Hmmmm......38hz isn't even a half octave lower than 48hz (36hz would be a half octave), much less a full octave lower (which would be 24hz).The perfect example of what a TCAB box does for you! Both scores achieved with a pair of type R 12's and 650 watts. 139.7 @ 48hz with a "custom designed" ported box. 142.5 @ a crazy low 38hz in the TCAB boxes!! Thats a full OCTAVE lower...