Now that I've discussed the theory behind the design and the locations of the two baffle boxes, onto how I actually built them. In this article I am mostly talking about the bigger box (the one that would go outside the studio), but both boxes were very similar design. To begin with, I halved some lengths of 2by4 to make pieces of 2by2 using a mitre saw and a guide (you could also just buy 2by2, but I had lots of 2by4 left over). I then used this to make the frame of the box, before covering the sides with pieces of 11mm plywood as you can see below:
I then measured and cut pieces of plasterboard to fit on the inside, using Green Glue in between the plasterboard and the plywood to maximise soundproofing. For the actual baffles, as shown in the image below, I cut 12mm notches out of the corners of three more pieces of 2by4, and screwed these across the two longer sides of the frame section. I also cut holes (using a jig saw) for the ducting to enter and exit the box as you can see below. (Clearly, the positions of these holes depend on the exact location of the build, so a different building geometry would require different positions of holes.)
The picture below shows the completed baffle setup for the smaller box (an almost identical design but without the outermost plywood lining, and with only two baffles instead of the three in the bigger box)
As an aside, please note that if you are cutting Rockwool, you should 100% be wearing a ventilator/mask, gloves, as well as a protective outer layer so that the fibres don't get caught on your clothes. I made the mistake of only using gloves the first time and had some exposed skin which gave me a rash for several days. Rockwool is fantastic at absorbing sound but it really is very bad for you, so heed my warning!
Next, I added the flexible ducting, and filled up all the remaining spaces in the box with rockwool, before covering the entire assembly with two more slabs of it. This is what it looked like now:
As I had opted for the insulated ducting, I had to remove the outer layer of insulation in order to pass it through the 6 inch holes on both ends of the box. I decided to add a 10cm length of piece of 6" pipe protruding by about 1cm on the entrance and exit holes, which the ducting either passed through, or fixed to, depending on the box . This allowed for a much stronger connection at the ducting joints, and meant that I was able to seal the joint with silicone. The image below shows an example of where the pipe (circled in red) was used as a termination for the ducting. The brown grille in the picture would eventually cover the pipe end to form the outside air-intake.
For the smaller box, where I needed ducting protruding from the ends in order to connect it up to the fan, after I had threaded the ducting through the holes in the box, I then re-attached the insulation and the outer sleeve to the box using aluminium tape. This was to provide some extra acoustic insulation on the ducting sections that would link to the other components. Again, more on the overall setup later.
For the outside box, I then used silicone to seal up all the cracks and used four coats of Ronseal weatherproof paint in order to give it protection against the elements. The final assembly for the bigger box is shown below (with the lid off):
In this picture, the intake is the brown grille that is on the top, and the outtake (from where the air would enter the studio) is on the back face. The whole box would then be flipped upside down so that the grille was on the bottom (to avoid rain getting down the ducting), and mounted to the outside wall of the studio. I will discuss this mounting process a bit further down the line.