Hey Stuart,
This is the first i've heard of two silencers for supply and two more for return... I was figuring one of each. Can you point me to some info on that?
Wisconsin basement mix room
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paulmitch
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Soundman2020
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Re: Wisconsin basement mix room
Assuming that you need high levels of isolation, you need one silencer where the duct goes through the inner-leaf, and another where it goes through the outer leaf. If you only need medium isolation they could do without one of them, but realizing that it will have consequences.
Think of it this way: You have a two-leaf wall, where you put a lot of time and money into ensuring that each leaf is massive, perfectly sealed, and fully decoupled. Installing an HVAC duct basically means that you have to chop a huge hole in the leaf to get the duct through, thus totally trashing all the hard effort. A hole that big kills about 90% of the isolation that you had, because it removed all of the mass and all of the seal in that location. The job of the silencer box is to replace that mass, in such a way that the air can get through but the sound cannot. It does that by providing just as much mass in, but in in the form of a series of baffles plus the mass of the box itself.
If you only put one single silencer box on just one leaf, but nothing on the other leaf, then you have made up for the lost mass on that first leaf, but there is still missing mass on the second leaf. So your isolation is way down. a partial solution is to have a massive duct that crosses the gap between the leaves, such as a thick plywood duct, but that would create a flanking path... unless you cut the duct in the middle and wrap it with thick rubber! That works, but is not as good as having a box on each leaf.
- Stuart -
Think of it this way: You have a two-leaf wall, where you put a lot of time and money into ensuring that each leaf is massive, perfectly sealed, and fully decoupled. Installing an HVAC duct basically means that you have to chop a huge hole in the leaf to get the duct through, thus totally trashing all the hard effort. A hole that big kills about 90% of the isolation that you had, because it removed all of the mass and all of the seal in that location. The job of the silencer box is to replace that mass, in such a way that the air can get through but the sound cannot. It does that by providing just as much mass in, but in in the form of a series of baffles plus the mass of the box itself.
If you only put one single silencer box on just one leaf, but nothing on the other leaf, then you have made up for the lost mass on that first leaf, but there is still missing mass on the second leaf. So your isolation is way down. a partial solution is to have a massive duct that crosses the gap between the leaves, such as a thick plywood duct, but that would create a flanking path... unless you cut the duct in the middle and wrap it with thick rubber! That works, but is not as good as having a box on each leaf.
- Stuart -
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paulmitch
- Posts: 12
- Joined: Sat Oct 12, 2013 12:54 pm
- Location: Madison, WI USA
Re: Wisconsin basement mix room
I've been knee deep in "beefing up" the ceiling between the floor joists. This process is no joke. No. Joke. There has been a lot of creative drywall attachment going on, but I feel like I'm getting closer and closer to sealing this room up. I'll post more photos when I've caulked up what I've done, but my outer leaf is gaining mass every day lately. This is by far the most time consuming part that I've dealt with so far and pretty challenging to do on my own with my 2 year old sleeping upstairs.
Anyway, I'm chasing this thing down the rabbit hole.
Anyway, I'm chasing this thing down the rabbit hole.
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Soundman2020
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Re: Wisconsin basement mix room
...This is by far the most time consuming part that I've dealt with so far
But you are only just getting started! There'll be plenty more "entertainment" for you along the way... 
But did you take the blue pill or the red pill? Only one will allow you to see just how deep that hole goes...Anyway, I'm chasing this thing down the rabbit hole.
- Stuart -