OK I have ordered the Rockwool; just need a sanity check to make sure I am pointed basically in the right direction.
There is a convenient cross beam about 40 inches down from the apex of the cathedral roof so I am going to use this (and others similarly positioned) as the ends of the frame. This means the frame (and the bass trap) will be 2m (6ft 6ins wide). There are convenient beams which cut the length into two handy lengths of about 9ft. So basically I am planning to build two roof bass traps each 9ft long, 6ft 6in wide and 40 in deep. I intend to use 4in of Rockwool RW3 (60Kgm/cm or 4pcf) all the way along then 8in of regular roofing fibreglass insulation throughout.
I have done some room measurements and there seems to be significant resonances at the mix position of around 42Hz, 58Hz, 90Hz, 105Hz, 120Hz, 135Hz, 150Hz, 185Hz, 260Hz, 280Hz, 315Hz, 340Hz, 380Hz, 400Hz, 440Hz and 460Hz. According to my calculator 40in is a quarter wavelength at about 85Hz so it looks like I am in the right ball park.
Any comments?
Cheers
Ian