I posted a question with no replies earlier, but maybe it was too specific.

I'm buying an amp that has an external speaker jack, and was wondering how this works? Does it cut out the internal speaker when you use it, or does it combine the two?

Depends on the amp, I've seen both. With most amps, you just have jacks for different impedances on the back and the internal speaker is plugged into one of them, so you can use it or unplug it however you wish. There's a couple of things you have to keep in mind when combining speakers in this scenario, but that's probably not the info you're looking for here.

Anyway, consult the manual/manufaturer's site for the answer.
Quote by ethan_hanus
Depends on the amp, some amps it cuts out the internal speaker, other amps it runs them in line with each other. Gotta read the manual of that particular amp to know for sure.

this ^, what amp do you have?