speakers aren’t limited to a sample rate or necessarily 20khz. I can say just about all tweeters DO NOT have a low pass on them to prevent them from producing anything above 20khz. Tweaters are however limited to their audiable specturm that they are capable of producing, that is just a limitation due to their design, they will roll off and usually have a nasty response even aboe 18khz. To get clean highs above 18khz you would need something like a super tweeter which is designed to play fairly cleanly above 20khz, some can go up to 30khz fairly cleanly.
There will also be limitation in the amplifier design, definitly on the low end (below 10hz), and possibly on the high end.
Just because a speaker might be rated at 20hz-20khz doesn’t mean that they won’t produce anything audiable above or below that, this is simply the limitations of the human ear, and what most would desire to hear. Most of us that are into hard core home/car audio WANT to FEEL the basssss below 20hz