You won't need two, don't worry!
It will be cheaper and less labor to make one. You still have the option of swapping out the driver and getting another 3db which would be like doubling anyway. I think that is a good decision, but you will let us know when you hear it. Plus....you can always build a second one later if you want.
I have been hemming and hawing (sp?) about how to route the kitchen sink drain. It currently feeds into an older section of the drain pipe, has no venting and drains poorly.
It also hangs down too low.
I was thinking I wanted to go through the joists and take it to a newer section of drain where there is a vent to the roof. The problem is that there is heating pipe in the way so I'd have to go maybe 10-12 feet instead of a straight 6 feet. Since I have to drop 1/4" per foot, I'd run out of joist area so that I could keep the pipe 2" from the top and/or bottom.
THEN I realized the heating pipe is in the way of where the steel beam will go!
Why I hadn't seen that before is a mystery to me. So, I let the situation stew in my head for a few hours.
I think I will be removing more heating pipe and rerouting it to the other side of the beam. That will allow me to put the steel beam up flush with the joists. It will also allow me to do a straight shot for the kitchen sink drain. It also means the $100 of couplers for the 2" threaded pipe to copper are for naught and I have to buy some 1.25" couplers on top of that. Still, I'm saving a ton of money even with some small mistakes like this. I can probably eBay the couplers anyhow.
So, all good and making slowish progress. Hopefully tomorrow I can get that heating pipe moved and all of the electrical squared away. (I did move some electrical around earlier this am.)