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 store, step by step.
Step 1: the room
A typical store of 50 × 30 ft with a 13 ft ceiling has a volume of about 19,500 ft³. With hard and bare surfaces (tile, concrete, glass and little soft furniture), its echo time is about 3.77 seconds. The target for stores is 0.80 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 0.80 s, the room needs about 1,196 ft² sabins of absorption in total. It already has about 254 from its surfaces, so the panels must add the rest.
Step 3: what one panel adds
A 24 × 48 in diamond panel, 2 in thick has about 4.0 ft² of face. At NRC 1.00, and allowing for the surface it covers, it adds about 3.8 sabins.
Step 4: the answer
About 248 panels bring the room from 3.77 s to 0.80 s.
| Thickness | NRC | Panels needed | Echo time after |
|---|---|---|---|
| 1 in | 0.8 | 315 | 0.80 s |
| 2 in | 1 | 248 | 0.80 s |
| 4 in | 1.15 | 215 | 0.80 s |
| Room | Size | Volume | Echo time now | Panels needed |
|---|---|---|---|---|
| Small | 38 × 23 × 13 ft | 11,362 ft³ | 3.34 s | 140 |
| Typical | 50 × 30 × 13 ft | 19,500 ft³ | 3.77 s | 248 |
| Large | 75 × 45 × 15 ft | 50,625 ft³ | 4.80 s | 682 |
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.