Augmented reality devices must also produce correct sounds, and compensate for environmental noise. Creating virtual sounds based on the real world requires sound reflections to spread and interact with the environment appropriately. For example:
- • Airports offer limited sound reflections, and have significant ambient sound.
- • Hotel rooms have significant sound dampening.
- • Conference rooms are enclosed room with reflective surfaces.
- • Virtual people should sound like they are in the conference room.
To deal with all those different conditions the augmented reality system must employ noise cancelation and environment modeling, positional audio, noise filtering, and reverberation dampening.
Headphones can be built into helmets, and earbuds are also an acceptable means of providing the user with audio input for either headsets, smart glasses, or helmets. Sound is a necessary capability for when the unit is to be used in loud environments.
Google Glass was one of the first augmented reality devices to employ bone conduction technology BCT which transmits sound through bones in your skull to the inner ear. BCT has a proven track record as it is used in the Military and medical world (Fig. 8.53).
This type of speaker does not have a moving membrane like traditional speakers, rather a small metal rod is wrapped with a voice coil. When current is pulsed through the coil, the magnetic field causes a piece of metal to expand and contract. When pressed against the jaw or skull it turns bone into a speaker. The effect is quality sound that seems to be coming from within one’s head which others cannot hear, yet
Fig. 8.53 Bone conduction sound device cannot be heard by others (Cochlea.org)
since the ears are not covered the user is not isolated from ambient sounds and therefore not vulnerable to the dangers of traditional earphones.
One commercial example is the Buhelusa’s SGO5 headset that features a built-in bi-directional microphone, and provides bone conduction technology that allows one to listen to calls and music with no headsets or earphones.