What Max said, it's about the midrange and un-ported, single/full bandwidth element speakers have a rather unique transient response that is very revealing. Setting vocal/drum/guitar levels in a speaker like this is very effective.
Unlike Max, I use only one speaker in mono. If the stereoplacement rules I might have to reconsider. Gotta try it.
As for real-world reference, what's that today ? A car, iPod headset, laptop cmptr speakers, your hot tub's built in speakers, club PA, airplane headset (mono sometimes), plasma tv speakers, McDonald's happy meal toy playing the Black Eyed Peas in 4 bit resolution..
I dunno, I mix 'til I feel good and trust the mastering guy with the rest.
