ADC Speakers?

I just bought a CD copy of the Telarc "1812" recording. Having had the
LP version of this recording, I always wondered what kind of speakers
they had monitoring this one, as there are cannon shots as part of the
recording. The booklet says ADC speakers, what are they? Can they
actually reproduce these caccons at anything like realistic levels?

ref: http://classicalcdreview.com/1812.htm

Per.