Quarter wave resonator installed to reduce drone, it works!
 

I've got a full P-Tuning 3" exhaust and P-Tuning 4-1 header installed.

I had a Random Tech cat welded in the front pipe in an effort to quiet it down a bit as well as reduce the exhaust smell. Even with the cat welded in, the drone was a bit much for me.

So I had my buddy weld in an adjustable quarter wave resonator. I have a PST carbon fiber driveshaft, which gave me much more room to work with over have the factory 2-piece driveshaft taking up space.

http://i.imgur.com/PcNs0kp.jpg

I used a Burns Stainless super tight radius 2.5" elbow welded into a 2.63" OD straight. The 14" long end cap is a 2.5" straight with the flat cap welded on it.

http://i.imgur.com/CnUrcVY.jpg

I have a Torca stainless clamp to keep the end cap assembly from blowing off.

http://i.imgur.com/J8DgvQR.jpg

This combo gives me an adjustment range of about 29" OAL to almost 40" OAL if I need it. I do have a small bracket welded in place to help support the end of the 2.63" OD straight section.

I adjusted it to 32" OAL and it kills the drone by probably 80%! My ears don't hurt anymore after driving the car.

All the guides online about quarter wave resonators are based on theory. Your best bet is to installed the biggest diameter one you can fit and make it adjustable so you can tweak it. I plan on adjusting mine more to kill the drone as much as possible.

One more pic from the back with natural lighting.

http://i.imgur.com/90krMW8.jpg

I had a pre-made helmholtz resonator on my test pipe, I had similar results to you with an Invidia N1 and a UEL header. Drone city without the resonator.