Soffit as partial bass trap
Let's say I'm building a soffit that wraps around my entire theater and mostly exists as a chase for HVAC ducts and wiring. In fact, the entirety of both sides and 3/4 of the back of the soffit are monopolized by the ductwork. That does leave a roughly 13' x 4' x 10" section of soffit above the stage that will have nothing practical in it.
So I'm thinking I can do double duty on that part and turn it into a bass trap by stuffing it with insulation. The question is "how"?
The soffit will be built with dual layers comprised of 5/8" OSB + 5/8" Drywall (since most of it is to hide possibly noise HVAC). I'm assuming that that will also effectively reduce the "bass trap" ability of the soffit to unmeasurable levels.
If that's true, then that implies that I will need a hole in my soffit? Maybe covered with fabric?
If so, then how big should said hole be, to be an effective bass trap?
Just pink fluffy stuffing, or would it really help to use rigid fiberglass?