Therefore, if you need to densely measure noise levels at a large number of locations, you will need a larger number of sound level meters and a larger number of qualified persons to perform measurements for a longer period of time.Īnother approach of collecting data is to use noise mapping calculations with known acoustic sound power of sound sources (traffic, industry, etc.). In addition, this type of measurement is very expensive simply because Class 1 sound level meters are very complicated and expensive equipment. In terms of traffic noise measurement, such manual data collection method at each measurement position can be very time-consuming and expensive ( Mitsunobu et al., 2012) i.e., due to the nature of sound and noise, it is necessary to measure noise levels especially densely at a particular location. These calibrators generate a pure tone at 1000 Hz, and they produce nominally 94 dB or with some calibrators 114 dB. Sound level meters should be calibrated before use, using a pistonphone calibrator placed over the microphone. In addition, there are several other classes of sound level meters however, in this chapter, they will not be discussed (i.e., they are not significant with respect to the theme of this chapter).įinally, the sound level meter acquires the sound pressure level at a particular location, and furthermore, it needs to be calibrated before and after each set of measurements. It is usually used for assessing noise in work environments, basic environmental measurements, entertainment noise, construction noise, and vehicle noise. Ĭlass 2-general purpose grade for field use with a tolerance of ☑.0 dB.It is ideal for laboratory use, environmental applications, building acoustics, and traffic assessments. Ĭlass 1-precision grade for laboratory and field use with a tolerance of ☐.5 dB.Sound level meters are graded according to the International Standards ( IEC 60942:2017): “A”- and “C”-weighting coefficients for several tertiary frequency bands are shown in Fig. 15.8 ( Finn et al., 2011). In majority of real case scenarios, sounds are not pure tones on the contrary, sounds are very complex signals with many different tones ( Brüel & Kjær Online Library). One reason and explanation for this lack of correlation between subjective tests and “B” and “C” weighted measurements is that the equal loudness contours were based on experiments, which used pure tones. Nowadays the “A”-weighting network is the most widely used since the “B” and “C” weightings do not correlate well with subjective tests. This does not weight the signal, but it enables the signal to pass through unmodified. In addition to one or more of these weighting networks, sound level meters usually have a linear or “Lin.” network. A specialized characteristic, the “D”-weighting, has also been standardized for aircraft noise measurements. The “A”-weighting network weights a signal in a manner, which approximates an inverted equal loudness contour at low Sound Pressure Levels (SPLs) the “B”-weighting network corresponds to a contour at medium SPLs and the “C”-weighting network corresponds to an equal loudness contour at high SPLs. This has resulted in three different internationally standardized characteristics termed “A,” “B,” and “C” weightings. The signal may pass through a weighting network, which is an electronic circuit whose sensitivity varies with frequency in the same way as the human ear, thus simulating the equal loudness contours ( ISO:226:2003). Therefore, the sound pressure filter is used to filter the sound signal according to different coefficients for evaluation at different frequencies. The human ear does not represent a linear system, i.e., the “sensing” level is not the same for different frequencies (e.g., 100 Hz and 1 kHz).
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