6.8 Noise Levels and Room Acoustics Treatment

Background Noise Levels
The key to successful open plan design is reducing background noise levels, and conversely, increasing speech levels. Reducing noise levels is important as high background noise levels are disturbing, compromise concentration and make speech unintelligible over distance. Therefore to make an open plan space work correctly, with multiple activities taking place simultaneously, it is necessary to control noise levels.

Reverberation times
Reverberation times and room acoustics are extremely important elements in the acoustic design of open plan teaching spaces. Soft treatments are needed to ensure good speech intelligibility, to absorb sound and to control the build up of noise. One of the principle factors affecting noise levels is reverberation time. The ‘snowball effect’ of reverberation time is illustrated in Image 1. This illustration shows noise levels in a room increasing relatively constantly, as the number of people talking increases. At the snowball point, noise levels dramatically increase as people sub-consciously begin to raise their voices to be heard over the background noise. These noise levels are obviously detrimental to the performance of the open plan space. In order to mitigate this effect, it is important to add sufficient soft and absorbent treatments to achieve a reverberation time of 0.4 seconds. This reverberation time can only be achieved by adding the required levels of soft treatment; see the Room Acoustics and Reverberation section which provides an indication as to the required levels of treatment.


Positioning Treatments
Where soft treatments are located in the open plan space will have an effect on their efficiency. Acoustic absorption placed close to a particularly noisy area will be more effective than material placed on the soffit much further away. In addition to soft treatments, it is also important to consider the positioning of hard reflective surfaces. These should ideally be placed behind the teacher and above an audience. The effects of finishes should ideally be assessed using ray tracing modelling software 2.