Drum Dome Construction started: Decoupling

Hi all, first let me say that I really like this forum -- it's full of invaluable information! Thanks for that! But I must also say that I'm a bit disappointed that nobody really answered my questions in the Studio Design half a year ago... Drum Dome Design Nevertheless I started construction last week and -- of course -- I've got some questions I really hope you can answer :) The design thread mentioned above shows, that I'm using a cubical frame for my drum booth. This is because I didn't want to drill big holes in the ceiling of the cellar (this is were the booth is located). So the walls support the ceiling: 1) How can I decouple the wooden frame from the floor? I think, neoprene or similar stuff is not suitable because of the heavy weight (wall + ceiling). It also has to be airtight... What do you think about that? 2) I started building the ceiling because the cellar room is not very big so I have to build it "upside down". There is a little gap left on the frame around the ceiling: an outline of about 5 cm width where the wood is not covered with drywall. Is this a really weak point? Thanks for your answers! :D

First, I've never seen framing done like this - usually the bottom and top plates are 2x4's (actual metric size 37 x 90mm), and they are placed so the thicker dimension defines the thickness of the entire wall, not sideways. Second, if your ceiling frames are the same size have you any local span information that will tell you if your frame will support the ceiling material you intend to use? Our span calculators are based on nominal US and Canadian sized lumber so won't be of much help. Third, if you intend to float a floor I'd plan on resting your wall frames on TOP of that floor, with increased isolator sizing under the wall to take the extra weight. See the first page of Aaron's thread http://www.johnlsayers.com/phpBB2/viewt ... 39&start=0 for my method of accomplishing this. Also, you'd want to make that floor as heavy as possible and use enough rockwool so that it gets slightly compressed when you add the floor layers - otherwise the floor will ring/resonate/boom. Remember than any sound you "let out" of the drum room will then be in the rest of the basement, so each and every surface of your drum room needs to be heavy - 2, or even 3 layers of 1/2" gypsum will be necessary, and probably on two separate frames for a mass-air-mass construct. The good news - this might not be necessary due to the double concrete ceiling, but if that foam core is solid then the entire assembly will act as ONE mass, and your entire sound blocking capability will be directly related to total mass law (which isn't as effective as mass-air-mass) So, before you get going much further I'd recommend finding a sound level meter and making some tests - you or someone else playing the drums while a helper checks the sound levels in upstairs or neighbors' spaces. Without this, you don't even know if you HAVE a problem. Sorry your other thread "fell through the cracks", hopefully we're not to late to help... Steve

jeez, another *ROMAN* on the forum 8) greets, RO(man)

Thank you very much knightfly! I'm very happy you answered :) I know it wasn't the best idea to start without any proof of concept but I try to explain some things...

First, I've never seen framing done like this - usually the bottom and top plates are 2x4's (actual metric size 37 x 90mm)

I planned to make the walls 80mm thick. I use 80x80mm for the outer 12 edges of the cubical. The inner frames are 80x60 mm. So the thicker dimension does define the thickness of the wall. I actually planned to make the walls 100mm thick but 100x100mm and 100x80 mm frames a nearly twice the price of the wood I chose. Also I want to realize three "inside-out" walls (see Design Thread) so I thought the thickness of the frames is not a big issue, besides of being thick enough to support the ceiling.

Second, if your ceiling frames are the same size have you any local span information that will tell you if your frame will support the ceiling material you intend to use? Our span calculators are based on nominal US and Canadian sized lumber so won't be of much help.

To tell the truth I made a good guess that the frame construction will be stable. But you're right -- I will check that out before setting the ceiling on top of the walls.

Third, if you intend to float a floor I'd plan on resting your wall frames on TOP of that floor, with increased isolator sizing under the wall to take the extra weight.

Yes I also considered to float the whole floor and build the walls on top of that. But I planned to do a inner floor without contacting the wall for two reasons: First, to build a drumriser is simply cheaper (would cost me about 50 EUR=65$). Second, I thought a drumriser would be better for decoupling. My drumset and me will not weigh as much as four walls and the ceiling... One of the main problems I have considering sound isolation is subsonic noise.

Remember than any sound you "let out" of the drum room will then be in the rest of the basement, so each and every surface of your drum room needs to be heavy - 2, or even 3 layers of 1/2" gypsum will be necessary, and probably on two separate frames for a mass-air-mass construct.

The drum room will be located in the corner of the cellar room, so I've got three sides (two walls and ceiling) facing the cellar walls/ceiling. I planned to use the "inside-out" design for these three walls, as you can see in my design thread. On these walls will be two layers of 1/2" gypsum. The other two walls are planned as single frame: outside leaf: one layer of gypsum, inside leaf: one layer of OSB. I thought these walls were not very critical for isolating sound upstairs... I also considered double frame walls but for budget reasons I decided for single frame and the "inside-out" design.

The good news - this might not be necessary due to the double concrete ceiling, but if that foam core is solid then the entire assembly will act as ONE mass, and your entire sound blocking capability will be directly related to total mass law (which isn't as effective as mass-air-mass)

The foam core is rather massive so it will probably act as one mass. The walls of the house are indeed VERY massive because of the building standards for that type of building ("passive house"). Isn't it better for my inside-out approach if the ceiling act as one mass? So, I've got the two layers of gypsum, air, cellar ceiling (concrete/foam/concrete).

So, before you get going much further I'd recommend finding a sound level meter and making some tests - you or someone else playing the drums while a helper checks the sound levels in upstairs or neighbors' spaces. Without this, you don't even know if you HAVE a problem.

Yes, I already did that test without sound level meter. But I could repeat it with sound level meter. My wife could even hear the drums "loudly" in our appartment three floors above... although my neighbour in the first floor said she could hear it but not "that" loud.. so my guesses of this test were: 1) Drums are really loud ...and I'm not playing jazz :wink: 2) It's very subjective how "loud" you hear something. 3) the main problem is subsonic noise which "travels" from the cellar floor through the walls upstairs to the other floors..

Sorry your other thread "fell through the cracks", hopefully we're not to late to help... Steve

It's never too late! :wink: Thank you!

Ro wrote:

jeez, another *ROMAN* on the forum 8)

Hi Roman, nice to meet you :D ...and there is even a third one but I forgot his nick, from austria I think. Greetings, Roman

You're right about the concrete walls/ceiling only needing a second mass, with air/insulation between - but I tend to think that your existing ceiling is as much responsible for flanking into the surrounding structure as the floor, since the floor (assuming it's on the ground) would be damped more than the ceiling - either way, the walls are carrying sound to the upper levels so you need to EXCLUDE the sound from reaching those walls/ceiling, and floor as well. One thing that may help is to increase the space between your inner walls and the existing ones - this will lower the mam frequency, improving low end isolation. One relatively inexpensive test you could make first is to lay down a couple of layers of MDF or OSB on top of 3 or 4 inches of mineral wool (3 PCF or 48 kG/m^3 is good) and set your drums on this riser - then repeat your tests to see if it's much quieter upstairs. This will give you an idea how much help just getting the drums somewhat isolated from the floor will help. When asking for local engineering help, find out how large your ceiling frames would need to be to put 3 layers of gyp board on them - you won't have much of a choice in the depth of air gap at the ceiling without losing too much headroom inside, so increasing the mass there should help... Steve

At the weekend I will do a test with the the sound level meter. Then I will repeat the test using a drum riser as you suggest. Hopefully I will get some clarification. If the ceiling and the corner walls are as much as responsible for flanking into the surrounding structure or even more critical as the floor, does inside-out design for this three walls facing the building structure directly make sense? Because I do not exclude sound from reaching those walls when applying inside-out design, do I?

you won't have much of a choice in the depth of air gap at the ceiling without losing too much headroom inside

Yes, this is indeed a problem. I would like to record drums in this booth and because of the low ceiling I plan to make a "cloud" at the ceiling inside the drum room avoiding early reflections in the overhead mics. I originally planned to make the booth 220 cm in height but decided to gor for 230 cm. There is an air gap of 15 cm to the concrete ceiling. Considering early reflections, is there a big difference between 230 cm and 220 cm height when I'm hanging up a cloud? So I may have about 10 cm I can additionally spend for the air gap at the ceiling. 220 cm height is also better for more balanced room modes (220/250/300 will give a ratio of 1:1.14:1.36 which is nearly a recommended ratio). Although I will lose headroom which doesn't make the drum room very comfortable... Regards Roman

So, I did some sound level test this weekend. I played the drums while a friend of mine measured the sound level upstairs. I attached the results in a drawing. I built a kind of shaky drum riser... rigid mineral wool is hard to find here, so I used Isover Acoustic TP1, which is not very dense, but fluffy. I think that's the stuff Rod calls sound-batt insulation in his book. I plan to reuse it for wall insulation later. I attached some pics where you can see me playing on in a not very comfortable position (laid back as my timing is sometimes ) :wink: The interesting thing is, that the sound level in the room directly above where I was playing did not differ whether I was playing on the drum riser or not. Both times it was 54 dBA. For all other rooms, the sound level using a drum riser differed from 2 to 4,5 dBA, as you can see on the drawing. So my conclusion is, that in the living room directly above, sound transmission through the ceiling is the problem. For all other rooms, mainly in 2nd and 3rd floor, sound traveling through the walls and flanking into the rooms is the major issue. What do you recommend as the next step? Is inside-out wall design really the way I should go?

I think you may have skewed the test by having the kick drum facing into the corner - I would think that the two corner walls would be more coupled to the drum that way. Can you possibly repeat the test, only this time face the kick drum out into the room? IF that doesn't help much, you may not be able to improve things with the lack of space you have - the ONLY thing that can help loud drums in a case like this is WIDE air gaps, HEAVY masses, and De-coupled inner leaves (including the floor) - for that low frequencies, you're talking at least a foot of air space with heavy masonry - more like TWO feet with gypsum or MDF construction - so no, for this the 'inside out" walls aren't the answer... Steve

Thanks for you answer Steve -- even if it's a bit discouraging... I did not repeat the test, yet because I have to borrow it every time I need it. But, I think there won't be such a difference, because the first tests without the drum riser (only measured at second and third floor) were made with the bassdrum facing to the middle of the room. Any Case, I have to assume worst case, which means 54dbA sound pressure level without any construction. I don't understand yet what exactly I should aim at: Is it 1) to isolate the booth itself (inner room) using decoupled double frame walls and ceiling so that the sound pressure level in the outer room (basement) is minimized or 2) to include the existing ceiling of the basement as a leaf in the calculation to minimize the spl in the room above (living room). Your answer looks like option 1) but: If I build a double frame ceiling for my booth you can consider this as three leafs in the whole system (or four if we assume the green foam between the existing concrete ceiling leafs does not couple them...). Because from the perspective of the living room, there is: 1.) floor/ceiling 2.) outer frame of the booth 3.) inner frame of the booth But three leafs is not as good as two leafs -- so this sounds contradictory to me :shock: