imports4life

So today i hooked up an alpine type r sub to the stock headunit with a 2channel LOC(line out converter). I took both(2channels) the + and - speakers wires on the LOC and wired them to one side of the rear speaker instead of both the rear speakers. On the LOC it has gain adjustments on it but idk how to set the gains properly on the LOC so i just let it in its default setting for now. Does anyone know the correct way to set the gains on a LOC. also in my amp kit, the rca wires are blue and black instead of the traditional red and white. Is there a wrong way to hook up rca cables? i took a guess and said the blue RCA was for the red rca input and the black one was for the white rca. Everything works however now i have to turn up the volume up to like 40 instead of 30 like i usually had it to achieve the same loudness from the stock speakers. Has anyone else had this problem? Any ideas on how i could fix this? I'm hoping i could just turn the gain up on the LOC and it will fix it but i dont want to send a clipping signal to my amp if i turn the gain up to much so idk what to do. Any help/advise is appreciated..