[konafocuswrc]

looks like you wired sub to rear speaker that is why you are getting all range of sound..
letting you klnow that speakers are capable of playing 20~20k frequency(audible range)but there is no reason to run mid-high range through sub..
that is why you need to get LOC.

you do need LOC, that is when adding sub to factory unit or to get a most sound out of it, using LOC is better than using the one from headunit(sub out)..
since you are using factory hu, get LOC, t-tap(solder them) to rear speaker wires to LOC and and run RCA from LOC to amp..




low filter is not neccesary..

LOC is all you need