Lining for silencer boxes

[chrispire]

I've been exploring various posts in this form about silencer box designs. Many of the designs I've seen appear to use plain ol' OC703 (or equivalent) to line the inside of the box. Here's one example: http://www.johnlsayers.com/phpBB2/viewt ... 2&start=16

Thinking about health and safety...

Could tiny fibres break loose and be carried through the duct, or is that only a problem with rockwool (as opposed to fibreglass insulation)?

I'm also concerned about moisture and the possibility of mould growing on the insulation. Is this concern unfounded?

Is "proper" duct liner preferable, such as this? https://www.knaufinsulation.com.au/prod ... enum-liner.

This one has a black tissue facing, but others I've seen have a foil facing. I imagine that foil facing would be more resistant to moisture, but less absorbing of high frequencies, so would this make it less fit for purpose inside a silencer box?

Thanks all.

[Gregwor]

Is "proper" duct liner preferable

Yes.

I imagine that foil facing would be more resistant to moisture, but less absorbing of high frequencies, so would this make it less fit for purpose inside a silencer box?

I doubt it would have any effect on moisture as the foil facing isn't going to be air tight. It will have voids throughout joints and such. The foil would have an effect on high frequency absorption for sure. I personally would go for the stuff that doesn't have a foil exposed.

Greg

[Hub]

We are lining our silencer boxes with 50mm 48kg Polyester recommended for duct lining. I can say it works amazingly. It doesn't have any film over the surface.

[chrispire]

We are lining our silencer boxes with 50mm 48kg Polyester recommended for duct lining. I can say it works amazingly. It doesn't have any film over the surface.

Sounds good. Would love to know exactly what you are buying and where.

Thanks!

[Hub]

We used an Autex duct lining product.
Actually the same product is used in some of the walls and bass traps as well.

Silencer box scale.jpg

[chrispire]

Love it. Thanks for the info and action shot.

[Hub]

We are building 8 of these. They weigh over 100 kg each!

[chrispire]

They weigh over 100 kg each!

Is that with or without the addition of a human occupant?

[Hub]

Without the young lad.
Actually the box is about 100kg plus about 10kg of polyester = 110kg.

[chrispire]

I can appreciate why the boxes need to be so big. I just received an inline fan for air supply and it's LOUD. The model I bought (Fanco TT Silent) is rated at 33 db, but that's just wrong. False advertising to be honest. It puts out over 55 db at 3 metres and has quite a lot of deep low frequency energy too. This might be unworkable.
https://www.fansonline.com.au/fanco-tt- ... -lead.html

Not sure if I'm going to be able to silence this thing, but I've revised my silencer box design so that's it's bigger and more heavily insulated than originally planned. They are about the size of yours now.

I'm contemplating sending this fan back to the supplier (because the claimed stats are so wrong) but I don't really know what else to use instead. If you (or anyone) can recommend a quiet air supply fan with an output of around 150 litres per second (give or take) please let me know.

By the way, I noted that you've only used two baffle turns in your box design. Do you find that's enough to attenuate noise coming through the box? This is new territory for me and I'm a bit paranoid about mine underperforming.

Cheers!
Chris

[Hub]

Our silencer boxes are designed for the air conditioning supply and return.

We have 6 for the control room(3 supply & 3 return air)
Also 2 for the small live room( 1 x Supply & 1 x Return air)

Our fresh air into the studio will be supplied to the Air conditioning fan unit.

Our boxes are made of 33 mm thick white melamine HMR particle board( this is to match the thickness of our studio wall mass)

I did a basic test with a sound meter in the control room before we cut a hole out in the ceiling to test the sound getting through the ceiling.

Test 1 - before cutting hole through the control room ceiling: Ambient 31db - We beat a couple of tom drums that put out 82db and played some music through the monitors at 70db measuring in the control room.

Test 2 -I climbed into the ceiling space above Control room and measured: Ambient 32db - Tom drums were 42db and music 32db.

Then I cut the hole in the control room ceiling exposing the roof space, now sound can get through in and out of the studio.
I installed one Silencer box in the roof space and sealed it to the hole. Now the hole in the studio ceiling continues through the silencer box exiting into the roof space.

Test 3 - I conducted the same test in the control room and measured in the roof space. Ambient 32db - Tom drums were 42db and music 32db.(amazing! could not believe it)

When I was up in the roof and my friend was beating the drum in the control room I had the sound meter pointing to the middle of the roof horizontally. I was amazed with the fact that there was no more sound getting out of the control room than when we had no hole in the ceiling.

I slowly moved the meter to the silencer box that had a 250mm diameter metal spigot attached and proceeded to point the meter right into the spigot and then put my arm into the top of the silencer box and lowered the meter and the reading did not change! I was blown away. These boxes perform far greater than my expectations.



It sounds like you are only creating a fresh air supply into the studio therefore your duct sizes will be way smaller. Can you only put the fan in your room? or can it go in an adjacent room or ceiling space?

Roof space.jpg

[chrispire]

Thanks for the information. To answer your question, yes I will be able to mount the fan inside the wall cavity and surround it with an insulated box to silence it. I'm pretty sure it won't be audible from inside the room but I won't be 100% sure until I build a box to test it.

I asked the manufacturer (Fanco) to explain how they specify this fan at 33db from 3 metres when I measured it at over 55 db from 3 metres. There response was:

"The TT Silent sound data was measured in accordance with ISO 3741:2014. It was measured at a distance of 3m and as ducting is assumed to be attached at either end only environmental noise was considered."

Forgive my skepticism but I took this explanation to mean, "We don't care about reality because we've got a bit of paper with a test result on it."

33db is very quiet. This fan is not. May this thread serve as a warning to anyone ordering ventilation fans: Published specifications may be wildly inaccurate.

[Hub]

You could even isolate the fan box from the frame so the vibration does not transmit. Hopefully the fan noise is going to get cancelled through your baffling system.

[chrispire]

You could even isolate the fan box from the frame so the vibration does not transmit. Hopefully the fan noise is going to get cancelled through your baffling system.

That’s exactly the plan.