AVS Forum banner

101 - 120 of 136 Posts

·
Registered
Joined
·
872 Posts
Discussion Starter #101
Thank you for the comments about the permit. I’ll have to ask next week about what is required. The HVAC is in. There is no plumbing. And I am about to start the wiring. Sheetrock is up and taped. I know they don’t inspect the drywall here. Just final. So maybe when the soffits are done and the down lights are final, maybe I can close it.

I guess I thought they wanted to make sure the fit and finish of the new room was consistent with the rest of the house, which is why I thought I needed finished materials on the floors and what not. But then again, the inspectable building stuff (framing, insulation, roofing) is all complete. I’ve been so focused on getting to the electrical portion I hadn’t thought about what is really required for building.
 

·
Registered
Joined
·
872 Posts
Discussion Starter #104
I ran 2x4s horizontally in the stud channels. Stapled it from both sides (18ga x 1”) every foot or so.





Ripped some 3/4 MDF to 14” wide and painted it flat black so it doesn’t show through the eventual fabric. Added a 3/4” x 2” flange on the bottom. That will be for mounting down lights along the length of the soffit. I will cut a stretcher between the soffit face and the wall and mount the cans in them. That way I can stuff the soffit full of insulation as a bass trap with a mostly open bottom side. I can also reposition the lights before I affix them too.

Hanging the faces with liquid nails, 16ga nails, and a few construction screws for good measure.





So the goal for today is to finish the soffit faces. (Still need to paint the flange, too, for the same reason - so it doesn’t show through the fabric.)
 

·
Registered
Joined
·
872 Posts
Discussion Starter #106 (Edited)
Uh-oh — that doesn’t sound good ... “creative”

I guess there are the tried-and-true, known to work, conventional ways to do it, and there is my way.

I’m just making this up as a I go. But please stop me if I make a critical error. I don’t want things to fall on my head.

I built a fairly large deck at my last house. My dad (a civil engineer, schooled in the principles of structures and what not) commented that it was definitely designed by an electrical engineer ...
 

·
Premium Member
Joined
·
541 Posts
I built a fairly large deck at my last house. My dad (a civil engineer, schooled in the principles of structures and what not) commented that it was definitely designed by an electrical engineer ...
Brian - I really like your sarcasm & sense of humor!

My little brother is a civil engineer, so I get it.
 

·
Registered
Joined
·
872 Posts
Discussion Starter #109
Mission accomplished! Soffit faces are up. I’ll dress the screw holes and seams later and run some paint over the bottom flange. But the goal for today was to have something up upon which to start attaching electrical wiring, so I’m done for the day. Time to go enjoy the rest of the day with my daughter in the pool.



 

·
Registered
Joined
·
872 Posts
Discussion Starter #110
I’ve designed a pretty awesome baffle box for my air supply duct over the door. It goes over the door and against the ceiling and back wall. I designed it so it would hit three ceiling hat channels and the top wall channel on two sides.

It’s going to weigh 210 pounds!

I’m not sure about hanging that from the ceiling. The clips are rated for 36 pounds. They are spaces 48 inches apart on 16” OC joists, so each clips supports 5.3 square feet. So they are rated 6.75 pounds per square foot. The double drywall is 4.5 pounds per square foot so I have 2.25 pounds to play with. My baffle box is 9.5 pounds per square foot.

I can get enough screws in so I I’m not as worried about pull out strength in the channel, but I don’t want the clip to fail.

One option I am pretty certain I will do is a floor-to-ceiling support column in one corner. There is a “normal” aesthetic column in the rear for a wall mount rear surround speaker. I can run a 2x4 inside the column from the (decoupled) floor to the underside of the baffle box. Hidden all the way in the column. That will relieve some weight. (The column is where the purple stripe is.). I can do something similar next to the door where the little triangle platform is and disguise it in a corner bass trap.



Other than that, though, I’m at a loss. The only option in the corner out in the open (besides hanging from the channels) is to drive one lag through the box, through the drywall, past a channel, and into a joist.

The lag screw head would be in a soundproof/damped/massive/insulated enclosure itself. It would pass through the drywall so I guess it could excite the drywall itself along the shaft, but even the drywall itself is massive and damped.

Would a single lag destroy the soundproofing efforts I have done?

Will the ceiling grid of Genie RST clips and 25ga hat channel hold?

Thoughts?
 

·
Registered
Joined
·
601 Posts
I’ve designed a pretty awesome baffle box for my air supply duct over the door. It goes over the door and against the ceiling and back wall. I designed it so it would hit three ceiling hat channels and the top wall channel on two sides.

It’s going to weigh 210 pounds!

Thoughts?
:eek: I can't help but think it might be a tad over-engineered. Can you share details about the baffle box? Maybe there is somewhere we can save some weight.
 

·
Registered
Joined
·
872 Posts
Discussion Starter #112
Thanks for checking my design.

The box is 43.5" x 49.5" x 14.75", as noted below:

The external width (front of room to back of room) is 43.5". Any less and it won't reach to the back wall, where I was going to use the rear wall upper chanel for support. The 6" duct through the wall above the door is 40" from the back wall, plus 2" of insulation inside of 1.5" of double 3/4 MDF (with green glue) gives me a width of 43.5".

The external height is 14.75". The bottom of the 6" duct is roughly 11.25" from the ceiling, plus 2" of insulation inside of 1.5" of double 3/4 MDF (with green glue) gives me a height of 14.75".

The external length is 49.5". If I go 46" I can hit a third ceiling hat channel (they are perpendicular to the length dimension). So to get more support I wanted to hit that third channel. There, too, there is 2" of insulation and 1.5" of double MDF.

The side against the ceiling, against the back wall, and against the side wall (all against decoupled walls) are all single layer 3/4" MDF. The other three sides (facing into the room) are double layer 3/4" MDF with green glue.

With all of the insulation, the internal height is 8.5" and the internal length is 43.25 inches. If I do three baffles (four paths) each path is 9.7 inches wide, so the cross section of the flow path is 82 square inches. I calculated just shy of 70 square inches to get below 250 FPM with 120 CFM.

So, to make a box that size, with three sides of single layer MDF and three sides of double MDF, I've got about 76 square feet of MDF (roughly 2-1/2 sheets). My MDF is 91.5 pounds per sheet (weighed it), so 2.77 psf. - 210 pounds total.

I'll sketch it and post a picture.

But I appreciate any thoughts on where I may be able to save some weight.

Thanks!
 

·
Registered
Joined
·
872 Posts
Discussion Starter #114 (Edited)
I suppose I could make it a floor standing dead vent, on the riser. Come in from the hole above the door, turn toward the back wall, and then snake down the back wall and eject near the floor. Then the weight of the dead vent is supported by the floor instead of the ceiling. I don't have to worry about the strength of the materials, or lagging through the box into the ceiling joists.

I would have wanted the fresh air to come in from above, but the best compromise might be having it come in lower. The exhaust is clear across the room so there should be plenty of mixing as it travels to the return vents. (Fan will pull from outside the room.)

Or I can run the duct chase down the wall and then back up the wall. Air/noise from the supply vent would get one 90 degree bend and one 180 degree bend and then it can exit high near the ceiling. Or even turn 90 degrees again and into a more modest ceiling box just for the diffuser. Maybe that's it ... air comes in high, turns right, turns down the wall, U-turns up the wall, turns into the soffit, flows out through a slot diffuser.
 

·
Registered
Joined
·
601 Posts
Well, that looks about like it should. I went back to soundproofingcompany.com and checked their diagrams to refresh my memory and they look the same as yours. They do recommend putting clips on every joist to support the soffit and it sounds like yours are every 3 joists. I think your best bet is to make it a vertical floor standing solution as you suggested. It could be made into a column but I don't think that would fit with your design of the room. It may just have to be tucked in to the back corner. Just my .02 as I have never actually built one myself.
 

·
Registered
Joined
·
872 Posts
Discussion Starter #116
Thanks. I think I have come to some of the same conclusions you have.

...recommend putting clips on every joist to support the soffit and it sounds like yours are every 3 joists.
In hindsight, yes, I should have put more clips up. Maybe used IsoMAX clips with 20ga channel on every joist, like I did for the Mini Split HVAC head. There is no way I am taking down the ceiling at this point, so I think I boxed myself into a corner, so to speak. Speaking of corners ...

I think your best bet is to make it a vertical floor standing solution as you suggested. It could be made into a column but I don't think that would fit with your design of the room. It may just have to be tucked in to the back corner.
I am thinking of a triangular duct box in the corner. Come out square above the door where the vent comes in, jog over to the corner, and then come down the corner of the room. Just have it dump out at the bottom of the corner column. That might be sufficient. By straddling the corner, I can make it look like a floor-to-ceiling bass trap. I'll probably actually put a bass trap in the other corner for symmetry as well as actual acoustical treatment.

I just need to figure out if triangular duct will cause undesired flow characteristics.
 

·
Registered
Joined
·
3,743 Posts
Nice build thread and subscribed! I'm not too far from you...Ballantyne.
 
  • Like
Reactions: skylarlove1999
101 - 120 of 136 Posts
Top