A sound wave is described by D$($y$,$t$)=(0\mathrm{.}0200$mm$)$D$($y$,$t$)=(0\mathrm{.}0200$mm$)$

sin$[(8\mathrm{.}96$rad$/$m$)$y$+(3140$rad$/$s$)$t$+$$/4$rad$]$sin$[(8\mathrm{.}96$rad$/$m$)$y$+(3140$rad$/$s$)$t$+$$/4$rad$],$ where yy is in mm and tt is in ss$.$