As you may or may not know, i have built a recordign studio inside a prefab garage. I've put up a stud wall between the rehearsal room and the control room. But due to the air tight seal in the door system and all the soundproofing, there is no air exchange between the rooms which sometimes lead to condensation in the rehearsal room.
So i've decided i want to install a fan ventilation system from outside into the rehearsal room etc. The ventilation part I think i know what to do, and i've been given a in-line mixed flow duct fan to use.
But what i was worried about was how i could still retain the soundproof isolation of the rehearsal room, but still provide air exchange.
The key to achieving ventilation while also keeping the space soundproof is using a baffle system. You can make a box from MDF with pieces o f wood protruding into the box so that the air has to follow a maze like path from end to end. You must then line every surface inside the box with a sound absorbant foam like SA25FR. If you make the baffle (air path long you will also need to use a fan in the system to keep the air moving.
I would also recommend using two baffles one for air in and one for air out with fans positioned close to the end that noise doesn't matter at. So for a recording studio I would put the fans as far away from the recording area as possible.