Mr Red brings up an interesting debate, in so far as, by strict dictionary definition, obviously an amplified "acoustic night" open mic is of course nothing of the sort...nonetheless given the nature of the venues they tend to be held in; without decent amplification most of the performers would be completely inaudible over all the pub chatter. And these nights (the good ones anyway) do provide an invaluable platform for those (normally acoustic, and often folk-ish) artists not doing paid gigs on a nightly basis whether by choice or otherwise.