A horn loaded installation shell not be mono, period!
I have observed this phenomenon for years and I insist that it is impossible to make a properly performing horn-loaded playback. I have no explanation for it but I take it a rule: the monophonic horn installations produce honk.
There are many different reasons for honk in horns: wrong horns, too low crossover points, and many others. They all perfectly deflectable if person know what he is doing but there is no remedy for mono honk in horns. Take ANY perfectly performing stereo horn installation and disconnect one channel. It would be irrelevant if you feed the active channel with right/left ingredient of the signal or with mixed signal or with a full mono signal, you ALWAYS get a degree of honk when you have a signal channel working. Activating another channel, even if you play mono from two channels will eliminate any presents of honk (if your horns did not have I to begin with).
So, say no to mono horn ideas: it is imposable to make them honk-free. At least I never ever was able to see any horn systems that did not honk with one channel, although I have seen/heard many that were honk-free in stereo version and then picked honk when they were used as single channels mono systems…
Romy the caT
"I wish I could score everything for horns." - Richard Wagner. "Our writing equipment takes part in the forming of our thoughts." - Friedrich Nietzsche