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Profile picture for user J de Berker

Hello,

My first post on here...
Does anyone have some guidance and/or plans of silencers for use with a ventilations system i a studio?
I am using 220x90mm rigid PVC duct in the ceiling space above the room within a room.
I plan to drop the duct in opposite corners of the room in plenums and build silencers/baffles within these plenums.
I have seen a number of pictures of these made of MDF or similar and lined with insulation normally with a series of bends which stop the sound waves from travelling in straight lines(Build it like the Pros by R Gervais has some drawings and gives some info on this)
What I am unclear of is how bends will effect air flow, what I don't want is to create too many and end up making it impossible for my fan to push or pull air because I have created too much resistance/friction, equally I want to make sure that as little sound as possible leaves or enters the room through the ducting.
Secondly what is suggested to line such a silencer? I have been told Melamine foam, this is available in 25 or 50mm sheets or tiles but it pretty expensive stuff and I'll be building a total of 6 silencers (2 each for 3 rooms) I wondered if a high density mineral wool would do the job?

My rooms are all approx 35 cubic meters the fans have been specced to easily cope with this and give sufficient air changes, velocity should be good and be low enough to run quietly.

Many thanks

Comments

Profile picture for user Brien Holcombe

Brien Holcombe Wed, 04/26/2017 - 15:25

Here's my thinking on this. One of the main reason a person goes thru the trouble of developing a room with in a room is to develop high isolation...right?

To that end everything you do from the exterior structure to the interior structure you have to incorporate a decoupling mechanism on each and every item that goes from the exterior structure to the interior structure, right?

So your including rigid pvc as a trunk line is already bordering on the side of short curcuiting the high isolation you are building towards.

If this rigid pipe is already in place then you must decouple this pipe from the interior structure. Or if it is easier to do, decouple it from the exterior structure.

It should not be there to begin with and ideally it would be decoupled from both the exterior and the interior structures as it is a path for vibration and that defeats, little by little, everything done to this point.

As to the the boxes..whatever Rod has drawn up use it. The only way you will cripple your air system is if you build these boxes 6 inches by 6 inchs....meaning a very small box.

If the box is as big as the air in flow or bigger which is more likely, then it will be fine.

Lining the boxes typically takes a usual product used in hvac development meaning, you are attempting to keep the noise levels down from room to room and from outside of the hvac trunks and feeders and not introduce fibers, or rather, anything that can aggrevate the respritory system.

Does that help?

Profile picture for user J de Berker

J de Berker Wed, 04/26/2017 - 15:42

Thanks for your thoughts Brien

I agree with everything you've written. I have a design whereby the duct is attached to the ceiling of the inner room and only bridges the inner and outer room once, and that is for 25mm around the circumference of the duct. I have deliberated about it a lot but could not reduce this anymore unless I didn't seal the outer room and I think maintaining an air tight seal around the inner room should take priority (I may be wrong on this)
I hope that the silencers are effective enough that they will reduce the transmission sufficiently that there will be minimal sound travelling in the ducts that can be transmitted at this point where the two rooms and the duct touch......

Somehow the duct has to leave the inner room and pass out of the outer room so it must unfortunately connect the two, I couldn't think of any way around this?
I may also install air con and the same problem will again. I'm assuming this must be a fairly common problem? In Rod's book the door frames are also connected in one of the designs so which I understand this goes against the principal I understood that sometimes things (flanking) cannot be avoided?

With regard to lining materials in the UK air con is not that common in domestic properties, the duct lining products associated that I've read about in US publications I haven't been able to source.

Thanks again

Profile picture for user Brien Holcombe

Brien Holcombe Wed, 04/26/2017 - 16:14

The idea when making an hvac connection from exterior to interior is "flexable" ducting...that eleminates a multitude of sin in respect to a hard connection.

Profile picture for user DonnyThompson

DonnyThompson Fri, 04/28/2017 - 23:15

Back when I had my commercial studio - it had already been a studio on the past, and built pretty well for ISO and acoustics - although I had the control room re-designed from the ground up, because it had been originally built back at a time -late 70's - when the "small and dark control room / huge performance area" thing was all the rage ... I ended up tripling the size of the control room ...
And I remember the contractor ended up using a "flexible " duct system, IIRC it was similar to what you'd commonly find in people's basements for clothes dryer vents, just bigger and insulated on the outside.
Now, whether it was decoupled completely from the two walls (int/ext) I don't know.
I know I never had any issues with heat or AC making any noise that was noticeable...then again, the HVAC system in place then wasn't really all that noisy to begin with.
I can say that I've worked in studios in the past that were very well-isolated acoustically, but that had little-to-no ventilation, and it did manifest itself in fatigue, lack of creativity, and even short tempers. I know it sounds silly, but I'm pretty sure the lack of ventilation had a part to play in those things.
FWIW