Quantification of the Envelopment Sensation by Sound during Underwater Listening Experience: the Work of a Bimodal Perception?

Investigating human hearing underwater through auditory thresholds have been of interest for nearly a century.The qualitative perception of sound underwater is however underexplored despite a growing quest by humans to enchant their senses in the water.We conducted two observational experiments involving underwater listening (ears underwater) and showed that Envelopment Sensation by Sound (ESS) was highly frequent (40 people out of 49) in both live aerial and underwater loudspeaker broadcasting (speech and music).This sensation involved the whole body, with a predilection for the head region (77.5%)followed by the trunk (55%).Our study, supported by an extensive bibliography, shows that the ESS is probably a bimodal perception; auditory and vibro-tactile.Our results corroborate the hypothesis that bone/soft tissue conduction mechanisms predominate in the stimulation of human hearing underwater, presumably reinforced by the vibrotactile stimulation of skin mechanoreceptors in the presence of low frequency acoustic stimuli (<1kHz).This bimodal synergy would be the source of the enveloping and penetrating sensation of sound described by the participants.Careful recommendations for the level and frequency content of underwater sound broadcasting will thus allow for an optimal musical experience underwater, particularly via low frequencies.