[PStamler]

It is alleged that even fairly benign speakers such as AR3s would force the
protective circuits to react audibly.

AR3s weren't all that benign. First off, they had unusually low
sensitivity, meaning they needed more voltage than yer average speaker
to produce a given SPL.

Second, trey were nominally 4 ohms, in an era when 8 ohm speakers were
the norm, and they could dip down to 3 ohms at some frequencies,
meaning they also needed a lot of current to produce a given SPL.

Finally, it was the beginning of the era when rock music was taken
seriously by audio fans, who had mostly listened to classical, jazz
and Persuasive Percussion. In his excellent book on solid-state power
amp design, Bob Cordell discusses how repeated low-frequency signals
(read: kickdrum hits) can interact with the back-EMF from an
underdamped woofer (the AR speakers had a Qtc of 1.1, meaning they
were mildly underdamped) to make the speaker draw a good deal more
current than its nominal impedance rating would imply. The AR3s, when
hit by kickdrum-type signals, demanded current levels corresponding to
an effective load impedance of 1-1.5 ohms.

Most of the craze for super-powered amplifiers in the 1970s (think
Phase Linear, Ampzilla, etc.) was fueled by the desire to drive AR-
type speakers to high volumes on rock music. It took a while for folks
to realize that current delivery mattered more than raw power, and
that an amp which voltage-clipped at, say, 100W (but with ample
current capability) could do as well as a "700W" amplifier. I have
such an amp (from Parasound) in the other room, and it will drive just
about anything happily. Doesn't burn up, either.

Peace,
Paul