The LOC is always hooked up to the amp, not the speaker. A LOC takes high level speaker outputs (wires) and turns them into low level outputs (RCA connectors). They are only necessary when you can't get the low level outputs from the head unit as with our car. There are many amps/powered subs that have high level inputs but I've found the quality of those inputs is not so good. Also, some LOC's have trigger/remote turn-on capabilities and some do not. If your amp requires this wire, you need a LOC that supplies it. That was the case with my install.