According to the
Specs from Klipsch these speakers are very efficient at 98dB @ 2.83V / 1m. (About one watt.) That means they don't need a much power to get really Loud.
I'm guessing that
@Petrolhead is driving them too hard, and is into Clipping and may have damaged them if the duration was too long. Get a Sound Meter and see what the level is 3 feet away from the speaker just as it starts to distort. If you don't have a meter, use a free App on a Cell phone. Please advise the level you obtain and we can go from there.