Help! Strange subwoofer balance issue.

[4 door 330]

Well just got new subs, speakers, and 2 amps installed.

Speakers and amp work perfectly but I'm having trouble with the subwoofer.

I'm using the rear L + R Inputs to feed the subwoofer amp so that I can use the fader to control the subwoofer volume.

The problem is that when the balance is in the center the sub doesn't work. When I balance the HU(stock) Right or Left the sub works great, but then my speakers are balanced to one side only.

Have I wired something incorrectly?

The amp is an Alpine MRP-M500 with L+R Rear Inputs run to L + - and R + - on the amplifier connector. I am using the speaker level inputs, not the RCA plugs, and I've already called Alpine to verify they accept a balanced-differential signal. I'm using an Alpine MRP-F300 for the speakers and they are working correctly.

[HELLAS NC]

Might be just a switched positive and negative wire on the feed line to the sub. Since the sine waves cancel each other out when you got the (+) and (-) turned around, you will lose the sound.

[4 door 330]

That make sense, I'll check it when I get back to the car.

Do you mean on the input or the output side, or would it even make a difference?

[HELLAS NC]

That make sense, I'll check it when I get back to the car.

Do you mean on the input or the output side, or would it even make a difference?

First check the outputs since its the quickest. If that is fine, you can either:1)Open up the HU and make sure its correct from the HU to the amp. Be very sure that the wiring can be identified (+) and (-).
or 2) See if you can correct the problem by switching the output wires (Go for this one first)

[4 door 330]

Gotcha, yeah everything should be correct behind the HU because its never been touched, everything was done at the amp connector.

Edit: That completely fixed the problem. One input wire at the amp connector was backwards!

It produces much more volume than I expected for a single 10". Very Happy. Thanks for the tip.

-Dylan