Excel – Diffraction of Sound Waves on an Obstacle

There is a source of sound waves at a distance “d” from a rectangular obstacle with dimensions a and b as seen in the picture. I need calculations done in Excel to show the diffraction of the sound waves on that obstacle. The graph should look similarly to the picture I added (can be 3D graph or whatever).
You need to use physics calculations – how the waves diffract or deflect from the obstacle, don’t just make random circles or lines, please. I also need to be able to change parameters such as distance d, a,b and wavelength. If you need more time, no problem, just tell me how long you need. But please, don’t give me links to websites as your answer. I want an Excel file with the graph, that is all.