Suppose I wanted to throw a silent rave party some day, and said event would be open to anyone to attend provided they bring their own headphones and receiver.
What would be the best form of legal broadcast such that 1) the event could happen in a small park, 2) the required receiver is relatively easy to obtain, 3) the broadcast is heard relatively synchronously, and 4) doesn't require the attendees have a radio license, and 5) doesn't require me to have an expensive license?