I had the same problem with music...I kept having to adjust the volume to get the bass response correct. When I plotted my frequency response, it looked like a roller coaster between 30Hz and 80Hz.

To fix the problem, I purchased a Behringer Feedback Destroyer Pro ($120) and used the parametric equalizer to flatten my response curve. My plot with the BFD in place...ruler flat from 25Hz to 80Hz.

The change has been amazing...the old Velodyne has NEVER sounded this good.