blowing my subs

i have 2 12'' Alpine type R's and i keep blowing them. i am pushing each sub with a Kenwood KAC7201 at 4 ohms and the subs handle 500 rms and the amps put out about 470 rms what am i doing wrong??

not quite all the way up but just below where they start to clip

You are: 

1)  Clipping your amplifier badly, sending more than 500w to them, and not moving the driver enough for it to cool properly. 

or

2)  Using a ported enclosure, not clipping your amplifier, but just hitting your sub's mechanical excursion limits...

or

3)  Both.

Read http://www.bcae1.com/ for information on gain setting.  Like another poster said, we need more information to help you.  Are you using a ported enclosure?

the power supply running to the amps is fine i have a volt meter and it is steady at 14.7-8 even when at a stop.  the box size is 1.25 cubic feet sealed which is the recommondation for the subs. the bass boost is off.  the frequency is set to about 55 hz