For example here are two different failed meshes. The first image is when I allowed ANSYS to generate default mesh and the second image is when I tried to define contact sizing between the mechanical components and the acoustic domain.  The acoustic domain is a sphere and these pictures are from a sectional view. 

As can be seen in the pictures the areas of the mechanical components that meet the acoustic domain have very fine mesh. Is there any option in ANSYS to for the enclosure to match all boundary conditions mesh?