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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
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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,
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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
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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