Calculation of power required by driver

Is there a simple way of calculating power required by a driver? I am interested particularly in a 89dB sensative midbass that will be playing from 100Hz to 2500Hz. I know that there is a lot of musical information in this reigon, but the amounts of excusion required are small. I will be playing at max 105dB, but that is in-room with both speakers going, in a small room. I know that there is no hard and fast rule for this, but I want to know how much heat my amp will produce to determine if my heatsinks are large enough.

Thanks,
Paul Hilgeman