Making a brick walled garage even more soundproof

Hello, I have a few questions I'd like some help with if possible. I have a friend who is trying to soundproof his garage to be able to play drums inside without his neighbors hearing. It's about 30 square meters in size and it's built from solid brick similar to this... http://www.leier.pl/malbork/katalog/img/3145_cegla.jpg His idea is to float the floor, and build a room inside a room using brick like the one at the bottom of this page... Pustaki - Of course he knows he has to put a ceiling on top of these brick walls that would be framed and covered with drywall. My question is do you think making the inside walls out of brick would be the best route? I told him it might be better (and cheaper) to frame the walls on the floating floor and use a few layers of drywall. His two main concerns are of course sound isolation but also how much space he's going to lose inside the room. I know there's a lot more to it but any insight in where to start would be much appreciated! Thanks, Chris

Hi Chris, and welcome to the forum! :)

His idea is to float the floor, ...

That may or may not be necessary, but very likely isn't. Also, floating a floor correctly as not as easy as it sounds, and is not cheap either. Here's a thread that deals with this subject in great detail, so your friend can understand the issues he would be facing if he decides to do that. viewtopic.php?f=2&t=8173 Most studios do not have floated floors, and do not need them. It's one of those myths that seem to float around the internet eternally, and refuse to die...

and build a room inside a room using brick like the one at the bottom of this page

Room-in-a-room is definitely the way to go, and brick will give you very good isolation... provided that the entire room is done the same way. Isolating ("soundproofing") a room is like building an aquarium: just like you have to have well sealed glass on all sides of an aquarium if you want to keep the water in, so to you need well sealed "leaves" on all sides of the studio if you want to keep the sound in. If you build an aquarium with all four walls made of glass but the bottom made of cardboard, then guess how well that will work? :) If you build a studio with all four walls made of brick but the ceiling made of thin drywall, well guess how well that will hold the sound in? About as well as an aquarium with a cardboard bottom. In other words, you have to isolate all sides of the room to the same level. Sound will just ignore those fantastic walls and take the easiest path out through the ceiling and the roof. Isolation is only as good as the weakest link. So, if you plan to do the walls in brick, then the ceiling should be done with something that has the same surface density. Or at the very least, the ceiling needs to be done to the level of isolation that you actually need, even though the walls will be better. So the big question is, How much isolation do you need? In terms of decibels. The answer to that question is the key to selecting the construction technique and materials that will provide the correct amount of isolation.

Of course he knows he has to put a ceiling on top of these brick walls that would be framed and covered with drywall.

Just to put that in perspective: the density o drywall is roughly 700 kg/m3. The density of brick is around 2100 kg/m3. So if you have bricks that are 10cm thick, then you'd need drywall that is 30cm thick to get the same amount of mass... :shock: So, since the ceiling is clearly going to be the weak link here, your objective should be to ensure that the ceiling design provides the amount of isolation that you need, regardless of the walls providing much more. So, for example, if you determine that your friend needs 60 dB of isolation, then the ceiling should be designed to give you that, even if the walls are giving you 75 (for example: don't take those numbers as Gospel! I'm just using them to illustrate the point).

I told him it might be better (and cheaper) to frame the walls on the floating floor and use a few layers of drywall.

That would be another option, yes. In that case, you would design the walls and the ceiling to provide the same level of isolation, as a unit.

His two main concerns are of course sound isolation but also how much space he's going to lose inside the room.

That's hard to say, without knowing how much isolation he needs. But the total thickness of a typical studio wall built with drywall using the fully-decoupled two-leaf MSM design, is about 25cm, (from the outside face of the outer leaf to the inside face of the inner leaf). Whether that is "enough" or "too much" for your friend, depends on how much isolation he needs. - Stuart -

Thanks for the reply! Yes you're right,I doubt he needs to float the floor. I think one of the reasons he was thinking about brick was to maybe lose less space inside his room. I have a couple more questions. 1. If he uses brick, how much of an air space does there need to be between the brick and his existing (brick) outer structural wall? 2. If he went with drywall for the inner wall would you use dry wall on both sides of the stud? Wouldn't that together with the structural wall be a 3 leaf? 3. With drywall how much of an air space does there need to be between the drywall and the structural wall? As far as reduction goes...his goal is to be able to play drums without his neighbors (8 meters away) hearing them. Thanks again! Chris

I think one of the reasons he was thinking about brick was to maybe lose less space inside his room.

Maybe, or maybe not: A brick wall is going to eat up about 10cm or so, due to the thickness of the brick: That's roughly the same amount that you'd need for 2x4 studs with one layer of 16mm drywall: Yes, the brick will give much better isolation for the same use of space, but is it cheaper? Is it easier? Is it faster? And do you need that extra isolation?

1. If he uses brick, how much of an air space does there need to be between the brick and his existing (brick) outer structural wall?

That depends on the numbers: Specifically, how much isolation (in decibels) does he need? And what is the lowest frequency he needs to isolate? depending on those answers, he might be fine with a 2cm gap, or he might need a 20cm gap. There are equations and guidelines for calcualting all this, but you do need the actual numbers.

2. If he went with drywall for the inner wall would you use dry wall on both sides of the stud?

No, just one side.

Wouldn't that together with the structural wall be a 3 leaf?

Correct. You might need several layers of drywall, but they all go on top of each other, on only one side of the studs.

3. With drywall how much of an air space does there need to be between the drywall and the structural wall?

same answer as for Question #1! :) "That depends on the numbers: Specifically, how much isolation (in decibels) does he need? And what is the lowest frequency he needs to isolate?"

As far as reduction goes...his goal is to be able to play drums without his neighbors (8 meters away) hearing them.

Yes, but those are subjective statements, not objective numbers. You can't take the equation for calculating MSM resonance, and plug in "Do Not disturb Neighbors" as a parameter! And you can't take the equation for mass law and plug in "Plays Loud Drums" as one of the variables.... :) You need actual numbers. Your friend need to get a sound level meter and measure how loud he plays, then also measure what his neighbors consider acceptable. Those are the numbers you need. Anything less is just guesswork, and doomed to failure. Acoustics is a science, based on physics, so the numbers are important! :) - Stuart -

Thanks Stuart, I'll get some numbers for you. He checked with his contractor and strangely enough he said the brick route would be cheaper than the drywall route. We're in Poland so I guess that has something to do with it. I know in Canada where I"m from the drywall would likely be much less. Thanks again, I appreciate the info. Chris