I recently purchased 2 alipne r2 12wd4 subs and Installed them into a box I already had. They were doing great then on my way home from work all of a sudden they "cut power" and sounded like the volume was turned down on them. They still produce bass just seems to be turned down. I'm running them on a phoenix gold 1200.1 wired down to 1 ohm final. Is there a way do diagnose if I have a bad wire or rca without running new ones? I'm also running 2 jl 10's but on separate amps and they work fine. I have y connectors between all 4 subs to to the head unit.
Just use the RCAs of the other amp with the JLs and see how it goes.
If its still the same you need to focus on the amp, check the alpine subs with a multimeter, if impedance is normal check with the multimeter the amp terminals voltages, if those are OK you have a faulty amp.