Here is a summary of the book that I mentioned yesterday, it is called ‘Earth Sound, Earth Signal‘. This might be of interest as it tells the story of how the invention of the telephone led to the discovery of ‘natural’ radio (as well as an understanding of telephone and telegraph technology, and a lot of other fascinating examples of energy transmission). This could be suggestive in terms of thinking about how the bridge might receive and transmit sound. Another review here.
It is a pretty dense book and would take a bit of getting through but there are some technical accounts that could be useful. If it is not in the library I can bring my copy to New York for you to look over.