beefing up doors

the plan for my studio build has double walls with a 6'' airspace and 2 layers of drywall with green glue per wall. the doors will be two communicating interior prehung 1 3/4'' solid core wood doors to fit in 3 1/2'' deep openings. a layer of 5/8'' drywall, followed by a layer of 3/4'' plywood will be added to the back of each door, with GG between layers. should i use two layers of seals (the type 'k' trunk rubber), one for the wooden door, and another for the drywall+plywood? if so, would i need to add wood stops around the door? would the fact that the door frame is only 3 1/2'' deep be a problem? also, should i use formaldehyde-free birch plywood or the less expensive softwood plywood?

I'd suggest that you buy Rod's book and take a look at the chapter on doors and windows. He includes several diagrams and some good descriptive text on how to do it right, where to put the seals, how to build the jambs, the hinges, etc.

I don't think 2 sets of seals is going to improve isolation. 2x drywall with 6" gap is not THAT massive. I think the doors you are planning are much more robust than your walls already. I mean the door itself is already more massive per square foot without adding anything (of course the door needs to be heavier probably because it can move more easily). Anyway, you can design it so that another seal can be added later if you want. But, seals don't really make much difference in low frequencies, they affect mostly the highs.

Dan Fitzpatrick wrote:

I don't think 2 sets of seals is going to improve isolation. 2x drywall with 6" gap is not THAT massive. I think the doors you are planning are much more robust than your walls already. I mean the door itself is already more massive per square foot without adding anything (of course the door needs to be heavier probably because it can move more easily). Anyway, you can design it so that another seal can be added later if you want. But, seals don't really make much difference in low frequencies, they affect mostly the highs.

I agree with the majority of this, but would recommend that you take care to use seals especially on the innermost door of the two. They are high frequency precautions as Dan said, but seal failure is a potential problem.