I have recently bought a new jl 12w3v3-4 which is rated @ 300 watt rms by jl. People have told me that jl under rates their products. Could someone tell me if they know how under rated they actually are?

 

My JL manual has a nice little power chart that shows minimum, optimal maximun and warantee void.
Yes, you can run them in the warantee void range and take the chance of frying them.
(WARRANTY VOID):
We do not recommend operating woofers at
this level of power. In this zone, there is a very high
probability that the driver will fail due to excessive
heat and/or mechanical stress.
Subwoofer drivers operated at these levels of
power are NOT covered under warranty.