I have a pair of old Akai speakers (SW-121A) that I'm running through an amp. One of the speakers makes loud popping noises. I've tried switching the speakers, so I know it's not the amp, and I've tried changing the speaker wire. The popping sound can happen whether or not there is any sound coming through (like if I forget to turn the amp off, sometimes it will surprise me with popping sounds). What could the problem be?
You are sure it's not the amp?
When you exchanged the input to the speakers the same one popped?
Passive speakers can add distortions to the input but don't generate their own noises when there is no input.
A bad component in the crossover of the speaker could be putting the amp in distress.
Usually a popping noise when there is sound is because the woofer is being driven too hard or the speaker surround is deteriorated enough for the woofer to no longer move linearly.