Might not be a Theater 4 Pi if you changed it that much. You could go a bit smaller, but enough to really matter would reduce the output between 30 and 45 Hz considerably (3dB). Except for a bit more output around 30 Hz that would be nearly the same bottom end as a Stage series Four Pi, but I bet you want the deep bass if you want a Theater 4. Perhaps a Theater 3 would be small enough. I hear it plays deep and sounds great. Stage 4 pi has a real nice motor for the money though.