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Siren Disk
A siren disk is used in pneumatic siren (noisemaker), sirens and has holes which are variously spaced apart. When the disk is spun in front of a jet of air, the holes modulate the air-jet which produces a sound. The pitch (music), pitch of a siren is produced by "the audio frequency, frequency of the impulses of compressed air passing through the openings in a rotating disk."(Nov 1922). "Siren Played by Sliding Drive Belt", ''Popular Science'', Vol. 101, No. 5, p.35. ISSN 0161-7370. The pitch is therefore determined by the speed at which the disk rotates, the number of holes which air passes through, the size of the holes and their spacing apart. Typical usages of siren disks Siren disks were once used as the active element of sirens, but the majority of siren disks currently manufactured are used as instructional aids in teaching the mechanics of sound and music. For example, the Ontario Science Centre has a metal siren disk set up as an interactive teaching exhibit for children. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hypothetical Siren Disk
A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can testable, test it. Scientists generally base scientific hypotheses on previous observations that cannot satisfactorily be explained with the available scientific theories. Even though the words "hypothesis" and "theory" are often used interchangeably, a scientific hypothesis is not the same as a scientific theory. A working hypothesis is a provisionally accepted hypothesis proposed for further research in a process beginning with an educated guess or thought. A different meaning of the term ''hypothesis'' is used in formal logic, to denote the antecedent (logic), antecedent of a proposition; thus in the proposition "If ''P'', then ''Q''", ''P'' denotes the hypothesis (or antecedent); ''Q'' can be called a consequent. ''P'' is the :wikt:assumption, assumption in a (possibly Counterfactual conditional, counterfac ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pneumatic
Pneumatics (from Greek ‘wind, breath’) is a branch of engineering that makes use of gas or pressurized air. Pneumatic systems used in Industrial sector, industry are commonly powered by compressed air or compressed inert gases. A centrally located and electrically-powered Gas compressor, compressor powers Pneumatic cylinder, cylinders, air motors, pneumatic actuators, and other pneumatic devices. A pneumatic system controlled through manual or automatic solenoid valves is selected when it provides a lower cost, more flexible, or safer alternative to electric motors, and hydraulic actuators. Pneumatics also has applications in dentistry, construction, mining, and other areas. Gases used in pneumatic systems Pneumatic systems in fixed installations, such as factories, use compressed air because a sustainable supply can be made by compressing Atmosphere of Earth, atmospheric air. The air usually has moisture removed, and a small quantity of oil is added at the compressor ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Siren (noisemaker)
A siren is a loud noise-making device. Civil defense sirens are mounted in fixed locations and used to warn of natural disasters or attacks. Sirens are used on emergency service vehicles such as ambulances, police cars, and fire engines. There are two general types: mechanical and electronic. Many fire sirens (used for calling the volunteer fire fighters) serve double duty as tornado or civil defense sirens, alerting an entire community of impending danger. Most fire sirens are either mounted on the roof of a fire station or on a pole next to the fire station. Fire sirens can also be mounted on or near government buildings, on tall structures such as water towers, as well as in systems where several sirens are distributed around a town for better sound coverage. Most fire sirens are single tone and mechanically driven by electric motors with a rotor attached to the shaft. Some newer sirens are electronically driven speakers. Fire sirens are often called "fire whistles", "fir ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pitch (music)
Pitch is a perceptual property of sounds that allows their ordering on a frequency-related scale, or more commonly, pitch is the quality that makes it possible to judge sounds as "higher" and "lower" in the sense associated with musical melodies. Pitch is a major auditory attribute of musical tones, along with duration, loudness, and timbre. Pitch may be quantified as a frequency, but pitch is not a purely objective physical property; it is a subjective psychoacoustical attribute of sound. Historically, the study of pitch and pitch perception has been a central problem in psychoacoustics, and has been instrumental in forming and testing theories of sound representation, processing, and perception in the auditory system. Perception Pitch and frequency Pitch is an auditory sensation in which a listener assigns musical tones to relative positions on a musical scale based primarily on their perception of the frequency of vibration. Pitch is closely related to frequency, but ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Audio Frequency
An audio frequency or audible frequency (AF) is a periodic vibration whose frequency is audible to the average human. The SI unit of frequency is the hertz (Hz). It is the property of sound that most determines pitch. The generally accepted standard hearing range for humans is 20 to 20,000 Hz. In air at atmospheric pressure, these represent sound waves with wavelengths of to . Frequencies below 20 Hz are generally felt rather than heard, assuming the amplitude of the vibration is great enough. High frequencies are the first to be affected by hearing loss due to age or prolonged exposure to very loud noises. Sound frequencies above 20 kHz are called ultrasonic. Frequencies and descriptions See also *Absolute threshold of hearing *Hypersonic effect, controversial claim for human perception above 20,000 Hz *Loudspeaker *Musical acoustics *Piano key frequencies *Scientific pitch notation *Whistle register The whistle register (also called the flute regi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ontario Science Centre
The Ontario Science Centre, formally the Centennial Museum of Science and Technology, is a science museum in Toronto, Ontario, Canada. It is located near the Don Valley Parkway about northeast of downtown on Don Mills Road just south of Eglinton Avenue East in the former city of North York. It is built down the side of a wooded ravine formed by one branch of the Don River located in Flemingdon Park. History Planning for the Science Centre started in 1961 during Toronto's massive expansion of the late 1950s and 1960s. In 1964, Toronto architect Raymond Moriyama was hired to design the site. Construction started in 1966 with plans to open the "Centennial Centre of Science and Technology" as part of the Canadian Centennial celebrations in 1967. However construction was not completed in 1967, and the Science Centre did not open to the public until two years later, on September 26, 1969. The buildings and design were part of a broader change in Canadian architecture, and remain an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Harmonic Series (music)
A harmonic series (also overtone series) is the sequence of harmonics, musical tones, or pure tones whose frequency is an integer multiple of a ''fundamental frequency''. Pitched musical instruments are often based on an acoustic resonator such as a string or a column of air, which oscillates at numerous modes simultaneously. At the frequencies of each vibrating mode, waves travel in both directions along the string or air column, reinforcing and canceling each other to form standing waves. Interaction with the surrounding air causes audible sound waves, which travel away from the instrument. Because of the typical spacing of the resonances, these frequencies are mostly limited to integer multiples, or harmonics, of the lowest frequency, and such multiples form the harmonic series. The musical pitch of a note is usually perceived as the lowest partial present (the fundamental frequency), which may be the one created by vibration over the full length of the string or air co ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Major Scale
The major scale (or Ionian mode) is one of the most commonly used musical scales, especially in Western music. It is one of the diatonic scales. Like many musical scales, it is made up of seven notes: the eighth duplicates the first at double its frequency so that it is called a higher octave of the same note (from Latin "octavus", the eighth). The simplest major scale to write is C major, the only major scale not requiring sharps or flats: The major scale had a central importance in Western music, particularly in the common practice period and in popular music. In Carnatic music, it is known as '' Sankarabharanam''. In Hindustani classical music, it is known as '' Bilaval''. Structure A major scale is a diatonic scale. The sequence of intervals between the notes of a major scale is: : whole, whole, half, whole, whole, whole, half where "whole" stands for a whole tone (a red u-shaped curve in the figure), and "half" stands for a semitone (a red angled line in the figu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Ptolemy's Intense Diatonic Scale
Ptolemy's intense diatonic scale, also known as the Ptolemaic sequence, justly tuned major scale, Ptolemy's tense diatonic scale, or the syntonous (or syntonic) diatonic scale, is a tuning for the diatonic scale proposed by Ptolemy, and corresponding with modern 5-limit just intonation.Chisholm, Hugh (1911). The Encyclopædia Britannica', Vol.28, p. 961. The Encyclopædia Britannica Company. This tuning was declared by Zarlino to be the only tuning that could be reasonably sung, it was also supported by Giuseppe Tartini, and is equivalent to Indian Gandhar tuning which features exactly the same intervals. It is produced through a tetrachord consisting of a greater tone (9:8), lesser tone (10:9), and just diatonic semitone (16:15). This is called Ptolemy's intense diatonic tetrachord (or "tense"), as opposed to Ptolemy's soft diatonic tetrachord (or "relaxed"), which is formed by 21:20, 10:9 and 8:7 intervals. Structure The structure of the intense diatonic scale is shown ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Minor Scale
In music theory, the minor scale is three scale patterns – the natural minor scale (or Aeolian mode), the harmonic minor scale, and the melodic minor scale (ascending or descending) – rather than just two as with the major scale, which also has a harmonic form but lacks a melodic form. In each of these scales, the first, third, and fifth scale degrees form a minor triad (rather than a major triad, as in a major scale). In some contexts, ''minor scale'' is used to refer to any heptatonic scale with this property (see Related modes below). Natural minor scale Relationship to relative major A natural minor scale (or Aeolian mode) is a diatonic scale that is built by starting on the sixth degree of its relative major scale. For instance, the A natural minor scale can be built by starting on the 6th degree of the C major scale: : Because of this, the key of A minor is called the ''relative minor'' of C major. Every major key has a relative minor, which starts ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Just Intonation
In music, just intonation or pure intonation is the tuning of musical intervals Interval may refer to: Mathematics and physics * Interval (mathematics), a range of numbers ** Partially ordered set#Intervals, its generalization from numbers to arbitrary partially ordered sets * A statistical level of measurement * Interval e ... as whole number ratios (such as 3:2 or 4:3) of Frequency, frequencies. An interval (music), interval tuned in this way is said to be pure, and is called a just interval. Just intervals (and chords created by combining them) consist of tones from a single harmonic series (music), harmonic series of an implied fundamental frequency, fundamental. For example, in the diagram, if the notes G3 and C4 (labelled 3 and 4) are tuned as members of the harmonic series of the lowest C, their frequencies will be 3 and 4 times the fundamental frequency. The interval ratio between C4 and G3 is therefore 4:3, a just fourth (music), fourth. In Western musical practice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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