Plays strong and flat from below 25hz on up to 60-65hz then drops off.
Low pass is set to 25hz with mild curve on a SFB3000.1
I modeled the box off of the old Bose Accustamass modules from the 80's
I calculated their box at .25 cubes at 180hz for the mid acoustic chamber, .5 cubes at 45hz for their rear chamber and 1 cube at 90hz for the front chamber. Everything doubling octaves. My box here for the 6.5s is .4 cubes at 112hz, .8 cubes at 28hz, and 1.6 cubes at 56hz. Super sound quality mixed with chest pounding SPL coming from 2 little 6.5s . All on factory power...only drawback is the box is 4ft wide, 10 inches tall and 21 inches deep... and it needs a makeover to look good.