What density rockwool for bass traps

Hi! I'm looking forward to building a broadband bass trap to hang in the front wall of my mixing desk. I would like it to absorb bass frecuencies as the measurements I have done of my room with REW peak at 60Hz and 144Hz and have a dip in 77 Hz. I'm a newbie but I have made my research in the web, I would like to know what density of Rock Wool should I use for 4" bass traps of this characteristics. In my local store I find 144 Kg/m3(9 lb.pcf) and 80 Kg/m3(5 lb.pcf) . Thanks, any other suggestions wil be helpfull.

Hi hernangil. Please check the forum rules for posting. You seem to be missing something! :)

In my local store I find 144 Kg/m3(9 lb.pcf) and 80 Kg/m3(5 lb.pcf) . Thanks, any other suggestions wil be helpfull.

Both of those are way too dense. For bass you need something much lighter, around 40 kg/m3. Having said that, absorption will not do much for such low frequencies, unless it is very thick, and/or spaced a long distance away from the wall. A quarter wave at 70 Hz is already 4 feet, so theoretically you should space that insulation 4 feet from the walls, for maximum effect. - Stuart -

So as far as I understand, 40 kg/m3 is the best variant. But what about a bit heavier, 60 kg/m3 which I'm going to use)? [SPAM SIGNATURE DELETED BY MODERATOR]

Contrary to popular belief, higher density is NOT better for bass: it is WORSE. For good bass trapping, you want lower density. - Stuart -