After the effort of sealing every joint in every layer of construction it seems a shame to make a hole for ventilation! However we do need to breathe. Every time we penetrate a layer of construction we need to limit the transmission of sound. Each room has two fresh air inlet vents, two stale air exhaust vents, then on the outer shell we have one inlet and and one outlet.
Six attenuators for each room, a total of twelve for my project.
They are quite big so I built six at a time.
They are built from 18mm MDF. Lined with 50mm Rockwool RW45, wrapped in a garden fleece 17gm2.
I used 4*60mm torx head MDF screws
150mm vent pipe
150mm top hat spigots
Tescon and Tyvek Airproofing tape.
In total I needed:
24 tops and bottoms 1000mmx500mm
24 sides 1000mm x 314mm
24 ends 464mm x 314mm
24 baffles 464mmx182mm
I used Sketchup to draw a cutting list to make the most economical use of MDF sheets, 2440mmx1220mm
Once I cut all the above,I used a pilot with countersink to drill all the fixing holes.
I then assembled one box at a time caulking all the joints.
The Rockwool is rigid and easy to cut with an old bread knife. I used a garden fleece to wrap each peice. I simply used a line of PVA on the back of the RWA45 to stick the fleece which when positioned in the box also kept it stuck in place. (Although I found that friction was sufficient to hold it all in place.)
The first box I made I screwed to a piece of OSB, which is the first layer of ceiling. It was already very heavy so needed the board lifter to get into place. I will cover with the cover the boxes plasterboard to maintain the integrity of the ceilings mass .
I decided to put the 4 external inlet and outlet boxes in place and assemble in position. The main reason was drilling the hole in the correct place. And the other is they are heavy enough as it is!
I made a template so I could be sure I would miss the gable end studs and the truss concealed behind the plasterboard. (I marked their position off on the wall after each layer so I knew where they were.)
The board lifter was used to help man handle the four boxes into position, and they were screwed to the gable end wall. (Caulking the screw heads)
Using a 150mm hole saw I drilled through the several layers of MDF, Plasterboard, OSB to get to the outside world. I inserted a 150mm pvc pipe through the attenuators straight to the outside. I kept a slight decline from inside to outside in case any moisture were to get in the pipe so it would run to the outside and not into the box. I used expanding foam from the outside to seal the penetration and acoustic caulk on the