Only 6 extra locations today (bringing the grand total to 70) because I had to spend my time making this:

I mainly explored the area around Zou-no-hana Park: it was very quiet, as I expected, but I couldn’t hear a pin drop because the floor surface was very rough. I am guessing that it dissipates the impact more than a smooth surface does, and so less energy is transferred as sound. However, it did work on those same paving stones in one corner of the park, near a sign, and I wonder if that was to do with the sign reflecting the sound?