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Background noise is created by all the sounds which exist in the measurement spot and are not considered as an object of measurement or analysis (e.g. installations, industrial plants, roads). It can be also described as general noise level characteristic for a particular area excluding temporary or random acoustic events which are unusual or not linked with the region. The first definition of background noise is directly connected with metrological matter and estimation of noise emission of examined object while the second one is applied to assessment of acoustic climate in given area. Estimation of background noise level is a very complex task to perform and it is mostly impossible to unambiguously state it. Therefore, it is a common problem amongst acousticians who perform any type of environmental measurement. One of the reasons for such state of affairs is a lack of possibility to precisely determine the emission and annoyance of examined objects. Another reason is the nature of background noise. It can constitute a number of phenomena, each of different characteristics. They are mostly unpredictable and random. Therefore, measurement of background noise level involves many issues which make it difficult to create a universal indicator or coefficient which would unambiguously describe it. First of them is variability depending on the time of the day. Another one occurs when the acoustician faces a situation, when turning off the source is impossible. An example of this can be an industrial plant. Turning off a production even for a short period of time would involve huge financial losses. Another example is roads. There is no way to close off an area for measurement. On the other hand, it would also mean a considerable change in the characteristics of noise in the area which is not the point. Lastly, the biggest problem while estimating a background noise level is the impossibility to measure it directly during the acoustic event, only before or after it occurs. The most common way to evaluate the background noise level and to recognize its source is the use of statistical levels in 1/3 octave bands in particular. The aim of the project is to present the results of all day measurements in two different places in respect of acoustic environment and to assess the effectiveness of using statistical noise levels in the estimation of background noise level. Comparison of statistical levels calculation and direct background noise measurement has been the basis for this assessment. The method, called “silence cutout”, consisted in subjectively selecting “silences” from the measurement recording and denoting them as actual background noise which eliminated random acoustic events. It showed how different times of the day are characterized by different values of background noise level and, therefore, should be described with different statistical levels. The uncertainty of proposed estimation method has been analyzed. Additionally, a way was proposed to evaluate acoustic climate of particular area with the help of spectral examination. For this purpose statistical analysis of 1/3 octave spectra characteristic for given acoustic climates has been carried out.
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