The number of panels depends on three things: the room's volume, how much its surfaces already absorb, and how short you want the echo to be. Here is the calculation for a typical bedroom, step by step.
Step 1: the room
A typical bedroom of 13 × 12 ft with a 8 ft ceiling has a volume of about 1,248 ft³. With soft surfaces (carpet, upholstered furniture and curtains), its echo time is about 0.54 seconds. The target for bedrooms is 0.50 seconds.
Step 2: how much absorption is missing
Sabine's formula says RT60 = 0.161 × V ÷ A, with V in cubic meters and A, the total absorption, in square-meter sabins. To reach 0.50 s, the room needs about 122 ft² sabins of absorption in total. It already has about 114 from its surfaces, so the panels must add the rest.
Step 3: what one panel adds
A 24 × 48 in pill panel, 1 in thick has about 7.1 ft² of face. At NRC 0.80, and allowing for the surface it covers, it adds about 4.6 sabins.
Step 4: the answer
About 2 panels bring the room from 0.54 s to 0.50 s.
| Thickness | NRC | Panels needed | Echo time after |
|---|---|---|---|
| 1 in | 0.8 | 2 | 0.50 s |
| 2 in | 1 | 2 | 0.49 s |
| 4 in | 1.15 | 2 | 0.48 s |
| Room | Size | Volume | Echo time now | Panels needed |
|---|---|---|---|---|
| Small | 10 × 9 × 8 ft | 720 ft³ | 0.46 s | 2 |
| Typical | 13 × 12 × 8 ft | 1,248 ft³ | 0.54 s | 2 |
| Large | 20 × 18 × 10 ft | 3,600 ft³ | 0.75 s | 26 |
These are estimates for speech frequencies (500–1,000 Hz). Use the room calculator with your own measurements, then load the result into the designer.