It is amazing how far sound systems have come in the 40+ year life of this band.
To illustrate a point, I was at the McCartney show at Citifield a couple of Fridays ago, and Sir Paul joked that he had played at this venue before (well, not exactly, the Beatles played Shea, which was next door, and is a parking lot now). He remarked how the Beatles couldn't hear anything - the sound was channeled thru the baseball PA system! Imagine that!
The sound at Citifield was pretty good for an outdoor concert, and you know the band was able to hear each other.
I had heard about the Beatles at Shea and the bad sound and all the girls screaming; the band was so tight in those days that even though they couldn't hear each other, they had been playing those songs every night for several years, and if you listen to the Beatles at Shea today, they actually were a pretty darn good live group!