takin from soundpressure forum....
Well, the difference was always in the cone and the suspension. The 9500 uses a standard paper cone. The 9900 used a very strong, very light composite cone. The motors are the same. The two subs are so similar that DD stopped calling a 9900 a 9900, and started calling it a 9500 with composite cone upgrade.
The composite cone is lighter and stronger. Because of this it is typically a little louder, and will handle more power before breaking. How much louder really depends on the setup. How much more power does also. If a setup runs into a thermal barrier before breaking a standard 9500 cone, then the composite cone really isn't going to help a whole lot, because it really doesn't cool any better. If you can fold a standard cone, before running into a thermal issue, then the composite cone is going to help........a lot...for the power handling. They are probably the strongest cone used on any woofer. Plus they are dead sexy.