The first error appears in Eq. (18) of Ref. , where the right-hand side is given to be −∂q/∂t, instead of the correct one –q, where q is the volume displacement per unit volume. So, the correct form of Eq. (18) in Ref.  is
with Ψ the velocity potential and c0 the sound speed in the fluid media. Equation (1) can be easily found from Eq. (7.1.16) of Ref. , combined with , on page 325 of Ref.  and also from Eq. (III.4) (page 46 of Ref. ) by using its form in the time domain, combined with the equation p = ρ...