Axiom Home Page Forums General Discussion Home Theater Maybe I should start a v4.0 build thread somewhere

Concerning the sound flanking from walls to untreated ceiling. I know you're supposed to leave a gap between each flat surface so that it is not in direct contact with the next surface, such as wall to ceiling, or wall to wall, or wall to floor. Then this gap gets filled in with some sound damping material, like green glue, but not green glue. (Just can't remember what it's called.) It seems that this should eliminate most of the flanking.

I'd like to know what the square footage cost of the extra expense of doing your ceiling with the clips/channel that the Soundproofing company is selling you + cost of extra lumber needed to mount it.

For my room, the ceiling is basically 14 feet by 24 feet. I had to build my soffits before the main layers of drywall to avoid some complications with the inspector. So my area in-between the soffits is what I am going to be working with since the soffits themselves effectively decouple that area...

So now I am at about 11 feet wide by about 22 feet. The ceiling joists run "width-wise" meaning that my clips/channels will be that 11 foot length. You need one for each end as well, so that comes to (not quite perfect in my situation) 13 rows of channel with 4 clips on each row.

Again, the clips go every 4 feet and the rows should be spaced every 24 inches apart (They can be closer than 4 feet and 2 feet respectively, but not further. The point is to decouple, so going to the max distance is ideal).

So that is 52 clips and 143 linear feet of channel.

Clips are $1.98 each and the channel at $0.34 per foot. So that comes to $102.96 in clips and $48.62 in channel.

Add one 2x4 stud per row at $2 each 7% tax included (my joists are about 20 inches on center) and there is $26 in studs.

Total additional cost for mine will be $177.58 plus the shipping costs on the clips and channel. I am already going to be paying a chunk for shipping of the green glue, but I don't have a total for that yet. I will be getting two 5 gallon buckets for $189 each and $29.99 for the speedloader gun.

Using $185 ballpark figure for total additional cost (assuming shipping) that works out to about $0.76 per square foot.

I had assumed the cost would be much higher than that. It would probably be worthwhile to do if I can keep the space loss to around 1/4 inch, or so.

I just decided to look, and I can buy the hat channel locally for pretty much the same price at a home improvement store and then I don't have to try to ship 11 foot long sections. (They come in 12 foot lengths at the store, not sure about the place I am buying the GG from.)

I should end up with something kind of like this only my channel will be running parallel to the joists to save height...



This method adds Decoupling, Mass, Absorption and Damping, which is all 4 of the 4 aspects of soundproofing.

UPDATE: They don't sell the hat channel. Which is fine. I will get it locally anyway.

Let me see if I got this right.

You fasten the portions of 2x4 to the joists, lengthwise, near the bottom edge, but up a bit, so that the bottom of the rail that you fasten the drywall to is only 1/2 below the existing joists.

These 2x4's would need to hold a lot of weight. I think I'd use liquid nails and a couple of bolts to hold them in place.

Thanks for the picture, Nick. That helped me a lot.

My joists are engineered I-beams, so I am going to take some time and cut my 2x4 to the distance where the vertical part of the joist is (the "skinny" part) and then notch the bottom so that it will literally sit on top of the bottom part of the I-beam. Glued (Liquid Nails sounds about right) and nailed. That way a bulk of the weight is on the bottom "plate" of the I-beam, and not just supported by a few nails, liquid or real....

Here is a quick MSPaint picture.

Dude, I hope you don't get tranferred again.