Tracking Down Vibrations

[davidbrady]

A smart phone can sometimes be used to track down vibrations. Download one of the vibration analyzer apps, I use "FFT Vibration Analyzer" on my Android. This tool will give you a graph of vibration frequencies versus amplitude. Our tires rotate at approximately 500 rotations per minute at 60 mph, or 8 Hz. Assuming a sixth gear ratio of 0.639 and a final drive of 4.56, we can calculate the following approximate fundamental frequecies for tire, driveshaft, and engine vibrations at 60 mph:

Tire: 8 Hz

Drive Shaft: 8 (tire Hz) * 4.56 (final drive ratio) = 36 Hz

S60 Engine: 1450 (engine rpm) / 60 / 2 * 6 (number of cylinders) = 72 Hz

8V Engine: 1450 (engine rpm) / 60 * 8 (number of cylinders) = 190 Hz

Of course it's not as simple as it sounds because each of the vibration sources will generate harmonics at multiples of their fundamental frequencies; however, the fundamental is the highest amplitude.

[GregOConnor]

goes back to my wish for a program to digitize noise in the engine compartment and tow'ed then compare the file to normal digitize noise to find abnormality in real time while driving. this measure could also show issues pending