### Strutt Help

Duct Breakin    1/1, 1/3

Strutt|Mechanical Services|Duct Breakout|Duct Breakin inserts the sound power level of sound transmitted into a duct into the active row of the worksheet.

The sound power level associated with sound transmitted into a duct through the duct walls from the space outside the duct is given by:

L_(W,"in") = L_(W,out) + TL - 3

L_(W,"in")=L_(p,rev)+10logS+TL-9

where,
L_(W,"in") is the sound power level of sound transmitted into the duct and then transmitted upstream or downstream of point of entry, dB
L_(W,out) is the sound power level of sound incident on outside of duct walls, dB. Strutt calculates this from the incident reverberant sound level L_(p,rev) as:
L_(W,out)=L_(p,rev)-6+10logS
S is the exposed surface area of the duct (m²)
TL is the duct break-in transmission loss, dB (this can be input manually or via Duct TL function).
Note: TL values must be negative for formula to calculate correctly.

References:

• ASHRAE Handbook, p47.24