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Hearing threshold measurements for infrasound combined with audiosound

Since infrasound exposure on humans is usually accompanied by sound in the conventional hearing range (between 20 Hz and 20 kHz, hereafter called “audiosound”), it is highly valuable to investigate which role the combination of infrasound and audiosound plays for the perception of infrasound. Therefore, we performed hearing threshold measurements for infrasound combined with audiosound. One aim was to investigate whether the presence of audiosound influences the hearing threshold levels of infrasound, and vice versa, whether the presence of infrasound influences the hearing threshold levels of audiosound.

13 normal hearing subjects aged between 18 and 30 years participated in the hearing threshold measurements. The sound signals were generated by a specially developed sound source system (see Fig. 1, described in the previous newsletter of July 2017) and were presented to the subjects through eartips.

All in all, we observed that the threshold levels of audiosound were hardly influenced by the presence of infrasound. On the contrary, the threshold levels of infrasound were on average increased by the presence of audiosound presented at a moderately loud level. In addition, we have found that some subjects were hardly affected by the presence of audiosound, whereas others showed large threshold shifts of infrasound.