Part III: Measuring hearing-critical job tasks 121 Figure 2. Decay in sound pressure level in dB SPL for the Automatic Train Protection (ATP) and The Driver’s Safety Device (DSD) signal measured in Mat64. The ATP signal was filtered with a high-pass filter and a cut-off frequency of 400 Hz. Noise-field In total, 63 noise field measurements took place in 14 different trains with driving speed ranging from 40 to 130 km/h. The noise can be regarded as continuous noise. Figure 3 presents for each of the six train types the mean octave-band spectra and the mean LAeq of the background noise for the driving speeds 80 km/h, 100 km/h and for the maximum speed. When driving at 80 km/h, measured LAeq values range from 57.0 to 70.3 dBA. When driving at maximum speed, LAeq values range from 67.3 to 77.1 dBA. The differences in LAeq between the three driving speeds differ between the train types and this speed dependence is the largest in the ICM and the smallest in the Sprinter. No obvious changes in spectrum are observed when increasing the driving speed, except in the mDDm. When driving 100 or 130 km/h rather than 80 km/h, higher spectral noise levels were observed between 1 and 8 kHz. The results of the generalised linear model show that LAeq varies significantly between the different train types (df = 5, F = 29.70, p < .001) and driving speeds (df = 11, F = 6.80, p < .001). Additionally, the interaction term is significant (df = 18, F = 2.16, p = .032), which indicates that the effect of speed depends on the train type. The post-hoc tests reveal that three pairs of trains do not differ significantly from each other, specifically Loc1800 & Mat64, Mat64 & Sprinter, and ICM & V-IRM. The LAeq of Loc1800, Mat64, and the Sprinter are significantly higher than the LAeq of the ICM and the V-IRM. The LAeq of the Loc1800, is significantly higher than the LAeq of the Sprinter. Since LAeq significantly differs between the train types, we will evaluate the signal detectability of the different trains separately.
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