| 词条 | Tonewheel |
| 释义 |
A tonewheel or tone wheel is a simple electromechanical apparatus for generating electric musical notes in electromechanical organ instruments such as the Hammond Organ. {{citation needed span|It was invented around 1910|reason=Telharmonium was invented circa 1896 and patented in 1896 as a US Patent 580035A|date=September 2016}} by Rudolph Goldschmidt and was first used in pre vacuum tube radio receivers as a beat frequency oscillator (BFO) to make continuous wave radiotelegraphy (Morse code) signals audible. DescriptionThe tonewheel assembly consists of a synchronous AC motor and an associated gearbox that drives a series of rotating disks. Each disk has a given number of smooth bumps at the rim; these generate a specific frequency as the disk rotates close to a pickup assembly that consists of a magnet and electromagnetic coil.[1] As each bump in the wheel approaches the pickup, it temporarily concentrates the magnetic field near it, and thus strengthens the magnetic field that passes through the coil, inducing a current in the coil by the process of electromagnetic induction. As the bump moves past, this concentrating effect is reduced again, the magnetic field weakens slightly, and an opposite current is induced in the coil. Thus, the frequency of the current in the coil depends on the speed of rotation of the disk and the number of bumps. Typically, the coil is connected to an amplifier through a network of switches, contacts, resistor banks, and transformers which can be used to mix the fluctuating current representing the note from one coil with similar currents from other coils representing other notes. A single fundamental frequency can thus be combined with one or more harmonics to produce complex sounds. {{citation needed span|Tonewheels were first developed for and used in the Telharmonium|reason=How can we verify that the rheotome-cylinder was a kind of tonewheel ?|date=September 2016}} circa 1896[2] and later in the original Hammond organs. Tonewheel leakage occurs in the Hammond organ and in similar situations, where the large number of tonewheels causes pickups to overhear tonewheels other than their own. This causes the organ to add chromatics to played notes. In some kinds of music this is undesirable, but in others it has become an important part of the Hammond sound. On some digital simulations of Hammond organs tonewheel leakage is a user-set parameter. Early uses{{citation needed span|The tonewheel was invented in 1910|reason=As already mentioned above, Telharmonium was invented circa 1896 and patented in 1897 as a US Patent 580035A|date=September 2016}} by Rudolph Goldschmidt as a beat frequency oscillator in early radio receivers to make continuous wave radiotelegraphy (Morse code) signals audible.See also
Notes1. ^This is electrically and magnetically similar to a guitar pickup, in that a permanent magnet is placed within the coil and the moving element is unmagnetized. Unlike most generators or dynamos, there is no external field applied through the moving part. 2. ^{{US patent reference | number = 580035 | y = 1897 | m = 04 | d = 06 | inventor = Thaddeus Cahill | title = [https://patents.google.com/patent/US580035A Art of and apparatus for generating and distributing music electrically]}}, filed 1896-02-04. References{{Reflist}}External links{{Commons category|Tonewheels}}
2 : Electronic organs|Electric and electronic keyboard instruments |
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