Classic Looseness
Three characteristics of impacting noise: raised noise floor, peak at periodic rate, and harmonics due to non-linear impacts.
Case Study Time: Classic Looseness (Nature of Looseness!)
Three characteristics will be present in the spectrum:
First, because there is impacting, the noise floor will be raised. This is due to the fact that impacts impart all frequencies into the spectrum, meaning there will be some amplitude at all frequencies. That raises the noise floor.
The second characteristic is that because the impacting is repeating periodically, there is a peak in the spectrum at the periodic rate, which in this example is shaft turning speed.
The third characteristic is that because the impacts are non-linear (clipped or not even + and -), there are harmonics of that frequency.
Additional Images
