In my opinion (without knowing too much about how those old hydros worked), the sound you get from the speaker/headphones is an electric current. It will be louder (more current/voltage) when it's closer, and less when it's further away. Does that sound plausible?
If so, I wonder why they didn't match the hydrophones with a pair of calibrated volt meters, going of known volume levels for near/far away merchants and warships.
|