Thanks, I know a popular toolbox used in my field - k-wave, uses a PML. I thought that was primary due to them using a spectral method to solve the acoustic wave equation though. I wasn’t sure if a hacky solution of just setting the pressure at the edges to zeros constantly would be feasible.
But once I include acoustic attenuation it should be relatively easy to implement a PML - hopefully 
But thank you for the hints relating to “sponge” boundaries!