| STC | NRC | |
|---|---|---|
| Measures | Sound blocked between spaces | Sound absorbed inside a space |
| Scale | About 20 to 70+ | 0 to about 1.2 |
| Improves with | Mass, isolation, airtightness | Porous, thick, soft materials |
| Fixes | Neighbor noise, privacy | Echo, loud rooms, clarity |
| Example product | Double-stud wall, acoustic door | Fabric-wrapped panel |
A heavy concrete wall has high STC and almost zero NRC: it blocks sound but makes the room echo. An acoustic panel has a high NRC and adds almost no STC. Most projects need some of each.
If you can hear your neighbor's words, you need STC. If your own room sounds loud and echoey, you need NRC. Panels are for the second problem.