Traps between joists in ceiling corners?

[RyanC]

I'm looking to start planning for a re-do of my control room, I'm curious if anyone thinks it would be worth it to remove the drywall on the ceiling going around the top corners and put in mdf boxes that are filled with 703? I will still be doing a full superchunk below it, but the room is only 200sf, so I would like to get as much of it trapped out as possible. The Joists run long wise in the room (basically 10x20) and the last joist is on the wall (obviously) so both sides would have a full 15 and 1/2 inches (minus the mdf). It's a peaked roof, so the boxes could be very deep in the middle of the room, but I would think 8 inches around would add significantly to the total amount of trapping.

Any thoughts? Thanks guys.

[RyanC]

Also has anyone done any 3 way mitering for the corners of superchunks? Just curious how you pull that off. . .

[PaulP]

Originally Posted by RyanC

Also has anyone done any 3 way mitering for the corners of superchunks? Just curious how you pull that off. . .

You mean like this ? (imagine another vertical superchunk instead of the
cabinet :


He stuck a big cube of rockwool in the corner then cut the extra off with
a handsaw before covering everything up :





The pictures were stolen from studiotips, thread Mark's Studio Build Diary.

Paul P

[PaulP]

Geometrically the corner absorbers meet like this :



Paul P

[RyanC]

Thanks for the answer on the mitering question, The first pics where more what I imagined. But the 2nd looks nice also. . .

As for between the joists, that's not what I mean. At least not what you could tell from the pic.

What I mean is that I have an attic space (goes up 5 feet at the peak of the roof), and standard 8 foot cielings. Cathedraling isn't really an option because the roof has truss framing (too much work and money). But I figure why not take advantage of the extra space acoustically if not visually.

The joists are the part of the ceiling framing that run just above the drywall (assuming you all know that but just so we all know what we're talking about). So my joists are on 24" centers (it turns out) So I would have space for traps, above the superchunks and even a built in cloud. I'm thinking it will be worth it. I'm planning to pull out the HVAC line and get a decent portable AC/heater that will feed the control room from the machine room, it seems by the time I do that, I might as well rip out the drywall and get something more out of it.

[jhbrandt]

Ryan,
you will need some drywall between you and the attic for isolation.

- actually, with all that space, if there were some way to seal off the roof acoustically by boxing it in with drywall or osb and sealing the cracks to eliminate unwanted noise from outside and to keep you from bothering the neighbors... you could remove your current drywall ceiling, put some acoustic tiles as the ceiling (as acoustically transparent as possible), and fill the attic space with pink attic blanket.

-- that would turn that space into a very good trap.

[PaulP]

You haven't said, but if your room is a garage it may not be open to the
attic if the attic communicates with the attic over the rest of the house
in some way. A garage has to be wrapped in drywall for fire reasons.

Paul P

[RyanC]

Originally Posted by jhbrandt

Ryan,
you will need some drywall between you and the attic for isolation.

- actually, with all that space, if there were some way to seal off the roof acoustically by boxing it in with drywall or osb and sealing the cracks to eliminate unwanted noise from outside and to keep you from bothering the neighbors... you could remove your current drywall ceiling, put some acoustic tiles as the ceiling (as acoustically transparent as possible), and fill the attic space with pink attic blanket.

-- that would turn that space into a very good trap.

Yeah the drywall get's replaced by mdf boxes that fit between the joists, so the isolation is still intact. It's all truss framing, so it would not be possible to have one box that was wider than 23.5".

And it's not a garage, it's on the 2nd floor and I live downstairs. The entire cieling between the two is doubled up 5/8" drywall with green glue or more (fired down cieling with 4, 1 hour leaves.) Zoning is B2 and it's WAY more than a 1 hour firewall.

Anyway I think it sounds like this would be worth it. So the next question is should I build the boxes so that they are out of parallel with the floor? And or should they have different depths from one another? There are 6 joists, 5 gaps between them. Thanks guys-

[jhbrandt]

Originally Posted by RyanC

should I build the boxes so that they are out of parallel with the floor? And or should they have different depths from one another? There are 6 joists, 5 gaps between them. Thanks guys-

Out of parallel w/floor will not affect their function or your standing waves. So, I wouldn't bother.

Yes, you could have different depths, but if you are building what I think you are... the standard bass trap - They work are 1/4 wavelengths. - the depth of the box will be at 1/4 wavelength of the frequency of interest. If at 100 Hz, your box will need to be 2.825 feet deep.

If you make the boxes follow the shape of the roof, that will give you the different depths and make your trap(s) broadband.

Good luck.