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69-632: Since the end of the 19th century, the excellent acoustics of the church has allowed it to serve as a venue for concerts of classical music , in particular for the Passions of Johann Sebastian Bach . Returning unharmed from the Crusades , the knight Henri de Müllenheim undertook the construction of a monastery for the Hermits of Saint William , an order of mendicant monks , in this marshy neighbourhood situated extra muros , that is, beyond

138-596: A Bachelor's degree or higher qualification. Some possess a degree in acoustics, while others enter the discipline via studies in fields such as physics or engineering . Much work in acoustics requires a good grounding in Mathematics and science . Many acoustic scientists work in research and development. Some conduct basic research to advance our knowledge of the perception (e.g. hearing , psychoacoustics or neurophysiology ) of speech , music and noise . Other acoustic scientists advance understanding of how sound

207-441: A specific range of frequencies . The audible frequency range for humans is typically given as being between about 20 Hz and 20,000 Hz (20 kHz), though the high frequency limit usually reduces with age. Other species have different hearing ranges. For example, some dog breeds can perceive vibrations up to 60,000 Hz. In many media, such as air, the speed of sound is approximately independent of frequency, so

276-744: A building from earthquakes, or measuring how structure-borne sound moves through buildings. Ultrasonics deals with sounds at frequencies too high to be heard by humans. Specialisms include medical ultrasonics (including medical ultrasonography), sonochemistry , ultrasonic testing , material characterisation and underwater acoustics ( sonar ). Underwater acoustics is the scientific study of natural and man-made sounds underwater. Applications include sonar to locate submarines , underwater communication by whales , climate change monitoring by measuring sea temperatures acoustically, sonic weapons , and marine bioacoustics. Frequency Frequency (symbol f ), most often measured in hertz (symbol: Hz),

345-572: A definite mathematical structure. The wave equation emerged in a number of contexts, including the propagation of sound in air. In the nineteenth century the major figures of mathematical acoustics were Helmholtz in Germany, who consolidated the field of physiological acoustics, and Lord Rayleigh in England, who combined the previous knowledge with his own copious contributions to the field in his monumental work The Theory of Sound (1877). Also in

414-411: A fractional error of Δ f f = 1 2 f T m {\textstyle {\frac {\Delta f}{f}}={\frac {1}{2fT_{\text{m}}}}} where T m {\displaystyle T_{\text{m}}} is the timing interval and f {\displaystyle f} is the measured frequency. This error decreases with frequency, so it

483-551: A key element of mating rituals or for marking territories. Art, craft, science and technology have provoked one another to advance the whole, as in many other fields of knowledge. Robert Bruce Lindsay 's "Wheel of Acoustics" is a well accepted overview of the various fields in acoustics. The word "acoustic" is derived from the Greek word ἀκουστικός ( akoustikos ), meaning "of or for hearing, ready to hear" and that from ἀκουστός ( akoustos ), "heard, audible", which in turn derives from

552-416: A known frequency near the unknown frequency is mixed with the unknown frequency in a nonlinear mixing device such as a diode . This creates a heterodyne or "beat" signal at the difference between the two frequencies. If the two signals are close together in frequency the heterodyne is low enough to be measured by a frequency counter. This process only measures the difference between the unknown frequency and

621-402: A repeating event is accomplished by counting the number of times that event occurs within a specific time period, then dividing the count by the period. For example, if 71 events occur within 15 seconds the frequency is: f = 71 15 s ≈ 4.73 Hz . {\displaystyle f={\frac {71}{15\,{\text{s}}}}\approx 4.73\,{\text{Hz}}.} If

690-400: A result of varying auditory stimulus which can in turn affect the way one thinks, feels, or even behaves. This correlation can be viewed in normal, everyday situations in which listening to an upbeat or uptempo song can cause one's foot to start tapping or a slower song can leave one feeling calm and serene. In a deeper biological look at the phenomenon of psychoacoustics, it was discovered that

759-405: A rock concert. The central stage in the acoustical process is wave propagation. This falls within the domain of physical acoustics. In fluids , sound propagates primarily as a pressure wave . In solids, mechanical waves can take many forms including longitudinal waves , transverse waves and surface waves . Acoustics looks first at the pressure levels and frequencies in the sound wave and how

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828-483: A second (60 seconds divided by 120). For cyclical phenomena such as oscillations , waves , or for examples of simple harmonic motion , the term frequency is defined as the number of cycles or repetitions per unit of time. The conventional symbol for frequency is f or ν (the Greek letter nu ) is also used. The period T is the time taken to complete one cycle of an oscillation or rotation. The frequency and

897-456: A sound wave to or from an electric signal. The most widely used transduction principles are electromagnetism , electrostatics and piezoelectricity . The transducers in most common loudspeakers (e.g. woofers and tweeters ), are electromagnetic devices that generate waves using a suspended diaphragm driven by an electromagnetic voice coil , sending off pressure waves. Electret microphones and condenser microphones employ electrostatics—as

966-407: A string sounds the note C when plucked, a string twice as long will sound a C an octave lower. In one system of musical tuning , the tones in between are then given by 16:9 for D, 8:5 for E, 3:2 for F, 4:3 for G, 6:5 for A, and 16:15 for B, in ascending order. Aristotle (384–322 BC) understood that sound consisted of compressions and rarefactions of air which "falls upon and strikes the air which

1035-438: A wave comparable to a water wave extended to three dimensions, which, when interrupted by obstructions, would flow back and break up following waves. He described the ascending seats in ancient theaters as designed to prevent this deterioration of sound and also recommended bronze vessels (echea) of appropriate sizes be placed in theaters to resonate with the fourth, fifth and so on, up to the double octave, in order to resonate with

1104-465: A way of echolocation in the caves. In archaeology, acoustic sounds and rituals directly correlate as specific sounds were meant to bring ritual participants closer to a spiritual awakening. Parallels can also be drawn between cave wall paintings and the acoustic properties of the cave; they are both dynamic. Because archaeoacoustics is a fairly new archaeological subject, acoustic sound is still being tested in these prehistoric sites today. Aeroacoustics

1173-432: 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 while someone working in the field of acoustics technology may be called an acoustical engineer . The application of acoustics is present in almost all aspects of modern society with

1242-513: Is affected as it moves through environments, e.g. underwater acoustics , architectural acoustics or structural acoustics . Other areas of work are listed under subdisciplines below. Acoustic scientists work in government, university and private industry laboratories. Many go on to work in Acoustical Engineering . Some positions, such as Faculty (academic staff) require a Doctor of Philosophy . Archaeoacoustics , also known as

1311-495: Is called a radio wave . Likewise, an electromagnetic wave with a frequency higher than 8 × 10  Hz will also be invisible to the human eye; such waves are called ultraviolet (UV) radiation. Even higher-frequency waves are called X-rays , and higher still are gamma rays . All of these waves, from the lowest-frequency radio waves to the highest-frequency gamma rays, are fundamentally the same, and they are all called electromagnetic radiation . They all travel through vacuum at

1380-416: Is concerned with noise and vibration caused by railways, road traffic, aircraft, industrial equipment and recreational activities. The main aim of these studies is to reduce levels of environmental noise and vibration. Research work now also has a focus on the positive use of sound in urban environments: soundscapes and tranquility . Musical acoustics is the study of the physics of acoustic instruments;

1449-408: Is defined by ANSI/ASA S1.1-2013 as "(a) Science of sound , including its production, transmission, and effects, including biological and psychological effects. (b) Those qualities of a room that, together, determine its character with respect to auditory effects." The study of acoustics revolves around the generation, propagation and reception of mechanical waves and vibrations. The steps shown in

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1518-405: Is equivalent to one hertz. As a matter of convenience, longer and slower waves, such as ocean surface waves , are more typically described by wave period rather than frequency. Short and fast waves, like audio and radio, are usually described by their frequency. Some commonly used conversions are listed below: For periodic waves in nondispersive media (that is, media in which the wave speed

1587-411: Is generally a problem at low frequencies where the number of counts N is small. An old method of measuring the frequency of rotating or vibrating objects is to use a stroboscope . This is an intense repetitively flashing light ( strobe light ) whose frequency can be adjusted with a calibrated timing circuit. The strobe light is pointed at the rotating object and the frequency adjusted up and down. When

1656-430: Is how our ears interpret sound. What we experience as "higher pitched" or "lower pitched" sounds are pressure vibrations having a higher or lower number of cycles per second. In a common technique of acoustic measurement, acoustic signals are sampled in time, and then presented in more meaningful forms such as octave bands or time frequency plots. Both of these popular methods are used to analyze sound and better understand

1725-458: Is independent of frequency), frequency has an inverse relationship to the wavelength , λ ( lambda ). Even in dispersive media, the frequency f of a sinusoidal wave is equal to the phase velocity v of the wave divided by the wavelength λ of the wave: f = v λ . {\displaystyle f={\frac {v}{\lambda }}.} In the special case of electromagnetic waves in vacuum , then v = c , where c

1794-628: Is next to it...", a very good expression of the nature of wave motion. On Things Heard , generally ascribed to Strato of Lampsacus , states that the pitch is related to the frequency of vibrations of the air and to the speed of sound. In about 20 BC, the Roman architect and engineer Vitruvius wrote a treatise on the acoustic properties of theaters including discussion of interference, echoes, and reverberation—the beginnings of architectural acoustics . In Book V of his De architectura ( The Ten Books of Architecture ) Vitruvius describes sound as

1863-402: Is red light, 800 THz ( 8 × 10  Hz ) is violet light, and between these (in the range 400–800 THz) are all the other colors of the visible spectrum . An electromagnetic wave with a frequency less than 4 × 10  Hz will be invisible to the human eye; such waves are called infrared (IR) radiation. At even lower frequency, the wave is called a microwave , and at still lower frequencies it

1932-400: Is the speed of light in vacuum, and this expression becomes f = c λ . {\displaystyle f={\frac {c}{\lambda }}.} When monochromatic waves travel from one medium to another, their frequency remains the same—only their wavelength and speed change. Measurement of frequency can be done in the following ways: Calculating the frequency of

2001-416: Is the electronic manipulation of acoustic signals. Applications include: active noise control ; design for hearing aids or cochlear implants ; echo cancellation ; music information retrieval , and perceptual coding (e.g. MP3 or Opus ). Architectural acoustics (also known as building acoustics) involves the scientific understanding of how to achieve good sound within a building. It typically involves

2070-400: 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 to distinguish it from spatial frequency . Ordinary frequency is related to angular frequency (symbol ω , with SI unit radian per second) by a factor of 2 π . The period (symbol T ) is the interval of time between events, so the period is

2139-431: Is the scientific study of the hearing and calls of animal calls, as well as how animals are affected by the acoustic and sounds of their habitat. This subdiscipline is concerned with the recording, manipulation and reproduction of audio using electronics. This might include products such as mobile phones , large scale public address systems or virtual reality systems in research laboratories. Environmental acoustics

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2208-413: Is the study of noise generated by air movement, for instance via turbulence, and the movement of sound through the fluid air. This knowledge was applied in the 1920s and '30s to detect aircraft before radar was invented and is applied in acoustical engineering to study how to quieten aircraft . Aeroacoustics is important for understanding how wind musical instruments work. Acoustic signal processing

2277-460: Is usually small, it is still noticeable to the human ear. The smallest sound that a person can hear, known as the threshold of hearing , is nine orders of magnitude smaller than the ambient pressure. The loudness of these disturbances is related to the sound pressure level (SPL) which is measured on a logarithmic scale in decibels. Physicists and acoustic engineers tend to discuss sound pressure levels in terms of frequencies, partly because this

2346-688: The audio signal processing used in electronic music; the computer analysis of music and composition, and the perception and cognitive neuroscience of music . The goal this acoustics sub-discipline is to reduce the impact of unwanted sound. Scope of noise studies includes the generation, propagation, and impact on structures, objects, and people. Noise research investigates the impact of noise on humans and animals to include work in definitions, abatement, transportation noise, hearing protection, Jet and rocket noise, building system noise and vibration, atmospheric sound propagation, soundscapes , and low-frequency sound. Many studies have been conducted to identify

2415-444: The harmonic overtone series on a string. He is reputed to have observed that when the lengths of vibrating strings are expressible as ratios of integers (e.g. 2 to 3, 3 to 4), the tones produced will be harmonious, and the smaller the integers the more harmonious the sounds. For example, a string of a certain length would sound particularly harmonious with a string of twice the length (other factors being equal). In modern parlance, if

2484-408: The reciprocal of the frequency: T = 1/ f . Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals ( sound ), radio waves , and light . For example, if a heart beats at a frequency of 120 times per minute (2 hertz), the period—the time interval between beats—is half

2553-555: The speed of sound in air were carried out successfully between 1630 and 1680 by a number of investigators, prominently Mersenne. Meanwhile, Newton (1642–1727) derived the relationship for wave velocity in solids, a cornerstone of physical acoustics ( Principia , 1687). Substantial progress in acoustics, resting on firmer mathematical and physical concepts, was made during the eighteenth century by Euler (1707–1783), Lagrange (1736–1813), and d'Alembert (1717–1783). During this era, continuum physics, or field theory, began to receive

2622-415: The 19th century, Wheatstone, Ohm, and Henry developed the analogy between electricity and acoustics. The twentieth century saw a burgeoning of technological applications of the large body of scientific knowledge that was by then in place. The first such application was Sabine 's groundbreaking work in architectural acoustics, and many others followed. Underwater acoustics was used for detecting submarines in

2691-461: The above diagram can be found in any acoustical event or process. There are many kinds of cause, both natural and volitional. There are many kinds of transduction process that convert energy from some other form into sonic energy, producing a sound wave. There is one fundamental equation that describes sound wave propagation, the acoustic wave equation , but the phenomena that emerge from it are varied and often complex. The wave carries energy throughout

2760-594: The acoustic phenomenon. The entire spectrum can be divided into three sections: audio, ultrasonic, and infrasonic. The audio range falls between 20 Hz and 20,000 Hz. This range is important because its frequencies can be detected by the human ear. This range has a number of applications, including speech communication and music. The ultrasonic range refers to the very high frequencies: 20,000 Hz and higher. This range has shorter wavelengths which allow better resolution in imaging technologies. Medical applications such as ultrasonography and elastography rely on

2829-491: The alternating current in household electrical outlets is 60 Hz (between the tones B ♭ and B; that is, a minor third above the European frequency). The frequency of the ' hum ' in an audio recording can show in which of these general regions the recording was made. Aperiodic frequency is the rate of incidence or occurrence of non- cyclic phenomena, including random processes such as radioactive decay . It

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2898-429: The archaeology of sound, is one of the only ways to experience the past with senses other than our eyes. Archaeoacoustics is studied by testing the acoustic properties of prehistoric sites, including caves. Iegor Rezkinoff, a sound archaeologist, studies the acoustic properties of caves through natural sounds like humming and whistling. Archaeological theories of acoustics are focused around ritualistic purposes as well as

2967-493: The central nervous system is activated by basic acoustical characteristics of music. By observing how the central nervous system, which includes the brain and spine, is influenced by acoustics, the pathway in which acoustic affects the mind, and essentially the body, is evident. Acousticians study the production, processing and perception of speech. Speech recognition and Speech synthesis are two important areas of speech processing using computers. The subject also overlaps with

3036-436: The city walls. The elongated building, consecrated in 1301 and realised in 1307, is the only remnant of this group. Entirely brick and unvaulted , the church corresponds well to the ideal of the order, namely by its single nave and the simplicity of its exterior form. Sheltered by a pitched roof , its nave is topped and prolonged by a deep polygonal choir illuminated by high windows , which betrays its original function as

3105-438: The complete laws of vibrating strings (completing what Pythagoras and Pythagoreans had started 2000 years earlier). Galileo wrote "Waves are produced by the vibrations of a sonorous body, which spread through the air, bringing to the tympanum of the ear a stimulus which the mind interprets as sound", a remarkable statement that points to the beginnings of physiological and psychological acoustics. Experimental measurements of

3174-536: The disciplines of physics, physiology , psychology , and linguistics . Structural acoustics is the study of motions and interactions of mechanical systems with their environments and the methods of their measurement, analysis, and control. There are several sub-disciplines found within this regime: Applications might include: ground vibrations from railways; vibration isolation to reduce vibration in operating theatres; studying how vibration can damage health ( vibration white finger ); vibration control to protect

3243-456: The first World War. Sound recording and the telephone played important roles in a global transformation of society. Sound measurement and analysis reached new levels of accuracy and sophistication through the use of electronics and computing. The ultrasonic frequency range enabled wholly new kinds of application in medicine and industry. New kinds of transducers (generators and receivers of acoustic energy) were invented and put to use. Acoustics

3312-421: The frequency of the strobe equals the frequency of the rotating or vibrating object, the object completes one cycle of oscillation and returns to its original position between the flashes of light, so when illuminated by the strobe the object appears stationary. Then the frequency can be read from the calibrated readout on the stroboscope. A downside of this method is that an object rotating at an integer multiple of

3381-475: The monks' meeting room. In 1331, by reason of its proximity to the port and wharfs, the church was chosen as parish by the newly established corporation of shipbuilders. The convent closed however, during the less than prosperous 15th century, before the reform movement arrived at the end of the century. The Church, including the Rood screen was classified a Monument historique in 1985. Founded in 1885 by

3450-605: The more desirable, harmonious notes. During the Islamic golden age , Abū Rayhān al-Bīrūnī (973–1048) is believed to have postulated that the speed of sound was much slower than the speed of light. The physical understanding of acoustical processes advanced rapidly during and after the Scientific Revolution . Mainly Galileo Galilei (1564–1642) but also Marin Mersenne (1588–1648), independently, discovered

3519-467: The most obvious being the audio and noise control industries. Hearing is one of the most crucial means of survival in the animal world and speech is one of the most distinctive characteristics of human development and culture. Accordingly, the science of acoustics spreads across many facets of human society—music, medicine, architecture, industrial production, warfare and more. Likewise, animal species such as songbirds and frogs use sound and hearing as

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3588-545: The number of counts is not very large, it is more accurate to measure the time interval for a predetermined number of occurrences, rather than the number of occurrences within a specified time. The latter method introduces a random error into the count of between zero and one count, so on average half a count. This is called gating error and causes an average error in the calculated frequency of Δ f = 1 2 T m {\textstyle \Delta f={\frac {1}{2T_{\text{m}}}}} , or

3657-556: The organist Ernst Münch (1859–1928) the Wilhelmer Choir, also known as the 'Chœur de Saint-Guillaume' has established itself as one of the leading choirs of the region. It has been led by several famous choirmasters, including Wilhelm Furtwangler , John Eliot Gardiner and Charles and Fritz Munch the sons of the founder of the choir. 48°34′55.5″N 7°45′28″E  /  48.582083°N 7.75778°E  / 48.582083; 7.75778 Acoustics Acoustics

3726-601: The period are related by the equation f = 1 T . {\displaystyle f={\frac {1}{T}}.} The term temporal frequency is used to emphasise that the frequency is characterised by the number of occurrences of a repeating event per unit time. The SI unit of frequency is the hertz (Hz), named after the German physicist Heinrich Hertz by the International Electrotechnical Commission in 1930. It

3795-406: The propagating medium. Eventually this energy is transduced again into other forms, in ways that again may be natural and/or volitionally contrived. The final effect may be purely physical or it may reach far into the biological or volitional domains. The five basic steps are found equally well whether we are talking about an earthquake , a submarine using sonar to locate its foe, or a band playing in

3864-410: The reference frequency. To convert higher frequencies, several stages of heterodyning can be used. Current research is extending this method to infrared and light frequencies ( optical heterodyne detection ). Visible light is an electromagnetic wave , consisting of oscillating electric and magnetic fields traveling through space. The frequency of the wave determines its color: 400 THz ( 4 × 10 Hz)

3933-435: The relationship between acoustics and cognition , or more commonly known as psychoacoustics , in which what one hears is a combination of perception and biological aspects. The information intercepted by the passage of sound waves through the ear is understood and interpreted through the brain, emphasizing the connection between the mind and acoustics. Psychological changes have been seen as brain waves slow down or speed up as

4002-560: The rotation rate of a shaft, mechanical vibrations, or sound waves , can be converted to a repetitive electronic signal by transducers and the signal applied to a frequency counter. As of 2018, frequency counters can cover the range up to about 100 GHz. This represents the limit of direct counting methods; frequencies above this must be measured by indirect methods. Above the range of frequency counters, frequencies of electromagnetic signals are often measured indirectly utilizing heterodyning ( frequency conversion ). A reference signal of

4071-414: The same speed (the speed of light), giving them wavelengths inversely proportional to their frequencies. c = f λ , {\displaystyle \displaystyle c=f\lambda ,} where c is the speed of light ( c in vacuum or less in other media), f is the frequency and λ is the wavelength. In dispersive media , such as glass, the speed depends somewhat on frequency, so

4140-444: The sound wave strikes the microphone's diaphragm, it moves and induces a voltage change. The ultrasonic systems used in medical ultrasonography employ piezoelectric transducers. These are made from special ceramics in which mechanical vibrations and electrical fields are interlinked through a property of the material itself. An acoustician is an expert in the science of sound. There are many types of acoustician, but they usually have

4209-461: The strobing frequency will also appear stationary. Higher frequencies are usually measured with a frequency counter . This is an electronic instrument which measures the frequency of an applied repetitive electronic signal and displays the result in hertz on a digital display . It uses digital logic to count the number of cycles during a time interval established by a precision quartz time base. Cyclic processes that are not electrical, such as

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4278-468: The study of speech intelligibility, speech privacy, music quality, and vibration reduction in the built environment. Commonly studied environments are hospitals, classrooms, dwellings, performance venues, recording and broadcasting studios. Focus considerations include room acoustics, airborne and impact transmission in building structures, airborne and structure-borne noise control, noise control of building systems and electroacoustic systems. Bioacoustics

4347-456: The time varying pressure level and frequency profiles which give a specific acoustic signal its defining character. A transducer is a device for converting one form of energy into another. In an electroacoustic context, this means converting sound energy into electrical energy (or vice versa). Electroacoustic transducers include loudspeakers , microphones , particle velocity sensors, hydrophones and sonar projectors. These devices convert

4416-420: The ultrasonic frequency range. On the other end of the spectrum, the lowest frequencies are known as the infrasonic range. These frequencies can be used to study geological phenomena such as earthquakes. Analytic instruments such as the spectrum analyzer facilitate visualization and measurement of acoustic signals and their properties. The spectrogram produced by such an instrument is a graphical display of

4485-500: The verb ἀκούω( akouo ), "I hear". The Latin synonym is "sonic", after which the term sonics used to be a synonym for acoustics and later a branch of acoustics. Frequencies above and below the audible range are called " ultrasonic " and " infrasonic ", respectively. In the 6th century BC, the ancient Greek philosopher Pythagoras wanted to know why some combinations of musical sounds seemed more beautiful than others, and he found answers in terms of numerical ratios representing

4554-416: The wave interacts with the environment. This interaction can be described as either a diffraction , interference or a reflection or a mix of the three. If several media are present, a refraction can also occur. Transduction processes are also of special importance to acoustics. In fluids such as air and water, sound waves propagate as disturbances in the ambient pressure level. While this disturbance

4623-419: The wavelength is not quite inversely proportional to frequency. Sound propagates as mechanical vibration waves of pressure and displacement, in air or other substances. In general, frequency components of a sound determine its "color", its timbre . When speaking about the frequency (in singular) of a sound, it means the property that most determines its pitch . The frequencies an ear can hear are limited to

4692-462: The wavelength of the sound waves (distance between repetitions) is approximately inversely proportional to frequency. In Europe , Africa , Australia , southern South America , most of Asia , and Russia , the frequency of the alternating current in household electrical outlets is 50 Hz (close to the tone G), whereas in North America and northern South America, the frequency of

4761-457: Was adopted by the CGPM (Conférence générale des poids et mesures) in 1960, officially replacing the previous name, cycle per second (cps). The SI unit for the period, as for all measurements of time, is the second . A traditional unit of frequency used with rotating mechanical devices, where it is termed rotational frequency , is revolution per minute , abbreviated r/min or rpm. 60 rpm

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