[The Evil Dead] Why did Professor Knowby record himself uttering the evil incantation to summon the Kandarian Demon?

In the film The Evil Dead, Ash and his friends play a random tape from the cellar that plays the audio of a professor named Dr Knowby talking about his experience finding the Necronomicon and its history. Then eventually, he says a bunch of evil incantations that summom the Kandarion Demon and turns Bruce Campbell's friends into DeaditesWhy would Professor Knowby record himself saying the incantations if it would cause summoning a demon? IIRC, it was already in the Necronomicon so why risk recording yourself saying it and cause danger for people like a group of dumbass teens to play??