Architectural Layout:

The layout of the Barabar Caves typically includes a rectangular hall with a circular dome-shaped chamber (stupa) at the far end. The caves' entrances are usually smaller compared to the inner chambers, which are spacious with high ceilings. The symmetrical architecture is thought to symbolize the order and harmony of the universe, a concept that was significant in ancient Indian cosmology.

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