Thanks, everyone, for all the responses that really helped me
understand what was going on and also encouraging me to write and
complain. I'm doing that shortly, and as suggested will keep it
non-technical, focusing on the high level.

It surprised me that one response was from a fellow who is actually
familiar with the Beckman. What are the chances...?

But that made me think that I should have included this information in
my original post about the Beckman from
http://fob.caltech.edu/tech-info/beckman.shtml
so folks would have better understood the situation. On the left of the
page there is a link for the technically inclined that give details of
the sound equipment in the auditorium:

Building Shape: Circular with conical shaped roof
Seating Capacity: 1150 (850 main floor, 300 balcony)
Dimensions: 60 feet high, 120 feet in diameter

So I'm sure that the Beckman is indeed an acoustic nightmare, but the
fact remains that the sound was just fine to my old ears when it was
moderate, but pretty horrid when it was breaking up every few seconds
because the tech had the level too high.

And, yes, the Persuasions is a classic acapello vocal group, so no
drums. I suppose that seriously dates me.

But I should tell you about the time my then-19 daughter took me to a
Steve Vai concert in Boston in the club district. I had this mental
image going in of a lone acoustical guitarist sitting on a stool in
sort of a coffee house environment wry grin....

Thanks again for everyones' kind assistance here, and I'll let you know
if anything ever comes of the complaint.

-Harry