NPL has recently been part of a study with the University of Salford, funded by the Noisefutures Network, to assess the difference between how noise is measured and perceived in urban environments.

The study has been conducted in Festival Square in Edinburgh (located between Usher Hall and the Sheraton hotel). The square was 'mined' with DREAMSys units, the MEMS microphone based noise measurement equipment (designed by an industrial consortium led by NPL), which were making their debut public appearance. Eight units were used to produce real-time sound level data (in decibels) across the area being studied, which were then post-processed to determine noise maps according to the European Noise Directive.

Perception was simultaneously determined by 'soundwalks' - each participant in the study was guided along a determined path in the square, stopping in specific places to listen, and completed a questionnaire to assess perception of noise on scales like 'vibrancy' or 'pleasantness'. This technique allowed for the production of a second type of map illustrating the perceived nature of the soundscape. This meant it was possible to make an easy and practical visual comparison of the two approaches.

The study demonstrated the limitations of classical decibel-based noise levels, when used to assess the subjective perception of sound. The two types of map illustrating the iso-perception and the iso-energetic curves were strikingly different. Questionnaires identified how the expectations of the end-user may play a determinant role in the perception of an urban open area, but showed their limits in terms of standardisation. The use of DREAMSys units showed the benefits of having many simultaneous measurement points while designing user-oriented actions to tackle unwanted sounds in urban open areas. These results, soon available on the Noisefutures website, fostered discussion on the need for new, perception-based indicators to design more welcoming cities and innovative actions to cope with environmental noise, more cost-effective in terms of improving the well being of residents.

The questionnaires were designed by Dr Bill Davies, Senior Lecturer in Acoustics, University of Salford.

Find out more information on this work on the DREAMSys website

Find out more about NPL’s Sound in Air research

Contact: Richard Barham