Estimating sound attenuation where ducts splits to terminals.
Splitting ducts to terminals will reduce the sound power level - LN - transferred to each terminal.
The sound power is reduced according reduced volume of air.
For equal terminals the attenuation to each terminal is indicated in the diagram below.
Example - Sound Attenuation from a Duct to Equal Terminals
According the diagram above - for a duct that splits into four equal terminals the sound attenuation from duct to each terminal is approximate