Degradation of Front-Back Spectral Cues Induced by Tactical Communication and Protective Systems

Invited paper

Thomas Joubaud

ISL - APC

Wednesday 3 june, 2015, 09:20 - 09:40

0.4 Brussels (189)

Abstract:
In many military or civilian situations, it is important to be able to communicate, perceive and interpret the acoustic environment while still being protected against damaging continuous and impulsive noises. Tactical communication and protective systems (TCAPS) correctly protect the listenerís ears from hazardous sounds and preserve intelligibility, thus allowing low-level speech communication. Our actual problematic deals with the conservation of the sound localization capability when wearing TCAPS. A previous subjective experiment, in which listeners were asked to localize sound sources in the horizontal plane with and without acoustically transparent earmuffs, highlighted that wearing the protection significantly degraded the listenersí localization capability. This degradation was mainly caused by front-back confusions. It has therefore been concluded that the protector altered the spectral cues used in open ear condition for the resolution of front-back ambiguities. In order to characterize the TCAPS-induced degradation of the spectral cues, directional transfer functions (DTFs) have been measured in the horizontal plane on an artificial head with and without TCAPS: passive and active earplugs and acoustically transparent earmuffs. DTFs are first averaged in each quadrant and the number of measurement positions which are needed in each quadrant is discussed. Front-back spectral cues are then defined, separately for ipsilateral and contralateral side, as the difference between front and back mean DTF. Results confirm that ipsilateral cues are preponderant for the resolution of front-back ambiguities in open ear condition, and show that wearing TCAPS affects not only ipsilateral but contralateral spectral cues. An index characterizing the alteration of the spectral cues allows the ranking of the different TCAPS according to how they induce degradation of the sound localization capability.

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