Symptoms of damaged drivers / crossovers?

What type of symptoms show that a driver or a crossover is damaged and in need of repair or replacement? - I.e. what type of bad sound indicates that the culprit is the loudspeaker, as opposed to the amplifier or the source?
No DC resistance and a scraping feel/sound when you gently push the cone in and out are the two most common.
Buzzing or distortion is often audible when a driver fails. Swap L & R channels to test speaker versus amp/source.
Thanks. Good idea about the the DC resistance.
If you're measuring across the speaker terminals, only a failed lowest frequency driver will show up as infinite resistance.
Sounds like Frying Bacon!!