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Strutt|Mechanical Services|Regenerated Noise|Junction/Split inserts sound power levels into the active row of the worksheet.

Input required is the junction type, duct dimensions (main and branch) and flow rates.

SRL calculates regenerated noise from junctions using:

X-Junction frequency sound power levels are calculated by:

`L_(W_(branch))(f_0) = K_J + 10log_10(f_0) + 50log_10(U_B) + 10log_10(S_B D_B) - 18`

Where:
`f_0` is the octave band centre frequency, Hz
`D_B` is the equivalent diameter of the branch duct, m
`U_B` is the flow velocity in the branch duct, m/s
`S_B` is the cross sectional area of the branch duct, m²
`K_J` is the characteristic spectrum (taken from Figure 8.12 SRL)

and,

`L_(W_(mai n))(f_0) = L_(W_(branch)) + 20log_10(D_M/D_B)`

Where:
`D_M` is the equivalent diameter of main duct, m
`D_B` is the equivalent diameter of branch duct, m

`L_(W_(branch))(f_0) = K_J + 10log_10(f_0) + 50log_10(U_B) + 10log_10(S_B D_B) - 18`

Where:
`f_0` is the octave band centre frequency, Hz
`D_B` is the equivalent diameter of the branch duct, m
`U_B` is the flow velocity in the branch duct, m/s
`S_B` is the cross sectional area of the branch duct, m²
`K_J` is the characteristic spectrum (taken from Figure 8.12 SRL for `U_(M1)/U_B = 1`)

and,

`L_(W_(mai n))(f_0) = L_(W_(branch)) + 3`

`L_(W_(branch))(f_0) = K_J + 10log_10(f_0) + 50log_10(U_B) + 10log_10(S_B D_B) - 18`

Where:
`f_0` is the octave band centre frequency, Hz
`D_B` is the equivalent diameter of the branch duct, m
`U_B` is the flow velocity in the branch duct, m/s
`S_B` is the cross sectional area of the branch duct, m²
`K_J` is the characteristic spectrum (taken from Figure 8.12 SRL for `U_(M1)/U_B = 1`)

and,

`L_(W_(mai n))(f_0) = L_(W_(branch)) + 20log_10(D_M/D_B)`

Where:
`D_M` is the equivalent diameter of main duct, m
`D_B` is the equivalent diameter of branch duct, m

References:

• Woods Practical Guide to Noise Control, p101.
• SRL Noise Control in Building Services, pp238-240