High Fidelity Modeling and Experimental Evaluation of Binaural Bone Conduction Communication Devices

Bone conduction (BC) headsets can present audio when ambient sounds must be either blocked by hearing protection, or preserved to maintain situational awareness. Binaural BC is especially desirable to enable simultaneous talkers using spatialized audio. Development of advanced binaural BC devices has been limited by lack of empirical data, inadequate modeling and design tools, and difficult experimental procedures. We discuss our research with binaural BC, and present advanced modeling/simulation tools that use novel coupled AcousticsStructures Interaction modeling to analyze sound propagation from a BC speaker, through the elastic cranial bone, brain tissue, and cerebral spinal fluid to the cochlea, and further on to the hair cells on the basilar membrane. This high-fidelity anatomyand biomechanics-based modeling is used to analyze BC device performance at various head contact points, and to obtain parameters for compact (mass-spring-damper) models and “bone related transfer functions”. Those functions are used to predict speech intelligibility, which is then measured using psychophysical studies involving human listeners, and fed back into the models. The resulting listener-validated models can be used to further study BC processes in humans, and to develop more advanced binaural BC devices for use in the most challenging acoustical environments. INTRODUCTION Auditory displays are often delivered to a listener through headphones. Headphones allow private presentation of high-fidelity dichotic (stereo) sounds to a listener, without the perception changing as a person moves and turns, all in a portable package. On the other hand, there are problems with headphones. Covering the ears with headphones deteriorates detection and localization of ambient sounds in the environment. These external sounds may be of particular interest in augmented reality and tactical situations that require high situational awareness, as well as for visually impaired users who rely on environmental audio cues as their primary sense of orientation. Furthermore, headphones do not allow auditory display to occur simultaneously with earplugs. Bone-conduction headsets may lead to a useful alternative to headphones, since they avoid covering the ears of the listener. This may facilitate improvement in the detection and localization of environmental sounds, and allow the display of auditory information with hearing protection inserted into the ear canal. Bone-conduction devices also cater to the preferences of users who would rather not have their ears occluded for social, aesthetic or other reasons (e.g., visually impaired users [1]. With binaural bone conduction devices now becoming available, it is important to investigate whether they can serve as headphone replacements in situations where spatialized audio (stereo, 2D, or full 3D) has been beneficial. For example, one of the important uses of virtual 3D audio displays is the ability to increase detectability of signals amidst distracters and noise [2]. There has been considerable development in new bone-conduction hearing apparatus designed for use in auditory displays (see www.oiido.com; www.temco-