Measurement of low-frequency noise during CNC machining and its assessment

The aim of the paper is to point out the necessity to measure noise exposure by means of weighting filter Z, not only weighting filter A, which is prescribed by the standard. The measurement in the paper confirms the various acoustic pressure levels using weighting filter A and weighting filter Z at a low-frequency from 16 Hz to a frequency of 100 Hz. Such measurements suggest that the way in which this noise is evaluated must be adjusted. Due to the risks of exposure to excessive noise, the legislation prescribes regular measurement of permissible noise levels. European legislation and technical standards (e.g. ISO 1996) prescribe weighting A in case of such noise. However, this does not respect the energetic effect of sound on the auditory organ, as well as the neuropsychic and cardiovascular system of humans and sensory-motor functions. Experiments and research show that when evaluating low-frequency sounds with strong acoustic energy, the evaluation procedures should be adjusted to the impact of real acoustic energy affecting humans. The noise exposure measurement described in the paper was carried out during production of cars parts that were machined by a CNC machine. The measurement results showed that when weighting filter Z was used, the acoustic pressure levels were higher than those measured by weighting filter A by 22.8 dB. The measured equivalent L-Zeq values for the given work activity were 73.4 dB(Z) and L-Aeq was 50.6 dB(A). At low frequencies, this difference was the most pronounced, up to several times higher.