  The simulation of two-dimensional (2D) wave propagation is an affordable
computational task and its use can potentially improve time performance in
vocal tracts' acoustic analysis. Several models have been designed that rely on
2D wave solvers and include 2D representations of three-dimensional (3D) vocal
tract-like geometries. However, until now, only the acoustics of straight 3D
tubes with circular cross-sections have been successfully replicated with this
approach. Furthermore, the simulation of the resulting 2D shapes requires
extremely high spatio-temporal resolutions, dramatically reducing the speed
boost deriving from the usage of a 2D wave solver. In this paper, we introduce
an in-progress novel vocal tract model that extends the 2D Finite-Difference
Time-Domain wave solver (2.5D FDTD) by adding tube depth, derived from the area
functions, to the acoustic solver. The model combines the speed of a light 2D
numerical scheme with the ability to natively simulate 3D tubes that are
symmetric in one dimension, hence relaxing previous resolution requirements. An
implementation of the 2.5D FDTD is presented, along with evaluation of its
performance in the case of static vowel modeling. The paper discusses the
current features and limits of the approach, and the potential impact on
computational acoustics applications.
