Audi A3 8P (2003-2011) Hatchback Rear Speaker 13cm Adapter

The new mounting holes should be pretty universal, if the mounting latches of your new speaker are too wide, you can add a negative modifier in Prusa Slicer adjacent to the existing cutouts I have put into the model.

The holes for the speaker are sized for M4 heat set inserts.

Printed 180% rotated on the Y axis, with classic supports enabled; 4 outer walls, 45% infill, worked perfectly.

If your existing speaker doesn't have the foam gasket anymore due to detoriation, you can use the dampener file to print one out of TPU.