I'm with
@shadyJ on this. Pro drivers have a very high Fs, and to operate below their resonance requires GOBS of power. To be fair, the Motor and Suspension are designed to take it, and I've seen numbers that indicate they can usually operate to an excursion of just under 2/3 of their gap before things get ugly... But if they lose their efficiency ~35Hz, and are approaching their excursion limits by 18-20Hz pushing these much further becomes more about your DSP, Transform function, voltage limiter, and available current and voltage to the Amp.
That PSA Sub with its 960w Amp capable of hitting Peaks of over 2000w will be drawing hard on whatever circuit its plugged into if engaging some deep and heavy low frequency and infrasonic output.
I would really love to see some good measurements of PSA Subs to see what they are doing. It's all good to say that in-room they can hit 10Hz while being -3dB at 14Hz... but at what SPL?
Moreover, I would like very much to see what kind of voltage is going into that thing at 20Hz and below!