I bought a used 9851 Alpine headunit which runs the front 6.5 coax 2-way speakers + amp in the back with 2 ED 6" subs in sails (amp is hooked up to the subwoofer RCA connections on the deck).

I've read enough info on cut outs, what ranges and crossovers to get the idea in theory. In reality it doesn't work - I can't seem to isolate bass notes from the front speakers.

Tremble at the deck is set at 7.5Khz, sub output at 100Hz. Here is the problem: if I set bass at 0 on 9851, the fronts sound the way they should with no bass there and great highs. However, the rear subs don't produce anything. On 9851 the subwoofer setting is at the maximum. If I increase the bass volume, I get nice sound out of sail subs + the front speakers (wtf?). The amp is set at low pass, the range is at 80-100Hz (hard to tell - it is a rotary ****).

The reason I bought that head unit is that it could do the cross over function.

What am I doing wrong? Does anyone have the similar Alpine head unit/setup and can recommend what settings I should input? I'd appreciate any advice.

Thanks!