The influence of preconceptions on perceived sound reduction by environmental noise barriers

The paper presents research that answers three main questions: (1) Do preconceptions held about the constituent materials of an environmental noise barrier affect how people perceive the barrier will perform at attenuating noise? (2) Does aesthetic preference influence the perception of how a barrier will perform? (3) Are barriers, which are deemed more aesthetically pleasing, more likely to be perceived as better noise attenuators? In a virtual reality setting with film to improve the contextual realism of the intersensory interaction test, participants were required to compare the perceived effectiveness of five standard 'in-situ' noise barriers, including concrete, timber, metal, transparent acrylic and a vegetative screen. The audio stimulus was held at a constant sound pressure level (SPL), whilst the visual stimulus changed, as the influential factor. As the noise levels projected during the study were held constant, it was possible to attribute the participants' perception of noise attenuation by the barriers, to preconceptions of how the varying barrier material would attenuate noise. There was also an inverse correlation between aesthetics and perception of how a noise barrier would perform. The transparent and deciduous vegetation barriers, judged most aesthetically pleasing, were judged as the least effective at attenuating noise. (c) 2010 Elsevier B.V. All rights reserved

A framework for improving urban soundscapes

Sound in public urban spaces is often considered in negative terms as both intrusive and undesirable - its referred to as noise! However, this issue is multi-facetted and goes much deeper than simply reducing levels. There are many positive aspects of a soundscape. In an attempt to progress thinking on positive soundscapes and move towards more practical planning approaches and decision making tools for soundscape assessment, this paper proposes an approach traditionally used in product development and manufacturing quality - The Kano Model. The approach is captured in the form of a broader framework which covers: the composition of a soundscape in objective terms; the factors affecting whether it might be perceived as positive; and how the Kano model for product development can be used as a means of understanding the range of applicability of approaches to create positive soundscapes (including several novel approaches which are the subject of other papers in this issue). It can be considered to be complementary with previous frameworks, some of which have concentrated on sound sources, others on the factors affecting perception or even as a model for understanding individual evaluation. In this case the motivation behind the framework is to help assess the likely impact of practical interventions on the positive aspects of a soundscape. The framework proposes that the meaning of "positive" for a public space is quite different for three types of people, each with a different level of direct engagement with the soundscape: planners; serious listeners; users of the space. The first two are influenced by the soundscape itself, either in meeting legislation and reducing nuisance, or as an artistic or creative opportunity. However the third, arguably most important group of people, users of the space, are more concerned with the space itself and have their perception of it influenced by the soundscape, which is an inconvenient and highly complex intermediate step. This influence is largely determined by their activity e.g. reading, holding a conversation, shopping or sightseeing. The paper discusses the further implementation of the framework, and how barriers to the wider application of the concept of positive soundscapes might be overcome. It shows how adapting an approach previously used in automotive sound quality can be adapted for urban soundscapes. It concludes with recommendations for taking the framework forward as a practical approach

Field study on the influence of spatial and environmental characteristics on the evaluation of subjective loudness and acoustic comfort in underground shopping streets

A large-scale measurement and subjective survey was undertaken in five underground shopping streets to determine the influence of spatial and environmental characteristics on users’ subjective loudness and acoustic comfort. The analysis on the spatial characteristics shows that the subjective loudness is higher in “street type” than in “square type” underground shopping streets when the equivalent continuous A-weighted sound pressure level (LAeq) is relatively high (75 dBA). Acoustic comfort is higher in “square type” than in “street type” underground shopping streets where LAeq is relatively low (55 dBA). Considering spatial functions, it is found that acoustic comfort is higher in a dining area than in a shopping area. In terms of environmental characteristics where air temperature, relative humidity, luminance and visual aspect were considered, the subjective loudness is influenced by humidity and luminance, with correlation coefficients of 0.10 to 0.30. The evaluation of acoustic comfort is influenced by air temperature, humidity, and luminance, with correlation coefficients of 0.1 to 0.4. There are significant correlations between the evaluation of environmental factors and subjective loudness, as well as, acoustic comfort. The correlation coefficients are 0.1 to 0.5. Moreover, respondents’ attitude to sound environment could influence their evaluation of subjective loudness and acoustic comfort

An Assessment of Psychological Noise Reduction by Landscape Plants

The emphasis in the term ‘Green Transportation’ is on the word ‘green’. Green transportation focuses on the construction of a slow transport system with a visually pleasing, easy and secure trip environment composed of urban parks, green roadside spaces and some other space that is full of landscape plants. This trip environment encourages residents to make trip choices that reduce fuel consumption and pollution and is one of the most important ways of popularizing green transportation. To study the psychological benefits provided by urban parks and other landscape environments, we combined a subjective approach (a questionnaire) with an objective quantitative approach (emotional tests using an electroencephalogram; EEG). Using a questionnaire survey, we found that 90% of the subjects believed that landscape plants contribute to noise reduction and that 55% overrated the plants’ actual ability to attenuate noise. Two videos (showing a traffic scene and a plant scene) were shown to 40 participants on video glasses. We detected and recorded EEG values with a portable electroencephalograph, and a comparison between the results of the two groups revealed that there was a highly significant asymmetry between the EEG activity of the vegetation scene and traffic scene groups. The results suggest that the emotions aroused by noise and visual stimuli are manifested in the synchronization of beta frequency band and the desynchronization of alpha frequency band, indicating that landscape plants can moderate or buffer the effects of noise. These findings indicate that landscape plants provide excess noise attenuating effects through subjects’ emotional processing, which we term ‘psychological noise reduction’

Using natural means to reduce surface transport noise during propagation outdoors

This paper reviews ways of reducing surface transport noise by natural means. The noise abatement solutions of interest can be easily (visually) incorporated in the landscape or help with greening the (sub)urban environment. They include vegetated surfaces (applied to faces or tops of noise walls and on building façades and roofs ), caged piles of stones (gabions), vegetation belts (tree belts, shrub zones and hedges), earth berms and various ways of exploiting ground-surface-related effects. The ideas presented in this overview have been tested in the laboratory and/or numerically evaluated in order to assess or enhance the noise abatement they could provide. Some in-situ experiments are discussed as well. When well-designed, such natural devices have the potential to abate surface transport noise, possibly by complementing and sometimes improving common (non-green) noise reducing devices or measures. Their applicability strongly depends on the available space reserved for the noise abatement and the receiver position

Combined acoustical and visual performance of noise barriers in mitigating the environmental impact of motorways.

This study investigated the overall performance of noise barriers in mitigating environmental impact of motorways, taking into consideration their effects on reducing noise and visual intrusions of moving traffic, but also potentially inducing visual impact themselves. A laboratory experiment was carried out, using computer-visualised video scenes and motorway traffic noise recordings to present experimental scenarios covering two traffic levels, two distances of receiver to road, two types of background landscape, and five barrier conditions including motorway only, motorway with tree belt, motorways with 3 m timber barrier, 5 m timber barrier, and 5 m transparent barrier. Responses from 30 participants of university students were gathered and perceived barrier performance analysed. The results show that noise barriers were always beneficial in mitigating environmental impact of motorways, or made no significant changes in environmental quality when the impact of motorways was low. Overall, barriers only offered similar mitigation effect as compared to tree belt, but showed some potential to be more advantageous when traffic level went high. 5 m timber barrier tended to perform better than the 3 m one at the distance of 300 m but not at 100 m possibly due to its negative visual effect when getting closer. The transparent barrier did not perform much differently from the timber barriers but tended to be the least effective in most scenarios. Some low positive correlations were found between aesthetic preference for barriers and environmental impact reduction by the barriers

Effects of Changed Aircraft Noise Exposure on Experiential Qualities of Outdoor Recreational Areas

The literature indicates that sound and visual stimuli interact in the impression of landscapes. This paper examines the relationship between annoyance with sound from aircraft and annoyance with other area problems (e.g., careless bicycle riding, crowding, etc.), and how changes in noise exposure influence the perceived overall recreational quality of outdoor recreational areas. A panel study (telephone interviews) conducted before and after the relocation of Norway’s main airport in 1998 examined effects of decreased or increased noise exposure in nearby recreational areas (n = 591/455). Sound from aircraft annoyed the largest proportion of recreationists, except near the old airport after the change. The decrease in annoyance with sound from aircraft was accompanied by significant decreases in annoyance with most of the other area problems. Near the new airport annoyance with most factors beside sound from aircraft increased slightly, but not significantly. A relationship between aircraft noise annoyance and perceived overall recreational quality of the areas was found

Perception of urban park soundscape

A number of studies have been initiated to explore how to improve the soundscape quality in urban parks. However, good soundscape quality in parks cannot be provided without a thorough understanding of the complex relationships among sound, environment, and individuals. As acoustic comfort is considered to be an important outcome of soundscape quality, this study investigates the relative impacts of the factors influencing acoustic comfort evaluation by formulating a multivariate ordered logit model. This study also explores the inter-relationships among acoustic comfort evaluation, acceptability of the environment, and preference to stay in a park using a path model. A total of 595 valid responses were obtained from interview surveys administered in four parks in Hong Kong while objective sound measurements were carried out at the survey spots concurrently. The findings unveil that acoustic comfort evaluation, besides visual comfort evaluation of landscape, also plays an important role on users’ acceptability of the urban park environment. Compared with all the studied acoustic related factors, acoustic comfort evaluation serves as a better proxy for park users’ preference to stay in urban parks. Hearing the breeze will significantly increase the likelihood of individuals in giving high acoustic comfort evaluation. Conversely, hearing the sounds from heavy vehicles or sounds from bikes will significantly reduce the likelihood in giving a high acoustic evaluation.Department of Building Services EngineeringDepartment of Mechanical Engineerin