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PostPosted: Wed May 27, 2020 6:40 am 
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Posts: 58
Location: USA Pacific Northwest
Thanks, this helps a lot. Yes, the diagram you added is what I meant by mirror image.

I agree with what you said about HVAC techs. I've had zero luck finding any who have a clue about what I'm trying to achieve. I even tried a couple MEs and a guy who said he was an acoustic consultant. One of the MEs wanted to charge $17k for a very simple system in a 350sq foot room but didn't provide a lot of detail on what it entailed.

I'll reply further on my design thread, which hasn't been updated in a while. Thanks again!

For the record, I also watched the series of YouTube videos as described above (TrueSound Studios) and had my doubts about his silencers. He did a bit of testing which seemed to indicate it was working better than nothing, but I still had some doubts. I think he got bits of free advice from guys like John Brandt throughout his build and pieced together a design from that. I scratched my head here and there at some of his decisions, but, if in the end he is able to produce mixes that translate well while not having the cops called by his neighbors, I'd say he did alright.


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PostPosted: Sat Jun 13, 2020 7:21 am 
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Location: San Antonio, Texas USA
Gregwor –

About the HVAC Ducts and Silencers…

I am planning a 4000 sq ft build in Texas. Three control rooms – one cutting room. If I am doing individual Mini-Splits in each room – I do not need Ducts and Silencers for that – correct?

But I do need Ducts and Silencers for the fresh air (ERV) unit – right?

And… do I need two silencers for the ERV - one for the duct of the fresh air coming in and one for the stale air going out?

The dimensions of the control rooms are 20 feet by 23 feet by 12.5 feet height.

And it seems to me that the ERV would not be moving as much air as a typical conventional AC system – so perhaps those ducts could be smaller…

Marius Perron
San Antonio


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PostPosted: Sun Jun 21, 2020 2:14 am 
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Location: St. Albert, Alberta, Canada
Quote:
If I am doing individual Mini-Splits in each room – I do not need Ducts and Silencers for that – correct?
But I do need Ducts and Silencers for the fresh air (ERV) unit – right?

Correct. You only need the duct work and silencers to bring fresh air in and dump stale air out.

Quote:
And… do I need two silencers for the ERV - one for the duct of the fresh air coming in and one for the stale air going out?

Ideally you want one silencer box for each wall penetration. So, if you have a traditional 1 stud wall, you would only need 1 silencer box for supply, and 1 for return. If your room is a true room in a room, that means you have 2 walls that your penetrating. So, you would need 1 silencer for your outer leaf supply, 1 for your inner leaf supply and then 1 for your inner leaf return and 1 for your outer leaf return.

Some people who are very limited for space and still have a room in a room will use a single silencer for both walls but personally I don't think 1 box is enough unless it is absolutely massive and does not couple the two leaves together.

Quote:
And it seems to me that the ERV would not be moving as much air as a typical conventional AC system – so perhaps those ducts could be smaller…

Yes. The fresh air you're bringing in is only about 30% of the volume of air compared to a ducted forced air system.

Greg

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PostPosted: Mon Aug 24, 2020 12:42 pm 
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Location: Denton, TX
Gregwor wrote:
Hopefully this helps some people with designing basic single path silencer boxes.
Attachment:
Gregwor's Silencer Box.png

Greg


Firstly, thank you so much for this wonderful info and this mock up. This is exactly the kind of thing I am researching right now for my studio. Would you say it would be a good or bad idea to have a smaller channel width (X) if you have the available ceiling height to make the box taller? Is there a minimum value for X to give optimal air flow with sufficient sound dampening? I don't have a ton of space where I would be installing one of these but for my application I'm thinking Y = 3'-0" making the inside channel width 1'-2 1/2" and using that dimension for height making the overall height of the box 1'-5 1/2". This makes for a pretty large box, if I could save on space by going with a smaller value for Y and X , that would be fantastic.


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PostPosted: Mon Aug 24, 2020 7:06 pm 
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Location: Wales, UK
Bryanf87 wrote:
Gregwor wrote:
Hopefully this helps some people with designing basic single path silencer boxes.
Attachment:
Gregwor's Silencer Box.png

Greg


Firstly, thank you so much for this wonderful info and this mock up. This is exactly the kind of thing I am researching right now for my studio. Would you say it would be a good or bad idea to have a smaller channel width (X) if you have the available ceiling height to make the box taller? Is there a minimum value for X to give optimal air flow with sufficient sound dampening? I don't have a ton of space where I would be installing one of these but for my application I'm thinking Y = 3'-0" making the inside channel width 1'-2 1/2" and using that dimension for height making the overall height of the box 1'-5 1/2". This makes for a pretty large box, if I could save on space by going with a smaller value for Y and X , that would be fantastic.


You need to have the CSA of the inside of the box ATLEAST double that of your fresh air inlet duct CSA.

So, work out what size of the inlet duct, work out its CSA, then double it. That will be the minimum size you can use for your boxes.

Paul

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PostPosted: Wed Aug 26, 2020 12:12 pm 
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Thanks for the additional info, Paul.

Since I will be running a main trunk of probably 12 inch dia insulated flex duct, the measurements I figured up on my previous post should be fine if I branch off with 6 inch flex duct to feed the silencer box since the channel width will be over 1 foot. Obviously, the smaller I go with the branch feeding the silencer box, the more air flow I will have exiting the box. I'm wondering if 6 inches is going to be too small and if I should try to go larger for the inlet? I've never built a silencer box before so I'm not sure at how effective it is at slowing air flow and reducing noise at the outlet.


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PostPosted: Wed Aug 26, 2020 8:54 pm 
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Bryanf87 wrote:
Thanks for the additional info, Paul.

Since I will be running a main trunk of probably 12 inch dia insulated flex duct, the measurements I figured up on my previous post should be fine if I branch off with 6 inch flex duct to feed the silencer box since the channel width will be over 1 foot. Obviously, the smaller I go with the branch feeding the silencer box, the more air flow I will have exiting the box. I'm wondering if 6 inches is going to be too small and if I should try to go larger for the inlet? I've never built a silencer box before so I'm not sure at how effective it is at slowing air flow and reducing noise at the outlet.


You need to work out how much CFM you need, then size your inlet duct to suit. If you are branching off from a trunk then divide the CFM by the amount of branches, then size the branches according to that number.

Paul

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PostPosted: Tue Feb 16, 2021 5:04 pm 
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Location: Finland
I'm strugling to find duct liner locally, what are the downsides of using thin plastic film on top of some normal (mineral wool/fiberglass etc) insulation in silencer box instead of real duct liner?


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PostPosted: Wed Feb 17, 2021 2:13 am 
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duct board is more effective, but if it's not available and shipping is too costly, then using the semi-rigid insulation and lining it with plastic will work.

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