Alright, after a lot of help, and a lot more research (
you were a ton of help as was
). I've come to some good conclusions:
The ventilation has been the real headache but I think I have a better grasp on it. Ideally we want to aim for around 6-8 air changes per hour.
ACH= CFM*60/VOLUME. In this case the only variable I have is CFM, a little bit of algebra get's me CFM=ACH*VOLUME/60 whic h means in order to hit 7ACH, I need to get 330CFM.
I'd like to use a deadvent system (or in this case a soffit muffler) to pull air and push air out and in order to hit that 330CFM, I need to aim for a fan with a higher capacity (since they report in 0 air pressure tests and I don't want to run it at full capacity). A FG-6XL does almost 500 which should be the perfect size and speed for me. Which means I'll be using two fans on both ends of this push and pull and wiring them up to one switch so I can keep a continuous airflow but speed them up if I'm holding a party in there.
Now, those are FG6XLs, which means 6 inch ducts. With CFM and knowing the surface area of a cross section of those 6 inch ducts, we get LFM (air velocity) which comes out to a 420LFM. Now we all know we should be aiming for 250LFM unless we want to hear that air coming in and out of the room. A sufficient soffit muffler that runs for 15 feet using mass and dampening and a large duct boot should be enough to lessen the sound energy exiting the room and entering the ducts to create a problem. So what we're left is finding a way to slow down this speed at the registers. If I'm correct in assuming, if the theater side transitioned into a 8" flex duct, or even 12", that should drop my LFM well under 250, (105 in the case of the 12" duct).
With that done properly, I should have the correct amount of ventilation, with the proper air velocity to not be bothered, and my sound proofing shell will not have been compromised.
Now, I have two questions
, one small, one giant. I've seen a few people terminate their flex duct with a collar at the point of entry only to connect a duct once the room is drywalled whereas others have left the appropriate amount of extra flex duct in so they don't need to get more once dry wall is in. Is this completely up to the HVAC installer/theater owner?
Doesn't seem like one would have an edge over the other.
Now the $1 million dollar question.
I'm in the basement below grade for the theater, the adjacent space is not going to be the best place for air exchange since it's smaller and I'll have my equipment and a wine cellar exhausting hot air into the lobby. It is an open stair well, but I don't think that matters. I cannot connect it to the HRV system that ventilates the two upper floors, however I have a giant air reservoir since the first floor (directly above the theater) is an open floor and a rarely used part of the house. Is there any issue, with properly used soffit mufflers, with exchanging air with that reservoir?
I would, for convenience sake, probably want to slow down the air around those ends as well.
TLDR; Bolded the areas of my concern.
* This will only address my ventilation concern, cooling down the room will have to be addressed separately. I will need to cool this room with a mini split AC. That's practically a done deal at this point. Potentially a MR Slim.
** Mind you these are all in calculations, as introducing things like bend and taking into account air pressure drops will surely drop and affect my CFM/LFM readings. The only way to really know for sure is measure it once I'm done and adjust the fans.