The silencing plenum box is generally installed at the supply/return air outlet of fans or air handling units. Sound-absorbing materials are attached inside the plenum box. It can not only stabilize airflow, but also effectively attenuate noise generated by fans and air handling units through sudden cross-section changes and the sound absorption effect of the inner surface of the box.
Structure
The inner wall of the silencing cavity is filled with 50 mm thick centrifugal glass wool, covered with glass cloth and perforated plate with aperture of Φ3 mm. The keel is made of galvanized steel sheet.
Brief Introduction to Measured Performance of AXX Type Silencing Plenum Box
| Working Condition | Frequency | 63 | 125 | 250 | 500 | 1000 | 2000 | 4000 | 8000 | 10000 |
| Bare Duct | Static State | 65.0 | 71.0 | 95.5 | 97.0 | 90.5 | 90.5 | 77.5 | 60.5 | 84.5 |
| 3m/s | 65.5 | 71.5 | 95.5 | 97.0 | 90.5 | 90.5 | 77.5 | 60.5 | 84.5 | |
| 6m/s | 66.5 | 71.0 | 95.5 | 97.0 | 90.5 | 90.5 | 78.0 | 60.5 | 84.5 | |
| 9m/s | 68.5 | 71.5 | 95.5 | 97.0 | 90.5 | 91.0 | 78.0 | 60.5 | 84.5 | |
| With Silencer Installed | Static State | 64.5 | 70.5 | 87.5 | 82.5 | 72.5 | 79.5 | 69.0 | 55.5 | 69.5 |
| 3m/s | 64.5 | 71.0 | 87.5 | 82.5 | 71.5 | 79.5 | 69.5 | 55.0 | 69.5 | |
| 6m/s | 66.0 | 70.5 | 87.5 | 93.0 | 71.5 | 79.5 | 70.0 | 55.0 | 70.0 | |
| 9m/s | 68.0 | 71.0 | 87.5 | 93.0 | 71.5 | 80 | 70.0 | 55.0 | 70.0 | |
| Noise Reduction | Static State | 0.5 | 0.5 | 8.0 | 14.5 | 18.5 | 11.0 | 8.5 | 5.0 | 15.0 |
| 3m/s | 1.0 | 0.5 | 8.5 | 14.5 | 19.0 | 11.0 | 8.0 | 5.5 | 15.0 | |
| 6m/s | 0.5 | 0.5 | 8.0 | 14.0 | 19.0 | 11.0 | 8.0 | 5.5 | 14.5 | |
| 9m/s | 0.5 | 0.5 | 8.0 | 14.0 | 19.0 | 11.0 | 8.0 | 5.5 | 14.5 |
when the air velocity is 6 m/s, the pressure loss ΔH = 2.0 mmH₂O;
when the air velocity is 9 m/s, the pressure loss ΔH = 5.5 mmH₂O.