If Xmax shouldn't be exceeded, why have a Xlim?

rich_gale wrote: .. why in real life terms (not boring theoretical paperwork crap) should i not drive a speaker past its xmax???

One word:
DISTORTION

If a more "boring theoretical paperwork crap" answer is needed, willing to elaborate

rich_gale wrote: why do manufacturers publish a xlim/xmech figure alongside an xmax figure, often the xlim/xmech is 4 times the travel of the xmax.  if you shouldnt drive a speaker past its xmax, why can they cater for further excursion? what % excursion over the published xmax is considered too much?  i have had a pd186 sounding twice as loud with about 1" excursion than when it was within its 9mm xmax limit.  and it sounded no less defined than when keeping within xmax.  why in real life terms (not boring theoretical paperwork crap) should i not drive a speaker past its xmax???

MunkeyQ wrote: Xmech/Xlim is when the suspension mechanically reaches its limits and is damaged.

.. or when the voice coil slams into the back plate, which is also a thing you would normaly NOT want it to do

If the voicecoil is out of the xmax, its not like you lose the total control, its just that you lose the more control the more you are out of the xmax, what means distortion.
a good example why there is a xlim is the ciare 12sw.
it has a very big true xmax about 11,5mm, but unfortunately xlim is just slightly bigger
the proof is my blown ciare, the voicecoil hit the magnet as i pushed it too far in the wrong enclosure,
now its damaged, but the wire in the coil is still fine -.-

I also think, but i have no proofs, its just my personal opinion, that
some manufactures are not exactly about there xmax specs,
coz some speakers with lower xmax seem to push more air than other speakers with a higher rated xmax,
even if they are in the same type of enclosure with the same tuning.

nice to see not everyone is blasting on about distortion.  going out of xmax does not add distortion from what i have heard in real life situations, using well engineered woofers.  running out of amp headroom makes this distortion, not exceeding xmax.  exceeding xlim will produce distortion.   going 3-5mm over a 9mm xmax still means a cabinet will go lower or louder or both, and i dont think the negative effects are anywhere near what most people go on about.  

When going over Xmax, harmonic distortion increases significantly, no matter what you say. Completely different matter wheter you can hear it or do care about it. Of course you can do that, it doesn't cause any damage to speaker, or at least to well designed speaker. But sound quality does suffer.