Almost perfectly reflective at every frequency. Rooms with concrete walls ring at all pitches, including bass.
Absorption by the numbers
A poured concrete surface absorbs about 2% of the sound that hits it at 500 Hz (coefficient 0.02). A fabric-wrapped 2 in panel absorbs about 100%. Covering even a fifth of the wall with panels changes the room dramatically.
| Surface | Approx. absorption at 500 Hz |
|---|---|
| Poured concrete | 0.02 |
| Carpet on pad | 0.30 |
| Heavy curtains | 0.50 |
| 1 in panel | 0.79 |
| 2 in panel | 1.14 |