The Stack Exchange team is open to the possibility of sponsoring conventions as a way of promoting a Stack Exchange site (see A Recipe to Promote your Site). I'd like to compose a list of possible conventions/trade shows/festivals who's attendees would fit the audio.se target audience.
Fort Wayne, Indiana
I've attended the Sweetwater GearFest for the last couple of years. They draw a large number of musicians, engineers, and producers ranging from hobbyists to pros. They have a place for vendors and sponsors to set up booths.