Speaker
Description
This study was carried out within CEN TC256 WG3 as part of ongoing work towards a new European standard for evaluating audible warnings in train drivers’ cabs. The purpose was to investigate and compare methods of assessing audibility to inform the proposal for a standardised methodology.Controlled subjective tests were conducted in a mock-up train cab, where ambient noise recordings from several train cabs were replayed at realistic levels and eight representative warning sounds were superimposed. Participants rated the audibility of each sound presented at each of seven signal-to-noise ratios. These subjective results were compared to the TSI LOC&PAS homologation requirement (+6 dB signal-to-noise ratio) and to sound levels computed using ‘Detectsound’, a tool developed by the University of Ottawa to predict the audibility of sounds in noise from the one-third octave band spectra of the signal and noise. Detectsound models the auditory filter characteristics of the ear and takes into account the hearing abilities of different listener populations.Initial findings confirm that the +6 dB signal-to-noise criterion aligns with perception for speech signals but tends to be conservative for tonal warning sounds, resulting in warning sounds that are sometime louder than desirable. Detectsound calculations show closer agreement with perceived audibility, although discrepancies remain. Detectsound also highlights the substantial influence of hearing ability. Warning sound levels need to be increased by 5 dB to 7 dB for persons just meeting the minimum hearing requirement for train drivers in Europe compared with persons with normal hearing.