Virtually all electric bikes now use radial flux brushless DC motors (BLDC). These motors however, vary considerably in audible noise level. Many (particularly geared hub motors) produce quite a noticeable hum, particularly under load, accelerating or when climbing a hill. The hum is gear clash that stems from the high frequency electrical pulsing that all hubmotors generate in the process of controlling motor power and speed.
The power controller, or “controller” for short, is the interface between the throttle, battery and motor. It is the device that generates and controls this high frequency pulsing (switching). Most e-bike power controllers employ a “square-wave” pulse (a series of on-off-on electrical bursts). The abrupt switching that is an inherent part of such controllers, results in considerable noise.
We use a controller having a “softened” waveform, which virtually eliminates motor noise. Such “sinusoidal wave” controllers are more expensive, but we feel the quiet is worth the price.