Strutt|Mechanical Services|Duct Breakout|Duct TL Low Frequency Correction inserts the correction to the duct breakout transmission loss for bends and other duct fittings which have improved low-frequency TL compared to the base case.
The corrections are taken from Table 7 ASHRAE 2011 guide. Strutt implements the most common/useful corrections. Refer to Table 7 for additional (unusual) situations
Reference: ASHRAE Handbook - HVAC Applications 2011, Chapter 48