Activate motor on speaker sound using speaker wire
You could build a simple AC signal voltage detection circuit like this one that I designed many years ago: -



V2 is the audio line but you should be able to get away with a small current transformer with one of the speaker wires inserted through it.

C2 gets rapidly charged when a signal is detected and by making C2 bigger (say) 10 uF you can keep the LED lit for several seconds. I don't know what interface circuit you require so this is about as much help as I can give right now.