Re: high frequency noise
The slower the repetition. the lower the frequency of the noise
The level of low frequency noise from a sound source is determined primarily by the rate at which the changes in force, pressure, and speed are repeated. The longer the time between changes, the lower the frequency of the noise generated. The level of noise depends on the amount of the change.
Example
Two gears have the same pitch diameter but different numbers of teeth. If they rotate at the same speed, the gear with fewer teeth will produce a lowerfrequency noise.
High frequency sound is strongly directional and more easily reflected
When high frequency sound strikes a hard surface, it is reflected much like light from a mirror. High frequency sound does not travel around corners easily