High pitched acoustic reverb from semi circle monument

Question

I went on a trip last week and encountered a rather peculiar phenomenon here, when standing in the middle of the circle that's marked by the bricks, and clapping my hands, a very high pitched noise would seem to emanate from my hands, like a squeak from a toy duck.

This is a rough sketch of the place:

There's a semi-circle concrete bench on one side and the other some sort of statue.

I tried to investigate the location and here are my findings:

1. This happens with claps, stomps, and when breaking dry branches.
2. There's no echo when talking or playing sounds
3. Reports from a friend imply that the effect doesn't reproduce when blocking with one's body the statue.
4. I wasn't able to record it to add a sound sample here.

My current hypothesis is that the sound travels from my hands to the statue, echoed in a higher pitch, and then the concrete bench acts as an acoustic lens that focuses its focal point.

Any other ideas?

Answer 1

My comment was too long so I turned it to an answer.

Waves with different frequencies interact differently with a structure due to the relation between the size of the structure and the wavelength (see this answer).

Thus, you have different regimes:

• For low frequencies you would have a wave that it is not that affected by your semicircle. This is the main reason of using just one speaker for sub-woofers, they are not that directional because of the large wavelengths-

• For mid frequencies you have really complex behavior involving diffraction and reflection.

• For high frequencies, it is common to consider only reflection and you have a regime of "geometric acoustics".

The frequency/wavelength limits for these regimes are not absolute and they would depend on relative sizes for the structure and wavelength.