Some general queries as I plan my next build. Yes, I've searched the forum, but am still unclear about these:
1. I've read that flexible ducting is quieter than rigid. But they also make rigid ducting with insulation on the inside - would this be even better? Not sure what the insulation is made of - most of it seems to be some kind of 1" foam around the inside.
2. I've also read that wider ducting is better so that you can achieve the same amount of air movement with slower fans (and thus less noise). Makes sense, and I've seen ducting available up to 30cm and even bigger (though I wouldn't want to use any bigger than that for space reasons).
But it doesn't seem possible to get insulated ducting that big. Does anyone know anyone in the UK who does it?
Alternatively, would it be feasible to buy ordinary 30cm ducting and glue insulation to the inside of it oneself?
3. How does the effect of insulated ducting compare to the effect of a silencer box or plenum room? Aren't they effectively doing the same thing - basically running the air over an insulated surface to soak up the sound as it goes? Given that one needs to install some kind of ducting anyway, doesn't using insulated ducting make more sense from a space and simplicity POV than dealing with huge great splitter boxes and then running the air through ordinary ducting? Is there any reason why what would be achieved via a silencer box or plenum can't be achieved via insulating the duct run itself? Particularly if the run is quite long, with some angles.
Thanks in advance...
Insulated ducting - questions
Originally posted at johnlsayers.com, topic 13363.
a flex duct does resonate less than a rigid one. so it can be more quiet. Insulation inside will help dampening the duct. You can also box it in. Rigid steel ducts have better airflow (more efficient)1. I've read that flexible ducting is quieter than rigid. But they also make rigid ducting with insulation on the inside - would this be even better? Not sure what the insulation is made of - most of it seems to be some kind of 1" foam around the inside.
It all depends on how much air you want to supply. I haven't seen any numbers so I can't really advise you. But don't overdo, a 100mm duct can deliver a fair amount of fresh air while still be very quiet.2. I've also read that wider ducting is better so that you can achieve the same amount of air movement with slower fans (and thus less noise). Makes sense, and I've seen ducting available up to 30cm and even bigger (though I wouldn't want to use any bigger than that for space reasons).
No. don't go messing with that. Air itself is quiet, it's mostly external noise that travels through the ducts. Box them in 'n use "silencer-boxes to get rid of that phenomenon.Alternatively, would it be feasible to buy ordinary 30cm ducting and glue insulation to the inside of it oneself?
3. How does the effect of insulated ducting compare to the effect of a silencer box or plenum room? Aren't they effectively doing the same thing - basically running the air over an insulated surface to soak up the sound as it goes? Given that one needs to install some kind of ducting anyway, doesn't using insulated ducting make more sense from a space and simplicity POV than dealing with huge great splitter boxes and then running the air through ordinary ducting? Is there any reason why what would be achieved via a silencer box or plenum can't be achieved via insulating the duct run itself? Particularly if the run is quite long, with some angles.A duct can be engaged anywhere that's why you need it dampened / boxed in. A silencer box is to "kill" sound within the duct and prevent it to enter a room. Thanks in advance...
You might look to use the flex and insulate around it. The amount of insulation on standard flex is minimal. For real absorption, you would surround the flex as seen in this image
External image, not preserved — original: http://www.soundproofingcompany.com/media/cim/spc-soffit-construction.gif
Soundproofing Soffit ConstructionThanks guys.
The ducts in my current studio make a whooshing noise when the fans are turned up above about halfway. I've always presumed that that was because of the airflow itself, but it may be that it's just the mechanical noise of the fans being transmitted. They ARE very loud fans. But why not insulate inside a duct? I have seen three types of product that go under names such as "insulated ducting" or "acoustic ducting". The first is (usually flexible) ducting with an inch of rockwool or similar wrapped around the outside, followed by a layer of aluminium to hold it on. The second is like the first, but the inner layer of ducting has perforations in it. I've only seen this once, through an Ebay shop - and they were careful to call this "acoustic ducting" and claim that it gives greater soundproofing than the kind without perforations (which may be bullshit). I presume the perforations are so that the air passing through actually makes contact with the insulation. The third is solid ducting with foam stuck to the inside. This is basically what I'm talking about making, only for the reason that they don't seem to make it in wider duct sizes. It seems to me there are two different issues here: One is the amount of noise MADE by the air moving through the duct. Airflow against a rockwool or foam surface is likely to make less noise than airflow against a plastic surface, isn't it? The other issue is preventing the noise from escaping once it has been made, which would be achieved by the insulation around the outside of the duct in the first type of product, or Ted's idea of boxing it in. But it seems like if you can prevent the air from making as much noise in the first place, that's gotta be good.No. don't go messing with that. Air itself is quiet, it's mostly external noise that travels through the ducts. Box them in 'n use "silencer-boxes to get rid of that phenomenon.Alternatively, would it be feasible to buy ordinary 30cm ducting and glue insulation to the inside of it oneself?
What I mean is; don't go messing with that yourself. Get pre-insulated ducts. :)
Deal with the source of the noise. flexduct have more resistance concerning airflow so I'd advise not to use it too much. box your duct in would be the best solution. Wrap some mass around it and ye save with noise comming from the duct.
Add sustainboxes to absorb some more noise so you'll have less noise traveling from one room to another room.
I would also add that you can effectively create "silencer" boxes through careful planning of your supply and return paths. If you make it so that adjacent rooms have supply paths that are far enough away from each other, that makes a silencer box via all the turns in the pathway. This avoids the efficiency loss created by a silencer box. Every turn in a duct creates resistance in airflow that will reduce the CFM into that room and build up static pressure in the system that the blower has to overcome.
Also, once the duct is at or in the room, double its size to slow the air down and quiet the airflow itself. Then box the duct in a soffit and run it inside the room a bit before venting out. Use real good vents and big ones!
-ashley