Mains hum

Electric hum (or "mains hum," depending on colloquialisms) is an audible oscillation with fundamental frequency of AC current, usually 50 or 60 cycles (Hertz), depending on one's public electric utility configuration. The most common cause of electric hum is magnetostriction, wherein ferromagnetic materials change shape minutely when exposed to magnetic fields.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Magnetostrictive (see magnetostriction) electric hum is most often noticed around large linear transformers, particularly when the transformers are handling large amounts of current.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In the realm of sound reinforcement (Public Address systems -- loudspeakers, etc.), electric hum is usually caused by induction. This hum is generated by oscillating electric currents induced in sensitive audio circuitry by the alternating electromagnetic fields emanating from nearby mains-powered devices. The audible aspect of this sort of electric hum is produced by amplifiers and loudspeakers. A common source of electric hum in sound reinforcement systems is the "ground loop."

Related Topics:
Induction - Ground loop

~ ~ ~ ~ ~ ~ ~ ~ ~ ~