Soundscape design of water features used in outdoor spaces where road traffic noise is audible
Calarco, Francesca Maria Assunta
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This research focused on the soundscape design of a wide range of small to medium sized water features (waterfalls, fountains with upward jet(s), and streams) which can be used in gardens or parks for promoting peacefulness and relaxation in the presence of road traffic noise. Firstly, the thesis examined the audio-visual interaction and perceptual assessment of water features, including the semantic components and the qualitative categorisation and evocation of water sounds; and secondly, the thesis investigated the effectiveness of the water features tested in promoting relaxation through sound mapping. Different laboratory tests were carried out, and these included paired comparison tests (audio-only, visual-only and audio-visual tests), semantic differential tests, as well as tests aimed at the qualitative categorisation and evocation of water features. Sound maps of the water generated sounds were developed through the use of propagation models based on either point or line sources. Three acoustic zones (‘water sounds dominant zone’, ‘optimum zone’ and ‘RTN dominant zone’ (RTN: road traffic noise)) were defined in the maps as the zones where relaxation/pleasantness can be promoted over a 20 m × 20 m area for different road traffic noise levels. Paired comparisons highlighted the interdependence between uni-modal (audio-only or visual-only) and bi-modal (audio-visual) perception, indicating that equal attention should be given to the design of both stimuli. In general, natural looking features tended to increase preference scores (compared to audio-only paired comparison scores), while manmade looking features decreased them. Semantic descriptors showed significant correlations with preferences and were found to be more reliable design criteria than physical parameters. A principal component analysis identified three components within the nine semantic attributes tested: “emotional assessment,” “sound quality,” and “envelopment and temporal variation.” The first two showed significant correlations with audio-only preferences, “emotional assessment” being the most important predictor of preferences, and its attributes naturalness, relaxation, and freshness also being significantly correlated with preferences. Categorisation results indicated that natural stream sounds are easily identifiable (unlike waterfalls and fountains), while evocation results showed no unique relationship with preferences. The results of sound maps indicated that small to medium sized water features can be used mainly in environments where road traffic noise levels are equal or lower than 65 dBA.