Exterior Drum Practice room build plan, Wales, UK

I have a little problem with my baffle boxes - I'm doing 4 of them (on outside and one inside for the inlet and outlet). I've done one of each so far, and I've realised that the inside box has the inlet and outlet in the right place for my requirements, but the wrong place to get 3 baffles in it in an alternating pattern. I have pasted a picture below. So - I'm guessing that 2 baffles (leaving out the middle one) would significantly impact on performance. However, would adding an additional one (as I have done in the below picture) work? There will be more of a squeeze for air to get around, which may be the issue?

I'm thinking that the entire silencer box needs a re-design! Once you add your duct liner on all the inner surfaces, there won't be anywhere near enough cross section left over. The basic concept is that whatever cross sectional area you have inside the duct needs to be doubled inside the silencer box, and maintained for the entire length. So for example, if the area of the duct is 180 cm2, then you need at least 360 cm2 cross section throughout your silencer box. That could be, for example, 19cm x 19cm internal. Adding 25 mm on each side for the duct liner takes you to 24cm x 24cm for the internal dimensions of the wooden box itself, which also implies that your baffles would have to be spaced at least 24cm apart (since they will also have duct liner on them). So sadly, I reckon you need to re-think your silencer plan, as I can't see it working out well like that. Air flow velocities will be way too high, there will be lots of turbulent flow, cause lots of air noise, plus the lack of impedance mismatch at the entrance and exit won't be providing the isolation that you are hoping for. - Stuart -

I've reconfigured the problem box so that the inlet is in the bottom (out of view) and the outlet will be in the top. I'm having a slight problem with the foam peeling back. I've used stronger glue in some places - the foam was self adhesive - but I'm concerned that it may peel in warm weather. I'm assuming a few tacks would be a bad idea as introducing hard surfaces on top of the foam would compromise the box?

That looks much better! :thu: If you need to put a couple of tacks or staples in there to keep it firmly in place, that would not be a problem. It won't cause the box to not work: worst case, it will cause a bit of additional turbulence, but as long as you don't overdo it with dozens of tacks, you should be fine. - Stuart -