Can you deduce the quality of watermelons by tapping on them?

Question

It is believed that by tapping on a watermelon and listening to the feedback sound, one can deduce whether the watermelon is ripe and tasty or not. This belief seems to be very common in some areas of the world.

Some references which mention it:

whataboutwatermelon.com

Some say a ripe watermelon will produce a hollow sound, while a “thick” or “solid” sound indicates a watermelon that’s not ripe or too ripe. Others say a hollow or “tight” sound is bad, and your watermelon should instead sound “firm.” Still others say a ripe watermelon should produce a B-flat sound. (What?!)

scotlynn.com

Unlike other watermelon suppliers who use the “tapping” method of quality control, Scotlynn uses the most advanced x-ray machines available.

Answer 1

There are a few papers assessing methods and results of acoustic measurements to determine the quality of watermelons:

1. Diezma-Iglesias et al evaluated "[d]ifferent acoustic parameters...for spectral characterisation: resonant frequency, maximum amplitude of the spectrum and band magnitude (BM) of the acoustic spectrum" and found that "[t]he BM parameters...were the best indicators of internal quality, especially the BM encompassed between 85 and 160 Hz (BM1), which showed the minimum overlap between good and hollow watermelons".

2. There is also a recent literature review that examines different methods for "nondestructive determination of internal quality in watermelon/melon", where they point out how acoustic methods are "greatly influenced by the angle and location of the impact on the fruit surface".

So, the answer seems to be yes, you can deduce certain qualities of watermelons if you have an appropriate device to detect and analyze the sounds and tap on the watermelon at the right angle and location.