Got some time to plot response curves of the new box. Did two trials, T1 and T2 to check for consistent data.
Autosound 2000 test disc with sin waves from 10Hz - 99Hz in 1Hz steps. AVR at -15dB, O Audio Amp gain at 50% Room is 6330 ft^3 and sub is located along a side wall.
This is only the isoTL subwoofer as the other subs were off. X-Over is at 80Hz so the other speakers in the system are participating somewhat at 80Hz and above.
Original Radio Shack analog SPL meter. Slow reponse, C Weighting. Recorded the raw data and added some generic correction factors found on AVS. So take anything below 32Hz with a grain of salt.
Lots of variables of course. Meter was about 1 meter from sub however the microphone was pointing away from the cabinet but was facing the front of the room.
Meter did not register any SPL at 10Hz - 12Hz but started to move the needle at 13Hz.
My purpose was to identify the enclosure resonance and compare it to the measured speaker resonance of 30Hz. I see a small blip around 28Hz but it only occurred in T1. I was thinking that this resonance would be more obvious but perhaps the absence of large peaks is a good thing.
Also I don't have a good way to measure the outputs of the line and woofer separately. On the other had, it looks to have a -3dB point starting at 36Hz, plateauing until 28Hz before dropping if I compare this graph to classic 3rd or 4th order T&S response curves.