That's one of the Grateful Dead "
wall of sound" rigs circa 1973-74. It is important to understand that the concept was essentially a separate
system for each source (in fact the
bass was treated as four sources, one per string) and every
speaker reproduced only one source. Being behind the band the
system also served as the
monitor system, letting the band hear the same mix the audience heard, in fact mixing was from on
stage.
Feedback was avoided by using a dual 'differential' mic approach where each vocal mic had a second identical mic attached to it that was wired out of
polarity so that when the two were summed most of the
system content was cancelled out. A good summary of the
system is posted here,
http://dozin.com/wallofsound/index.html
Before dismissing this
system, realize that not only was this
system very technically advanced at the time, but the concept of separating sources is also gaining new popularity. For the last Red Hot Chili Peppers tour, Dave Rat used a dual
line array configuration that allowed assigning sources to either
array, thus reducing the 'load' each
array carried and providing increased clarity. For example, you're not asking a
speaker or
driver reproducing the vocals to at the same time reproduce the impact of a snare or crash and vice versa. So sometimes the idea that everything old is new again can also apply to technology.