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post #1 of 14 Old 06-03-2020, 10:10 AM - Thread Starter
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Dead Vent Preference Question

So ... I'm at the point where I need to think about the construction details on the dead vent supply to the back of the theater. The supply will truly be dead - I intend to put the fan in the exhaust on the other side of the room.

I've seen two schools of thought in these forums:
1.) Flex duct snaked through a GG damped box, stuffed with fiberglass batts
2.) Linacoustic-lined baffle box for "ductless" flow through the box itself

Is one preferred over the other? Or is it just personal preference, and the space available for the construction? (Seems the cross section of the baffle box might be different than the duct snake option.)

It appears my hypocrisy knows no bounds.

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post #2 of 14 Old 06-03-2020, 10:44 AM
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you can probably get a bigger cross section of airflow which means slower quieter air with a lined box. Be careful selecting your fan and duct size, you can easily exceed 250 ft per minute and create air noise. This is one weapon to attack air speed, Just because you buy a 6 inch fan doesn't mean you have to use a 6 inch duct.


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post #3 of 14 Old 06-03-2020, 11:37 AM
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My supply line is 8" insulated flex duct in the joists above the ceiling it drops into a MDF box lined with Linacoustic and probably 18' to the T8 fan which is outside the room and you cannot hear it at all until about speed 6 of 8, I usually run it at 2. The return T8 is above the equipment alcove and is also 8" but t's to 6" for the return and 4" to the top of the equipment alcove, both terminate in larger MDFf boxes sealed and lined with Linacoustic. This run is much shorter 10' on the return and about 6' on the 4" and can be heard if run above 3 since I run on 2 not an issue but I would do this one differently next time. I would have used a longer run of flex pipe and gone with 8" to the return and 6" to the alcove. All 3 terminate to the larger ends like Big shows above.

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post #4 of 14 Old 06-03-2020, 06:13 PM
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Dead Vent Preference Question

For the adapter that is shown in the picture, do you just screw that into a wall stud to keep it secure or is there a special bracket you use ?

I’m thinking about just putting them in my wall without the duct. If I find that it’s stuffy I want them there so I can easily attach a duct to another room.


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post #5 of 14 Old 06-03-2020, 06:32 PM
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they are pretty light if you secure the ducts they will hold it in place, you do want to be sure they don't rattle. You could use a plastic duct hanger belt to hold in place. Not sure they would fit in any 2x4 or 2x6 framed walls



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post #6 of 14 Old 06-03-2020, 06:42 PM
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Quote:
Originally Posted by flynfish View Post
For the adapter that is shown in the picture, do you just screw that into a wall stud to keep it secure or is there a special bracket you use ?

I’m thinking about just putting them in my wall without the duct. If I find that it’s stuffy I want them there so I can easily attach a duct to another room.


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I made mine out of MDF and used a couple screws and silicone to secure them, they were on the end of a box but the same concept could be used elsewhere. I removed the two inch ring as well

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post #7 of 14 Old 06-03-2020, 07:15 PM - Thread Starter
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How does one attached the linacoustic inside the box? Spray adhesive? Or screws with fender washers?

It appears my hypocrisy knows no bounds.

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post #8 of 14 Old 06-03-2020, 08:19 PM
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either or both. if you cut them to fit they pretty much are friction fit.
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post #9 of 14 Old 06-03-2020, 09:30 PM
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Mine are fiction fit

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post #10 of 14 Old 06-03-2020, 10:47 PM - Thread Starter
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We're talking about the linacoustic stuff that comes in a roll, correct? Seems too floppy to friction fit on the underside ("ceiling") of the box, no? Or am I thinking of a different product?

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post #11 of 14 Old 06-04-2020, 03:29 AM
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put the ceiling in first, than the other sides keep it up, once you get your hands dirty you will see what we mean, a few screws if you need them.
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post #12 of 14 Old 06-04-2020, 06:30 AM
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Is the dead vent required to feed right into the room itself?

Would I be able to just put a metal duct end piece on the wall for now, and then at a later point connect insulated duct to it and to a dead vent when/if I need it? I will have access to the other side of the room to do it later


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post #13 of 14 Old 06-04-2020, 06:57 AM
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Quote:
Originally Posted by Sands_at_Pier147 View Post
We're talking about the linacoustic stuff that comes in a roll, correct? Seems too floppy to friction fit on the underside ("ceiling") of the box, no? Or am I thinking of a different product?
Like Big said put the top in first its definitely stiff enough.




Quote:
Originally Posted by flynfish View Post
Is the dead vent required to feed right into the room itself?

Would I be able to just put a metal duct end piece on the wall for now, and then at a later point connect insulated duct to it and to a dead vent when/if I need it? I will have access to the other side of the room to do it later
I think you definitely could do this but I will tell you I would be surprised if you seal up the room and decide you don't need dead vents. Ours are on whenever we're in the room. Sealed rooms can get stuffy pretty quick and the HVAC is not always running, here in MN think spring and fall.
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post #14 of 14 Old 06-05-2020, 06:04 PM
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I built 2 baffle boxes for my theater. I used spray adhesive and cabinet screws with fender washers. The spray adhesive definitely sticks to the loose fiberglass but the coated side could separate from the fibers so the screws and washers are like a belt and suspenders approach.

You want to try to get the area of the duct to double in size from entry to exit. Look up Rod Gervais, the recording studio designer for tips on baffle boxes.



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