Beat Schäffer

Short-term annoyance reactions to stationary and time-varying wind turbine and road traffic noise: A laboratory studya)

Current literature suggests that wind turbine noise is more annoying than transportation noise. To date, however, it is not known which acoustic characteristics of wind turbines alone, i.e., without effect modifiers such as visibility, are associated with annoyance. The objective of this study was therefore to investigate and compare the short-term noise annoyance reactions to wind turbines and road traffic in controlled laboratory listening tests. A set of acoustic scenarios was created which, combined with the factorial design of the listening tests, allowed separating the individual associations of three acoustic characteristics with annoyance, namely, source type (wind turbine, road traffic), A-weighted sound pressure level, and amplitude modulation (without, periodic, random). Sixty participants rated their annoyance to the sounds. At the same A-weighted sound pressure level, wind turbine noise was found to be associated with higher annoyance than road traffic noise, particularly with amplitude modulation. The increased annoyance to amplitude modulation of wind turbines is not related to its periodicity, but seems to depend on the modulation frequency range. The study discloses a direct link of different acoustic characteristics to annoyance, yet the generalizability to long-term exposure in the field still needs to be verified.

Aircraft noise: Accounting for changes in air traffic with time of daya)

Aircraft noise contours are estimated using model calculations and, due to their impact on land use planning, they need to be highly accurate. During night time, not only the number and dominant types of aircraft may differ from daytime but also the flight paths flown may differ. To determine to which detail these variations in flight paths need to be considered, calculations were performed exemplarily for two airports using all available radar data over 1 year, taking into account their changes over the day. The results of this approach were compared with results of a simpler approach which does not consider such changes. While both calculations yielded similar results for the day and close to the airport, differences increased with distance as well as with the period of day (day<first hour of the night<second hour of the night, respectively, day<evening<night). Only the detailed calculation always accounted for the flight path changes in full detail. Possible legal consequences of such different modeling approaches are estimated, and the model results are compared to monitoring measurements. Finally, the situations for which the simpler approach is sufficiently accurate are ascertained.

Aircraft Noise Emission Model Accounting for Aircraft Flight Parameters

Today’s aircraft noise calculation programs either use simple sound source descriptions with few input parameters or highly sophisticated models with input parameters, which are difficult to obtain...

Sound absorption of textile curtains – theoretical models and validations by experiments and simulations

Textile curtains can be designed to be good sound absorbers. Their acoustical performance, as usually described by the sound absorption coefficient, not only depends on the textile itself but also on the drapery fullness and the backing condition, that is, the spacing between the fabric and a rigid backing wall, or the absence of a backing in the case of a freely hanging curtain. This article reviews existing models to predict the diffuse-field sound absorption coefficient, which to date can only predict the case of flat curtains. A set of existing models is extended to the case of curtains with drapery fullness using a semi-empirical approach. The models consider different backing conditions, including freely hanging curtains. The existing and new models are validated by comparing predicted sound absorption coefficients with data measured in a reverberation room. Hereby, curtains consisting of different fabrics and with different degrees of fullness are considered. Besides situations with rigid backing, also the measurement data of textiles hung freely in space are included in this study. Comparisons reveal a very good agreement between measured and predicted sound absorption coefficients. Compared to currently available commercial sound absorption prediction software that can only handle the situation of flat textiles with rigid backing, the results of the presented models not only show a better agreement with measured data, but also cover a broader range of situations. The presented models are thus well applicable in the design and development of new textiles as well as in the room acoustical planning process.

Conversion between noise exposure indicators Leq24h, LDay, LEvening, LNight, Ldn and Lden: Principles and practical guidance

This article presents empirically derived conversion rules between the environmental noise exposure metrics Leq24h, LDay, LEvening, LNight, Ldn, and Lden for the noise sources road, rail and air traffic. It caters to researchers that need to estimate the value of one (unknown) noise metric from the value of another (known) metric, e.g. in the scope of epidemiological meta-analyses or systematic reviews, when results from different studies are pooled and need to be related to one common exposure metric. Conversion terms are derived using two empirical methods a) based on analyzing the diurnal variation of traffic, and b) by analyzing differences between calculated noise exposure metrics. For a) we collected and analyzed diurnal traffic share data from European and US airports as well as data on the diurnal variation of traffic from roads in several European countries and from railway lines in Switzerland which were derived from counting stations and official records. For b) we calculated differences between noise metrics in over 50000 stratified randomly sampled dwellings in Switzerland. As a result of this exercise, conversion terms, including uncertainty estimates, are systematically tabulated for all variants of the target metrics. Guidance as to the practical applicability of the proposed conversions in different contexts is provided, and limitations of their use are discussed.

OP XI – 5 The proportion of high noise sensitivity and annoyance in the hermes cohort study of swiss adolescents

Background/aim The World Health Organization considers children to be of particular risk of suffering negative cognitive and health consequences through exposure to transportation noise. However, little is known about how adolescents experience exposure to noise in their everyday life. The purpose of this study is to examine level of both noise annoyance and sensitivity in a cohort of adolescents. Methods Noise sensitivity and annoyance was measured in a cohort of 892 participants aged 12 to 17 with one year follow-up. Noise annoyance for five different noise sources, including transportation vehicles, industry and people, was measured using a verbal 4 point Likert scale, where the annoyance was classified as follows: none (0), little (1), clearly (2), severely (3). Participants were classified as highly annoyed if they scored 2 or higher. Noise sensitivity was measured with the Zimmer/Ellermeyer (1998) scale ranging from 0 to 27. Individuals were classified as sensitive if they had a score over 13.5. Proportion of noise annoyed and noise sensitive participants are presented. Change between baseline and follow-up proportions were compared with the McNewmar-test. Results 847 students participated at the baseline measurement of the annoyance of road noise. Follow-up participation was at 806 (participation rate: 95.1%). The proportion of highly annoyed students was 4.40% (n=39) at baseline and 2.74% (n=23) at follow-up. The change in proportion after a year was quite significant (p=0.028). The noise sensitivity questionnaire was filled out by 887 students at baseline and follow-up was at 840 (participation rate: 94.7%). The proportion of highly noise sensitive students was 24.32% (n=206) at baseline and 24.07% (n=194) at follow-up, with no indications for a difference between baseline and follow-up (p=0.834). Within all comparisons gender was not substantial, except for baseline noise annoyance of two noise sources. Conclusion Our study suggests that prevalence of high noise annoyance is low in this age group and tends to decrease during puberty. Noise sensitivity seemed to be prevalent in a quarter of adolescents and stayed constant after a year. Future analyses should explore the relationship between annoyance, sensitivity, actual noise exposure and health outcomes.

Effects of Different Spectral Shapes and Amplitude Modulation of Broadband Noise on Annoyance Reactions in a Controlled Listening Experiment

Environmental noise from transportation or industrial infrastructure typically has a broad frequency range. Different sources may have disparate acoustical characteristics, which may in turn affect noise annoyance. However, knowledge of the relative contribution of the different acoustical characteristics of broadband noise to annoyance is still scarce. In this study, the subjectively perceived short-term (acute) annoyance reactions to different broadband sounds (namely, realistic outdoor wind turbine and artificial, generic sounds) at 40 dBA were investigated in a controlled laboratory listening experiment. Combined with the factorial design of the experiment, the sounds allowed for separation of the effects of three acoustical characteristics on annoyance, namely, spectral shape, depth of periodic amplitude modulation (AM), and occurrence (or absence) of random AM. Fifty-two participants rated their annoyance with the sounds. Annoyance increased with increasing energy content in the low-frequency range as well as with depth of periodic AM, and was higher in situations with random AM than without. Similar annoyance changes would be evoked by sound pressure level changes of up to 8 dB. The results suggest that besides standard sound pressure level metrics, other acoustical characteristics of (broadband) noise should also be considered in environmental impact assessments, e.g., in the context of wind turbine installations.

Noise exposure-response relationships established from repeated binary observations: Modeling approaches and applications

Noise exposure-response relationships are used to estimate the effects of noise on individuals or a population. Such relationships may be derived from independent or repeated binary observations, and modeled by different statistical methods. Depending on the method by which they were established, their application in population risk assessment or estimation of individual responses may yield different results, i.e., predict weaker or stronger effects. As far as the present body of literature on noise effect studies is concerned, however, the underlying statistical methodology to establish exposure-response relationships has not always been paid sufficient attention. This paper gives an overview on two statistical approaches (subject-specific and population-averaged logistic regression analysis) to establish noise exposure-response relationships from repeated binary observations, and their appropriate applications. The considerations are illustrated with data from three noise effect studies, estimating also the magnitude of differences in results when applying exposure-response relationships derived from the two statistical approaches. Depending on the underlying data set and the probability range of the binary variable it covers, the two approaches yield similar to very different results. The adequate choice of a specific statistical approach and its application in subsequent studies, both depending on the research question, are therefore crucial.

On the effect of acoustic diffusers in comparison to absorbers on the subjectively perceived quality of speech in ordinary rooms

Acoustic diffusers are used to control unwanted reflections responsible for degrading sound quality, or to increase sound diffuseness in spaces such as auditoria. To control unwanted reflections, diffusers are not the only solution. An alternative approach is the use of acoustic absorbers. Whether diffusers or absorbers are chosen as treatment depends on whether the energy conserved by the application of diffusers improves or detracts other aspects of room acoustics including the subjectively perceived qualities. However, not much is known to date about subjectively perceived qualities, e.g., of speech, in ordinary rooms. The aim of this study was twofold. The first aim was to investigate the effect of acoustic diffusers on the subjectively perceived quality of speech in ordinary rooms. The second aim was to determine if and to what extent there are perceptual differences if the diffuser are replaced by acoustic absorbers. Two separate listening tests were performed with stimuli obtained from the convolut...