Say I am using a 500 watt RMS amp with an 8 ohm cab. If I am not blasing the thing at concert or gig level volume but playing at home, am I still using the 500 watts (RMS) all the time? Or am I using a fraction of the watts since the volume is low? Is there a way to figure out how many watts I am using at a particular volume and impedance. Thanks for all information in advance.