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PostPosted: Mon Jan 27, 2020 3:26 am 
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Location: Tucson, AZ
Sorry for the delay, I forgot to turn on notifications.

Just to walk through the picture slowly, I see the 3 boxes for the return. They appear to all be ducted back to the left large box in the picture, which would be on the outer layer. The supply comes to the right box in the picture (outer layer) then ducted to the middle box which has the outlet into the room. So the middle boxes is mounted to the inner room? It must fit between the studs? How does the duct from the right box get to the middle box without going through a stud (I'm going to go back and scan the pictures to see if I can answer my own question here).

Does the dark vs. light gray in the ducting indicate rigid vs. flexible coupling? What materials/products were used?

Regarding the small boxes between the joists (or big box between studs), is there concern that the air gap is being consumed with the boxes? My understanding is that they are attached to the inner room/leaf so the top of them may be very close to the outer layer above?

Thanks!

Gregwor wrote:
Quote:
Can you explain the HVAC scheme in a little more detail? I see six boxes were made. How does the air flow through the system, and how is routing done with respect to the inner and outer room walls?

Sure! The reason there are 6 boxes instead of 4 is because we were limited for space. We needed the air to flow across the entire room and the supply is coming from the middle large box. That meant that the return had to be on/near the opposite side of the room.

Instead of putting a huge box inside the room, I decided to try and fit silencers up in the existing joists. In order to have enough cross sectional area and get the air velocity low enough, I needed 3 boxes. After seeing/testing them in real life I realized that making those little ones slightly longer (maybe a 4th or even 5th baffle in them) would have helped some.

There is one fan on the return side of the system (in his storage room) that pulls air through the entire room/system. On the first page of the thread you can see the system. Here's a link to the picture I'm referring to:

download/file.php?id=65346&mode=view

The reason I put the supply sleeve where I did was so that it would supply fresh air right above where Darren might put his mini split head. That would allow the head to throw nice fresh air around the room then have the 3 little return boxes suck up the stale air from above where Darren sits at his drums. Does that make sense?

Greg


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PostPosted: Tue Jan 28, 2020 5:48 pm 
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Location: St. Albert, Alberta, Canada
Quote:
So the middle boxes is mounted to the inner room?

Correct.

Quote:
It must fit between the studs?

Well, it doesn't HAVE to, but in our case, yes, it did.

Quote:
How does the duct from the right box get to the middle box without going through a stud (I'm going to go back and scan the pictures to see if I can answer my own question here).

Ignore some details in the pictures as these were early drawings. But, you can see here that there is about 12" between the inside out inner leaf sheathing and the outer leaf framing. This is where all 3 big silencers are situated. You can see the two outer leaf silencers are mounted to the outer leaf. The middle silencer (the inner leaf supply silencer) is mounted to the inner leaf.
Attachment:
Silencer Placement.jpg

In the following picture you can see the duct work connecting the inner and outer leaf supply silencers. The duct work in the drawing was metal duct with a flexible connector between them. In real life Darren just used flex duct.
Attachment:
Outer To Inner Connection.jpg

Quote:
Does the dark vs. light gray in the ducting indicate rigid vs. flexible coupling?

In the drawing, yes.
Quote:
What materials/products were used?

We mounted round flange connectors (I'm not an HVAC junky so that probably isn't what it's called in the industry but I hope it's clear enough for our purposes) onto the silencers to make connections to the boxes easy. The majority of the runs were just flex duct. We used some couplers from the local HVAC supplier in our city in order to join the 3 smaller duct runs into a larger 5" one that fed the outer leaf return silencer. All connections used worm gear clamps to ensure good connections. Over that we used aluminum foil tape.
Quote:
Regarding the small boxes between the joists (or big box between studs), is there concern that the air gap is being consumed with the boxes?

100%. But due to his space restrictions, it was something we had to sacrifice. In a perfect world we would have more space and never have to worry about those sort of things. For the ceiling boxes if he had more height, I would have suggested to have the sheathing on the ceiling modules that are underneath the boxes (or boxed in mechanical) sit lower. This is what I will be doing with my personal build.
Quote:
My understanding is that they are attached to the inner room/leaf so the top of them may be very close to the outer layer above?

They are in fact sitting on, and are attached to the inner room ceiling joists.
Attachment:
Return Silencers.jpg

It is suggested that the silencers be decoupled by sitting on something like Sorbothane but space was just too tight on this project.

I finally got to record in this room this weekend. I can't stress enough how impressed I am with the sound.

Greg


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PostPosted: Fri Jan 31, 2020 4:51 am 
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For my project I want to share air with the adjacent room. Would it be a bad idea to build two boxes and mount them one above the other between the wall studs, one attached to the inner room and one the outer, joined by a short section of flexible duct? This would be convenient from an installation perspective. I think we're going for 24" on center studs, so the boxes could be wide and flat to fit in the ~7-8" cavity.


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PostPosted: Fri Jan 31, 2020 6:53 am 
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For my project I want to share air with the adjacent room. Would it be a bad idea to build two boxes and mount them one above the other between the wall studs, one attached to the inner room and one the outer, joined by a short section of flexible duct?

For sure! That would be fine!

Quote:
I think we're going for 24" on center studs, so the boxes could be wide and flat to fit in the ~7-8" cavity.

I'm not sure that you're aware of the size of these suckers. Check out my simplified design template:
Attachment:
Gregwor's Silencer Box.png

If you have 7" to work with, you will have 1" of MDF with 1" of duct liner, then your air path, then 1" of duct liner, then 1" of MDF again. So, 7" minus the 4" of MDF and ductliner. This leaves you an air path of only 3". Your box will have to be super wide in order to achieve a decent cross sectional area. Also, there is a rule you should try to adhere to if possible:
Attachment:
Rect Duct Aspect Ratio.png

Greg


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PostPosted: Fri Jan 31, 2020 7:22 am 
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Thanks, yeah I understand that it's a narrow space. My options are to live with low flow, extend the inner wall further into the room, or bump the boxes out into the room. None of these is ideal.


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PostPosted: Sat Feb 01, 2020 2:09 am 
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Dumb question, but how did you get the duct liner? I don't see it stocked at big box outlets around here. Contractor places want me to "call for quote" and it appears to come in 100 foot rolls anyway. Thanks!


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PostPosted: Sat Feb 01, 2020 2:51 am 
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how did you get the duct liner? I don't see it stocked at big box outlets around here. Contractor places want me to "call for quote" and it appears to come in 100 foot rolls anyway. Thanks!

Correct. It is not available at big box stores. I believe I called the manufacturer and got a list of places that carry it. It was either that or else I just called every place google pulled up for HVAC supplies. And it did come in a big roll. The good thing is that the duct liner can be used as general acoustic treatment anywhere you'd use OC703 as it's a similar product. So, you can use duct liner for regular acoustic treatment but you can't use regular insulation in your silencer boxes!

Greg

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PostPosted: Fri Feb 14, 2020 11:57 am 
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Did you mount the inner room directly to the concrete, or was some sort of product use to provide a bit of isolation? If you didn't use isolation here, under what circumstances would you recommend it, if ever?


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PostPosted: Tue Feb 18, 2020 8:37 am 
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Did you mount the inner room directly to the concrete, or was some sort of product use to provide a bit of isolation? If you didn't use isolation here, under what circumstances would you recommend it, if ever?

Well, Darren did 99.999999% of this build himself. But, yes, he did anchor the inner framing directly to the concrete. John encourages people to "float" the walls on material but personally I have mixed feelings about it. Not about the fact that it would help isolation, rather the fact that I feel that in order to do it properly it adds a ton of work, money and risk of failure. I mean, in order to properly float it, you need to be able to accurately calculate the weight of the entire inner room so that you get the proper deflection of the material. Also, you'd need to find anchors that will maintain your isolation from the slab. That means isolation entirely surrounding the anchor. You'd need to seat the anchors in your slab and then somehow lift the insanely heavy inside out walls up and onto the anchors. These walls are often so heavy, people (including Darren with his build) assemble the walls in sections.

To conclude, if I could easily address all of the above concerns, I would personally float my walls. But chances are, even if I was able to stand and anchor the walls onto a material, I would probably screw up my weight calculations and then the material wouldn't actually isolate. If anyone has any advice on the matter, I'd love to hear some pointers!

Greg

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