Yes, they can. Adams suggestion of the Radio Shack fan is another option. However,
DO NOT hook the fan directly to the remote wire (blue) of the head unit. 90% chance it'll cause interference & you'll hear the humm of the electric motor at low volume comming out of the speakers. 10% Chance of smoking the output from the head unit & now everything is broken
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The fan should have its own 12v supply wire from the battery, not jumpered from the amp. Using a Bosch style relay, tripped by the head unit (blue) wire, the fan(s) are electrically isolated. I've read some installers have needed to physically move the fan away from the amp and build a duct to move the air across the heatsinks because of radiant interference from the magnetic fields of the motor.
I'm making it sound worse than it is... just be smart about where and how you install it. Cheers,
