What are the specs of a full range speaker?

You probably mean a "speaker system", judging by how a number here are responding in a way that seems to equate "speaker" with "driver". In audiophile circles it is always good to deny whatever has been sound thinking for many years in favour of arguments that are tenuous at best, and pure folly at worst. I think that the most often agreed upon idea is that a “full-range” speaker system should ideally cover 20 Hz to 20 kHz, but that if it falls short on the low end by ten or twelve Hz it can still be considered as such. On the bottom end I don't think anyone should fret if it doesn't go down all the way to that point as anything around 30 is plenty of bass. The absolute bottom is more felt than heard and integration into the room is not always obvious. In the treble range what is mind-boggling is that many believe that the response should go way over 20 kHz when most adults can barely hear beyond twelve/fourteen kHz. All this will never stop subjective audiophiles from arguing all manner of things until they are blue in the face.

Pbb said:

"In the treble range what is mind-boggling is that many believe that the response should go way over 20 kHz when most adults can barely hear beyond twelve/fourteen kHz."

You're the first person I've EVER heard mention this online, even though I've silently wondered about it for years. I remember from the old days when "high bias" cassette tapes listed a frequency response extending up to about 16,000 hertz, and an audiogram I had a few years ago showed a slight rolloff at 12,000 hertz. They normally only tested to 8,000 hertz, but had the capability to test up to 12,000, which I requested and they did. Twelve thousand hertz is REALLY a high frequency, yet we audiophiles classically consider 20-20,000 to be "full range," and then sometimes go even further by purchasing super tweeters (out to 50,000 maybe?) and subwoofers (some going down to under 10 hertz).

I can say unequivocally that the Rel Storm 3 makes a big positive difference in my system. I cannot comment on supertweeters, other than to speculate that they may be useful in repelling insects and rodents, both of which have higher frequency hearing capabilities than do humans, even audiophile humans.

So.....I agree with the generally accepted 20-20,000 as defining "full range," but like Pbb I wonder if it's overkill on the high end.

If low frequencies that serve to merely shake the wall add to one's experience listening to music, then why is it unreasonable to accept that high, inaudible frequencies add to the experience as well? The fact that humans can not hear frequencies above a certain frequency does not mean humans do not experience these frequencies in other ways. Does it?

I don't believe there is a formal definition of "full range speaker." As such, it pretty much means whatever the person using it wants it to mean.

At the least demanding end of the spectrum it could simply refer to any speaker system that is designed to be used by itself (i.e., not specifically made to be used with a subwoofer, etc.) Such a definition would include speakers with limited bass below 50 or 60 Hz.

At the far end, one can insist that a "full range" system needs to solidly go down to 30 Hz or below.

A similar argument can be made at the high end. As such, I consider the term fairly meaningless.

Ultra-low frequencies have the power to shake the walls, and physically
pressurize the room. It adds to the visceral experience of say, a really big
diameter pipe.

High frequencies do none of this. Their reported presence in an audio system
just feeds into psychosomatic twitching of true believer's brain.