so my bass amp blew out or something and it sounds distorted. is the problem the speaker or could it be something else? and if it's the speaker then should I replace it? and what kind of speaker should I replace it with. the amp is old, peavey tko 80 and looks like a 12 inch sub.
What exactly are all the symptoms? Just sounding distorted can be a number of issues.

Try different instruments. Wiggle the cable at the input jack of the amp. I've repaired tons of amps that just had a broken solder joint at the input jack.

If you think it is the speaker, find a speaker known to be working (doesn't have to be bass speaker) and try the amp through that. Just don't turn the volume up very much and use higher notes if it isn't a bass speaker.
well I connected another amp to it. the pre amp out to the other amps input and it sounds fine, not distorted, so does that mean it is the speaker?
Nope. That means that the problem is somewhere after the preamp. It very well could be the speaker, but you'll have to try that amp into a different speaker or a different amp into that speaker.

You seem pretty dead-set on a bad speaker. You very well could be correct, but you need to test it out before you spend money on a new one.