Hi there. I don't know if this should be in this forum or the PA system forum, so here goes: I've built some 18" bass cabs using P.Audio speakers, and used Harris Technologies software for the box and porting design. These seem to work reasonably well although I seem to get more bass from behind the cabs than from the front. i think this may be a porting issue. I have the 18's front mounted and have 4 ports in the front panel corners. Does one include the porting volume in the total volume of the cab, or, do you deduct the volume for these ports from the internal cab volume as one would deduct the speaker and other intrusions into the cabinet's volume.