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Encyclopedia > Mains hum
Spectrum of mains hum at 60 Hz
Spectrum of mains hum at 60 Hz

Electric hum, mains hum, or power line hum is an audible oscillation at the frequency of the mains alternating current, which is usually 50 or 60 hertz depending on the local electric utility configuration (see Mains electricity). The sound often has heavy harmonic content. Image File history File links Mains_hum_spectrum. ... Image File history File links Mains_hum_spectrum. ... Mains may mean or refer to, or be a subject of: Mains electricity Electricity transmission Public utility, about mains services, including electricity, natural gas, water, and sewage disposal Mains (Scotland), about the central steading of a townland BMX racing See also: Main Mane Category: ... Sine waves of various frequencies; the lower waves have higher frequencies than those above. ... Mains may mean or refer to, or be a subject of: Mains electricity Electricity transmission Public utility, about mains services, including electricity, natural gas, water, and sewage disposal Mains (Scotland), about the central steading of a townland BMX racing See also: Main Mane Category: ... City lights viewed in a motion blurred exposure. ... The hertz (symbol: Hz) is the SI unit of frequency. ... A public utility is a company that maintains the infrastructure for a public service. ... Type F Mains power plug & socket The term “mains” usually refers to the general purpose AC electrical power supply (as in “Ive connected the appliance to the mains”). The term is not usually used in the United States and Canada. ... In acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. ...


The most common cause of electric hum is magnetostriction, wherein ferromagnetic materials change shape minutely when exposed to magnetic fields. Magnetostrictive electric hum is most often noticed around large linear transformers, particularly when the transformers are handling large amounts of current. Magnetostriction is a property of ferromagnetic materials that causes them to change their shape when subjected to a magnetic field. ... Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. ... Three-phase pole-mounted step-down transformer. ...


In the realm of sound reinforcement (as in public address systems and loudspeakers), electric hum is often caused by induction. This hum is generated by oscillating electric currents induced in sensitive (high gain) audio circuitry by the alternating electromagnetic fields emanating from nearby mains-powered devices like power transformers. The audible aspect of this sort of electric hum is produced by amplifiers and loudspeakers. This is a disambiguation page — a navigational aid which lists other pages that might otherwise share the same title. ... Closeup of a loudspeaker driver Wall-mounted loudspeaker. ... Electromagnetic induction is the production of an electrical potential difference (or voltage) across a conductor situated in a changing magnetic flux. ... Electric current is the flow of electric charge. ... A schematic representation of hearing. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... For the British rock band of the same name, see Amplifier (band) An amplifier can be considered to be any device that uses a small amount of energy to control a source of a larger amount of energy, although the term today usually refers to an electronic amplifier. ...


It is often the case that electric hum at a venue is picked up via a ground loop. In this situation, an amplifier and a mixng desk are typically at some distance from one another. The chassis of both items are grounded via the mains earth pin, and are also connected along a different pathway via the sheild conductor of sheilded cable. As these two pathways do not run alongside each other, an electrical circuit in the shape of a loop is formed. One gets the same situation occuring between musical instument amplifiers in stage and the mixing desk. To fix this, stage equipment often has a "ground lift" switch which breaks the loop. A more dangerous but frequently used option is to snap the earth pin off the power plug used at the mixing desk. The term ground loop has more than one meaning: In electrical and electronic engineering, a ground loop refers to an unwanted current that flows in a conductor connecting two points that are nominally at the same potential, for example ground potential, but are actually at different potentials. ...


The other major source of hum in audio equipment is shared impedances; when a heavy current is flowing through a conductor (a ground trace) that a small-signal device is also connected to. No conductor is perfect, and the small resistance present means that devices using points on that conductor as a ground reference will be at slightly different potentials. This hum is usually at the second harmonic of the power line frequency (100 Hz or 120 Hz), since the heavy ground currents are from AC to DC converters that rectify the mains waveform. See also ground loop. In electrical engineering, Impedance is a measure of opposition to a sinusoidal electric current. ... Ground symbols The term ground or earth usually means a common return path in electrical circuits. ... In science and engineering, conductors are materials that contain movable charges of electricity. ... In acoustics and telecommunication, the harmonic of a wave is a component frequency of the signal that is an integer multiple of the fundamental frequency. ... A wall wart style variable DC power supply with its cover removed. ... AC, half-wave and full wave rectified signals A rectifier is an electrical device, comprising one or more semiconductive devices (such as diodes) or vacuum tubes arranged for converting alternating current to direct current. ... In an electrical system, ground loop refers to an unwanted current that flows in a conductor connecting two points that are nominally at the same potential, ground, but are actually at different potentials. ...


Assuming a tempered scale with A=440Hz, a 60Hz tone is almost exactly halfway between A# and B two octaves below Middle C, and a 50Hz tone is between G and G# two octaves below Middle C, but slightly sharper than the quarter-tone. These notes fall within the range of a 4-string bass guitar. In music, the term middle C refers to the note C located between the staves of the grand staff, quoted as C4 in note-octave form. ... In music, the term middle C refers to the note C located between the staves of the grand staff, quoted as C4 in note-octave form. ... Martin EB18 Bass Guitar in flight case The electric bass guitar (also called electric bass or simply bass) is an electrically amplified plucked string instrument. ...

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    • 5 seconds of 60 Hz mains hum
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  • Mains hum ( file info) — play in browser (beta)
    • 5 seconds of 50 Hz mains hum
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Image File history File links Mains hum 60 Hz. ... Software development stages Development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... The hertz (symbol: Hz) is the SI unit of frequency. ... Image File history File links 50Hz. ... Software development stages Development stage terminology expresses how the development of a piece of software has progressed and how much further development it may require. ... The hertz (symbol: Hz) is the SI unit of frequency. ...

See also


  Results from FactBites:
 
Mains hum - Wikipedia, the free encyclopedia (478 words)
Spectrum of mains hum at 60 Hz Electric hum, mains hum, or power line hum is an audible oscillation at the frequency of the mains alternating current, which is usually 50 or 60 hertz depending on the local electric utility configuration (see Mains electricity).
This hum is generated by oscillating electric currents induced in sensitive (high gain) audio circuitry by the alternating electromagnetic fields emanating from nearby mains-powered devices like power transformers.
This hum is usually at the second harmonic of the power line frequency (100 Hz or 120 Hz), since the heavy ground currents are from AC to DC converters that rectify the mains waveform.
  More results at FactBites »

 
 

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