A tonewheel or tone wheel is a simple electromechanical apparatus used for generating electric

musical note In music, notes are distinct and isolatable sounds that act as the most basic building blocks for nearly all of music. This musical analysis#Discretization, discretization facilitates performance, comprehension, and musical analysis, analysis. No ...

s in electromechanical

organ Organ and organs may refer to: Biology * Organ (biology), a group of tissues organized to serve a common function * Organ system, a collection of organs that function together to carry out specific functions within the body. Musical instruments ...

instruments such as the

Hammond organ The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert, first manufactured in 1935. Multiple models have been produced, most of which use sliding #Drawbars, drawbars to vary sounds. Until 1975, sound was created ...

and in telephony to generate audible signals such as ringing tone. It was developed by

Thaddeus Cahill Thaddeus Cahill (June 18, 1867 – April 12, 1934) was a prominent american inventor of the early 20th century. He is widely credited with the invention of the first electromechanical musical instrument, which he dubbed the telharmonium. He st ...

for the

telharmonium The Telharmonium (also known as the Dynamophone) was an early electrical organ, developed by Thaddeus Cahill c. 1896 and patented in 1897. , filed 1896-02-04. The electrical signal from the Telharmonium was transmitted over wires; it was hea ...

c. 1896 and patented in 1897. It was reinvented around 1910 by Rudolph Goldschmidt for use in pre– vacuum-tube

radio receiver In radio communications, a radio receiver, also known as a receiver, a wireless, or simply a radio, is an electronic device that receives radio waves and converts the information carried by them to a usable form. It is used with an antenna. ...

s as a

beat frequency oscillator In a radio receiver, a beat frequency oscillator or BFO is a dedicated electronic oscillator, oscillator used to create an audio frequency signal from Morse code radiotelegraphy (Continuous wave, CW) transmissions to make them audible. The signal ...

(BFO) to make

continuous wave A continuous wave or continuous waveform (CW) is an electromagnetic wave of constant amplitude and frequency, typically a sine wave, that for mathematical analysis is considered to be of infinite duration. It may refer to e.g. a laser or particl ...

radiotelegraphy Wireless telegraphy or radiotelegraphy is the transmission of text messages by radio waves, analogous to electrical telegraphy using cables. Before about 1910, the term ''wireless telegraphy'' was also used for other experimental technologies f ...

(

Morse code Morse code is a telecommunications method which Character encoding, encodes Written language, text characters as standardized sequences of two different signal durations, called ''dots'' and ''dashes'', or ''dits'' and ''dahs''. Morse code i ...

) signals audible.

Description

The tonewheel assembly consists of a synchronous

AC motor An AC motor is an electric motor driven by an alternating current (AC). The AC motor commonly consists of two basic parts, an outside stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside roto ...

and an associated

gearbox A transmission (also called a gearbox) is a mechanical device invented by Louis Renault (who founded Renault) which uses a gear set—two or more gears working together—to change the speed, direction of rotation, or torque multiplication/r ...

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 A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, ...

and

electromagnetic coil An electromagnetic coil is an electrical Electrical conductivity, conductor such as a wire in the shape of a wiktionary:coil, coil (spiral or helix). Electromagnetic coils are used in electrical engineering, in applications where electric curre ...

. 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 Electromagnetic or magnetic induction is the production of an electromotive force, electromotive force (emf) across an electrical conductor in a changing magnetic field. Michael Faraday is generally credited with the discovery of induction in 1 ...

. 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 The fundamental frequency, often referred to simply as the ''fundamental'' (abbreviated as 0 or 1 ), is defined as the lowest frequency of a Periodic signal, periodic waveform. In music, the fundamental is the musical pitch (music), pitch of a n ...

can thus be combined with one or more

harmonics In physics, acoustics, and telecommunications, a harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the ''fundamental frequency'' of a periodic signal. The fundamental frequency is also called the ''1st harm ...

to produce complex sounds. Tonewheels were first developed for and used in the impractical

Telharmonium The Telharmonium (also known as the Dynamophone) was an early electrical organ, developed by Thaddeus Cahill c. 1896 and patented in 1897. , filed 1896-02-04. The electrical signal from the Telharmonium was transmitted over wires; it was hea ...

circa 1896, filed 1896-02-04. and later in the original

s. ''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

s tonewheel leakage is a user-set parameter.

Early uses

The tonewheel was independently invented in 1910 by Rudolph Goldschmidt as a beat frequency oscillator in early

s to make

(

) signals audible, before the existence of the

vacuum tube A vacuum tube, electron tube, thermionic valve (British usage), or tube (North America) is a device that controls electric current flow in a high vacuum between electrodes to which an electric voltage, potential difference has been applied. It ...

Notes

References

{{Electronic organs Electronic organs Electric and electronic keyboard instruments

Description

Early uses

See also

Notes

References