Recently I had one of my LST's woofer stopped sounding with a strange crack at moderate listening level, no smoke or other signs of the coil being fried. The cone moved freely. I removed the woofer, measured DC resistance, it was 2.8 Ohm. The battery test showed that the cone protruded when plus connected to plus, but did not retract when plus was connected to "minus". After some time of thinking, I figured that the most likely reason for the woofer's behaviour, was a cracked woofer coil. TT con