Glass is hard and smooth, so it reflects sound like a mirror reflects light, and single panes leak a lot of low-frequency sound.
Absorption by the numbers
A glass and curtain wall surface absorbs about 4% of the sound that hits it at 500 Hz (coefficient 0.04). 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 |
|---|---|
| Glass and curtain wall | 0.04 |
| Carpet on pad | 0.30 |
| Heavy curtains | 0.50 |
| 1 in panel | 0.79 |
| 2 in panel | 1.14 |