I got a radio shack spl meter, and set my speakers up at 75db. i set my sub at 85 dbs. reading on the net, it says about 3 dbs over the rest of the speakers. as it is 85 seems to low for me. is this a matter of preference or a must to prevent damage to the sub? my sub out is at 0db and my sub volume is about a 1/4 way up.