Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
paper ID: 347 /p.1 How to Evaluate Noise Impact K. Genuit HEAD acoustics GmbH, Ebertstraße 30a, 52134 Herzogenrath, Germany, [email protected] Men live in a landscape full of noises which are composed of both natural environmental noises and technically created sounds. Regarding an environmental impact, more and more people feel heavily annoyed by noises. Thus, the question arises, how this noise impact by the acoustical environment can be accurately recorded and defined, so that the resulting statements reflect, how the affected people feel and what they describe. This approach cannot be one-dimensional. In addition to the physical aspect of a sound event there also have to be considered the psycho-acoustical features of the ear as well as the psychological components of the affected people. 1. INTRODUCTION: WHAT IS NOISE? According to DIN 1320 noise is defined as an audible sound which either disturbs the silence or an intentional sound listening or leads to annoyance. Thus, it is clearly defined that the assignment of noise cannot be reduced to simple determining objective parameters, such as the A-weighted sound pressure level or the equivalent continuous sound pressure level offhand. According to DIN 1320 a sound event can be characterized as noise not until it disturbs or leads to annoyance. Thus, the question, whether a sound is sensed as noise can only be made a subject of discussion after the transformation from the sound event into an auditory event has been accomplished. This illustration resp. transformation from sound events into auditory events differs individually and depends on many parameters eluding from the metrological quantifiable determination. It is remarkable that, whenever noise annoyance is at hand, this noise impact being expressed by people is exclusively analyzed by simple measurement techniques, such as the determination of the A-weighted sound pressure level or the A-weighted equivalent continuous sound pressure level. These two measured values are certainly suitable to assess if particular sound events may lead to hearing damages. However, they are not sufficiently suitable to characterize a complex sound recording and analysis by the human ear in connection with the cognitive features of man. 2. EVALUATION OF NOISE The evaluation of noise depends on the physical characteristics of the sound event, on the psycho-acoustical features of the human ear as well as on the psychological aspects of man. Regarding the evaluation of noise, the consideration of the psycho-acoustical features of the human ear leads to significantly improved differentiated statements than the simple reflection by the A-weighted sound pressure level. Among other things, the loudness e.g. considers the spectral distribution in opposite to the A-weighted sound pressure level measurement. It is absolutely conceivable that noises with the same A-weighted sound pressure level are sensed as being unequally loud. In the field of psychoacoustics, another important dimension for the annoyance by noise has been defined by the sharpness. It describes the relation of higher frequent sound components to the total loudness. By means of the fluctuation strength and the paper ID: 347 /p.2 roughness, modulations in the sound event are characterized which -depending on its degreehave a noticeable influence on the noise impact. Finally, via sharpness, fluctuation strength and roughness certain patterns in the sound event are described. These patterns are fairly levelindependent, that means a reduction of the level with unmodified disturbing pattern in the sound event leads to almost unaltered annoyance by the noise. 3. SOUNDSCAPE According to figure 1 SoundScape means the complex interference of natural and technical noises. While judging the sound quality or the impact by noise it is important to know in which way what features of SoundScape have an effect on man. As generally known, the human ear is able to classify the complex SoundScape of noises into single sound events because of its binaural hearing and its consequential directional hearing and selectivity. Thus, it has not necessarily be assumed that only the sum is decisive for the annoyance by a sound event. It is absolutely conceivable that single contributions of SoundScape can be selected and influence the individual evaluation decisively. Thus, if in an existing SoundScape the affected people complain about noise annoyance, the actual reasons for this noise objection have to be found out first. · · · · · · Is it the time structure? Is it the informative features of the noise? Is it the people’s attitude towards the causes of the noise? Is the noise unpleasant or conspicuous due to modulation or noticeable patterns in time or frequency range unpleasant or conspicuous? Which of the existing sound sources causes noise annoyance? Etc. SoundScape Technical Noises Sounds of Nature Wind Water Animals Traffic Recreational Industrial Noise Pollution World Figure 1. Schematic Diagram of SoundScape Not until the reasons for the noise annoyance in a SoundScape are found, another analysis might be reasonable to bring about possible changes. On one hand, such changes at a SoundScape can be accomplished by reducing or eliminating possible sound sources with unpleasant features, paper ID: 347 /p.3 however, on the other hand it is also conceivable to mask other sound sources with less acceptance regarding sound quality by adding single sound sources with high acceptance. In other words, if there does exist a noise annoyance in a SoundScape, it is not advisable to base on the A-weighted sound pressure level or the equivalent continuous sound pressure level measurement in order to provide the evidence that no noise annoyance can be present. There does exist an immense misunderstanding regarding the aurally-accurate evaluation of sound events, indeed. While the dangers of noise regarding noise-induced hearing damage is necessarily describable by means of the A-weighted sound pressure level, a simple transference on the question regarding noise annoyance cannot be given offhand. Level, Linear A-B-CWeighted Duration Energy Spectral Distribution Subjektive Attitude Parameters of Sound Quality Time Structure Signal Information Spatial Distribution Movement Number Position Figure 2. Parameters Effecting Sound Quality When developing a measurement technique for the physiological evaluation of noise effects with regard to the psycho-acoustical features of the human ear [1] and in special consideration of the working place, it was attempted for the first time and on the basis of the artificial-head measurement technique and the psycho-acoustical methods of analysis to apply the new cognitions of the aurally adequate sound analysis to noise at the working environment–. These aurally adequate sound recordings and analysis techniques have found their applications in the automotive industry for many years, especially in regard of the vehicle interior noise quality [2, 3]. The studies of noise at working places basically were only carried out at working places showing an A-weighted sound pressure level noticeably falling below 85 dB(A), thus guarantying that an ear damaging effect of noise could be excluded. In the context of this analysis many new cognitions for both evaluation and validation of noise were gained, thus, among other things, the fact that the spatial distribution of different sound sources and their position to each other or even their movements have significant physiological effects on the test persons. Hence it can be derived - as shown in figure 2 - that the description of sound quality is clearly more comprehensive resp. multidimensional. The A-weighted sound pressure level surely paper ID: 347 /p.4 is not a wrong, but in no case a sufficient measurement technique to describe the subjectively sensed noise annoyance adequately. The lesser the A-weighted sound pressure level of a sound event or the loudness is, the more important become the patterns in time and frequency range of the sound event for the evaluation of sound quality or even of the subjectively sensed noise annoyance. This so-called adaptability [4] of the human ear refers to an important non-linearity of the hearing, that means an adaptation to the noise situation takes place. Changes in time and frequency range in a wide field are realized without consideration of the absolute level as a pattern and are consulted for the evaluation of a noise situation. 4. CONCLUSIONS The consideration of SoundScape regarding its effect on man becomes more and more important. Due to the fact that the human ear is always active and cannot simply be switched off as the eye, man is quasi committed to noises. Whereas the coherence between noise-induced hearing damage and the A-weighted sound pressure level still can be simply and safely presented in the high level range, , the general transformation of sound events into auditory events within a SoundScape and the involved possibilities of noise annoyance are much more complex and do need a stronger interdisciplinary co-operation between various branches of study, such as acousticians, psycho-acousticians, physicians, sociologists and psychologists. If people complain about noise and feel harassed and the engineer’s answer refers to the A-weighted sound pressure level, the danger of a misunderstanding is predetermined. Although it is known from the studies on the sound quality of vehicle interior noises that the complaints regarding noises cannot be determined by simple measurement techniques – for it is known that the signal processing of the human ear is more complex and the automotive industry and their suppliers therefore use ear-related measurement and analysis techniques throughout the world - it is still attempted to correlate environmental noises, noises at working places or generally SoundScapes with the casually resulting annoyance by noise with simple A-weighted sound pressure level. REFERENCES 1. K. Genuit, et.al., “Entwicklung einer Messtechnik zur physiologischen Bewertung von Lärmeinwirkungen unter Berücksichtigung der psychoakustischen Eigenschaften des Menschlichen Gehörs”, Schriftenreihe der BAU, Fb 774, Dortmund/Berlin 1997 2. K. Genuit, “Kunstkopf-Messtechnik - Ein neues Verfahren zur Geräuschdiagnose und –analyse”, Zeitschrift für Lärmbekämpfung 35, Dez. 1988, S. 103-108 3. K. Genuit, “Grundlagen der Psychoakustik”, HDT-Essen Fahrzeugakustik, 03.-04.12.1996, Essen 4. K. Genuit, Objective Evaluation of Acoustic-Quality Based on a Relative Approach, Inter-Noise’96, 30.07.-02.08.1996, Liverpool, England