also, clipping.
this is a clipped sinewave.
basically a square wave, but the top of the wave SHOULD be there. that top thats clipped is the 'cieling' that the amp can produce. the spikes you see are distortion, and can jump way higher than this image shows (overpowering subs)
now this is not what prolly caused your spiders to rip, as clipping is usually a thermal monstor and melts coils. but the overpowering + large box, could have lead to mechanical failure on the spiders.
the 'flat' part of that wave essentially makes the cone stop for miliseconds. and this equals "DC" current. the problem with this is, after enough time, it will heat up the coil because the vertical movement of the cone is what cools the voice coil down. when that movement stops, or is not efficent enough to cool the coil it will eventually melt.
but thats just to explain that now.