I have a DD 12 that I purchased from a friend. It seems to play fine but it gets warm / hot VERY quickly on low power. It doesn't have a model number. Just silver top and back plates with a double stacked magnet in a magnet boot. Red DD letters on the dustcap. I assume its a 4 ohm coil as there are only 1 set of direct leads. Its currently in a sealed box. What kind of problem / issue am I facing? I've given it maybe 200 rms.