Sound Containment - Air Cavity - soffit. - AVS Forum
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post #1 of 11 Old 10-21-2013, 07:56 AM - Thread Starter
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I have a main beam of the house running through the HT - I'm building a soffit around it (1 side attached to ceiling, other to the wall - basically an "L" shape). I understand that a main component of the sound containment is creating an air vacuum ("no sound in space") - thus the walls are sealed all around- so the cavity inside is a vacuum filled with insulation.
I would think that I have to do the same for the soffit, however the soffit is open on top due to the beam.
Should I have my ceiling (which decoupled via whisper clips/hat channel) go all the way and touching/sealed to this main beam - however if I do that how do I attach the IB3 clips to the ceiling joists, since the ceiling would then be between the IB3 clip and the joist?
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post #2 of 11 Old 10-21-2013, 09:12 AM
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I like to build the walls and ceiling first, double layers on clips and channel. Use OSB on the ceiling for first layer, build it close to beam but not touching. Then hang the L soffit off the decoupled ceiling and wall, use double layers with GG. I have pics on my other computer and can post tonight.
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post #3 of 11 Old 10-21-2013, 09:48 AM - Thread Starter
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thanks - looking forward to the pics.
Though being that the main support beam that I'm containing in the soffit extends below the joists (hence below the ceiling) how do I keep it air tight without connecting to the beam.
OR should I put the ceiling up very close to the main support beam, and using calking/sealant between the ceiling and main support beam>
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post #4 of 11 Old 10-21-2013, 12:24 PM - Thread Starter
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Being that the main support beam is within the soffit - like the diagram below:
Does that present a problem? Or is there a better way to approach this?


...... |X| .........
...... |X| .........
=== |X| ===
|..... |X| |
|..... |X| |
|..... |X| |
_ _ _ _
|
|
|
|

====== represents the ceiling
[X] = main support beam for house
... = insulation
wall on left
inside of HT on right
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post #5 of 11 Old 10-21-2013, 01:19 PM
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Think of the soffit as the ceiling only with multi-levels. It doesn't matter what is up in the soffit. I don't care if it is a beam, duct, pipes or a former wife, you just don't want the ceiling touching it. If you can build a soundproof airtight ceiling you can do the soffit, use the same materials, double layers, with GG, caulk all the seams etc,
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post #6 of 11 Old 10-21-2013, 01:42 PM - Thread Starter
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The ceiling isn't air tight - as the joists extend outside of the HT room
same thing here -the beam runs out of the HT room - the length of the house

So I guess the Q applies to both - how do you make it air tight when it contains beams, joists that run outside of the HT containment?

thx!
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post #7 of 11 Old 10-21-2013, 01:46 PM
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You make the theater shell air tight, everything else you stuff with pink fluffy. If you have big air cavities that extend to other areas of the house, Adding several inches of compressed high density insulation (ROXUL) as a barrier might satisfy your need for creating a vacuum

some pictures of the anatomy of a double layer drywall soffit. You build ladders down screwed up to the ceiling, either to an OSB first layer, A pre-calculated hat channel or both if you have OCD. Then you add a 2x2, or 2x3 to the wall using a level to be sure the bottom edge is level with the ladders. Then you add the drywall.



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post #8 of 11 Old 10-22-2013, 05:25 PM
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Does my old thread help? http://www.avsforum.com/t/1459757/help-with-decoupled-soffit

I did "option B" in my first post, although I made the tweak Big suggested in regards to order of installing the different drywall pieces.
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post #9 of 11 Old 10-22-2013, 10:15 PM - Thread Starter
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thanks, here's a picture of the corner w/ the main support beam and pipe.

you're facing the screen wall, and to the right is the side wall.
I can build a soffit as described

Though you can see that due to the beam and pipe the screen wall cannot extend to touch the side wall

Note the large (6" ) gap between the support beam and the screen wall is b/c I moved the side wall out - it used to be next to where the screen wall is. My new soffit is going to extend just 2" from the main support beam, so I was planning to append a 4" wall adjacent to the existing screen wall, and then attach a wall to the soffit to extend from the bottom of the soffit to the floor - OK - or is there a better way to do it?
thx



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post #10 of 11 Old 10-23-2013, 02:21 PM
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Quote:
Originally Posted by BIGmouthinDC View Post


some pictures of the anatomy of a double layer drywall soffit. You build ladders down screwed up to the ceiling, either to an OSB first layer, A pre-calculated hat channel or both if you have OCD. Then you add a 2x2, or 2x3 to the wall using a level to be sure the bottom edge is level with the ladders. Then you add the drywall.




Big - Is drywall now your preferred method for soffits? Getting ready to do mine and I was planning on modeling them on your "Summer Fun, Just down the Parkway" build using 3/4" MDF.

Advantages/Disadvantages of MDF vs Drywall?
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post #11 of 11 Old 10-26-2013, 09:19 PM - Thread Starter
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Q - re: the soffit
being that I extended out my wall, I have 6" of exposed ceiling joists between the existing ceiling and the main support beam (MSB) about to be covered with a soffit.
Option 1 - make Soffit 6" from MSB , however I need the extra few inches to fit my new screen/speaker arrangement
so.. I can make the soffit 1/2 in. from the MSB and use 2x2 for the top (attaching OSB to the 2x2)+GG+5/8DW = ~3"for the soffit
What should I do to fill in the 3" of space?
Not sure how I'd add such a small area of ceiling
Should I attach a few layers of DW on the top of the soffit like trimming - or do you have any other ideas
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