This gig was just too weird. Back in the early days, bands didn't know who they were dealing with when they organized a tour. Some local promoters thought that when the band asked for a PA system, that's all they needed, a public address system to talk to the audience.
A cheap promoter looked at Massey Hall, saw two very small PA boxes on the wall of the auditorium and assumed that's a PA system and fulfilled the band's requirements.
The band arrived with 2,000 watts of stage amps and was expected to sing through 50 watts of PA system!
Being the pros that they were, Cream went on stage, and Jack Bruce announced though a very faint microphone the futility of this gig regarding vocals.
They then proceeded to play the entire set without anyone hearing a single voice.
Even without microphones on the drums, Ginger Baker could keep up with the amplified power of Clapton and Bruce. They were loud, they were exquisite, and they didn't do an encore.