[NoHaveMSG]

Originally Posted by Goingnowherefast

Powertrain NVH engineer here...

I'm going to have two answers here, and feel free to ask me anything on the subject.

Short answer:

Without high-resolution noise/vibration data with a high resolution encoder or optical tachometer, it is effectively impossible to pin-point the source of a resonant vibration. However, if you can give me a relatively high quality video (with good in-car audio NO WIND NOISE) with CANbus RPM reading I can point you in the right direction.

Long answer:

There's multiple techniques we use to pin-point the root cause of a noise/vibration. Most notably, we use high resolution data to analyze the amplitude of the order content. An "order" is something that occur "X" times during a rotation event. In ICE applications, there's quite a few things rotating but the most important tends to be the crankshaft. Thus, we can figure out whether a noise/vibe is being caused by the combustion cycle of an engine by measuring the amplitude of source vs. engine RPM. In a four stroke, four cylinder a firing event will occur twice every revolution, meaning the primary order content of a four cylinder engine will be 2nd order.

Easy enough right? A high amplitude 2nd order indicates that the actual combustion of the engine is driving that vibration. The issue, is that there's obviously a LOT of things moving and spinning in an engine. You have alternators, A/C Compressors, Water Pumps all ran directly off of the crankshaft (all rotate at different rates depending on the pulley diameter) and you also have the things connected I.E the driveline. In this case, there will be torsional vibration transmitted through the crankshaft to the harmonic damper and the flywheel. Like you mentioned, harmonic dampers are tuned to damp a specific frequency spectrum. In the case of viscous fluid dampers, they target a broad frequency spectrum as opposed to traditional dampers which target quite a small frequency band. Past that, you have moving parts in the transmission (input/output shaft, ring/sun gears), driveshafts (you mentioned you have an aluminum driveshaft), and the differential. Order content can be looked at based on the # events per rotation. Additionally, every material has a natural resonant frequency (steel is different than aluminum etc.) which can create horrible noises, shakes etc.

So in the end, the real answer is extremely convoluted and complex. But if you want to give it a try, send me a video mentioned above (preferably a 3rd gear WOT up to max RPM) and I'll see what I can do.

That's awesome but google "brz one piece driveshaft vibration". It is well documented and frequent that an aftermarket one piece causes a bunch of extra NVH even on a stock car. A recommendation I got from a guy at the track that was retired doing the same thing for Boeing, said to put a wrap of tape a few layers thick about a 1/3 of the way up the driveshaft. I just haven't tried it yet.