I've spent a bit of time trying to figure this one out, but I don't know what I'm doing. The rear deck subwoofers in my car are broken, making everything have no bass and sound quieter than it should. So far, I've verified that the speakers themselves work just fine with a multimeter. Then, I found that the speakers are connected to a wire going into this small black plastic box with a TDK logo imprinted on it. I have no idea what this box is or whether it's the culprit, but there are other wires coming out of it that leads somewhere I can't see, behind the carpet on the walls of the trunk. Does anyone know whether this black box would contribute to my problem? What do I have to replace to make the audio system work?