EQ app for subs? Subwoofer damage?

I know this is a car auido forum but this question pertains to a recent shelf system i have purchased. I have an app on my iphone called equalizer. It allows you to boost the bass up to 14db. Right when i recieved the shelf system of course i plug everything in, set the bass boost up to 14db and start banging the subs loud as phuk. I know that all subs have a certian hz range and youre not supposed to go outside of those boundries, but i have no clue what the range is for my subs. I started messing with different frequency, and found at about 60hz it was hitting the low notes very well, whenever i went below 60hz it didnt sound as loud so i decided to stick with 60hz. I didnt do any research on what hz range to use, db boost, etc. like i should have. So here we are a few days later and im noticing the subs seem to sound a bit sloppier compared to when i first got them, there is a shaking type noise within the subwoofers that i dont think was there before. Then again maybe nothing has changed and im just paranoid. Did i goof? Perhaps set the bass too high, wrong hz range or something like that? Are eq apps for subs a bad idea? Have i caused permanent damage to my subs? Any help is appriciated. The shelf system i purchased is called the Sony LBT-GPX55 if that helps.