Soundproof ventilation dead vent or baffled box / acoustic box - AVS Forum
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post #1 of 15 Old 06-12-2013, 08:25 PM - Thread Starter
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This above box is used elbows to catch and absorb the sound energy in the acoustical foam. It does't have a great deal of insulation.
The image above uses a flax duct running in between the baffles. And uses insulation to absorb the sound. If one is using insulation One must use something on top of the insulation if they don't want to breathe fiber particles.

A baffled box or acoustic box looks like that this has insulation. The only thing is no one wants to breathe the fiber particles coming straight from the vent. And as i see somewhere that the length of the deadening vent needs to be three times the diameter of the hole. So if my hole will be 4 in diameter the length needs to be 16. However what if we can include the total length of the duct till the end.

this image is also not three times the length of the diameter on each row. The sub total (when you calculate the whole length of the air flow till the final outcome) is probably so...
The above is Ted White'
So im asking you do you know if its the same thing. Producing the same results.
This is findable in quite a few sites
My question is which one is better . And if i want to imply the four elements of Dead Vent Elbow Mass Damping Change in air volume, i can make it with the acoustic/baffled box also. Or it doesn't have this much insulation as Teds White' suggestion

I think to have a powerful fan. Because 90 degrees elbows takes slows down the air. However why do we need an inline fan.
I dont find any STC on that kind of traffic box
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post #2 of 15 Old 06-13-2013, 07:37 AM - Thread Starter
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I would like to ask you guys if the fan needs to be in between the duct or in the outer end is also fine.

Is acoustic foam enough or it needs insulation.

As by now i will make the baffled box, with insulation around as this image shows.

The walls outside and also the baffles it self will also be two layers of MDF GG in between, (so it will have mass and damping) then covered with insulation and on top of the insulation will be some acoustic foam or something alike. In the outer end will be some powerful fan. Maybe a fantech. The box itself will be 20 inch long on the inside. One of the rows will be double the air volume to achieve the method of the gun silencer. I don't want to insert a duct pipe to run in between the maze, because i think that the sound will not be absorbed in the insulation around the pipe. but will rosh and slide on the walls of the pipe to the outcome. I would prefer to have only the insulation as the walls of the duct, however i'd look for something to block insulation fibers from entering the air. So i will put on top an acoustical absorbing sheet. Or maybe i can go anly with acoustical absorbtion sheets.

I will share the results after making it with the help of heaven and you guys if you have some notes on it please reply
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post #3 of 15 Old 06-13-2013, 10:38 AM
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You need to put the fan in the dead-vent box. It generates a fair amount of its own noise that you'll want to dampen. Ideally the fan should be as far from the theater opening and as close to the adjacent room opening as possible.

You also need to treat this box as it's own little soundproofed room. That means that the walls all need to have as much mass and dampening as possible, i.e. incorporate drywall and Green Glue, and the only way in and out of the box needs to be through the duct holes. The mass does most of the work, followed by the tortuous path the air/sound has to take, increasing interactions with the mass. The fluffy insulation helps a bit too.

Here is mine in the construction phase. It's built into the wall between a hallway and bathroom. It actually has both the supply and return running through it, return on top and supply on the bottom.


DSC_6195 by matthewcummings99, on Flickr

Supply in the lower part of the false column:


DSC_6190 by matthewcummings99, on Flickr

Return in the false soffit. I also have a mini-split in case the dead-vent can't sufficiently cool the room. So far not really a problem.


DSC_6187 by matthewcummings99, on Flickr

Finished room:


DSC_9207 by matthewcummings99, on Flickr
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post #4 of 15 Old 06-13-2013, 08:04 PM
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Search for duct liner at a specialty HVAC supply shop, instead of insulation or acoustical foam.


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post #5 of 15 Old 06-14-2013, 06:04 AM - Thread Starter
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Is a duct liner enough for insulation/absorption.
http://www.owenscorning.com/around/sound/commercial_acoustics/fiberglas-ductboard.asp

Ted White strongly emphasizes a significant amount of insulation for a high level of absorption. Do you recommend only Duct Liner for the baffle box kind of dead vent.
Uscmatt99 writes that the main thing is mass. And insulation helps also a little.
I think if a Flax Duct Pipe even wrapped with insulation decreases the amount of absorbing because the sound energy will slide trough the wall of the pipe. And a fewer amount of sound will be absorbed in the underlayment insulation. May be thats why they claim all the time that insulation helps only a little bit.
However i don't want the walls to be covered by exposed insulation. Since we need clean air.
http://ductworks.com/air-duct-cleaning/fiberglass-air-duct-liners-a-serious-indoor-air-quality-concern/

One way is to lay on top of the insulation acoustic foam.
Another way is to use thick acoustic foam only and with the damped mass it will be enough for a high STC.
The thing is, i dont find any stc data on that kind of baffle box, which one tells that they can't hear nothing through the Vent
So do you have some proof that Duct Liner is enough
I work so long to make the room air tight so im looking for a high STC dead vent
Here is a data sheet of a kind of liner http://www.owenscorning.com/around/sound/commercial_acoustics/FIBERGLA.PDF

Im very concerned about the health issues here.
Anyway i find another company
So what do you say to this kind of liner

http://www.industrialnoisecontrol.com/pdfs/015-1001_Acoustic%20Ductliner%20DS.pdf

Claims to be healthy and noice reduction.

I think if acoustical foam is healthy to lay in a ventilation system.
Look to what value they need to assure
• Resists fungi, mold, mildew, bacteria growth, mild dust, dirt and humidity
Air is what we breath. And needs to be healthy.
I think that Roxul insulation is not a problem as long it's covered with drywall or alike.
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post #6 of 15 Old 06-14-2013, 06:48 AM
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Quote:
Originally Posted by nashoomoo View Post

Is a duct liner enough for insulation/absorption.
http://www.owenscorning.com/around/sound/commercial_acoustics/fiberglas-ductboard.asp

Ted White strongly emphasizes a significant amount of insulation for a high level of absorption. Do you recommend only Duct Liner for the baffle box kind of dead vent.
Uscmatt99 writes that the main thing is mass. And insulation helps also a little.
I think if a Flax Duct Pipe even wrapped with insulation decreases the amount of absorbing because the sound energy will slide trough the wall of the pipe. And a fewer amount of sound will be absorbed in the underlayment insulation. May be thats why they claim all the time that insulation helps only a little bit.
However i don't want the walls to be covered by exposed insulation. Since we need clean air.
http://ductworks.com/air-duct-cleaning/fiberglass-air-duct-liners-a-serious-indoor-air-quality-concern/

One way is to lay on top of the insulation acoustic foam.
Another way is to use thick acoustic foam only and with the damped mass it will be enough for a high STC.
The thing is, i dont find any stc data on that kind of baffle box, which one tells that they can't hear nothing through the Vent
So do you have some proof that Duct Liner is enough
I work so long to make the room air tight so im looking for a high STC dead vent

Linacoustic Duct liner is much different that open fiberglass as seen in that link you posted. It's much better designed to stand up to constant air flow.


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post #7 of 15 Old 06-14-2013, 07:36 AM
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post #8 of 15 Old 06-14-2013, 08:34 AM
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Insulation helps with the higher frequencies, which aren't really difficult to deal with. Lower frequencies are much harder to attenuate and require mass and dampening. These pass right through the flex duct and insulation. STC is a poor measuring stick for this application.
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post #9 of 15 Old 06-14-2013, 08:49 AM
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Another very important design consideration is noise generated by air flow through the duct and register. This is mostly related to flow rate and geometry, not materials.


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post #10 of 15 Old 06-16-2013, 08:04 AM - Thread Starter
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Can't find it on the web. May be i need to buy it in a store somewhere
This following is how it looks like


How can such a thin (relative to thick roxul etc.) material be that useful. If as Ted says needs a great deal of absorption.
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post #11 of 15 Old 06-18-2013, 07:20 AM - Thread Starter
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There are options





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post #12 of 15 Old 06-18-2013, 07:23 AM - Thread Starter
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post #13 of 15 Old 06-20-2013, 07:56 PM - Thread Starter
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post #14 of 15 Old 06-21-2013, 06:49 AM - Thread Starter
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post #15 of 15 Old 07-08-2013, 07:44 PM - Thread Starter
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It probably written in other threads.
Insulation absorbs sound energy. And so it doesn't reflect it back. However it will move it farther. Try to put a speaking device in insulation. You won't notice a big difference.
Vs. if you lay it in a sealed MDF box. So i rhink what the point of using high NRC rated sheets. When its either way not a sound-blocking thing.
The only time when we look at high NRC is, when we choose between reflaction and absorption. As to prevent the wall from become a resonator or DIY acoustic panels.
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