Need a quick approval of my silencer design

My silencer research here has led me to the following internal dimensions for a 6" duct with 2" rigid fiberglass lining/baffles (see pic). Would offsetting the inlet and outlets to one side be better then dead center? if so which way? Also, could I simply put a breathable fabric across the outlet hole to act as a filter for the fibers, or must I wrap every inch of the lining /baffles with cloth? Thank you for such a great resource.

delusion wrote:

My silencer research here has led me to the following internal dimensions for a 6" duct with 2" rigid fiberglass lining/baffles (see pic). Would offsetting the inlet and outlets to one side be better then dead center? if so which way? Also, could I simply put a breathable fabric across the outlet hole to act as a filter for the fibers, or must I wrap every inch of the lining /baffles with cloth? Thank you for such a great resource.

not quite there yet........ you need to widen up your individual baffles to force the air to the side walls - as it is right not the air will just do a short pass around the very edge. It works Soooooooo much better if you can come in (and out) through a side instead of the 2 ends. Next - no - you cannot cover the end of the box with fabric - that will just clog up with dust and choke off your air supply - the way that a filter does (but with a filter it's accessible and easy to change - this would be anightmare) - but what you can do is use a 1" polymer covered duct board (like the JM superduct) and cut 45 degree slots into it so you bend the matereial at the fabric to form 2" goods already covered. Rod

Thanks Rod. So would extending the baffles out from 6" to 8" put me where I need to be? Would 7" be better? I'm assuming that I would NOT make the internal dimensions of the box bigger to compensate the wider baffles because it would then have the same relative "short pass" flaw that my first design has. Please correct me if I'm wrong in this.

One thing I'd like to chime in with: I just finished my studio. I had band practice last night and had my drummer go crazy while I went into different rooms of the house. The noise level upstairs directly over drum room was a helluvalot better than it was, but my joists are only 8" deep. I used Isomax clips, R19 insulation and double layer sheetrock - caulked to specs. As for silencers, I only had room for one (my control room's supply duct). Both the control and live room's duct are all flexi-duct: EXCEPT for the live room's return duct. When I went into my son's room (on the seond level of the house - which is two levels up from the basement) I heard a faint sound of drumming in his return duct. Why? Because of the live room's all-metal return duct. I didn't hear anything really at all from the heat duct (even though I have no silencer). I play my monitors in the control room (loud) and did the same test. Nothing was heard upstairs. So what I'm trying to say is if you use flexi-duct, AND a silencer, they ARE going to work really nice - especially if the silencer is built correctly, like Rod pointed out.

delusion wrote:

Thanks Rod. So would extending the baffles out from 6" to 8" put me where I need to be? Would 7" be better? I'm assuming that I would NOT make the internal dimensions of the box bigger to compensate the wider baffles because it would then have the same relative "short pass" flaw that my first design has. Please correct me if I'm wrong in this.

7" will be fine - but be sure to offset the inlet/outlets like I said........ Youwant the air shooting in (out) right along side (parallel to) the first and last baffles.......... Rod

Got it. Thanks!