I'm having a hard time understanding how it could be so easy. Collo referred to equivalent-models, but I'm not into electrics as much to grasp it.
lol ... I'm having a hard time grasping how it could be anything but simple and easy!
Say you have a 4" vent which is 1m long. It is the same thing as having 4 x 2" vents of the same length. You could use 3 vents which add up to the total CSA of the single vent, and the tuning will be the same if the length is the same. Tuning is determined by vent area, length and the box volume. Simple!
Collo, I can just see your dream system now. A Tumult with a spare room dedicated to the custom made concrete vent! *chuckles*
I like your idea, I'm all for sharing ideas and results with the diy community. I feel that vent design is something that could be much better done overall. I also feel that passive radiators are a waste of money, and if vented designs were done better, we'd be spending more on better drivers, and work on really getting our vents right. To me this is a big part of diy.
You can make vents by heat bending PVC onto a template and get a flare that is bigger than your router bit.
The table idea is a good one, however it would take a LOT of work to actually determine all that properly. What I may in fact do is a bit simpler.
Use only a 4" vent with:
1. no flare
2. 18mm radius
3. 36mm
4. 72mm
5. a dimpled version
I could actually measure the SPL level of the chuffing @ 1m and at my listening position. I could then experiment with the required level of output to actually mask the chuffing, and find out where the threshold is - ie at what point it is just noticeable.
I might be able to say things like:
* doubling the flare radius decreases SPL of chuffing by 8db
* this has the same effect as half the vent velocity, hence a flare of x mm radius means the vent can be x % smaller in diameter ...