The world probably isn’t in desperate need of a bunch of new kinds of musical instrument, but sometimes necessity is the enemy of invention, and the participants in a Massachusetts residency sponsored by the Bang On A Can folks aren’t letting a lack of public clamor for their work discourage them. Among the new instruments now on display at Mass MOCA is the whirlycopter, which looks like “a cross between a helicopter and an electric chair,” yet sounds “like an Orthodox choir, chanting somewhere over in the next valley.” The idea, of course, is to make new music more accessible and, dare we say it, fun, as well as to free up the musical imaginations of the participants.