....Wheatstone also describes resonant chambers in his patents (no formula there, of course !).
The only resonant chambers, that I'm aware of, that are discussed in Wheatstone's patents relating to free reeds involve large pipes, which would be more convenient for reed organs and other, relatively large, console type instruments. Associating resonant chambers with reed mounting cavities in small, hand held instruments, however, is another issue. If you can confirm that Wheatstone has discussed the latter in patents, I would much appreciate it if you would supply the reference.