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 home theater, step by step.
Step 1: the room
A typical home theater of 20 × 14 ft with a 9 ft ceiling has a volume of about 2,520 ft³. With typical surfaces (drywall, a rug and some furniture), its echo time is about 1.06 seconds. The target for home theaters is 0.40 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 0.40 s, the room needs about 309 ft² sabins of absorption in total. It already has about 117 from its surfaces, so the panels must add the rest.
Step 3: what one panel adds
A 24 × 48 in rectangular panel, 4 in thick has about 8.0 ft² of face. At NRC 1.15, and allowing for the surface it covers, it adds about 8.4 sabins.
Step 4: the answer
About 23 panels bring the room from 1.06 s to 0.40 s.
| Thickness | NRC | Panels needed | Echo time after |
|---|---|---|---|
| 1 in | 0.8 | 35 | 0.39 s |
| 2 in | 1 | 27 | 0.40 s |
| 4 in | 1.15 | 23 | 0.40 s |
| Room | Size | Volume | Echo time now | Panels needed |
|---|---|---|---|---|
| Small | 15 × 11 × 9 ft | 1,485 ft³ | 0.91 s | 13 |
| Typical | 20 × 14 × 9 ft | 2,520 ft³ | 1.06 s | 23 |
| Large | 30 × 21 × 11 ft | 6,930 ft³ | 1.43 s | 73 |
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.