I have now swapped the speaker sockets round and plugged the internal jack and extension cable jack in opposite sockets, and the 1x15 still leaps into the air with a loud pop accompanying
What i didnt notice before, presumably because the four 10" drivers are so much smaller, is that they also jump, obviously its no where near as much as the 1x15 and the loud pop is not there.
Also, i tried switching off and then back on again in a few seconds, and this really lessens the speaker jump.
So what is happening there ? I leave it over night and the speakers all jump forward, the 1x15 a lot more than the 4x10, and the 1x15 also pops loudly, where the 4x10 do not
Is there some build up overnight that discharges when turning the amp on ?