Why is my Velodyne DD-18 "blowing up? "

Thx to each of you for your help. I will take it in to a tech right away

If turning down the lever does not work I would take it in to a tech asap, chances are it will be an easy fix now but it may end up being something major if you continue to use it. Plus, it is hard to enjoy listening to your rig when you are worrying about equipment that is not working properly.

The after one hour of listening is one thing that has me concerned.Otherwise,I think lowering the level some may solve it,and help stop possibility of damage to the woofer.Changing the EQ settings also,possibly less of the lowest frequency level like 20hz,to 30 hz.

If the sound is a short crack,like striking some metallic, or other material with a hammer,It could be the woofer bottoming out.What I'm saying is,the voice coil former (where the voice wire is wound),might be hitting metal against metal.If this is whats happening,the end of the former may get bent and scape,or break loose etc.Turning down the volume may solve this problem.It could be the amp running out of power too.I don't know if this would cause what you describe.The voice coil bottoming,of traveling to far sounds similar on all subs.If you changed to a lower frequency setting,that could be causing the sub to work harder(cone traveling further) than before.Check your settings to see if the sub is set higher in level than before,or a frequency setting may have been changed.If all the settings are the same,I don't want to say for sure,that the sub is going bad.If is under warranty,maybe it should be checked out.