Ventilation Systems - Acoustic Calculation Procedure
An acoustic noise calculation of a ventilation system following a systematic procedure to estimate sound sources, attenuation, and determine required silencer specifications.
Sound and Noise Sources
Estimate all sound power sources.
1. Sound Power Level from the Fan (LN)
Enter the manufacturer's sound power data or calculate the fan sound power.
2. Add Safety Factors
Add safety factors - 3 dB is recommended.
Attenuation
Estimate the attenuation in the system.
10. Room and Terminal Effect
The sound pressure levels are converted to sound power level at the terminals. The acoustic characteristics of the room as well as the number and location of the terminals must be considered.
- Determine the acoustic characteristics of the room
- Determine whether the receiver are in the direct or reverberant field
- Find the room's absorption characteristics
- Determine how many terminals the listener is influenced by
11. Allowance for End Reflection
Attenuation due to end reflection based on duct dimensions.
12. Duct Work Attenuation
Calculate the attenuation in unlined and lined ducts (in dB/m).
13. Elbow Attenuation
Calculate the attenuation in the elbows.
14. Power-level Split, Branch to Terminals
Determine the allowance for split - branch to terminals.
15. Power-level Split, Main Duct to Branch Duct
Determine the allowance for split - main duct to branch.
16. Other Attenuation
Add attenuation from other components.