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 café, step by step.
Step 1: the room
A typical café of 35 × 22 ft with a 11 ft ceiling has a volume of about 8,470 ft³. With hard and bare surfaces (tile, concrete, glass and little soft furniture), its echo time is about 2.98 seconds. The target for cafés is 0.70 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 0.70 s, the room needs about 594 ft² sabins of absorption in total. It already has about 140 from its surfaces, so the panels must add the rest.
Step 3: what one panel adds
A 24 × 21 in hexagon baffle, 1 in thick has about 2.6 ft² of face. At NRC 0.80, and allowing for the surface it covers, it adds about 2.9 sabins, including the extra absorption from its back face and edges when it hangs in the air.
Step 4: the answer
About 156 panels bring the room from 2.98 s to 0.70 s.
| Thickness | NRC | Panels needed | Echo time after |
|---|---|---|---|
| 1 in | 0.8 | 156 | 0.70 s |
| 2 in | 1 | 123 | 0.70 s |
| 4 in | 1.15 | 106 | 0.70 s |
| Room | Size | Volume | Echo time now | Panels needed |
|---|---|---|---|---|
| Small | 26 × 17 × 11 ft | 4,862 ft³ | 2.61 s | 86 |
| Typical | 35 × 22 × 11 ft | 8,470 ft³ | 2.98 s | 156 |
| Large | 53 × 33 × 13 ft | 22,737 ft³ | 3.89 s | 448 |
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.