Duct silencers in between the inner and outer leaf?

[Monkey-Engineering]

I'm just about to commit to how I build and install my silencers based on the answers on this thread. I hope to build them this week.
Watching with baited breath....

[Soundman2020]

I'm just about to commit to how I build and install my silencers based on the answers on this thread. I hope to build them this week.
Watching with baited breath....

Hi there, "Monkey-Engineering", and welcome!

Feel free to start your own thread and post your design for your in-wall silencers! It would be good to see that, and we can also "look over your shoulder" so to speak, to see if there is maybe something you can do to improve the design.

- Stuart -

[Monkey-Engineering]

Hi Stewart, thanks for the welcome!
I've been silently following this forum for years. I've read Rods book many times. It can be difficult to find answers in here so, withough hijacking this thread, I'm also very interested in the effects of changing the cross sectional area of the linking between two silencer chambers. My build is quite different but I have a similar need. Its a single room with double leaf design on separate frames. On its own on a cement floor in a tin shed.

The goal of my build is to reduce sound transmitted through from musos inside to neighbours outside. Same need as the vocal booth in the OP.

I have the opportunity to build the silencers into the ceiling cavity. I have not yet chosen a fan. Cooling is by a separate split system.
From what I can work out:
It is just under 50m3 of air volume. (1765cf)
With 6 changes per hour I need 300 m3/hr (10594 cf/hr)
To get optimal velocity of 0.5m/s the exit needs to be 450mm in diameter (huge! )
To get good velocity of 1.0m/s the exit is 3 20mm in diameter (big, but doable)

I can build the silencers as large or small as I want (within reason). Also I can build the reduced size links (or ducts in the OPs case) between the chambers any size. Is there a problem with them being too big? I understand having the chamber double the cross section of the link is desirable, but if you build a silencer bigger for a higher air flow than your fan, is there a problem or benefit? How big is too big? Surely this has an effect on the effective impedance. If it's detrimental can it be assisted by more turns in the baffles?

Stewart, if I'm on track, I think your next answer to the thread should answer most of my questions.

Cheers for the help lads,
Steve

[Quint]

I'm just about to commit to how I build and install my silencers based on the answers on this thread. I hope to build them this week.
Watching with baited breath....

Hi there, "Monkey-Engineering", and welcome!

Feel free to start your own thread and post your design for your in-wall silencers! It would be good to see that, and we can also "look over your shoulder" so to speak, to see if there is maybe something you can do to improve the design.

- Stuart -

Hi Stuart,

Please, please take a look at my previous question about using 8" duct. I saw that you had posted in my thread today and thought that I had finally gotten the answer I was hoping for and then I saw that you were responding to somebody else.

I think you missed the second half of my previous question about using 8" duct instead of 4" duct to create the impedance mismatch. I'm relatively certain it should work but I wanted to get some verification from you. I'm posting the question about 8" duct from my previous post below. This is the LAST piece of info I need to complete my build but I can't move forward until I'm assured it will work. Thanks.

Here's the previous question:

"Oh, and I have one other question. Instead of using 4" flex duct in between the boxes to create an impedance mismatch, could I use 8" flex duct and achieve the same thing? In that case, the duct would be the part of the flow path with double the cross sectional area (50.3 sq in) versus the cross sectional area (25.1 sq in) in the boxes. The advantage of this would be that I wouldn't run into potential limitations on maximum cfm with the 8" flex duct that I might with the 4" flex duct. Would this work?"

So to reiterate, I simply want to know whether flex duct which is double the cross sectional area of the silencer boxes will create an impedance mismatch of equal quality to flex duct which is half the cross sectional area of the silencer box? In either case, you have a doubling and halving of the cross sectional area as air travels between each pair of silencer boxes. The only difference is that 8" duct doesn't restrict cfm like the 4" duct might. That's potentially a huge advantage to me. Can I use 8" flex instead of 4" flex and achieve the same level of impedance mismatch and corresponding sound proofing?

[casaestudio]

I'm following this threat with great interest.

Instead of using 4" flex duct in between the boxes to create an impedance mismatch

What I understood is that, between boxes, the ducting should keep the same cross sectional area than inside the silencer boxes and is best NOT to use regular flexible ducting. I'll do it with some flexible rubber material in between boxes.

Maybe I understood everything wrong but I think it goes like this: Fan-flex duct-(through wall outter leaf)silencer box doubling the cross sectional area of previous ducting-rubberlike piece connecting both silencer boxes and keeping the same cross sectional area of the first silencer-inner silencer box-(through wall inner leaf) end of ducting to the room increasing the cross sectional area gradually.

I don't know of the consequences of increasing, decreasing and increasing again the cross sectional area in your silencers. Anyone?

Cheers.

Correct me if I'm wrong, please!!

[casaestudio]

Hello, any update in your silencer's design?