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 apartment living area, step by step.
Step 1: the room
A typical apartment living area of 20 × 15 ft with a 8 ft ceiling has a volume of about 2,550 ft³. With hard and bare surfaces (tile, concrete, glass and little soft furniture), its echo time is about 2.09 seconds. The target for apartments 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 250 ft² sabins of absorption in total. It already has about 60 from its surfaces, so the panels must add the rest.
Step 3: what one panel adds
A 24 × 48 in rectangular panel, 2 in thick has about 8.0 ft² of face. At NRC 1.00, and allowing for the surface it covers, it adds about 7.6 sabins.
Step 4: the answer
About 26 panels bring the room from 2.09 s to 0.49 s.
| Thickness | NRC | Panels needed | Echo time after |
|---|---|---|---|
| 1 in | 0.8 | 32 | 0.50 s |
| 2 in | 1 | 26 | 0.49 s |
| 4 in | 1.15 | 22 | 0.49 s |
| Room | Size | Volume | Echo time now | Panels needed |
|---|---|---|---|---|
| Small | 15 × 11 × 8.5 ft | 1,403 ft³ | 1.78 s | 14 |
| Typical | 20 × 15 × 8.5 ft | 2,550 ft³ | 2.09 s | 26 |
| Large | 30 × 23 × 10.5 ft | 7,245 ft³ | 2.85 s | 78 |
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.