1. Textured concrete walls. Instead of smooth rings, they are moulded with raised patterns (grooves, waves, facets). The sound wave is scattered in all directions instead of bouncing back like a mirror.
2. Acoustic panels on the dome. Rock-wool panels covered with perforated metal are installed in the upper part of the tunnel. They capture the residual sound energy the way a sponge soaks up water.
of echo — cathedral ambiance
of echo — library ambiance
The concrete result
A conversation at 3 metres stays clear, a shout doesn't hurt your ears, and the gentle hum of the ventilation creates a pleasant natural white noise.
The bonuses of this approach
- 100% non-combustible (concrete + rock wool + metal)
- No major maintenance for 30 years or more
- A unique architectural aesthetic (interplay of light and shadow with LED lighting)
Main sources. This page draws on our detailed analysis and the standards it cites: download the acoustic analysis (PDF).