Redefining NR Curves: A Mathematical Modelling Approach for BS 8233
- Daniel Goodhand
- Nov 13
- 2 min read
Title:Â Redefining NR Curves: A Mathematical Modelling Approach for BS 8233
Author:Â Daniel Goodhand, Goodhand Acoustics
Presented at: Acoustics 2025, Milton Keynes
Date: 20 - 21 October 2025
Abstract:
Noise Rating (NR) Curves have been a fundamental tool for assessing building services noise in the UK for several decades. Despite their widespread use, the origins of the NR Curves are not well known. Traditionally, they are defined as a series of linear functions across octave bands, typically derived from a table of coefficients. However, there are inconsistencies and errors in their reproduction, including previous versions of BS 8233. This talk will examine the historical development of the NR Curves, shedding light on their original purpose and highlighting the errors and variations that have arisen over time.
Building on these insights, a novel mathematical approach has been developed for the revised BS 8233 draft that models the NR Curves as a continuous function, providing a smoother and more consistent representation. This method enables the direct calculation of all the curves or the traditional table of coefficients. It also simplifies translation to one-third-octave band equivalents, allows the curves to be extended beyond traditional limits, and supports iterative curve design.
This approach has implications for standardisation across guidance documents, such as the CIBSE Guides. The ability to easily translate to one-third-octave bands will support updates to ProPG Gym Acoustics Guidance, which uses a one-third-octave band interpretation of NR Curves. Additionally, the potential for future development means variations of the curves can be produced and tested, leading to better acoustic specifications.
The revised BS 8233 is expected to present the NR Curves as tables derived from the new model.
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