Hi-

I am building a vocal booth in my apartment, on top of an existing wood finished floor that is not insulated and rather old.

I originally built a plywwood deck on top of 2X4 joists decoupled with u boats, but after reading Rod Gervais' book decided to dismantle the entire floor and just double up on the plywood.

As of now, I have a 1/2" rubber flooring underlayment directly on top of the existing wood floor. Someone recommended inserting a layer of 1" or 2" 703 in between the rubber and the 2 layers of plywood? Will this design work structurally? I know the 703 is rigid but can it support the weight on top and still maintain a level finished floor on top?

If not, can someone suggest an appropriate design for this floor?