation stats of a normal double wall construction. Better isolation = normal wall build. Cheers, John

jhbrandt wrote:

2cm from the beam is fine. The inside-out wall will not have the isolation stats of a normal double wall construction. Better isolation = normal wall build. Cheers, John

Just so no one who reads this without comparing both decoupled walls and inside out wall assemblies falls to the illusion that somehow the normal is "better" than the inside out wall... All things being equal, the only place an inside out wall is different from "normal walls" is that the air space is often reduced since it was designed as a means to save floor space. In that respect it is the optimum choice. Given the same air space as a "normal wall", I see no reason it would not perform at the same levels, within the same TL ranges.

xSpace wrote:

jhbrandt wrote:

2cm from the beam is fine. The inside-out wall will not have the isolation stats of a normal double wall construction. Better isolation = normal wall build. Cheers, John

Just so no one who reads this without comparing both decoupled walls and inside out wall assemblies falls to the illusion that somehow the normal is "better" than the inside out wall... All things being equal, the only place an inside out wall is different from "normal walls" is that the air space is often reduced since it was designed as a means to save floor space. In that respect it is the optimum choice. Given the same air space as a "normal wall", I see no reason it would not perform at the same levels, within the same TL ranges.

Ok, how is the airgap measured? From frame to frame or from gipsum layer form one wall to the first gipsum layer of the second wall in an msm assembly? Illustrations give me the idea from frame to frame, assuming the insulation in the frames is flush with the beams of the frame. Meaning in reality the airgap could be actually a bit wider or smaller, depending on the thickness of the insulation. But since fluffy insulation sometimes also is used to fill the airgap, I'm confused on what to see as the recommended airgap :?

how is the airgap measured?

Surface of drywall to surface of drywall. It is the depth of the air between the two surfaces that matters, not the depth between frames.

Meaning in reality the airgap could be actually a bit wider or smaller, depending on the thickness of the insulation.

Air gap and insulation are in the same place! Putting insulation in the wall does NOT change your air gap: it merely puts some damping on it. From the point of view of physics and MSM, the air is a spring, and the insulation is the damper on the spring. But they both occupy the same physical space.

But since fluffy insulation sometimes also is used to fill the airgap, I'm confused on what to see as the recommended airgap

The insulation does not "fill" the air gap: the air gap is still there, with or without insulation in it. The "recommended air gap" depends on a number of factors, but the most basic one is: what is the lowest frequency that you want the wall to isolate? Based on that you design the wall as a combination of air gap and the masses of the two leaves, to calculate the correct MSM resonant frequency such that your wall isolates well at the lowest frequency you are interested in. General rule of thumb is that your MSM resonance should be around half of the lowest frequency you need to isolate. So if you want your wall to isolate well all the way down to 20 Hz, then you would design the wall such that its resonant frequency is 10 Hz or lower. You do that by making the air gap large enough and putting enough mass on the leaves to achieve your target frequency. If you can't get a large enough air gap due to space restrictions, then you can add more mass to compensate. But the minimum air gap that you can use reasonably for must home studio situations is around 4 inches. Go much less than that and the amount of mass you need skyrockets. - Stuart -

+1 Excellent post Stuart! Just to clarify my earlier post comparing the two types of walls. The 2 main differences are; 1. smaller air space in the inside-out wall. 2. no insulation in the air-space of the inside-out wall, thereby reducing the TL. The inside-out wall is great for saving space! Looks good and works very well. I was being objective, as usual, in pointing the OP in the best direction for his application. 8) Cheers, John

no insulation in the air-space of the inside-out wall, thereby reducing the TL.

Glad you clarified that, John! I'm not sure why, but many people seem to think that John designs his inside-out walls without using insulation. However, I have never seen him do that, either in writing or in reality, and all the designs he has generously shared here show that he does, in fact, use insulation in the air gap. I guess it is just one of those acoustic myths that float around the internet: that inside-out walls are supposed to be built without insulation. In reality, they need (and have) insulation in them, just like any other MSM wall. The only real difference is where you put the frame!

Excellent post Stuart!

Thanks! :) - Stuart -

jhbrandt wrote:

The inside-out wall is great for saving space! Looks good and works very well. 8) Cheers, John

I actually do not know, even though I said it, if that was the catalyst for the development of Mr. Sayers inside out wall, to save space, since he seems to have designed many a recording studio not restricted to tight foot prints. Be that as it may, it (the inside out construction)has more uses as we each should have recognized, the main being that bar none he (Mr. Sayers) always includes slats in his designs. In the construction trade this seems a very effiecient use of materials when the mass is still part of the build, the interior acoustic treatment is installed, and the highs are not lost by simple inclusion of the slat design. To me it is an excellant design that could be used in most any room we have seen, the one in question included. The often always trip up is that people usually get dizzy when they stick thier heads in the waters of the acoustic world so getting thier heads around the many wall assemblies usually takes months, if not longer. But this is what Mr. Sayers does at this forum, uses the inside out wall, very successfully from what I have observed. Just going for clarity jhbrandt,