The Savart wheel is an
acoustical
Acoustics is a branch of physics that deals with the study of mechanical waves in gases, liquids, and solids including topics such as vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician ...
device named after the French physicist
Félix Savart
Félix Savart (; ; 30 June 1791, Mézières – 16 March 1841, Paris) was a French physicist and mathematician who is primarily known for the Biot–Savart law of electromagnetism, which he discovered together with his colleague Jean-Bapti ...
(1791–1841), which was
originally conceived and developed by the English scientist
Robert Hooke
Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that ...
(1635–1703).
A card held to the edge of a spinning
toothed wheel will produce a tone whose
pitch varies with the speed of the wheel. A mechanism of this sort, made using brass wheels, allowed Hooke to produce
sound wave
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...
s of a known
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
, and to demonstrate to the
Royal Society
The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
in 1681 how pitch relates to frequency. For practical purposes Hooke's device was soon supplanted by the invention of the
tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs (tines) formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it against ...
.
About a century and a half after Hooke's work, the mechanism was taken up again by Savart for his investigations into the range of human hearing. In the 1830s Savart was able to construct large, finely-toothed brass wheels producing frequencies of up to 24
kHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...
that seem to have been the world's first artificial
ultrasonic
Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies fr ...
generators. In the later 19th century, Savart's wheels were also used in physiological and psychological investigations of
time perception
The study of time perception or chronoception is a field within psychology, cognitive linguistics and neuroscience that refers to the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the ind ...
.
Nowadays, Savart wheels are commonly demonstrated in physics lectures, sometimes driven and sounded by an air hose (in place of the card mechanism).
Description
The basic device consists of a
ratchet-wheel with a large number of uniformly spaced teeth.
When the wheel is turned slowly while the edge of a card is held against the teeth a succession of distinct clicks can be heard.
When the wheel is spun rapidly it produces a shrill tone, whereas if the wheel is allowed to turn more slowly the tone progressively decreases in pitch. Since the frequency of the tone is directly proportional to the rate at which the teeth strike the card, a Savart wheel can be calibrated to provide an absolute measure of pitch. Multiple wheels of different sizes, carrying different numbers of teeth, can also be attached so as to allow several pitches (or
chords
Chord may refer to:
* Chord (music), an aggregate of musical pitches sounded simultaneously
** Guitar chord a chord played on a guitar, which has a particular tuning
* Chord (geometry), a line segment joining two points on a curve
* Chord ( ...
) to be produced while the axle is being turned at a constant rate.
Hooke's wheel
Hooke began work on his wheel in March 1676, in conjunction with the renowned clockmaker
Thomas Tompion
Thomas Tompion, FRS (1639–1713) was an English clockmaker, watchmaker and mechanician who is still regarded to this day as the "Father of English Clockmaking". Tompion's work includes some of the most historic and important clocks and watc ...
, following conversations with the music theorist
William Holder
William Holder FRS (1616 – 24 January 1698) was an English clergyman and music theorist of the 17th century. His most notable work was his widely known 1694 publication ''A Treatise on the Natural Grounds and Principles of Harmony''.
Life
He ...
.
He had a longstanding interest in musical
vibrations
Vibration is a mechanical phenomenon whereby oscillations occur about an equilibrium point. The word comes from Latin ''vibrationem'' ("shaking, brandishing"). The oscillations may be periodic, such as the motion of a pendulum—or random, such ...
, and a decade earlier in 1666 had even boasted to
Samuel Pepys
Samuel Pepys (; 23 February 1633 – 26 May 1703) was an English diarist and naval administrator. He served as administrator of the Royal Navy and Member of Parliament and is most famous for the diary he kept for a decade. Pepys had no mariti ...
that he could tell the rate a fly's wings were beating from the sound they made.
In July 1681, he demonstrated to the
Royal Society
The Royal Society, formally The Royal Society of London for Improving Natural Knowledge, is a learned society and the United Kingdom's national academy of sciences. The society fulfils a number of roles: promoting science and its benefits, re ...
his new device for producing distinct
musical tones by striking the teeth of fast-turning brass wheels.
[ ] In this way, he was able to generate for the first time
sound wave
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...
s of known
frequency
Frequency is the number of occurrences of a repeating event per unit of time. It is also occasionally referred to as ''temporal frequency'' for clarity, and is distinct from ''angular frequency''. Frequency is measured in hertz (Hz) which is eq ...
, and provide an empirical demonstration of the correspondence between the
human perception
Perception () is the organization, identification, and interpretation of sensory information in order to represent and understand the presented information or environment. All perception involves signals that go through the nervous system ...
of pitch and the
physical property
A physical property is any property that is measurable, whose value describes a state of a physical system. The changes in the physical properties of a system can be used to describe its changes between momentary states. Physical properties are ...
of sound-wave frequency.
[ Furthermore, by fitting different wheels alongside one another on the same axis, he was able to verify frequency ratios for musical intervals, such as ]perfect fifth
In music theory, a perfect fifth is the Interval (music), musical interval corresponding to a pair of pitch (music), pitches with a frequency ratio of 3:2, or very nearly so.
In classical music from Western culture, a fifth is the interval fro ...
s and fourths, etc.
Hooke published his findings in 1705. Despite providing an objective measure of pitch, for everyday use his wheel was soon made irrelevant by the invention in 1711 of the tuning fork
A tuning fork is an acoustic resonator in the form of a two-pronged fork with the prongs (tines) formed from a U-shaped bar of elastic metal (usually steel). It resonates at a specific constant pitch when set vibrating by striking it against ...
.
Savart's version
Hooke's device was not used again for study purposes for over a century.[ Its next documented usage was in 1830 when Savart reported his use of a system similar to Hooke's which he developed while investigating the lower range of ]human hearing
Hearing, or auditory perception, is the ability to perceive sounds through an organ, such as an ear, by detecting vibrations as periodic changes in the pressure of a surrounding medium. The academic field concerned with hearing is auditory ...
. Savart's specific contribution was to attach a tachometer
A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute (RPM) on a calibrated analo ...
to the axis of the toothed wheel to facilitate calibration of the tooth rate.[ Savart used his wheel as a practical alternative to John Robison's ]siren
Siren or sirens may refer to:
Common meanings
* Siren (alarm), a loud acoustic alarm used to alert people to emergencies
* Siren (mythology), an enchanting but dangerous monster in Greek mythology
Places
* Siren (town), Wisconsin
* Siren, Wisc ...
, which was also being adopted at the time by Charles Cagniard de la Tour
Baron Charles Cagniard de la Tour (31 March 1777 – 5 July 1859) was a French engineer and physicist. Charles Cagniard was born in Paris, and after attending the École Polytechnique became one of the ''ingénieurs géographiques''. He examined t ...
to test the range of human hearing. By 1834 Savart was constructing brass wheels with a width of 82 cm, containing as many as 720 teeth.[ These wheels, which could produce frequencies up to 24 ]kHz
The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that on ...
, have been tentatively proposed as the first artificial generators of ultrasound
Ultrasound is sound waves with frequency, frequencies higher than the upper audible limit of human hearing range, hearing. Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hea ...
.
Use in time perception experiments
In the later 19th century, Savart's wheel was adapted for use in physiological and psychological investigations of the human perception of time
The study of time perception or chronoception is a field within psychology, cognitive linguistics and neuroscience that refers to the subjective experience, or sense, of time, which is measured by someone's own perception of the duration of the ind ...
. In 1873, the Austrian physiologist Sigmund Exner
Sigmund Exner (also ''Sigmund Exner'', ''Siegmund Exner-Ewarten'', ''Siegmund Exner Ritter von Ewarten''; 5 April 1846 – 5 February 1926) was an Austrian physiologist born in Vienna.
Academic career
He studied in Vienna under Ernst Wilhelm ...
reported the auditory ability to distinguish successive clicks from the wheel (or, alternatively, rapidly snapped electric sparks) at time intervals as close as 2 millisecond
A millisecond (from '' milli-'' and second; symbol: ms) is a unit of time in the International System of Units (SI) equal to one thousandth (0.001 or 10−3 or 1/1000) of a second and to 1000 microseconds.
A unit of 10 milliseconds may be called ...
s (1/500 sec). A modified wheel that produced varying numbers of clicks at different intervals was later used by the American psychologists G. Stanley Hall
Granville Stanley Hall (February 1, 1846 – April 24, 1924) was a pioneering American psychologist and educator. His interests focused on human life span development and evolutionary theory. Hall was the first president of the American Psy ...
and Joseph Jastrow
Joseph Jastrow (January 30, 1863 – January 8, 1944) was a Polish-born American psychologist, noted for inventions in experimental psychology, design of experiments, and psychophysics. He also worked on the phenomena of optical illusions, ...
, who in 1886 reported on the limits to the human perception of acoustic discontinuities.
Musical and other applications
In 1894, French electrical engineer Gustave Trouvé
Gustave Pierre Trouvé (2 January 1839 – 27 July 1902) was a French electrical engineer and inventor in the 19th century.
Trouvé was born on 2 January 1839 in La Haye-Descartes (Indre-et-Loire, France) and died on 27 July 1902 in Paris. A pol ...
patented an electrically (or clockwork) powered keyboard instrument capable of playing a series of 88 variously-sized Savart wheels from a piano keyboard, allowing harmonic chords and dynamics. The same principle is used in modern-day electromechanical organs, such as the Hammond organ
The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Multiple models have been produced, most of which use sliding drawbars to vary sounds. Until 1975, Hammond organs generated s ...
, that make use of tonewheel
A tonewheel or tone wheel is a simple electromechanical apparatus used for generating electric musical notes in electromechanical organ instruments such as the Hammond Organ and in telephony to generate audible signals such as Ringing tone. ...
s.
The concept has also been adapted to produce an experimental musical instrument
An experimental musical instrument (or custom-made instrument) is a musical instrument that modifies or extends an existing instrument or class of instruments, or defines or creates a new class of instrument. Some are created through simple modi ...
created by Bart Hopkin
Bart Hopkin is a builder of experimental musical instruments and a writer and publisher on the subject. Hopkin runs the website windworld.com, which provides resources regarding unusual instruments.
Hopkin published the magazine ''Experimental Mus ...
. This application of Savart's wheel consists of a series of 30 wooden disks of increasing size mounted on a motorized axle. Rasping vibrations are induced in a plectrum
A plectrum is a small flat tool used for plucking or strumming of a stringed instrument. For hand-held instruments such as guitars and mandolins, the plectrum is often called a pick and is held as a separate tool in the player's hand. In harpsic ...
when it comes into contact with the ridges that line each disk at regular intervals, and are amplified in a styrofoam
Styrofoam is a trademarked brand of closed-cell extruded polystyrene foam (XPS), commonly called "Blue Board", manufactured as foam continuous building insulation board used in walls, roofs, and foundations as thermal insulation and water barrie ...
cup which acts as a sounding board. The instrument is claimed to make "the most obtrusive, obnoxious and irritating sound
In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid.
In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...
ever known."
Nowadays, Savart wheels are commonly used for demonstrations during physics lectures.[ In one variant, the wheel can be driven by an air hose blowing on the teeth; in this case, the pitch of the sound produced will vary with the force of the air current.]
See also
* Singing bird box
A singing bird box (''boîte à oiseau chanteur'' in French) is a box, usually rectangular-shaped, which contains within a miniature automaton singing bird concealed below an oval lid and activated by means of an operating lever.
Its origins are ...
* Tonometer
Tonometry is the procedure eye care professionals perform to determine the intraocular pressure (IOP), the fluid pressure inside the eye. It is an important test in the evaluation of patients at risk from glaucoma. Most tonometers are calibrate ...
* Tonewheel
A tonewheel or tone wheel is a simple electromechanical apparatus used for generating electric musical notes in electromechanical organ instruments such as the Hammond Organ and in telephony to generate audible signals such as Ringing tone. ...
Notes and references
Notes
References
External links
"Savart's Wheel" – musical instrument designed by Bart Hopkin
{{Plucked idiophones
Acoustics
Pitch (music)
Physics experiments
Ultrasound
Experimental musical instruments
Mechanical musical instruments
Lamellophones