Whoa, if you are really running 2 ohm load to that subwoofer with the amp bridged you probably haven't pushed it pretty hard. It isn't rated for anything under 8.

Crown's do a great job of protecting themselves, if you give them too little load they will just mute (and the IOC lights come on) on any of the older models (I have a DC300 Series II in my studio). The newer ones continue playing, but sound distorted as heck once you get below 1 ohm.

I would ask if you were sure they were parallel, but someone with that rack of amps should know the difference between parallel and series.

I just discovered Crown has the service manuals and schematics for all the discontinued amps for download on their site. That rocks.

gonk:

I hear 10 dB tossed around in some circles as well. I have a degree in sound design and in every class I have attended or taught, we have used 6 dB as the half/double. That matches up exactly to what you see on equipment. It is possible that if you take a measurement of actual air pressure coming off a cone it may line up more with 10dB being double, but that wouldn't correlate to what you see on your 990 display.

3 dB is considered the minimum amount of volume change to be noticed by most people with average hearing, although in my personal experience a great many people can hear smaller changes than that, even those often not discerning about what they are hearing (not mentioning my wife specifically....). This is a rule of thumb and depends on relative factors.