Chapter 5 120 background noise of many workplaces (Hung & Hétu, 1996; Laroche et al., 1999; Patterson, 1990; Zheng et al., 2007). The advised number of spectral components required varies from three to four. We consider the spectral requirements for audibility met, when the warning signal has a minimum of three spectral elements (spectral levels measured in 1/3 octave bands) within the design window. Results Descriptives Warning signals An overview of the level and spectrum of the DSD and ATP signal is presented in Figure 1. The LAeq varies between the train types from 71.7 to 84.2 dBA for the DSD signal and from 68.2 dBA to 81.5 dBA for the ATP signal. The level of the DSD signal remains relatively constant over time, whereas the level of the ATP signal decreases (Figure 2). The high frequency components of the ATP signal are about 4.5 dB higher at onset than the average level that was used in the calculations. Figure 1. Octave-band spectra in dB SPL of the dead man’s switch and automatic train protection system in six Dutch train types. Additionally, the A-weighted equivalent sound pressure levels are shown.
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