George - I use PX02 and PXO5 crossovers rigged for each model. They create an inverse of the roll-off characteristics of the speaker, therefore creating an ideal match by definition. That solution was patented. It seems to my ear to work very well. I have never heard better integrated bass, and it seemed to get high marks from reviewers. There are issues of amp noise and repairability.
Performance issues remain. One function of subwoofers is to increase the speakers' output. We run out of bass excursion first because we seek to tune the enclosure as low as possible. The PXO doesn't increase the system output limit, but only adds the missing low frequencies. Someone on this forum has an Integrator, which does increase output by allowing a higher crosspoint to be chosen. I want one.
There are also questions begging in the phase domain, since the reflex bottom rolloff approaches 4th order. (The Stereophile graphs look more like 3rd order 18dB/octave.) My admittedly shallow understanding is that the high-order crossover will create ringing, which Thiel speakers go to great lengths to avoid at the higher crosspoints. I don't hear artifacts and wonder if the ear might be less sensitive to phase anomalies in the low bass. Perhaps others might comment on that problem; ideas welcome.
I am not familiar with the SmartSub 2.2, and haven't seen any reviews of x.2 subs. I don't know much about the development history of the subs, being after my time. Might the .2 designation be New Thiel? My SS1 and SS2s have Jim's (again patented) room boundary interface, which works very well to set the proper level based on proximity to walls. I have experimented with 1 vs 2 subwoofers and found noticeable improvement with 2. The 2-series crosses over in the high forties where directionality is thought to be hard to hear. But it seems to my ear that directionality is an issue. I would choose 2 SS1s over 1 SS2.
