Why do we hear the sound produced by the humming bees while the sound of vibrations of pendulum is not heard?

The sound produced by a humming bee while vibrating its wings lies between $20\ Hz\ to\ 20\ KHz$ that making this sound audible to the human ear.

While sound produced by a pendulum while vibrating is below $20\ Hz$, it is out of audible range to the human ear.


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