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 sanctuary, step by step.
Step 1: the room
A typical sanctuary of 80 × 50 ft with a 24 ft ceiling has a volume of about 96,000 ft³. With typical surfaces (drywall, a rug and some furniture), its echo time is about 3.31 seconds. The target for sanctuaries is 1.40 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 1.40 s, the room needs about 3,365 ft² sabins of absorption in total. It already has about 1,424 from its surfaces, so the panels must add the rest.
Step 3: what one panel adds
A 48 × 96 in rectangular panel, 2 in thick has about 32.0 ft² of face. At NRC 1.00, and allowing for the surface it covers, it adds about 28.8 sabins.
Step 4: the answer
About 68 panels bring the room from 3.31 s to 1.39 s.
| Thickness | NRC | Panels needed | Echo time after |
|---|---|---|---|
| 1 in | 0.8 | 87 | 1.40 s |
| 2 in | 1 | 68 | 1.39 s |
| 4 in | 1.15 | 58 | 1.40 s |
| Room | Size | Volume | Echo time now | Panels needed |
|---|---|---|---|---|
| Small | 60 × 38 × 24 ft | 54,720 ft³ | 2.90 s | 35 |
| Typical | 80 × 50 × 24 ft | 96,000 ft³ | 3.31 s | 68 |
| Large | 120 × 75 × 26 ft | 234,000 ft³ | 4.08 s | 188 |
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.