We study the viscous van Wijngaarden–Eringen equation: ∂2u ∂t2 − ∂2u ∂x2 = (Red)−1 ∂3u ∂t∂x2 + a2 0 ∂4u ∂t2∂x2 (1) which corresponds to the linearized version of the equation that models the acoustic planar propagation ...