The audio jack of my 14-year-old computer stopped working. I bought a Packed Party ‘Turn it up!’ speaker for $10 on clearance at Mallwart. I had never gotten a bluetooth device to work and usually listen to people talking so don't need high fidelity or stereo so bought only one. When I finally got it to work (problems all mine) I bought another so I could listen in another room without turning up the volume. They pair with each other so a single bluetooth channel can power 2 speakers. I was pleasantly surprised that they separate stereo channels when there are 2.

I'm surprised.

I thought a lot of recordings had both tracks on both left and right, so if you lost one earphone you wouldn't just hear half the band/orchestra/whatever.

That's why I take offerings of polychannel sound with a grain of salt.

I listen to talk most of the time, so if it's stereo it doesn't matter. With music it can be significant. After stereo was invented (the '50s?) there were stereo demonstration albums that did all sorts of tricks. Listening on headphones could be a real experience. Dramas would have characters in separate channels.

I did a tv techie's course in 1977, and they instructed us on stuff like the ideal room positioning for a person listening to stereo. They even had 'bad' and 'good' videos with John Cleese as your serviceman(!). The 'good serviceman' sold a new hi-fi to some nut on the basis that it was so low-noise, you could hear the Orchestra's wind section breathing in! . Despite all that, I was a reasonably efficient tv techie coming out. Different times.

Shmup games need stereo. Move your spaceship to the left or right side of the screen, and you can hear it move.

You can get a stereo effect without depriving either earphone of sound. If you delay a sound by a few milliseconds on one side vs the other your ears/brain will interpret it as being located on the other side. But if you listen to either earphone you can still hear everything. It's pretty neat!

https://en.wikipedia.org/wiki/Precedence_effect

That's true - the ear is very phase sensitive. It has to be. What fascinates me is that we can locate sound in 3D, e.g. behind and above me to my left. You should need a minimum of three 3 ears to work that out, but we manage with two.