What is the difference between NR and TL?

Transmission Loss (TL) is a property of the partition alone — it measures how much sound energy the material blocks. Noise Reduction (NR) is the actual dB difference between the two rooms, which also depends on how absorptive the receiving room is. A very reverberant receiving room has low absorption, which reduces the effective NR even if the wall TL is high.

A sabin is a unit of sound absorption equal to 1 m² of perfectly absorbing surface (metric sabin) or 1 ft² (imperial sabin). A room's total absorption A is calculated by summing the product of each surface area and its absorption coefficient: A = Σ(Sᵢ × αᵢ).

Can NR be higher than TL?

Yes. If the receiving room is highly absorptive (large A relative to partition area S), the term 10 log₁₀(S/A) becomes negative, and NR exceeds TL. Conversely, a very live (reflective) room results in NR lower than TL.

What TL value should I use for a standard drywall wall?

A single-layer 5/8″ drywall on wood studs typically has a Sound Transmission Class (STC) of about 33–35 dB. Double-stud walls with insulation reach STC 50–60 dB. Use frequency-specific TL data for precise results; STC is a single-number rating for convenience.

Does this formula account for flanking paths?

No. The NR = TL − 10 log₁₀(S/A) formula models direct transmission through the partition only. Real-world NR is often 5–10 dB lower due to flanking (sound traveling via floors, ceilings, or ductwork). Always add a flanking margin in practice.

Noise Reduction Calculator

Name: Noise Reduction Calculator
Availability: InStock
Author: Nham Vu

Enter wall transmission loss and receiving room absorption to calculate the noise reduction in decibels.

Partition & Room Parameters

Units:

Transmission Loss (TL) dB

STC rating of the wall or partition (e.g. 35–55 dB for typical walls)

Partition Area (S) m²

Area of the shared wall / floor / ceiling between the two rooms

Room Absorption (A) metric sabins (m²)

Total absorption of the receiving room (sum of area × absorption coefficient for each surface)

Noise Reduction (NR)

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Formula Breakdown

Transmission Loss (TL) — dB

Partition area (S) —

Room absorption (A) —

10 × log₁₀(S / A) —

NR = TL − correction —

NR Reference Guide

< 25 dB Minimal isolation — speech clearly audible through partition

25–35 dB Basic isolation — loud speech audible, normal speech muffled

35–45 dB Good isolation — typical open-plan office partition target

45–55 dB High isolation — recommended for private offices and hotel rooms

> 55 dB Excellent isolation — recording studios and critical listening rooms

Summary