Most HVACs are sized for cooling and heat delivery through 100-400ft of ductwork with thick air filters, heat exchangers, rate dampers, multiple branches with multiple vents, with capacity sufficient for an entire house.
None of that is required here.
Mine will be sized for oxygen delivery for one directly-attached room.
Dedicated independent fans for both the supply and exhaust, with dedicated independent straight runs for each.
The majority of the length will actually be the muffle boxes, which is also the ONLY source of 90 degree turns.
If I can exchange the entire room once per hour that should be sufficient to maintain life, and basic comfort.
I figure I need about ~60cfm of supply and ~60cfm of exhaust, actually-delivered.
The muffle boxes will need to be built and tested well before the room is, to ensure it can actually deliver the desired flowrate quietly.
[and with the desired amount of bass attenuation, if that's even possible to achieve...]
If anything is gonna leak sound it will be the ducts. The air is free to flow and resonant. It's by-far the weakest link in the chain.
I fill the muffle boxes in with sand and no air or sound gets in or out of the room.
0 CFM, and I just have to walk-it-off, like I do now...
I'd rather have fresh air... but if the bass is massively escaping, then a basshead's gotta do what a bassheads gotta do.
Make sure your seat belts are fastened, tray tables are in their fully upright position, and O2 masks are securely adorned.