AudioCalcs
Noise Reduction Calculator — Sound Isolation Between Rooms
Calculate noise reduction between rooms based on wall construction, area and room volume.
How We Calculate This
NR = TL + 10 × log10(A / S)
Where NR is noise reduction in dB, TL is the transmission loss (approximated by STC/Rw), A is the absorption area in the receiving room (sabins), and S is the area of the separating wall.
The absorption A is estimated from the receiving room volume assuming an RT60 of 0.5 seconds: A = 0.161 × V / RT60.
This is an idealised, best-case estimate. It uses the laboratory STC/Rw rating as the field transmission loss and ignores flanking transmission (sound travelling via floors, ceilings, ducts and shared structure) plus any gaps or poor seals. Real measured noise reduction is typically several dB lower, so treat the result as an upper bound rather than a guaranteed figure.
Frequently Asked Questions
Sound Transmission Class (STC) is a single-number rating of how well a wall blocks airborne sound. Higher STC means better isolation. STC 30 allows normal speech to be clearly heard; STC 45 makes loud speech barely audible; STC 60 blocks most sounds. The UK equivalent is Rw (weighted sound reduction index).
Noise reduction also depends on the area of the shared wall and the absorption in the receiving room. A larger wall transmits more sound, while a more absorbent receiving room reduces the build-up of transmitted sound. The formula accounts for both factors.
Add mass (extra plasterboard layers), create air gaps (double-stud walls), break vibration paths (resilient bars, acoustic hangers), seal all gaps (acoustic sealant around edges), and treat flanking paths (floors, ceilings, ducts). Each improvement adds to the overall STC rating.
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Last updated: February 2026
All calculations are estimates based on standard formulas. Always verify results for critical applications.