Soundproofing my cave

So I finally paid for the first installment of "the dream" - a soundproof drum room. Now I have to finish it, and I could use some help.

My property is on a grade and I leveled it with fill. So it was pretty easy to dig out the fill and make a 5 meter by 5 meter basement room. It's a room that is completely underground beneath another room. The construction is all iron and brick and concrete and plaster and it's entirely underground with a very thick foundation as its roof.

The guy who built it is convinced that I could play drums in it, as is, and no sound would leak. I keep telling him that he's never heard drums live before. So I'm planning to build the room-within-the-room.

I don't think there's a need to build a floating floor as the room is three meters down and on bedrock. So my plan is to build a room shell - four walls and a roof - with iron or wood frame and sheetrock. There will be a couple centimeters space between this shell and the main room. The main room will have a soundproof door that opens out and the shell will have a thick door that opens in.

There is a ventilation hole in the roof of the basement. This is to provide a 4" space for ventilation tubing and also accommodate CAT6 cables, tubing for a split AC, etc. Because of the weird space due to the bracing for my retaining wall, this is in an area outside the planned inner room. I think I can seal most of this hole closed and use a baffle box to kill sound transmission through the part that has to stay open.

Does this sound like a workable solution? I would really like it to be as soundproof as possible, because I'm a night owl and I'd like to be able to drum at 3am but this neighborhood is crazy quiet all the time.

And do I need to do anything special where the shell room touches the floor of the outer room? The contractor is planning to put laminate wood flooring in the outer room, so it will be a sheet of sheetrock hitting a laminate wood floor. What is the best way to 'seal' the point where they meet? Would it be better to leave the outer room natural with a concrete floor and just put the laminate inside the inner room?

Thanks for any help!
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Senior Member
The only thing it seems like you're missing is air. If I'm reading your post correctly, you're planning on sealing the existing ventilation hole to reduce sound transmission. Unfortunately if your door is really soundproofed (which includes being sealed) and you do everything else right in the construction you will need some kind of air exchange system (fresh air in, stale air out)so you can breath in there. You'll need a qualified HVAC person to figure out what the capacity of that system is going to be. This is the bane of everyone who ever thought "hey, how hard can it be to make a soundproof studio?", because it's the easiest thing to not think about until it's too late and it's a pain in the ass to do right without negating all your other soundproofing construction. And in case you were wondering, a split AC doesn't count. It only cools the air in a space, doesn't move air back and forth at all.

In terms of where the sheetrock meets the floor, you leave a small gap just big enough to cram some backer rod in there, then cover it up with acoustic caulk. Acoustic caulk is a specialized product that doesn't shrink or ever completely harden so it can stay sealed despite the natural expanding, contracting, and general movement of different materials. There are other products not called "Acoustic caulk" that will do this as well (like pure silicone, I believe), but they end up actually being more expensive. The same process goes for wherever 2 perpendicular planes meet.

Agree that you don't need or want to float a floor in your situation.

Lastly, you didn't go into detail about your plan for this but it's worth mentioning: 2 layers of 5/8" sheetrock is a pretty good starting point when doing this kind of construction. Putting a layer of Green Glue in between will make it better even.

There is a book by Rod Gervais about building home studios. It's really worth checking out if youre going into this venture so you don't waste time and money unnecessarily doing things the wrong way.
Hey, thanks for the reply.

I'm scared of the air question, both because I don't want to die and because it seems somewhat unwinnable.

As I kind of described, the room is basically 5x5 meters. But one of the walls is just the retaining wall with concrete and plaster on it, and it's at a 55 or 60 degree angle so the room is wider at the ceiling than the floor, probably around 6 meters at the top. So the 5x5 inner room would leave a triangular open space against that wall and in that space I have a 30cm x 20cm rectangle cut in the ceiling for the 4" vent tubing and etc.

But that is now my weakest point for sound resistance. So I have to figure out how to leave the smallest possible portion of it open, seal the rest with concrete, not die from lack of air, and stop sound leaking. I think that's going to be the hardest part to solve.

Thanks for the info on the floor/wall joint, I'll look for acoustic caulk but we actually own a fair amount of silicon (it's not that expensive in Mexico) to re-seal our windows every year. I'll also look for backer rod. Since that will raise the inner walls a few centimeters it seems it would make sense to maybe add another inch or two of concrete on the floor inside the inner room, like a tiny stage, and put the laminate flooring on that.

If you have the time, a few questions:

- Is there a generic equivalent for Green Glue?
- Is there a generic equivalent for backer rod? Like, is the density of the polyethylene known? There are lots of foam/material factories here and if I can't find the actual product someone can probably fake it reasonably if I have details
- Any advice for how to build the frame for the inner room?
- What is the optimal distance between the outer sheetrock surface and the concrete walls that make up the room? I'm trying to maximize inner space so I'm thinking of 6cm or 2.5".

I remember looking through that Rod Gervais book before, I'll pick it up again and see what I can learn. I remember he said something about never wanting perpendicular walls of equal size so I'm planning to angle two of the walls about 5 degrees.

Should be a fun project.



Pioneer Member
I think before I put more money in I'd setup a small kit in the room and see where you really stand on sound transmission outside of the room


Platinum Member
There is no generic equivalent to Green Glue. There is a competitor, but it hasn't been tested like Green Glue and it's almost the same cost.

Backer rod is only for closing the gaps in the sheetrock that you purposefully made at the intersection of walls and ceiling. The gap can be anywhere from 1/4 to 1/2 inch. It's not important. The important thing is to stuff the backer rod in there so the acoustic caulk, (or your GE Silicone 2) can make a three sided seal. Three sides are needed for gap integrity. Two sides will eventually split and sound will escape.

You probably shouldn't do an outside sheet on the studs if it will allow an air gap between the sheet and the concrete. It could set up a resonant space which could make the transmission worse.

If you use z channel or Whisper clip type contraptions that hold the drywall off the framing, you need to have spacers for the light switches, lights, and electrical wall outlets. Those openings need to be blocked with fire proof clay or a light box cover.

If you use a contractor make sure he's done it before or you will find that he told you he did it correct, but he really didn't.
One length screw for the first layer of drywall and another length for the second. If the screws go into the studs, your expensive Green Glue won't work.

I worked on a house where the homeowner wanted to use Green Glue. When the plasterers we hired came in to put up the walls, they blew it off. They did one panel while we were there and then threw it all in the garage. 12 buckets. Too sticky I suppose.