OBRABOTKAMETALLOV Vol. 23 No. 3 2021 MATERIAL SCIENCE EQUIPMENT. INSTRUMENTS 4 4 2 Ta b l e 3 Acoustic signal spectrograms of 3G71M machine systems Active system Spectrogram (1) power supply + (2) hydraulic power plant + (3) spindle rotation + (4) longitudinal feed An important fact to be considered in the further research is the stable “dip” in the idle operation spectrograms in the range of 1,900–2,100 Hz. When new overtones appear in the indicated range, we can affirm that it was caused by something not related to the sound of the idle machine operation. Thus, the spectral composition presented in Table 3 (4) is the relatively constant background “noise” accompanying the processes under study. This acoustic component should not be taken into account when
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