DIY Sound Panels: A Mixed Bag of Acoustic Treatments

I recently tried a DIY approach to improving the acoustics in my home studio for mixing, aiming to reduce flutter echoes and tighten up the low end without breaking the bank. I built several 2x4 foot absorption panels using rock wool insulation, wrapped in breathable fabric, and then framed them with simple pine wood.

Placing them at first reflection points on the side walls and ceiling, along with two bass traps in the corners, significantly improved the clarity of my mixes. The harsh mid-range flutter was tamed, making dialogue and instrument separation much easier to discern. However, the bass traps, while effective at reducing some of the muddiness, still left a bit to be desired in terms of even low-frequency response across the listening position. I used my MixPre-10 II with an MKH 50 to measure the room before and after treatment, and while the decay times were better, the really low stuff (below 60Hz) still had some problematic peaks and nulls.

What truly worked was the primary absorption for mid-high frequencies; that was a game-changer for critical listening. What didn't work as well was expecting DIY bass traps to perfectly smooth out severe low-end issues. They helped, but professional, tuned resonators would likely be required for real precision. Has anyone found DIY solutions that effectively tackle problematic sub-bass without over-dampening the room?