STC to Rw converter
Convert wall sound insulation between the American STC and the European Rw, and see how much sound still gets through.
That's 2.5× as quiet as a blockwork wall, while a party wall is 2.5× better. A 75 dB television next door would come through at about 26 dB.
What it means
How much sound gets through?
STC and Rw use different weighting curves, so the one-decibel offset is a good rule of thumb, not an exact conversion. Both ignore low bass, where walls perform worst.
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Three things worth knowing
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Rw ≈ STC − 1
Close enough for specification work. Where the two really differ is at low frequencies, which neither number describes well.
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One number for a whole curve
A wall blocks different frequencies by different amounts. Both ratings slide a standard contour over the measured curve until it just fits, and read off a single figure.
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Ratings ignore the bass
Rw starts at 100 Hz and STC at 125 Hz, which is above most of what a subwoofer or a lorry produces. The Ctr correction exists precisely to account for that.
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Background
About STC and Rw
Both ratings compress a whole frequency curve into one number: how many decibels a wall takes off. STC is the North American version, Rw the international one, and for ordinary partitions STC runs about one decibel higher.
A 50 dB wall passes one part in a hundred thousand of the sound energy that hits it — which still leaves a loud television faintly audible.