Mono was the one and only way to listen to music and movies for decades.
But it's not ancient history. Mono's on something of a comeback, and thewill be offered in an all-mono box in September. You can listen to mono over just one speaker, or with two or more speakers. But mono at its purest is a single-speaker deal.
A fringe segment of the audiophile community still buys mono phono cartridges to get the best sound out of mono LPs. Over at BuyMeGetMe they're listening to an all out single speaker mono system with a mighty 175-pound, all-American Klipschorn speaker ($3,999).
Yes, you could use any speaker, but since you're paying half the price of a pair of speakers, you might as well get a nice one. The Klipschorn was originally introduced some 60 years ago. It's still an amazing speaker.