[arjf]

32.7 Hz is C1, lowest C on a standard piano (A440 tuning).

No inherent limitation of the technique, the resonators can be tuned to much lower frequencies. But indeed you‘ll need a better mic than the iphone’s to get frequencies below 50Hz iirc… too bad - the watermelon ripeness checker could be a really cool app :-)

[jmpman]

There apparently are a bunch of watermelon ripeness checker apps. None get great reviews. Maybe you can get it to work. I only learned about this phenomenon while walking through Costco trying to pick out a good watermelon and asked Claude to explain what characteristics are most strongly correlated with Brix (sugar) levels. This sound check had the highest correlation.

Let me know if you update your app or make a watermelon version.

[jmpman]

I just tried a watermelon app called MelonAid. It predicted my melon was ripe to overripe. Cutting it up, my son seems to agree with the assessment.