How to recreate like an echo chamber ?

I think you can use Natural reverb with max diffusion and max room size . Use long reverb times.

Checkout "REV Cave " from factory presets.

Quote from azertyvince

Thanks.

Are you sure, it's necessary to have max diffusion.

It seems to me echo chamber were chamber with concrete walls.

Diffusion is a parameter describing the sound scattering and has nothing to do with the material but more with its structure and layout (wall complexity). Such a shroeder diffuser can be made of concrete and does not interfere with its diffuse function. Concrete has a higher reflection coefficient but if it is'n flat it can be diffuser. In other words, if you want to simulate a room with regular shapes that gives clear reflections between parallel walls

, reduce diffusion.

Does echo chambers have regular shapes?

An additional complication is that the diffusion depends on the frequency. The smaller the wave length, the smaller the irregularities make the sound dissipate. I come slowly to the conclusion that in the new reverbs this distinction is missing for the diffusion of low and high frequency