  This paper considers methods for audio display in a CAVE-type virtual reality
theater, a 3 m cube with displays covering all six rigid faces. Headphones are
possible since the user's headgear continuously measures ear positions, but
loudspeakers are preferable since they enhance the sense of total immersion.
The proposed solution consists of open-loop acoustic point control. The
transfer function, a matrix of room frequency responses from the loudspeakers
to the ears of the user, is inverted using multi-channel inversion methods, to
create exactly the desired sound field at the user's ears. The inverse transfer
function is constructed from impulse responses simulated by the image source
method. This technique is validated by measuring a 2x2 matrix transfer
function, simulating a transfer function with the same geometry, and filtering
the measured transfer function through the inverse of the simulation. Since
accuracy of the image source method decreases with time, inversion performance
is improved by windowing the simulated response prior to inversion. Parameters
of the simulation and inversion are adjusted to minimize residual reverberant
energy; the best-case dereverberation ratio is 10 dB.
