I was just curious about this. I heard about it but I didn't know how you could find the mechanical limit of a woofer.

When the coil smacks the back plate or the spiders smack the top plate / basket or the cone smacks the spider landing is when you hit the mechanical limit..

You do this by either free airing something with power, or playing below tuning frequency of a ported enclosure with no subsonic filter.

put it in the box, power it up, and see if it bottoms out. the box size affects the mechanical power handling, generally a smaller box lets the sub handle more power (doesnt change thermal power handling though, so even if its in a small box and you can feed it a shitload of power without bottoming out, you could still smoke the coil/s from too much power)

I wouldn't recommend you actually drive a subwoofer to it's mechanical limits, however...

put it in the box, power it up, and see if it bottoms out. the box size affects the mechanical power handling, generally a smaller box lets the sub handle more power (doesnt change thermal power handling though, so even if its in a small box and you can feed it a shitload of power without bottoming out, you could still smoke the coil/s from too much power)

Yeah, I was just curious because I was browsing on the DD Audio website and noticed that the Z didn't really have any specs and didn't really even say anything about recommended enclosure volume.