Gregwor & Audiomutt's TL MSM Calculator - Units Error?

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Elusive Sounds
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Location: Moncton, New Brunswick, Canada

Gregwor & Audiomutt's TL MSM Calculator - Units Error?

Post by Elusive Sounds »

I have been going over the math in the "DATA" tab of the MSM TL Calculator Version 2.05 (found here: and found an anomaly.

In the MSM resonance equation f0 = C [ (m1 + m2) / (m1 x m2 x d)]^0.5 , C is the constant used to describe if the air cavity is empty or full of insulation.

I have read in a few different places (including here: that for imperial units C = 60 for an empty cavity, and C = 43 for a full cavity while for metric units, C=2650 for an empty cavity, and C=1900 for a full cavity. This obviously has a huge effect on the value of Fo.

So in columns K through N, metric values are used. However, in cells L10 and L11, it looks like the values for Imperial units (60 and 43) are used.
MSM V2.05 Anomaly.png
Why are the imperial constants used here?

I found this when debugging a discrephancy between manual calculations and the TL MSM Calculator.
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Re: Gregwor & Audiomutt's TL MSM Calculator - Units Error?

Post by gullfo »

just fyi - this document (i've found it to be useful) might provide a more practical approach to estimation.

however - in postings, Stuart has the imperial values in the equation. 60/43. the other values would be used in metric - however - i think the ^0.5 is also different.
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