### Strutt Help

Mechanical Services Calculation Sheet
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**Strutt|Blank Sheets|Mechanical** inserts a blank mechanical services Strutt calculation sheet into the current workbook.

The sheet includes columns for duct insertion losses or attenuation, as well as columns for regenerated noise levels.

A set of 'Cumulative Sound Power Level' columns keeps track of the down-duct sound power after each row:

`L_(W,i)=10log(10^((L_(W,i-1)+IL_i)/10)+10^(L_("W,regen,i")/10))`

where:

`L_(W,i)` is the sound power level immediately downstream of row `i` of the worksheet

`L_(W,i-1)` is the sound power level immediately downstream of the previous row (`i-1`) of the worksheet

`IL_i` is the insertion loss of the element in row `i` of the worksheet

`L_("W,regen,i")` is the sound power level generated by the element in row `i` of the worksheet

(Note references to 'downstream' refer to the direction that sound is propagating along the duct, i.e. from source to receiver)

The final down-duct sound power levels are used for a room noise level calculation, including both the reverberant level and the direct level.

The source directivity is pre-filled using the Internal Outlet Directivity calculation for convenience, but may be modified by the user as desired.

This function can also be accessed by right-clicking on the ply (the set of tabs at the bottom of the Excel window with the sheet names), using the Context-Sensitive Menus

Comments or suggestions to
strutt@arup.com