[Ted White]

You might consider installing a decoupled panel. 4 resilient clips, two sections of metal furring channel and a piece of ply.
Posted via Mobile Device

 

[Ted White]

Please stand by for an incoming transmission
Posted via Mobile Device

 

[Ted White]

This isn't a picture of precisely what I was describing since your ceiling is drywalled already. So imagine the ceiling is drywalled. Then apply the clips and channels. 4 clips, 2 channels.

Then attach a piece of MDF or plywood. You could router the edges up pretty. Attach the panel to the channel. The panel will move up and down like a shock absorber. This should help. At least it's an easy trial.

This make sense?

 

[Ted White]

That chain scenario brings up a good point. The chain isn't a spring, just like a suspended ceiling isn't resilient. So isolation isn't as good as it can be.

 

[Ted White]

Not thinking sistering or otherwise stiffening will affect change in the small zone around the projector. The rest of the floor system will still be oscillating even though the small area around the projector is stiffened.

A resilient mount will have a better chance to separate the projector from the ceiling.

 

[Ted White]

Projectors are mounted on ceilings decoupled with clips as a common practice. But the resulting spring has a low resonance due in part to the mass of double drywall hanging on it. To your point, Bill, a heavier panel attached to this little clip assembly would ensure a low frequency resonance.

 

[Ted White]

I'm thinking the mass would be much more critical than the damping in this instance. Not sure Green Glue would do a
thing, actually.

 

[Ted White]

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)

I agree. Not thinking foam and pads are the answer here.