Jtgofish,
Good point about thick surrounds and long cone excursion....there is a lot of non linear distortion that occurs at the cone to surround interface as the rubber roll decouples from the cone - often causing a sharp change in response at higher excursions. This problem usually occurs in a range between 500 and 1000 Hz and is therefore of greatest issue in two way systems which necessarily cover that range with a single driver. Sometimes a careful manufacturer may use an intermediate material between the rubber and the cone, sometimes a damped cloth surround is used with the benefit of overall reduced coupling and smoother response. Nevertheless, more often than not, most two way systems inherently have this problem in the all important mid range...