BillFitzmaurice.info

TimpBizkit wrote:Why is exceeding x-max so bad? (...)
A lab 12 has an X-max of 13mm and an X-lim of 22mm. So doesn't that mean that driving the speaker to 14 or 15mm momentarily is safe? (...)

Driving the speaker to 12mm xmax is safe - beyond 13 you run a great risk of destroying your driver..

Remember that excursion rises rapidly when you want to reproduce lower octaves.. Often, when it comes to midwoofers or similar, the driver will hit its thermal limit before its mechanical - thereby ruling out xmax as the limiting factor..

TimpBizkit wrote:Why is exceeding x-max so bad... it's often touted like it will blow the speakers.

That's because it will. Going past xmax you put more power in without getting more output, that results in heat build up and eventually magic smoke.

Eminence Alpha 6 - X-max 3.5mm, X-lim 4.0mm

That's because the Alpha 6 has a underhung coil.

If you want to push your drivers past xmax be my guest. Sensible builders will follow the plans and limit their subs.

TimpBizkit wrote:Why is exceeding x-max so bad?

Because you're taking the driver beyond it's design capability. Otherwise it wouldn't be called Xmax, it might be something like Xnom, as in nominal. Max to me means short for maximum.

Since you mentioned the Lab12, IIRC, in Bill's designs at least, Xmax and thermal limit occur at the same voltage limit for that driver.

It's already been mentioned that lower frequencies push the driver hardest in terms of travel.
And when you look at impedance graphs for a driver, if they have been supplied, you'll notice that's where the highest impedance is as well...