Really? I'm baffled as to why you need such a contraption. All you need to do is put a hole near the floor on one side, and near the ceiling on the other side of the stud bay of a wall.
Mate, don't need to make speakers when you can get Krix from S/Aust. I have got a wall fan to fit in one side and the other Intake side is passive. With the air conditioner going I normally get a good convection going. I always believed that a well ventilated darkroom protects you and your gear. These just have to be screwed to the wall and the fronts go on. Blackboard paint for the interior and solar guard for exterior. I'm renewing behind my enlargers with hanging framed MDF boards painted with blackboard paint. Light damping and great for notes on current print batches.
PDEEH they are for fans to allow for air in and out. Commercial darkrooms used large baffles for door entry too. I worked in a lab in Sydney where you walked down a hall and around a couple of turns to enter the mural room.
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