Well there are several points of view:
1. Machanical demage:
You would demage the surround and/or the spider and/or the Voice coil when you exceed the mechanical limit of movement, what is 44mm If I remember correct.
However to reach such a large excursion one would need a big amount of power (current) which would burn the VoiceCoil.
2. Acoustical output:
The Magnetic Gap is ca. 10mm deep and the VoiceCoil is ca. 37mm long.
This gives a linear excursion of ca. 26mm (+/-13mm)
When I don't count with the magnet structure's (thermal)power compression (however I should!!) then exceeding this excursion gives me a decreased BL product and THEN all TS parameters changes...
This means for example that at 31mm(+/-15.5mm) excursion I just have the -3dB points of the BL product. While F= BxIL, this means that for reaching this excursion, you would need ca. 3dB more power than you would need normaly (if you where in the linear excursion range)
This also means, that above 27Hz you surely can't exceed the
-6dB BL points (+/-18mm) with an INPUT power that wouldn't burn the VoiceCoil. This point would be maybe the absolute non repeated peak.
So if you use a HPF at 30Hz with a slope of -24dB/oct, you surely will not reach the mechanical Xmax.
Brad,
I agree, the 12" cone is a great winner in this application.
BTW I think, one could get ca. 3-4dB more output @30Hz with a pair of good 15" drivers, where the cones should be very stiff...
Cheers,
Tamas