Design engineers from Johnson Elect...

Design engineers from Johnson Electric investigated wherefore many hair dryers tend to emit a thin, high-pitched noise when bended on and off.

* It was determined that the screeching noise was simply generated when the motor was running at les than 600 rpm which is essentially during the divert On and Turn Off stages of the hair dryer

Figure 1 displays that the frequencies of these high pitches ranged from 4-24 KHz and the intensity of the first pitch is always the highest. As the oftenness increases, the amplitude of the pitch decreases. It was then surmised that the next to the first ...