Treating Floor in New Construction - Reducing Footfall and Vibration

Making floor joists deeper than necessary for the span, and/or shorter, will do more to increase stiffness than adding more joists, although 12 inches oc will not hurt in your listening room since there would be less opportunity for speakers and heavy equipment to not be fully positioned over joists.  Proper lateral bracing is also important.

let us know what your engineer says.

Stickman - One thing that I know for sure will stiffen a floor is to use good quality ply wood, glued directly to the joists.

The houses in our development were built with that cheapo board made from large flakes of wood. 

When I upgraded my kitchen I put reinforcing beams in the basement because we were putting ceramic floors down and I wanted to prevent bouncing.cracking - it worked somewhat.

Then I helped my neighbour replace a high traffic section of his kitchen floor - we ripped up the old floor and replaced it with quality plywood glued directly to the joists

The difference was amazing - his floor is like concrete (i.e. by comparison)

Both houses have joists at 12" centres

Hope that helps

I am thinking floor joists on 12" centers are a idefinite requirement.   I am not sure what the building code requires but since the room is fairly large at 22' x 29', 12" centers would seem reasonable.

I don't care for the OSB subflooring myself, so I will discuss with my builder the possibillity of using good quality 3/4 plywood.  Gluing the subfloor sounds reasonable also.  

I followed a recomendation to create a floating sub-floor with a layer of roofing felt over the normal plywood floor, then with a layer of 3/4 plywood screwed into the flooring  (not the joists). I then used a quality pad with Berber carpet..