Attic Shaped Studio

[Starlight]

Is there a way to lower the hose on the left, alter the placement of the baffles, basically swapping top to bottom and vice versa, leaving the last lower one next to the red structural cross beam? I suspect the external grille cannot be moved but if that could be lowered it would give you three and a half air flow turns.

[endorka]

Thanks Starlight. I've had a couple of drinks so may be getting the wrong end of the stick, but the grille is internal, not external. The hose goes to the external grille in the house soffits. Soffit in the architectural sense, not acoustical

So unfortunately I don't think that would work. The grille is pretty close to the floor already;

Cheers!
Jennifer

[endorka]

Hang in there chaps

But I may be able to work round them!

Sketching up a plan right now!

[endorka]

Thought experiment: add a "step" to the silencer to get the extra turns

The room wall forms one side of this step

Seems crazy but fits into the space well. In the standard silencer design the "dog ear" braces for the outer layer of the silencer already almost fit, they just need extended at the step and cut down around the house beam

These start to look massive if you look at the design to much, so here's a shot in context of the house structure to show they aren't that big really;

With "dog ear" braces;

On paper the cantilever forces look significant, but after my experience building the bass traps they might be ok. Load tests on those showed the OSB load bearing parts to be very strong indeed. And the OSB used to build the silencers is far less dense than the plasterboard used on the inner layer of the traps.

I'm confident I can build this, but imagine fitting it in place will be tricky. The alternative design with the cut down silencer plus extra silencer extension into the room (as part of the soffit) would certainly be easier to build and install.

I'm going to build the standard silencer on the other side first, hopefully it will give me a better feel for all these possible designs in the real world.

Cheers!
Jennifer

[Starlight]

Aha, I now see better what you are trying to do, the orientation and the space it needs to fit in.

Source of the postAnd the OSB used to build the silencers is far less dense than the plasterboard used on the inner layer of the traps.

Ordinary plasterboard and OSB have similar densities, around 640-650 kg/m3. Depending on the thicknesses you are using and the acoustic or fire rated plasterboard you are using has a higher density, around 720 kg/m3, so there will be differences. OSB wins because of its shear strength.

[endorka]

Cheers Starlight.

The fun continues! On inspecting the eaves at the supply side (left on this drawing) I just discovered the house walls are thicker than I thought. This matters somewhat because the only way to get access to the filter box to change the filter will be through a hatch in the ceiling of the room below. With the 3 baffle silencers, the filter box is positioned over the house wall, so access that way - or any other way - will not be possible.

Scaling down to a 2 baffle silencer will work though. On the upside, that also solves the problem of having only 2 baffles on the exhaust side. Every cloud and all that

Looks like having silencer extensions coming into the room as part of the soffits on both sides will be necessary if the 2 baffle silencers don't give enough attenuation. It was all part of the plan anyway, so no worries.

Onwards!

[endorka]

I've cut two sides & the top & bottom for the outer layer on the supply side silencer. A test fit in the eaves worked, phew! Even though it is only the two baffle version it's still a reassuringly decent size. The rectangular part of silencer box is about 600x900mm. The "dog ears" go higher and serve no silencing purpose, they are only there to spread the cantilever force over a larger area;

Popped to the shop for some spray glue for fixing the duct lining and some more sealant. Whoever said you can't have too much of this stuff wasn't kidding.

[garethmetcalf]

Interesting design. I should imagine it'll work fine and as you say only has to be better or the same as the house is already. I think your biggest challenge is going to be getting the damn thing into place. It might be worth leaving the final panel (the bit that faces the room) off until it's in, as that will cut down on weight, and then glue, seal and screw that into place once you've got the silencer properly mounted.

Regarding the filter, I wondered whether you could simply put that on the other end of the supply silencer, actually in the room? You could possibly take the outlet of the silencer up and out the top (ie directly up towards the sky), into some ducting and then a filter box, and then ducting out to a supply plenum at the top of the wall...? Easy access from within the room then through a hatch in the wall.

Just a thought.

Cheers
Gareth

[endorka]

Source of the post Interesting design. I should imagine it'll work fine and as you say only has to be better or the same as the house is already. I think your biggest challenge is going to be getting the damn thing into place. It might be worth leaving the final panel (the bit that faces the room) off until it's in, as that will cut down on weight, and then glue, seal and screw that into place once you've got the silencer properly mounted.

Good plan! I've had a lot of practice with that sort of doing doing these built in bass traps. Also, since the supply side can only have two baffles now, I've also able to reduce the length of the exhaust silencer to 2 baffles while retaining the "step". I reckon it will be a good match to the supply silencer this way, and will make fitting much easier too.

Regarding the filter, I wondered whether you could simply put that on the other end of the supply silencer, actually in the room? You could possibly take the outlet of the silencer up and out the top (ie directly up towards the sky), into some ducting and then a filter box, and then ducting out to a supply plenum at the top of the wall...? Easy access from within the room then through a hatch in the wall.

Nice one. It would be easier to do this, but then the filter won't protect the silencer from dust and other debris. It would work really well as a secondary filter though if you wanted to protect whatever is in the room from finer particles, for example with a HEPA filter.

Cheers!
Jennifer

[Starlight]

Source of the postRegarding the filter, I wondered whether you could simply put that on the other end of the supply silencer, actually in the room?

I thought about that, too, but I think it will be necessary to have a filter on the exterior side of the silencer to act as a barrier to birds, wasps or whatever from nesting in the box. I wondered whether a filter on the outside wall or soffit, wherever Jennifer will put the vent hole, will be accessible from a practical aspect (eg. how tall a ladder will be required?) to clean or change the filter.

[endorka]

Source of the post I think it will be necessary to have a filter on the exterior side of the silencer to act as a barrier to birds, wasps or whatever from nesting in the box.

Thanks Starlight. Fortunately large debris of that type is taken care of by the soffit grilles, which have a fly screen. I could probably clean the grilles occasionally from a nearby window with a vacuum cleaner with a long hose!

The soffits have ventilation strips with fly screen all along them so it is in keeping with the current house design & function. The red arrow points to an already existing bathroom fan grille. The new grilles will be on either side of the balcony.

The filter box is for finer dust particles and so on. Sometimes I do wonder if it is overkill - i.e. all the air entering the house just now is from outside and is unfiltered, so why should this be any different? I suppose the rate it is being sucked in at will be much greater. Still, it's build it in now or never, so I figured best not to take any chances.

I wondered whether a filter on the outside wall or soffit, wherever Jennifer will put the vent hole, will be accessible from a practical aspect (eg. how tall a ladder will be required?) to clean or change the filter.

It's a two storey house so the soffit is quite high up. I don't have a ladder high enough, and part of my goal in this design was something that could be changed by an ordinary person, let's say someone comfortable changing a light bulb or what have you.

Cheers!
Jennifer

[endorka]

I've built the outer structure of the supply silencer and done a test fit, thankfully it fits. The 2 baffle version makes everything much easier! It's still massive so I have a good feeling it's going to be enough.

Here's my current working design for the exhaust silencer. 2 baffles so should match the supply silencer. Going to 2 baffles for this one will make a multitude of additional obstructions I've discovered in the eaves on this side irrevlevant.

OK back in to the woodshed

[endorka]

Photo of the real thing a few hours ago. Supply side silencer, outer structural layer.

[Starlight]

My goodness, you are quick with both Sketchup and real life construction!

[endorka]

Source of the post My goodness, you are quick with both Sketchup and real life construction!

Totally in the zone here, adapting the design on the fly to match the demands of reality. What a buzz to be actually building this after all the theorising!