Looking for recommended specifications for MPX/SPS backer boxes that will maintain the speakers performance?

I'm Preparing to install 5 SPSs and 2 MPXs in a soundproofed dedicated HT with clip/channel, double 5/8" drywall and green glue. I would like to build backer boxes for these speakers to help with the soundproofing. I have read both Sandy's notes that mentions GE backer boxes are only recommended to prevent sound bleeding through to adjoining room and a previous post of the GE backer box causing performance issues and will be making my own. These boxes will also solve the issue installing MPX/SPSs in DD because the dog ears will not extend far enough.

Hi hattrickjunkie, I would recommend using a back box that has 1.76 cubic feet internal volume for each Invisa SPS, and a back box with 0.53 cubic feet internal volume for each Invisa MPX. I would also fill these back boxes roughly half full of Dacron or fiberglass insulation. Happy Listening!

Thank you very much, this is exactly what I was looking for. Should I assume volume recommendations are minimum values?

Hi hattrickjunkie, you are correct. These box sizes are minimum recommended sizes. You could always use back boxes that are a bit larger. Happy Listening!