I was surprised at how loud a friend played his system. He's already blown one formerly thought of as indistructable sub and is working on blowing the rest of his equipment.More than likely this was the insulation heating up on the voice coil. No harm done, likely, but "pretty hard" can mean different things to different people.
Running the subwoofer calibration level 8 dB hot and looping War Of The Worlds 'Pods Emerging 'ad nauseum at Master Volume 0.0, or playing 20 Hz sine waves until the window panes start to flex, are examples of overdriving/abusing the subwoofer. Not that you did that - these are just examples of customer enthusiasm gone awry. Trust me we've seen it all in Tech Support. :rolleyesno:
The Ultra woofer is rugged, but it's not indestructible - calibrate the subwoofer flat/even with the speakers and keep the master volume at a sane/reasonable level, and your Ultra will last many years without a problem.