I'm getting ready to mount my projector. I was planning on nailing a 2"x8" in between the floor joists and attaching the mount to that. However, that would mean I'd have to go buy a 2"x8" board and I already have a bunch of 2"x4"s left over from framing so I was thinking of just using two 2"x4" pieces beside each other.

I'm worried though that using two pieces instead of one big one will lead to more vibration or flexing going to the projector. Any thoughts? The pieces would be about 23" long.

Making a nailer from two flat 2x4s side-by-side wouldn't be any mechanically different than doing it with a single 2x8. Uncontrolled vibrations from upstairs transmitted to the joists would then get transferred to the nailer, no matter how it was constructed.

Since your joist spacing seems to be 24" OC however, you might want to consider using the 2x4s on edge rather than flat, to add a bit of lateral stiffness. This, more than the width of the nailer, might help control bouncing a bit more.

You should set your 2x4 spacing so that the projector mounting bolts hit them centred. If you wanted to, you could inset 3/4" up into the joist and finish with a sheet of ply or something....

good luck!
dc

What kind of projector are you mounting? For a small, lightweight digital projector, I'm sure it wouldn't really matter either way.

For a CRT projector, you'd probably want more than either of those options.

Thanks. It's a Studio Experience 50HD. DLP I think.

I have some ply wood scraps too so I'll look into that.