### Strutt Help

Regenerated Noise - Junctions (SRL Method)
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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, m^{2}

`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

T-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, m^{2}

`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`

90° Branch Take Off 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, m^{2}

`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

Comments or suggestions to
strutt@arup.com