John Sayers' Recording Studio Design Forum

Hello All,

I'm located on the outskirts of Aberdeen, Scotland, UK. I’m in the planning stage of a garage conversion to build my studio. It is going to be a private studio and NOT a business concern. It will be mainly used for recording, which might include recording drums occasionally and for some band rehearsals.

The existing garage is detached and about 12 metres (30 ft) from my own home and the neighbour’s house. We are located in a semi-rural location surrounded by moorland and farm fields.

The ambient noise around the garage is fairly quiet. There is some road noise from a usually quiet road about 100m away, although the occasional motorbike buzzes up that road on Friday or Saturday nights. There is the problem of the odd helicopter heading out to the oil fields in the North Sea. However, I’m mainly concerned with keeping the noise from leaking out of the studio and disturbing neighbours – I don’t mind so much having to pause or do a retake because of external noise.

I’d like to keep building costs down to below £20,000 including the cost of builder, etc.

Walls

I’d like to tackle issues about the build one at a time so I want to start with the walls.
I intend to use half of the current garage for my studio; the rest will remain as a storage area.



The current external walls are concrete brick 200mm (8 inch) with no internal finish (except paint). Obviously I’ll have to seal this wall as much as possible.

I’ve been reading Rod Gervais’s book, which is often mentioned in this forum. As far as I can make out, I should strive to make all the walls two leaf structures, with a mass-spring-mass structure. The outside masonry wall is obviously the outer mass, an inner wall would be the inner mass and the spring would be an air gap.
From the diagram it can be seen that there are two types of wall required; 3 walls adjacent to the existing garage walls and one which essentially divides the garage in two.

There are a number of questions I’d like to get everyone’s opinions on the options for the 3 next to the existing garage walls:
1. Do I need to “beef up” the outer walls, with either studs filled in with insulation (to help the damp the spring effect) or with plasterboard (drywall)? And which is best?
2. The inner wall. Which is best: another masonry wall or an inner leaf made from studs (with insulation and plasterboard on the inside?
The dividing wall would probably be: plasterboard – wooden studs (with insulation) – air gap – wooden studs (with insulation – plasterboard. The plasterboard could be a double layer if necessary.



What are the relative merits of the above options, including option C which is the one my builder has recommended (although I'm a bit worried because there is no air gap, i.e it becomes a single leaf construction)?

I'd be interested in any comments or advice about this. I'd also like to ask what insulation everyone recommends as I've read in another thread here that Rockwool slab (RWA45) is too dense and transmits lower frequencies.

Thanks,

Dave

Hello All,

Is Pink Fibreglass R13 more effective for transmission loss at low frequencies than rockwool RWA45, RW3 or RW5? Is it effective for heat insulation and does it comply with UK building regs? I'm very confused!

I've been having a look round at posts on this site but I can't seem to find a similar project where the garage has masonry walls.

I'm wondering if I've not supplied enough information in the above post. If there is something wrong, I'd appreciate if someone would please tell me.

Thanks,

Dave

If you have an existing concrete block exterior wall then you simply paint this block with a high quality oil paint, making certain to address any existing pits or holes in the mortar first!

Installing framing and sheetrock to this blockwork is not recommended. If you can install the mass (sheetrock) directly to the block, this would be better, but is not a requirement with an 8 inch/200mm block, assuming the block cells are poured solid.

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

But even this does not satisfy the overhead leaks.

You can construct the walls...everyone gets tunnel vision here...they see straight in front of themselves. But you have to look up...sound will look up and go out whatever the path of least resistance is...typically the roof/ceiling area/doors and windows.

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

Brien,

Thanks for the info, it's really good to get a response. These are difficult decisions to make on your own and I was beginning to feel a bit isolated (no pun intended).

Are you saying:

1. I don't even need an inner room, I just need to paint, seal and attach sheetrock to the inside of the existing external walls without the need for an inner room?
2. Or that I just paint and seal the external walls, but still build an inner room stud frame?

If I understand your advice right, it seems to be in agreement with a comment on the NRC Canada website which says:


I'd be interested whether option C in my original post is either too "over the top" or likely to behave worse than just the sealed concrete brick walls? At least it adds some heat insulation (it can get pretty cold here in Scotland).

Brien, in your diagram is the dividing wall concrete block also? How should the dividing wall be fixed to the external garage walls?

I'm not sure whether the existing block cells are hollow or not. I probably won't know this for certain unless I can remove a brick or two.

I'm going to plan the ceiling soon, but wanted to get the walls right before deciding on the right ceiling for the room. Having read a good portion of Rod Gervais's book I realise that the weakest point determines the sound isolation properties of the whole room.

Thanks for the advice. Sorry if I'm being a bit slow here.

Dave

I would follow the recommendations of the NRC. If that is choice A, B or C I do not know...but these are the things that I concern myself with.

Professional opinions from qualified spokespersons.

The simple answer is that the paint blocks the holes that exist in a concrete block. A concrete block is porous, it can leak water in or out, and if water can move through it, then air can move and where air goes, so does sound.

Next is that mass should be viewed as a single layer. The more opportunity for air or air cavities that exist, the less the wall assembly will perform in respect to isolation.

While it is a global wide issue that folks have a basement or concrete wall and all the information they get locally says "this is how it is done" in respect to installing a framed OR furred out area and then adding mass...they are only saying what they have heard, and that has been repeated in their respective country for decades.

It is still incorrect in the hunt for isolation. Air cavities, especially small ones, reduce the wall assemblies ability to contain the sound since you add more boundaries that will be excited(vibrate) and this cumulative effect is always detrimental to your sound proofing goals.

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

I absolutely agree with what Brien said, and to your question:

... I would answer that it is rather "under the bottom" than "over the top"! It is most likely the worst isolator of your three options.

It is, in fact, the one that the NRC warns you about "Finishing the walls by adding gypsum board on furring or studs creates a more complicated system where resonances can greatly increase or decrease the sound transmission loss": It is the one that "greatly decreases the sound transmission loss".

Option "B" suffers from the same disease. Of the three, option "A" is your best bet, but like Brien said, you don't need the frame up against the block wall: it serves no acoustic purpose.


It could be. Or it could be drywall on studs. Or brick. Or plywood on studs. Or OSB on studs. Or MDF on studs. Or fibercement on studs. Basically anything massive that is also stiff, dense, non-porous and sealed, will work.

It should NOT be attached to the garage walls at all! Not anywhere! That's the entire point of a decoupled MSM system: there must be no physical connection at all between the outer leaf and inner leaf. They are two independent structure, each of which stands on its own. They are both totally air tight (hermetically sealed, as Brien pointed out), there is an air gap between them, and the air gap is filled with insulation, such as rock wool, fiberglass, etc.

Or maybe I misunderstood you, and you are talking about the new outer leaf that Brien added, and that you did not have on your original diagram? If that's the case, then it depends on how you build it. If it is going to be stud and drywall, then bolt the end studs to the garage wall, but caulk carefully in between before you do (three beads), then caulk again after it is bolted in (both sides), then caulk again for each layer of drywall, in the gap that you leave at the end. Then caulk again, just in case. The same applies to the floor and existing ceiling/roof : you must have a hermetic seal.

Actually, you don't really need to "decide" at all! The decision is already made: the ceiling must be done exactly the same as the walls. If not, then either you wasted money on the walls, or you wasted it on the ceiling. The entire room is a TUNED SYSTEM. It must all be done the same way. So you need the same mass density on the ceiling as on the walls. For example, if you do your MSM calculations and they tell you that you need to go with 3 layers of 16mm drywall on the walls ,then for the ceiling too you also need 3 layers of 16mm drywall, or the equivalent mass from using other materials.

The same applies to doors, windows, HVAC, and electrical: All of it must be done to the same level. If not, then you wasted a lot of money. For example, if you do the math and decide that your MSM resonance will be 18 Hz (just an example), but then you put a pair of soundlock doors in that end up being tuned to 50 Hz, well then you wasted an awful lot of money on the rest of the room, since the doors are your weak point. Sound is like water: it leaks out through the easiest path. Cut a hole in the glass on one side of an aquarium and stick a piece of cardboard over it, and what happens? The water leaks out through the cardboard, so all the glass is a waste of money.

So your room has to be done to the same level all the way around: all six sides, plus windows, doors, HVAC, electrical and anything else that might interfere.

So what level do you need? What are your numbers? How much isolation do you need? That number will dictate the structure and materials for the walls and ceiling, and those in turn will dictate the design criteria for all the rest.


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

Brien,


Totally agree!



Unless I'm not understanding you, this point seems to contradict much of what I've read both here and in the Gervais book, as well as reports at the NRC Canada. They all seem to indicate that Mass-Spring-Mass assemblies increase TL as long as the mass is in the right places, i.e. on either side of the whole sandwich, and that the air acts as a spring to damp vibrations.

According to the NRC Canada these kind of assemblies can give you STC values in the mid 60s rather than the 45-50 you'd get from just the masonry wall.

What does everyone else think?

Dave

I'm beginning to think, from advice here and what I've read that something like the following might work better than the previous options.



Although I'm not sure how you would retain the insulation between the inner wall's studs. Glue or fabric meshing?

Opinions anyone?

Dave

Yup, that looks about right!

There are several ways of retaining the insulation in the stud space, depending on what type you use. If you use semi-rigid or batts, then it will just stay in place. Or you could put some kind of strapping or mesh across the back of the studs. Or you could use spiked hangers (don't recall the proper technical term). But not glue.

I think you missed the point that Brien was making: If you put one layer of "something" (Eg. drywall) up close to another solid surface, or even right against it, then you create small air spaces in between, which REDUCE your overall isolation. In your "B" option, you have exactly that: a layer of plasterboard tight up against a brick wall. If you do that, since surface of the brick is not smooth, then you will inevitably trap numerous tiny pockets and cavities of air sin there, and the overall effect will be to reduce the isolation of the wall. This is exactly what Brien was saying: "The more opportunity for air or air cavities that exist, the less the wall assembly will perform in respect to isolation." Entrapped air will decrease your isolation. This is not about the air gap in an MSM wall, which you do need: As Brien said, it is about entrapping air pockets between layers of what is supposed to be a single leaf of mass. The same applies to cavities inside your blocks: if they are empty, just like the NRC document says, you won't get as much isolation as if they are sand-filled, since without the sand they act a bit like two leaves, but with the sand they act more like one leaf: "Adding materials such as sand or grout to the cores of the masonry units makes them perform much like solid blocks; an increase in transmission loss results due to the increase in weight." Correct.

YEs then can. provided that you FOLLOW THE INSTRUCTIONS EXACTLY, which means NOT adding extra layers of drywall directly attached to a concrete or brick surface. If I recall correctly, they even mention that case specifically in one of the NRC documents: it reduced the isolation by several dB, (maybe 6 or 8, I think.) and all of that in the low end of the spectrum (below about 400 Hz) where you need it most. Even worse is the case of putting a layer of drywall (or similar) on thin furring strips, right up against a brick or block wall: that will really kill your low end.

Brien is not contradicting the NRC or any other research on walls: he is highlighting something that you seem to have missed, namely that entrapping air in thin layers reduces isolation.

But you are on the right track now, with your latest design. Have you figured out your numbers yet? How much isolation you are going to need? That will define how much mas you need on your inner leaf, and also the depth of the air gap. Once you do this basic math, the rest is easy, and it all starts coming together and making sense.

Just want to make sure: You are aware that STC is NOT a good method for judging the ability of a wall to isolate a recording studio, right? People often make that mistake, and think that a wall with a high STC rating is going to be great for their studio, then wonder why they can still here bass and drums booming through after they build it...


- Stuart -

_________________
I want this studio to amaze people. "That'll do" doesn't amaze people.

It is not a contradiction my friend, it is me often thinking that these basic parts of the assemblies are known and no further explanation needs to happen.

Yes, mass/spring/mass is the goal. When I said mass, it referred to one single side of a hard boundary...e.g. mass, since you and I were not in discussion on mass/spring/ mass, or even the often misrepresented mass/air/mass....we were simple talking about one mass

In some of the NRC's work, if you read enough of it, when they do the calculations, often they may refer to even the tiniest of air spaces between two hard boundaries under study as being the reason why the TL or STC was modified up or down.

They are everywhere, air spaces, much like the dreaded 3 leaf...it's all around you and I.

So we have a better understanding of what we are disscussing?

_________________
Brien Holcombe
_____________________________________________
Sound: You can't stop it, you can only try to contain it.

Brien and Stuart,

Apologies about my misunderstanding over the two types of air gap. Please forgive this poor noob! I really do appreciate you both taking the time to put me on the right track.

I think I'm beginning to get it now and it's good to read that Stuart approves of my latest option. Thanks for the advice on retaining the insulation between the studs.

On the subject of insulation, my builder had suggested using Rockwool RWA45, but I've read elsewhere in this forum that this might be too dense and not perform well for TL at lower frequencies. Should I be considering less dense options for insulation?

I realise STC is only a rough guide to TL, especially at low frequencies.

I just bought a sound meter, so I'm going to take some readings this weekend. A friend is coming round and we're going to get into the garage, make some noise and take some readings.

Thanks,

Dave