I popped onto a marvelous piece of acappella music (https://www.facebook.com/Musicianary/videos/2022499804432042/) reading through Facebook.  As I am listening, I can hear the bass singing away, comfortably making a foundation for the other three parts. 

I moved my computer away from the speaker system that I use to give full-bodied sound for my listening pleasure.  I played the song again.  The small speakers could not take the extended vocal range.  I just heard a trio singing.

Much vocal music that we listen to today is only in the higher frequencies.  Trio parts are featured.  Seldom do you hear a good bass voice. 

Did the transition to three part harmony come because of poor speakers on computers, or . . . ??