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 Post subject: air duct silencer
PostPosted: Tue Mar 20, 2007 2:32 pm 
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Location: anaheim california
I have seen several pics here of home made airduct silencers made from wood and rigid fiberglass. I have done a search but I can' find them for some reason. I found one in Len Morgans studio diary but there was a couple more that I was interested in.

DOes any body know what I am talking about?

Might you have those pics handy?

I would greatly appreciate it as that is next on my list to build.

Thanks


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PostPosted: Tue Mar 20, 2007 11:18 pm 
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Location: Ottawa, Canada
Here's some that I built:

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=8425

Not sure yet how well they work, but I can say that they do not impede airflow.

Cheers

Kris


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PostPosted: Wed Mar 21, 2007 12:42 am 
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I saw that. Thank you. But there was another one posted in the last few weeks. I would like to see that one if any one knows.


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PostPosted: Wed Mar 21, 2007 2:23 am 
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Location: Kentucky
Maybe this might help...

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=8410

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 Post subject:
PostPosted: Wed Mar 21, 2007 6:56 am 
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camistan wrote:


Yeah, I saw that too.

There is another one.

I wish I could find it.

I was made from a wood box like drfrankencopter made only a little different.


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PostPosted: Wed Mar 21, 2007 12:07 pm 
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Try this,

BTW- remember that this is sized specifically for the air-flow I needed in this particular iso-booth - make sure to size the unit to fit your specific needs.....


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 Post subject:
PostPosted: Wed Mar 21, 2007 5:01 pm 
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rod gervais wrote:
Try this,

BTW- remember that this is sized specifically for the air-flow I needed in this particular iso-booth - make sure to size the unit to fit your specific needs.....


That is probably what I need.......but I don't know it yet.
:oops:


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 Post subject:
PostPosted: Wed Mar 21, 2007 5:22 pm 
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Location: Gresham OR
I would love to think that they are mine but probably not
And they are dead quite
Tom


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PostPosted: Thu Mar 22, 2007 1:17 am 
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TomVan wrote:
I would love to think that they are mine but probably not
And they are dead quite
Tom


Yeah!!!!!!!!

That's the ones!! :D

Thanks

Did you cut the round hole with the sawsall?

What kind of glue is that?

I suppose Home Depot has that glue?

DId you ever wrap them in plastic? How did you secure the plastic if you did?

WHat is the red stuff?

What are the ruff dimensions?

My air ducts are 10 inch. I guess I will have to reduce them down as those fitting look smaller. I can't find those in 10 inch


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 Post subject:
PostPosted: Thu Mar 22, 2007 4:33 am 
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eruss wrote:
My air ducts are 10 inch. I guess I will have to reduce them down as those fitting look smaller. I can't find those in 10 inch


Russ,

if you do that then it may not work properly - because you'll be increasing the velocity - which creates it's own air noise -

the idea is to pass everything through a box which:

a. has material that absorbs sound -

b. causes enough turns in the air flow as to for the absorbers to do their job

c. creates either a decrease (or at least not an increase) in air velocity.

The slot through the box is best sized at about double the inlet - this will decrease the velocity through the box by 1/2

if you are feeding the box with square duct - then just bring the square duct directly to the box - you don't need to convert to round - if you're bringing round duct to the box - you can use a ceiling outlet - round to round the size of your duct.

Take a loot at page 8 of the attached PDF file - they're on the right available for 5, 6, 8, and 10" round duct - and then transition to 6, 8, 10 or 12" for the outlet.......

you could also use - (up to 12" round duct and the same page and side) a top diffuser or side outlet diffuser (depending on your particular duct run) both of which are flanged for the box connection -

Otherwise, if your duct was upto round 14" - then you could always get a 14 round to to 14" square conversdion - same page - same side - top of page.

If you had round larger than 14" you could always have a custom piece made at a metal fabricator near you.

Rod


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 Post subject:
PostPosted: Thu Mar 22, 2007 8:25 am 
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eruss,
Take warning in what Rod is saying. You want your box larger than your pipes. You can build it any size you want

Jig saw to cut the opening in the wood and a utility knife to cut the 703
Acoustical caulked all the corners acoustical caulk to glue in the 703
Tom


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 Post subject:
PostPosted: Thu Mar 22, 2007 11:21 am 
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Location: Ottawa, Canada
The cross sectional area of your baffles (which will likely have a rectangular shape) should be equal to the cross-sectional area of the pipes to which they attach...that way there will be no change in velocity (Bernoulli's equation).

Cheers,

Kris


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 Post subject:
PostPosted: Thu Mar 22, 2007 11:50 am 
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drfrankencopter wrote:
The cross sectional area of your baffles (which will likely have a rectangular shape) should be equal to the cross-sectional area of the pipes to which they attach...that way there will be no change in velocity (Bernoulli's equation).

Cheers,

Kris


Kris,

with all due respect I disagree with that approach,

By decreasing the velocity by 1/2 you decrease the possibility of buffeting taking place within the chamber as the air makes it's way past the baffles - and buffeting air makes noise.

Remember that the entrance and exit are the same size - and thus - with the chamber designed according to my system (which decreases velocity by 1/2 - but also increases volume by a factor of 2) you get a net result of no change once it reaches the other side.

Everything works exactly the same as if it was hard piped (from the point of view of overall velocity and volume) - but with much quieter results.

Especially seeing as I use a design of 100fpm max velocity in the entire system - so I'm down to 50 fpm passing through the chamber.

So if I was feeding a 12x12 in - and returning to a 12x12 leaving - it would be - 100cfm @ 100fpm to 200 cfm @ 50fpm to 100cfm @ 100fpm.

As you can see the net is a smooth transistion with much less chance of noise within the chamber itself.

Designing so that machine noise doesn't pass through the chamber is not a problem - but you have to include creating a chamber that doesn't create any noise itself as well.

Sincerely,

Rod

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Last edited by rod gervais on Thu Mar 22, 2007 12:04 pm, edited 1 time in total.

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 Post subject:
PostPosted: Thu Mar 22, 2007 11:57 am 
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Sorry Rod...you are correct, my suggestion was more as a minimum size (i.e. don't screw anything up by speeding up the flow). Bigger is better if it won't hurt transmission loss to the partition above (i.e. i.e. at some point your sacrificing the STC and TL of your partition for silencing the HVAC).

CHeers,

Kris


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 Post subject:
PostPosted: Thu Mar 22, 2007 12:08 pm 
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drfrankencopter wrote:
Sorry Rod...you are correct, my suggestion was more as a minimum size (i.e. don't screw anything up by speeding up the flow). Bigger is better if it won't hurt transmission loss to the partition above (i.e. i.e. at some point your sacrificing the STC and TL of your partition for silencing the HVAC).

CHeers,

Kris


Kris,

when I am lucky enough (and in the case of the Gemini Studio design I am that lucky across the board) I always make the outlet side of the baffle a hard connection to my framework - using an airtight seal - so it's a simple hard connection into the room - hopefully with no TL Loss (when I get real REAL lucky - which is pretty much always to date).

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