Full Range Drivers

For anyone who is desirous of that coherence thing, I can recommend the horns I use. They are, of course, very efficient and they are utterly seamless throughout a very broad operating range. They are quite directional with only a 40 degree dispersion pattern, you need a woofer, and you need to sit back 12 feet or more. Because they are very directional, room treatments are less necessary. My room is 15 by 22 and they work well but I always have a sense that they would be even better in a larger space. Oh, and did I mention, they are extremely dynamic and effortless sounding?

By one set of parameters your telephone is a full range driver. If you are looking for 20 to 20K range, you will not find a driver that can do it.
I use a horn with a compression driver that extends from 400 Hz. to 14Khz. Below that I have a 15 inch woofer which meets the horn at 400 and extends just below 50 Hz. Most guys on this forum would consider that unacceptably limited. I find that it covers most of the musical spectrum. At my age, high frequencies go to waste. The woofer delivers a sensuous, relaxed and accurate bass response so I'm happy.
What are you trying to learn? The advantage of a full range is no crossover. The disadvantage is compromised extension. Everything involves trade-offs and attendant choices.