Some ideas on torsional excitation:
120hz is an important torsional exciting frerquency since it exists for single phase motors or unbalanced 3-phase motors.
I don’t think 60hz is particular important. During DOL start, there is torque oscillation at a frequency (1-s)*60hz… but should not remain at 60hz for long.
I would think running speed and 2x running speed may be good to avoid. Possibly number of blades times running speed also.
Vfd could make life more complicated.
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(2B)+(2B)' ?