I’m curious about the sound made by some types of high powered electric motors and related control devices. Many (but not all) large electrical motor systems make high pitched sounds that correlate to acceleration. How to describe this sound? It is essentially a mid-high tone that rises in pitch as the drive system accelerates, and drops somewhat in deceleration.
One example is subway trains and streetcars, specifically modern electronically controlled electric motor unit “EMU” trains. As operators add power to move the trains forward, the tone rises in proportion to motor speed (and therefore overall vehicle speed). Older pre-war trolleys seem not to make these high tones, or if they do, they are drowned out by other noises. This seems to be associated with modern high power electronic switching devices, and not necessarily with the motors they drive.
Other electronic devices that make high tones are VFD motor controls, and going back a few years, camera strobe flash units that made a high rising tone as they recharged.
To generate a sound, some physical matter has to vibrate, and push adjacent matter until landing on an eardrum. I’d really appreciate knowing the precise source of these particular tones (i.e.: going beyond “well, high power electronics make sounds”).
Question 1: generally which specific types of component vibrate, and what force causes the vibration (e.g.: capacitors, thyristors, magnetism, etc)?
Question 2: are there associated structural considerations? Does the vibration cause any strain or mechanical fatigue to the device itself or surrounding wiring or mounting surfaces? Other interesting effects?