Hi Spliffscot, I to wanted to keep fan noise down as much as possible. Last box I built had fans for intake/ exhaust, and just got annoying listing to it all the time. Blowing one fan into the carbon filter, with the passive intakes. Seem to move enough air through the box. With the noise being cut in half. All you hear is air flowing through the carbon filter. No fan noise. All the noise is contained in box. I did have to take both ends off the carbon filter and silicon glue each end for air tight seal. The passive intakes are just some kind of aquarium filter. You can find them at the pet store. No carbon. Just to keep dust out, and block light, and noise from getting out of box. Hope the info helps for the re-design. Got to keep the wife happy if you want to grow in the house. Happy wife = happy lifeI'm doing a re-design for a slightly larger space than yours << but like the design/concept of a filter/baffle on the passive intakes < I'd need larger intakes so am just 'a light trapped hole' at the moment. Difficult to tell what you are using - just an air baffle - or something carbon coated?
The wife thru down a gauntlet and asked me to 1/2 the cooling noise << already use acoustic ducting and LEDs, 12V Silent Fans << so I'm thinking I could just add something to her ear drops....
and maybe some passive vent baffles lol...
Shame my space doesn't lend itself to making the filter a 'design' feature << and as an x-design lecturer I commend you highly for this 'feature' << I'm sure it will inspire others to think along similar lines.