Acoustic Properties: The caves have remarkable acoustic qualities. The inner chambers are designed in such a way that sound resonates across the smooth walls, creating a reverberating effect.

A rugosimeter, also known as a roughness tester or surface roughness meter, is a device used to measure the surface roughness of materials, including granite. Surface roughness is a quantitative assessment of the texture of a surface, calculated by measuring the bumps, valleys, and other imperfections on the material's surface. Rz (Average Maximum Height) measures the average vertical distance from the highest peak to the lowest valley across several sampling lengths.

On the left Barabar cave, the Rz is much lower compared to the right, where industrial granite is used which indicates that the polishing techniques are astounding.

I've marked the timestamp in the video where they discuss the Barabar site. Please watch the first 9 minutes.
https://youtu.be/ktxV4w2yzeg?t=1993

Then watch this small clip
https://www.youtube.com/watch?v=g05m6ZEtkDA

The Barabar Caves have intrigued scientists much like the pyramids do. They are perfectly symmetrical and resonate sound effectively. A team of researchers was experimenting with different frequencies and noticed that at 75 hertz, the sound resonated more than at other frequencies. Then, unexpectedly, their boom box died. They did the same exact experiment 1y later, and their boom box died again.

Now Listen to the background sound at exactly 1h51:40sec

https://youtu.be/xJhHYiVg9bI?t=6692

First, tell me what you heard.

Then, explain what could have happened.

What type of waves are generated in a resonance chamber?

In their report, the 3D mapping team concluded that the resonant frequency of the cave was 74.9 Hz.
Which german engineer born in 1821 developed a formula for calculating the resonant frequency of a 3D volume?