Showing papers by "Dick Botteldooren published in 2007"

Experimental investigation of noise annoyance caused by high-speed trains.

Abstract: The difference in perceived noise annoyance caused by train and highway noise at the same averaged noise level, has led to the introduction of the ’railway bonus’. This bonus has found its way to t ...

Comparison of measurements and predictions of sound propagation in a valley-slope configuration in an inhomogeneous atmosphere

Abstract: Mountainous areas form a very specific context for sound propagation: There is a particular ground effect and meteorological conditions are often extreme. In this paper, detailed sound propagation calculations are compared to noise measurements accompanied by meteorological observations. The sound source considered is road traffic along the center axis of a valley. Noise levels were measured in two cross sections, at three locations each: one on the valley floor and two on the slopes, up to 166 m above the source. For the numerical calculations, the rotated Green's function parabolic equation method is used, taking into account the undulation of the terrain and an inhomogeneous atmosphere. Typical parameters of this method were optimized for computational efficiency. Predictions agree with measurements to within 3 dBA up to propagation distances of 1 km, in windless conditions. The calculations further show that the terrain profile is responsible for an increase in sound pressure level at distant, elevated points up to 30 dBA compared to a flat ground situation. Complex temperature profiles account for level changes between -3 dBA and +10 dBA relative to a homogeneous atmosphere. This study shows that accurate sound level prediction in a valley-slope configuration requires detailed numerical calculations.

Microsimulation based corrections on the road traffic noise emission near intersections

Abstract: Urban noise mapping traditionally involves the use of a traffic simulation model, which is often based on the estimation of macroscopic traffic flows. However, intersections and other local traffic management measures are not always modeled correctly. It is well known that the specific deceleration and acceleration dynamics of traffic at junctions can influence local noise emission. Finding the best strategy for using traffic modeling results in noise mapping is a current topic of research in the IMAGINE project. In this paper, a case study is presented, consisting of a large set of microscopic traffic simulations and associated noise emission calculations, which provides some insight into the specific dynamics of the noise emission near different types of intersections. It will be shown that it is possible to refine current traffic noise prediction models, based on macroscopic traffic simulation, using a correction on the average vehicle emission, aggregated in lane segments. A spatial approach should be used, in which inbound and outbound lanes are divided into deceleration, queuing, stopline and acceleration zones. Results from regression analysis on the numerical simulations indicate that meaningful relations between noise corrections and traffic flow parameters such as traffic intensity and composition can be deduced.

Models for soundscape perception and their use in planning

Abstract: In this paper, our ongoing research towards a unified model for the perception of the sonic environment is discussed in the context of planning. In contrast to most research, which relates soundscape descriptors to perception in a fashion strongly related to epidemiologic research, a bottom-up approach is followed. The individual sensory, cognitive and emotional mechanisms that play a role in soundscape perception are discerned, and a first step is taken into making the knowledge available in literature explicit, by building a human mimicking software model. In particular, such a model is able to reproduce and explain, in a qualitative way, trends as observed in epidemiological research on soundscapes. For urban soundscape planning, the proposed model can complement or substitute auralisation. A mixture of existing and planned sounds is fed to the model. Taking into account the variability in personal characteristics of a synthetic population of visitors, noticing of natural, human, and mechanical sounds is evaluated. Taking into account the meaning of these various types of sounds within the given context (e.g. a city park), the sonic environment is evaluated. This evaluation conceptually involves cognitive processes that depend on personal and cultural background of each visitor. Since modern times, noise effect research has focused strongly on negative effects of mainly the mechanical and electronic sounds that have invaded our society since the 1930’s. The workplace and homes of the population are of main concern in this research because of the substantial amount of time people spend there. Soundscape research takes a more positive approach. The sonic environment is studied in a particular physical and social context taking into account its typical use. The description and evaluation of the sonic environment approaches the level of detail that music or landscape researchers have reached – or have been trying to reach – for many years. Appraisal by individual users of the soundscape is a key factor. It depends on personal factors in many different ways. An overview of recent advances in the field can be found in [1]. In soundscape research, remarkably little use has been made of simulation. Simulation involves incorporating all available knowledge on perception, appreciation, evaluation, etc. in a human-like computer model. By running this model, insight can be gained in the complex mechanisms involved. These models often exhibit emergence: new overall behavior that was not explicitly modeled is observed. Constructing the model on itself is a fruitful process since it forces the scientist to make available knowledge explicit.

The effects of noise from combined traffic sources on annoyance: the case of interactions between rail and road noise

Abstract: The combination of rail and road (highway, main roads) noise exposure is highly prevalent in European countries. In Germany, the number of people exposed to both were estimated to be around 11 millions. Although increasing consi deration has been given to the effects of noise from combined traffic sources at conferenc es during the last decade (Internoise 1996, 1997, 2000, 2001, 2006) the scientific community still lacks a full understanding of this issue. Its proper understanding is, however, i mportant for regulatory purposes. Therefore, it is not surprising that in current pra ctice the community response to noise is assessed source by source. In 2006, a socio-acoustic survey (N=1643) was repeated in the same alpine valley with the same questionnaire as in 1998 (N= 2007). Thus, we were able to evaluate and extend our earlier analyses. Results: Annoyance due to rail noise is significant ly modified through additional highway or main road noise. This modifying effect takes pre ferably place beyond 300m from the rail track. Overall, when the rail exposure is sign ificantly higher (>6dBA) than the highway noise the combined effect is strongest. Fin ally, the exposure pattern observed in this survey (alpine valley) differs substantially f rom the exposure pattern seen in a large survey (N=7500) in Flandern (plain area).

Soundscape classifying ants

Abstract: In this paper, the use of fuzzy ant clustering in classifying a large database of environmental soundscape recordings is outlined. Fuzzy ant clustering is a soft computing technique inspired by the clustering behaviour observed in colonies of several ant species. Virtual ants or “agents” move through the database, “pick up” soundscape recordings and drop them on places where similar recordings are present. Similarity of soundscape recordings is expressed by fuzzy resemblance of the shape of the SPL histogram, the frequency spectrum and the spectrum of temporal fluctuations, representing loudness, spectral and temporal content. The fuzzy IF-THEN rules, governing the behaviour of the virtual ants, are optimized using a specially adapted genetic algorithm, in order to achieve an optimal set of homogeneous clusters. Advantages of this approach, as compared to traditional clustering methods, are that no a priori information, such as the desired number of clusters, is needed, and that a more flexible set of indicators can be used. The clustering model is validated on a database of acoustic measurements of 1116 soundscapes, made in 16 urban parks in Stockholm, and results are compared with visitor survey data on soundscape quality.

Acoustic indicators of soundscape quality and noise annoyance in outdoor urban areas (invited paper)

Abstract: Acoustic indicators grounded in soundscape perception are needed for predicting the quality of soundscapes in urban outdoor areas. The present paper explores the predictive power of various acoustic indicators. A questionnaire study was conducted in 16 city parks and green open spaces in Stockholm. In total, 1116 respondents answered questions on, inter alia, perceived soundscape quality and road-traffic noise annoyance. One-third octave band levels were continuously logged during data collection. From these acoustic measurements, a number of indicators were calculated representing overall level, spectral content and timevariability of the soundscape. These indicators were calculated for each respondent separately, referring to the 10-min period during which the participant filled in the questionnaire. Indicators related to the overall sound level explained a substantial part of the variance in perceived soundscape quality and road-traffic noise annoyance. Indictors related to the spectral content only explained a small part of the variance not accounted for by overall sound level. Perception of nature sounds and technological sounds, as measured in the questionnaire, were strong predictors of soundscape quality and noise annoyance, also after adjustment for overall sound level. This suggests that prediction of soundscape quality would benefit from the development of acoustic indicators of sound source audibility within soundscapes. INTRODUCTION Outdoor environments, particularly parks and green areas, provide invaluable opportunities for physical exercise and psychological restoration. Walks in urban parks constitute preventive measures for ill-health caused by a sedentary or stressful life style. The risk is that noise pollution hinder people’s outdoor stay, which in a long-term perspective is a threat to public health. Therefore, the EC-directive on environmental noise points to the need for protection of existing quiet urban areas [1]. It also stresses the need for supplementary noise indicators for quiet areas (Annex I.3). Alternative acoustic indicators relevant for soundscape perception in outdoor spaces has been proposed [2,3]. The present paper explores the relationship between visitor’s assessments of outdoor soundscapes and various acoustic indicators, using data collected in several city parks and open green spaces in Stockholm. Previous studies has suggested that sound source identification is a main determinant of perceived soundscape quality [4,5,6]. Therefore, the relationship between sound-source identification, as measured in the questionnaire, and soundscape assessment was also explored.

The Rhythm of the Urban Soundscape

Abstract: The influence of noise on the quality of the urban living environment has traditionally been studied focusing on negative effects on man, such as noise annoyance and sleep disturbance. Recently a more holistic approach, including positive and negative aspects as well as non-residential functions of the urban environment, has gained renewed interest. The label “urban soundscape” is often used to refer to this approach. Research towards selection and quantification of the acoustic descriptors of the urban soundscape is, however, still in an early stage. This paper draws on the analogy with music and self-organization to propose an indicator for studying the temporal structure of the urban soundscape. Applicability is illustrated by drawing a map of music-likeness of the soundscape in an urban area.

An agent based modeling approach to explain the perception of environmental stressors

Abstract: Artificial intelligence traditionally draws inspiration from biological systems, in order to achieve a similar degree of intelligence in artificial systems. More recently, ideas from computational intelligence are being applied successfully in achieving a better understanding of the mechanisms underlying the emergence of group-level patterns in biological and sociological systems. In this paper, the use of an intelligent software agent for mimicking the human response to environmental stressors is proposed. The conceptual model for a single individual contains strongly interacting submodels for sensory observation of the environment, cognition and emotion. A partial implementation of this model, focused on auditory perception, is applied to gain additional insight in the underlying mechanisms that lead to the emergence of noise annoyance at the community level. In particular, it is shown that this new approach may give a possible explanation for the difference in annoyance between road and railway traffic for equal sound level, as is observed in numerous noise surveys and laboratory experiments.

Verifying the attenuation of earplugs in situ: comparison of transfer functions for HATS and human subjects

Abstract: Recent studies have clearly demonstrated that hearing protector’s attenuation determined in laboratory conditions significantly exceeds the actual protection offered to the individual user. Hence, the performance of hearing protection devices should also be verified in-situ, for instance by the MIRE-method (Microphone In Real Ear). The attenuation is hereby calculated from the difference in sound levels outside the ear and inside the ear canal behind the hearing protector. To apply this technique without altering the protector’s characteristics, a custom-made earplug with an inner bore that allows insertion of a miniature microphone can be used. However, this approach does not account for differences between the sound spectrum at the microphone and at the eardrum. Therefore, studies have been conducted with a head-and-torso-simulator and human subjects to determine the transfer function between these two points for protectors manufactured in acrylic and silicone. The use of different materials resulted in clearly distinguishable functions, but the characteristics of the spectrum in general correlated with the acoustical features of the earplug’s design. All transfer functions showed a comparable global configuration, however variability among humans was substantial for the exact frequency and amplitude of the major pressure differences.

Models for soundscape perception and their use in planning (invited paper)

Abstract: In this paper, our ongoing research towards a unified model for the perception of the sonic environment is discussed in the context of planning. In contrast to most research, which relates soundscape descriptors to perception in a fashion strongly related to epidemiologic research, a bottom-up approach is followed. The individual sensory, cognitive and emotional mechanisms that play a role in soundscape perception are discerned, and a first step is taken into making the knowledge available in literature explicit, by building a human mimicking software model. In particular, such a model is able to reproduce and explain, in a qualitative way, trends as observed in epidemiological research on soundscapes. For urban soundscape planning, the proposed model can complement or substitute auralisation. A mixture of existing and planned sounds is fed to the model. Taking into account the variability in personal characteristics of a synthetic population of visitors, noticing of natural, human, and mechanical sounds is evaluated. Taking into account the meaning of these various types of sounds within the given context (e.g. a city park), the sonic environment is evaluated. This evaluation conceptually involves cognitive processes that depend on personal and cultural background of each visitor. Since modern times, noise effect research has focused strongly on negative effects of mainly the mechanical and electronic sounds that have invaded our society since the 1930’s. The workplace and homes of the population are of main concern in this research because of the substantial amount of time people spend there. Soundscape research takes a more positive approach. The sonic environment is studied in a particular physical and social context taking into account its typical use. The description and evaluation of the sonic environment approaches the level of detail that music or landscape researchers have reached – or have been trying to reach – for many years. Appraisal by individual users of the soundscape is a key factor. It depends on personal factors in many different ways. An overview of recent advances in the field can be found in [1]. In soundscape research, remarkably little use has been made of simulation. Simulation involves incorporating all available knowledge on perception, appreciation, evaluation, etc. in a human-like computer model. By running this model, insight can be gained in the complex mechanisms involved. These models often exhibit emergence: new overall behavior that was not explicitly modeled is observed. Constructing the model on itself is a fruitful process since it forces the scientist to make available knowledge explicit.

Influence of temporal resolution of meteorological and traffic data on long-term average sound levels

Abstract: A theoretical study is conducted to investigate the impact of different time-averaging approaches with regard to meteorological conditions (influencing sound propagation), traffic intensity patterns, and correlation between them, on calculated noise levels. The indicators L den and L night , prescribed by the European Environmental Noise Directive for noise mapping, are of main interest. Sound propagation over flat ground from a long, straight highway is simulated, for receiver distances ranging from 50 m to 2000 m. Detailed, meteorological data from a tower (located near Mol, Belgium), for a full year, is used. An extended database containing yearly-averaged hourly traffic counts is available. Detailed sound propagation calculations are made with the Green's Function Parabolic Equation method, accounting for the refractive state of the atmosphere and range-dependent ground effect. The imprecision introduced by averaging meteorological conditions and traffic intensities over time, and by not fully accounting for the temporal correlation between them, may result in an underestimation up to 20dB(A) for one-day L den values, using this particular meteorological data set. For yearly-averaged values, the imprecision may reach 3dB(A). For L night , very similar conclusions could be drawn. Multiple linear regression analysis is used to rank the factors that contribute to the imprecision. This led to the conclusion that the decrease in accuracy resulting from different averaging approaches is mainly proportional to the variability in the refractive state of the atmosphere over a 24 hour-period. The type of traffic intensity profile may intensify this error up to 10dB(A). The use of meteorological data, statistically-averaged over the year, results in a small loss in accuracy compared to calculating noise levels for every hour of the year and averaging the result afterwards. The error introduced by the approach used to average meteorological condition and traffic intensity over the day is not affected by this.

Verifying the attenuation of earplugs in situ: the importance of transfer functions

Abstract: The European Noise Directive (2003/10/EC) on exposure limit values stipulates that the worker’s effective exposure must take account of the attenuation provided by the individual hearing protector. This can be fulfilled by measuring the noise level behind the protector. To address the issue without altering the protector’s characteristics, a custommade earplug with an inner bore that allows insertion of a miniature microphone can be used. However, this approach does not account for differences between the sound spectrum at the microphone and at the eardrum. Therefore, a study has been conducted with a head-and-torso-simulator to determine the transfer function between these two points.