What does it mean when people say good "clean" power

[CHEMMINS 10+ year member]

Thing with a dmm is you can be leaving power on the table.

 

[trumpet 5,000+ posts]

The bigger question is will you hear a difference between 600W RMS and 1,000W RMS? You'll run into power compression faster when you exceed the RMS power rating, which means the voice coil will run hotter. More heat = more risk of a blown woofer. Is it worth the bragging rights to say you run 1 kW rather than 600W? Yes, a good quality sub it will take the extra power, but it's not a large difference in output.