So here I am testing an amp which the buyer complained that one channel keeps going mute until the he knocks the amp chassis. Even when I personally use every single piece of equipment right before the transaction, shyt happens.
The left channel has a DC offset of 60mV, if my Minipa multimeter still can be trusted - that reminds me, I need to buy a new multimeter. 60mV is on the high side, but I've seen amps with 100mV and the speakers are fine.
It's usually the tweeters that die from anything - small excursion and low heat dissipation ability means it's the one that die first.
But then I realized, to kill a speaker with DC, the DC has to reach the speaker first. Tweeters have a low pass filter which usually involves a blocking capacitor, so no DC will ever reach the tweeter.
So that means I only have to worry about the woofer. And at 60mV the amount of heat is so low compared to the amount of heat the speaker has to dissipate at full load (speakers are very inefficient devices) it doesn't matter. (You can do the maths.)
Still, I'm leaving my multimeter hooked up to the speaker terminals (in case it decides to rise to 100mV or what). The good part about bi-wireable speakers is that the second pair of connectors can be use for anything useful.