It depends if your amp came with a bass BOOST knob or a remote knob. That pic shows a boost knob. For instance sundowns have remote knobs which the easiest way to put it, with the knob all the way up your subs see 100% what your amp gain is set to. When you turn the knob down it lowers the gain accordingly, so you're not using bass boost like a lot of amps have which is what can/does blow subs. Its like a governer if you will, letting you hold back the bass until you want it. The RCA knob is the same as a remote gain knob, the only diff is that with the rca one all the way down there is NO power to the subs, with a factory one (atleast the sundowns i have had) drop it down very low but there is still a minute amount of power going to them.