[tiggers97]

They make vibration isolation kits for projectors. i.e: http://www.htmarket.com/vibab.html

I don't have that problem with my projector, but my pot lights flicker when my kids jump on the floor above. The joists in my house are only 2x8's wherein something thicker might be better.

Just decouple the projector, like above, instead of the entire ceiling.

Only other suggestion I would have is to move the projector to another location. But that may not be an option depending on your setup.

 

[tiggers97]

I think the material in the link would have to be much denser than memory foam.
(I'm thinking you mean the type they use in pillows)