Just chiming in here to say I built 12 modules of 3 sizes each - 36 in total - from the designs in Tims original post and with some updated calculations from this 2023 video detailing design and build and with lots of helpful links
https://www.youtube.com/watch?v=WqnA...nnel=RamElijah
I used the updated calculations suggested in the video, and the links to room mode and absorber depth calculators to arrive at the design. I then installed them in the room corners, roughly according to Tims layout plan.
Iβm happy to tell you - they worked perfectly. I had a massive low end problem in my newly built control room, 50 hz particularly, and the modules totally solved it. Now very smooth all the way up to 120hz.
Things to note - the modules I built are much smaller than the one in the video, as per Tims original design. I did this for ease of installing them on the walls and ceiling and because Tim is a well respected audio designer (Buzz Audio) in my country (New Zealand) which gave me a bit more confidence that he knew what he was talking about.
They cost about $1000 NZD ($650 USD) in 2023 and took about a weeks labor I would guess. I used the tec sound for the membrane, like in the video. I used 18mm MDF for the boxes. I used builders strap attached to the internal cavity by small metal angle brackets to hold the insulation in place, at the distance specified in the design calculator. I used a brad nail gun and glue to construct the boxes. There was a lot of stapling involved to attach the membrane thoroughly, which wasnβt much fun.
I used Pink Bats Ultra R2.6 Wall for the insulation (This wonβt be useful to anyone outside New Zealand) which has a gas flow resistivity of 10,300 rayls. I found the whole gas flow resistivity thing confusing. The gear space thread on trying to find the data on common insulation materials is what I scoured through. Google βCommon Gas Flow Resistivity numbers gear spaceβ and you should find it.
And for anyone is Asia/Pacific, what got me the information I needed in the end was a google drive link at the bottom of page 7 in that thread, by Paul the Sparky
From memory, what may have made it confusing was it took me ages to realise βraylsβ where the same measurement as kPa.s/mΒ². So 10,300 rayls is 10.3 kPa.s/mΒ². I may be remembering this incorrectly, so donβt quote me on this.
Other things to note if you are planning on building these - as Tim said, follow the instructions exactly and they will work. The sound sealant caulk is crucial, they need to be airtight. Apply the caulk with a caulk gun, then work it in with your finger to make sure the seal is good. The boxes should be made out of dense material - MDF or ply. I have not seen any suggestion of using less than 18mm. I only note this because I was initially deterred by a comment on the above video saying they didnβt work, but the person had used chip board (not dense enough) and only built 2 of the smaller modules (not enough to make any difference).
I researched some other options that were either insanely expensive (Acoustic Fields DIY charcoal design) or didnβt have enough before and after measurements to make me confident of efficacy and so I was very grateful to eventually stumble across this design. Thanks Tim