Steam whistle
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A steam whistle is a device used to produce sound in the form of a
whistle A whistle is an instrument which produces sound from a stream of gas, most commonly air. It may be mouth-operated, or powered by air pressure, steam, or other means. Whistles vary in size from a small slide whistle or nose flute type to a larg ...
using
live steam Live steam is steam under pressure, obtained by heating water in a boiler. The steam is used to operate stationary or moving equipment. A live steam machine or device is one powered by steam, but the term is usually reserved for those that ar ...
, which creates, projects, and amplifies its sound by acting as a vibrating system (compare to
train horn In rail transport, a train (from Old French , from Latin , "to pull, to draw") is a series of connected vehicles that run along a railway track and transport people or freight. Trains are typically pulled or pushed by locomotives (often kn ...
).


Operation

The whistle consists of the following main parts, as seen on the drawing: the whistle bell (1), the steam orifice or aperture (2), and the valve (9). When the
lever A lever is a simple machine consisting of a beam or rigid rod pivoted at a fixed hinge, or ''fulcrum''. A lever is a rigid body capable of rotating on a point on itself. On the basis of the locations of fulcrum, load and effort, the lever is div ...
(10) is actuated (usually via a
pull cord A pullstring (pull string, pull-string), pullcord (pull cord, pull-cord), or pullchain (pull-chain, pull chain) is a string, cord, or chain wound on a spring-loaded spindle that engages a mechanism when it is pulled. It is most commonly use ...
), the valve opens and lets the steam escape through the orifice. The steam will alternately compress and rarefy in the bell, creating the sound. The pitch, or tone, is dependent on the length of the bell; and also how far the operator has opened the valve. Some locomotive engineers invented their own distinctive style of whistling.


Uses of steam whistles

Steam whistles were often used in factories, and similar places to signal the start or end of a shift, etc. steam-powered
railway locomotive A locomotive or engine is a rail transport vehicle that provides the motive power for a train. If a locomotive is capable of carrying a payload, it is usually rather referred to as a multiple unit, motor coach, railcar or power car; the us ...
s,
traction engine A traction engine is a steam engine, steam-powered tractor used to move heavy loads on roads, plough ground or to provide power at a chosen location. The name derives from the Latin ''tractus'', meaning 'drawn', since the prime function of any t ...
s, and
steam ship A steamship, often referred to as a steamer, is a type of steam-powered vessel, typically ocean-faring and seaworthy, that is propelled by one or more steam engines that typically move (turn) propellers or paddlewheels. The first steamships ...
s have traditionally been fitted with a steam whistle for warning and communication purposes. Large diameter, low-pitched steam whistles were used on light houses, likely beginning in the 1850s. The earliest use of steam whistles was as boiler low-water alarms in the 18th century and early 19th century. During the 1830s, whistles were adopted by railroads and steamship companies.Pringle, R.E. and J. Parkes (1839). The causes and means of prevention of steam-boat accidents. Mechanics Magazine 31:262.


Gallery

File:Wiki short long whistle.jpg, upHigh-pitched plain whistle (left) and low-pitched plain whistle (right) File:Wiki 3 bell image.jpg, up3-bell multi-tone (chime) whistle sounds a musical chord File:Wiki single bell chime image.jpg, upSingle-bell multi-tone (chime) whistle with compartments of differing length and pitch tuned to a musical chord File:Wiki 6 chime b.jpg, up6-note "step-top" multi-tone (chime) whistle with 6 compartments of differing length and pitch. The mouth of each chamber is partially walled File:Wiki organ.jpg, upA partial mouth whistle ("organ whistle") in which the mouth extends less than 360 degrees around the whistle circumference File:Wiki gong image.jpg, up"Gong" chime whistle, two whistles aligned on the same axis File:Wiki variable pitch whistle.jpg, upVariable pitch whistle; note the internal piston used for adjusting pitch File:WikiUltrawhistle.jpg, up“Ultrawhistle” with ring-shaped bell cavity File:HelmholtzWhistle.jpg, upHelmholtz whistle has a low pitch relative to its length


Railway whistles

Steam warning devices have been used on trains since 1833 Stretton, Clement Edwin (1903). The Locomotive Engine and its Development: a popular treatise on the gradual improvements made in railway engines between 1803 and 1903. Crosby Lockwood and Son. when
George Stephenson George Stephenson (9 June 1781 – 12 August 1848) was a British civil engineer and mechanical engineer. Renowned as the "Father of Railways", Stephenson was considered by the Victorians a great example of diligent application and thirst for ...
invented and patented a steam trumpet for use on the
Leicester and Swannington Railway The Leicester and Swannington Railway (L&SR) was one of England's first railways, built to bring coal from West Leicestershire collieries to Leicester, where there was great industrial demand for coal. The line opened in 1832, and included a tun ...
. Period literature makes a distinction between a steam trumpet and a steam whistle. A copy of the trumpet drawing signed May 1833 shows a device about eighteen inches high with an ever-widening trumpet shape with a six-inch diameter at its top or mouth. It is said that George Stephenson invented his trumpet after an accident on the Leicester and Swannington Railway where a train hit either a cart, or a herd of cows, on a
level crossing A level crossing is an intersection where a railway line crosses a road, Trail, path, or (in rare situations) airport runway, at the same level, as opposed to the railway line crossing over or under using an Overpass#Railway, overpass ...
and there were calls for a better way of giving a warning. Although no-one was injured, the accident was deemed serious enough to warrant Stephenson's personal intervention. One account states that
river A river is a natural flowing watercourse, usually freshwater, flowing towards an ocean, sea, lake or another river. In some cases, a river flows into the ground and becomes dry at the end of its course without reaching another body of wate ...
Weatherburn had 'mouthblown his horn' at the crossing in an attempt to prevent the accident, but that no attention had been paid to this audible warning, perhaps because it had not been heard. Stephenson subsequently called a meeting of directors and accepted the suggestion of the company manager, Ashlin Bagster, that a horn or whistle which could be activated by steam should be constructed and fixed to the locomotives. Stephenson later visited a musical instrument maker on Duke Street in
Leicester Leicester ( ) is a city status in the United Kingdom, city, Unitary authorities of England, unitary authority and the county town of Leicestershire in the East Midlands of England. It is the largest settlement in the East Midlands. The city l ...
, who on Stephenson's instructions constructed a 'Steam Trumpet' which was tried out in the presence of the board of Directors ten days later. Stephenson mounted the trumpet on the top of the boiler's
steam dome The steam dome is a vessel fitted to the top of the boiler of a steam engine. It contains the opening to the main steam pipe and its purpose is to allow this opening to be kept well above the water level in the boiler. This arrangement acts as a ...
, which delivers
dry steam Superheated steam is steam at a temperature higher than its vaporization point at the absolute pressure where the temperature is measured. Superheated steam can therefore cool (lose internal energy) by some amount, resulting in a lowering of i ...
to the cylinders. The company went on to mount the device on its other locomotives Locomotive steam trumpets were soon replaced by steam whistles. Air whistles were used on some Diesel and electric locomotives, but these mostly employ
air horns The atmosphere of Earth is the layer of gases, known collectively as air, retained by Earth's gravity that surrounds the planet and forms its planetary atmosphere. The atmosphere of Earth protects life on Earth by creating pressure allowing for ...
.


Music

An array of steam whistles arranged to play music is referred to as a
calliope In Greek mythology, Calliope ( ; grc, Καλλιόπη, Kalliópē, beautiful-voiced) is the Muse who presides over eloquence and epic poetry; so called from the ecstatic harmony of her voice. Hesiod and Ovid called her the "Chief of all Muses" ...
. In
York, Pennsylvania York ( Pennsylvania Dutch: ''Yarrick''), known as the White Rose City (after the symbol of the House of York), is the county seat of York County, Pennsylvania, United States. It is located in the south-central region of the state. The populati ...
, a variable pitch steam whistle at the New York Wire Company has been played annually on Christmas Eve since 1925 (except in 1986 and 2005) in what has come to be known as "York's Annual Steam Whistle Christmas Concert". On windy nights, area residents report hearing the concert as far as 12 to 15 miles away. The whistle, which is in the Guinness Book of World Records, was powered by an air compressor during the 2010 concert due to the costs of maintaining and running the boiler.


Lighthouse fog signals

Beginning in 1869, steam whistles began being installed at lighthouse stations as a way of warning mariners in periods of fog, when the lighthouse is not visible. 10" diameter whistles were used as fog signals throughout the United States for many years, until they were later replaced by other compressed air diaphragm or
diaphone The diaphone is a noisemaking device best known for its use as a foghorn: It can produce deep, powerful tones, able to carry a long distance. Although they have fallen out of favor, diaphones were also used at some fire stations and in other situ ...
horns.


Types of whistles

*Plain whistle – an inverted cup mounted on a stem, as in the illustration above. In Europe, railway steam whistles were typically loud, shrill, single-note plain whistles. In the UK, locomotives were usually fitted with only one or two of these whistles, the latter having different tones and being controlled individually to allow more complex signalling. On railroads in Finland, two single-note whistles were used on every engine; one shrill, one of a lower tone. They were used for different signaling purposes. The
Deutsche Reichsbahn The ''Deutsche Reichsbahn'', also known as the German National Railway, the German State Railway, German Reich Railway, and the German Imperial Railway, was the German national railway system created after the end of World War I from the regiona ...
of
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
introduced another whistle design in the 1920s called "Einheitspfeife", conceived as a single-note plain whistle which already had a very deep-pitched and loud sound, but if the whistle trigger is just pulled down half of its way an even lower tone like from a chime-whistle could also be caused. This whistle is the reason for the typical "long high - short low - short high" signal sound of steam locomotives in Germany. *Chime whistle – two or more resonant bells or chambers that sound simultaneously. In America, railway steam whistles were typically compact chime whistles with more than one whistle contained within, creating a chord. In Australia the New South Wales Government Railways after the 1924 re-classification many steam locomotives either had 5 chimes whistles fitted (this include many locomotives from the pre 1924 re-classification, or were built new with 5 chime whistles. 3-chimes (3 compact whistles within one) were very popular, as well as 5-chimes, and 6-chimes. In some cases chime whistles were used in Europe. Ships such as the ''Titanic'' were equipped with chimes consisting of three separate whistles (in the case of the Titanic the whistles measured 9, 12, and 15 inches diameter). The
Japanese National Railways The abbreviated JNR or , was the business entity that operated Japan's national railway network from 1949 to 1987. Network Railways As of June 1, 1949, the date of establishment of JNR, it operated of narrow gauge () railways in all 46 pref ...
used a chime whistle that sounds like a very deep single-note plain whistle, because the chords where just accessed in a simple parallel circuit if the whistle trigger is pulled down. *Organ whistle – a whistle with mouths cut in the side, usually a long whistle in relation to diameter, hence the name. These whistle were very common on steamships, especially those manufactured in the UK. *Gong – two whistles facing in opposite directions on a common axis. These were popular as factory whistles. Some were composed of three whistle chimes. *Variable pitch whistle – a whistle containing an internal
piston A piston is a component of reciprocating engines, reciprocating pumps, gas compressors, hydraulic cylinders and pneumatic cylinders, among other similar mechanisms. It is the moving component that is contained by a cylinder and is made gas-tig ...
available for changing pitch. This whistle type could be made to sound like a siren or to play a melody. Often called a fire alarm whistle, wildcat whistle, or mocking bird whistle. *Toroidal or Levavasseur whistle – a whistle with a torus-shaped (doughnut-shaped) resonant cavity paralleling the annular gas orifice, named after Robert Levavasseur, its inventor. Unlike a conventional whistle, the diameter (and sound level) of a ring-shaped whistle can be increased without altering resonance chamber cross-sectional area (preserving frequency), allowing construction of a very large diameter high frequency whistle. The frequency of a conventional whistle declines as diameter is increased. Other ring-shaped whistles include the Hall-Teichmann whistle, Graber whistle, Ultrawhistle, and Dynawhistle. *Helmholtz whistle – a whistle with a cross-sectional area exceeding that of the whistle bell opening, often shaped like a bottle or incandescent light bulb. The frequency of this whistle relative to its size is lower than that of a conventional whistle and therefore these whistles have found application in small gauge steam locomotives. Also termed a Bangham whistle. *Hooter whistle - a single note whistle of greater diameter with a longer bell, resulting in a deeper “hoot” sound when blown. These found use in rail, marine, and industrial applications. In the United States, the
Norfolk and Western Railway The Norfolk and Western Railway , commonly called the N&W, was a US class I railroad, formed by more than 200 railroad mergers between 1838 and 1982. It was headquartered in Roanoke, Virginia, for most of its existence. Its motto was "Precisio ...
made extensive use of these kinds of whistles and were noted for the squeaks and chirps produced when blown in addition to their low pitch.


Whistle acoustics


Resonant frequency

A whistle has a characteristic natural resonant frequency that can be detected by gently blowing human breath across the whistle rim, much as one might blow over the mouth of a bottle. The active sounding frequency (when the whistle is blown on steam) may differ from the natural frequency as discussed below. These comments apply to whistles with a mouth area at least equal to the cross-sectional area of the whistle. * Whistle length – The natural resonant frequency decreases as the length of the whistle is increased. Doubling the effective length of a whistle reduces the frequency by one half, assuming that the whistle cross-sectional area is uniform. A whistle is a quarter-wave generator, which means that a sound wave generated by a whistle is about four times the whistle length. If the
speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...
in the steam supplied to a whistle were 15936 inches per second, a pipe with a 15-inch effective length blowing its natural frequency would sound near
middle C C or Do is the first note and semitone of the C major scale, the third note of the A minor scale (the relative minor of C major), and the fourth note (G, A, B, C) of the Guidonian hand, commonly pitched around 261.63  Hz. The actual frequen ...
: 15936/(4 x 15) = 266 Hz. When a whistle is sounding its natural frequency, the ''effective'' length referred to here is somewhat longer than the physical length above the mouth if the whistle is of uniform cross-sectional area. That is, the vibrating length of the whistle includes some portion of the mouth. This effect (the “end correction”) is caused by the vibrating steam inside the whistle engaging vibration of some steam outside the enclosed pipe, where there is a transition from plane waves to spherical waves. Formulas are available to estimate the effective length of a whistle, but an accurate formula to predict sounding frequency would have to incorporate whistle length, scale, gas flow rate, mouth height, and mouth wall area (see below). *Blowing pressure – Frequency increases with blowing pressure, which determines gas volume flow through the whistle, allowing a locomotive engineer to play a whistle like a musical instrument, using the valve to vary the flow of steam. The term for this was “quilling.” An experiment with a short plain whistle reported in 1883 showed that incrementally increasing steam pressure drove the whistle from E to D-flat, a 68 percent increase in frequency. Pitch deviations from the whistle natural frequency likely follow velocity differences in the steam jet downstream from the aperture, creating phase differences between driving frequency and natural frequency of the whistle. Although at normal blowing pressures the aperture constrains the jet to the speed of sound, once it exits the aperture and expands, velocity decay is a function of absolute pressure.Birch, A.D., D.J. Hughes, and F. Swaffield. (1987). Velocity decay of high pressure jets. Combustion Science and Technology. 52:161-171. Also, frequency may vary at a fixed blowing pressure with differences in temperature of steam or compressed air. Industrial steam whistles typically were operated in the range of 100 to 300
pounds per square inch The pound per square inch or, more accurately, pound-force per square inch (symbol: lbf/in2; abbreviation: psi) is a unit of pressure or of stress based on avoirdupois units. It is the pressure resulting from a force of one pound-force applied to ...
gauge pressure (psig) (0.7 - 2.1 megapascals, MPa), although some were constructed for use on pressures as high as 600 psig (4.1 MPa). All of these pressures are within the
choked flow Choked flow is a compressible flow effect. The parameter that becomes "choked" or "limited" is the fluid velocity. Choked flow is a fluid dynamic condition associated with the venturi effect. When a flowing fluid at a given pressure and temperatu ...
regime, where mass flow scales with upstream absolute pressure and inversely with the square root of absolute temperature. This means that for dry
saturated steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...
, a halving of absolute pressure results in almost a halving of flow. This has been confirmed by tests of whistle steam consumption at various pressures. Excessive pressure for a given whistle design will drive the whistle into an overblown mode, where the fundamental frequency will be replaced by an odd
harmonic A harmonic is a wave with a frequency that is a positive integer multiple of the ''fundamental frequency'', the frequency of the original periodic signal, such as a sinusoidal wave. The original signal is also called the ''1st harmonic'', the ...
, that is a frequency that is an odd number multiple of the fundamental. Usually this is the third harmonic (second
overtone An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental i ...
frequency), but an example has been noted where a large whistle jumped to the fifteenth harmonic.Ommundsen, Peter (2013). "Steam whistle harmonics and whistle length." Horn and Whistle 129:31-33 A long narrow whistle such as that of the
Liberty ship Liberty ships were a class of cargo ship built in the United States during World War II under the Emergency Shipbuilding Program. Though British in concept, the design was adopted by the United States for its simple, low-cost construction. Mass ...
John W. Brown sounds a rich spectrum of
overtones An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental i ...
, but is not overblown. (In overblowing the "amplitude of the pipe fundamental frequency falls to zero.") Increasing whistle length increases the number and amplitude of harmonics, as has been demonstrated in experiments with a variable-pitch whistle. Whistles tested on steam produce both even-numbered and odd-numbered harmonics. The harmonic profile of a whistle might also be influenced by aperture width, mouth cut-up, and lip-aperture offset, as is the case for organ pipes. *Steam quality – The dryness of steam provided to a whistles is variable and will affect whistle tone frequency. Steam quality determines the
velocity of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as wel ...
, which declines with decreasing dryness due to the
inertia Inertia is the idea that an object will continue its current motion until some force causes its speed or direction to change. The term is properly understood as shorthand for "the principle of inertia" as described by Newton in his first law ...
of the liquid phase. The speed of sound in steam is predictable if steam dryness is known. Also, the
specific volume In thermodynamics, the specific volume of a substance (symbol: , nu) is an intrinsic property of the substance, defined as the ratio of the substance's volume () to its mass (). It is the reciprocal of density (rho) and it is related to the mol ...
of steam for a given temperature decreases with decreasing dryness. Two examples of estimates of speed of sound in steam calculated from whistles blown under field conditions are 1,326 and 1,352 feet per second. *Aspect ratio – The more squat the whistle, the greater is the change in pitch with blowing pressure.Liljencrants, Johan. (2011
Organ pipe sensitivity to pressure.
/ref> This may be caused by differences in the
Q factor In physics and engineering, the quality factor or ''Q'' factor is a dimensionless parameter that describes how underdamped an oscillator or resonator is. It is defined as the ratio of the initial energy stored in the resonator to the energy los ...
. The pitch of a very squat whistle may rise several semitones as pressure is raised. Whistle frequency prediction thus requires establishment of a set of frequency/pressure curves unique to whistle scale, and a set of whistles may fail to track a musical chord as blowing pressure changes if each whistle is of a different scale. This is true of many antique whistles divided into a series of compartments of the same diameter but of different lengths. Some whistle designers minimized this problem by building resonant chambers of a similar scale. *Mouth vertical length (“cut-up”) – Frequency of a plain whistle declines as the whistle bell is raised away from the steam source. If the cut-up of an organ whistle or single bell chime is raised (without raising the whistle ceiling), the effective chamber length is shortened. Shortening the chamber drives frequency up, but raising the cut-up drives frequency down. The resulting frequency (higher, lower, or unchanged) will be determined by whistle scale and by competition between the two drivers. The cut-up prescribed by whistle-maker Robert Swanson for 150 psig steam pressure was 0.35 x bell diameter for a plain whistle, which is about 1.45 x net bell cross-sectional area (subtracting stud area). The Nathan Manufacturing Company used a cut-up of 1.56 x chamber cross-sectional area for their 6-note railway chime whistle. *Cut-up in relation to mouth arc – A large change in cut-up (e.g., 4x difference) may have little impact on whistle natural frequency if mouth area and total resonator length are held constant. For example, a plain whistle, which has a 360-degree mouth (that extends completely around the whistle circumference), can emit a similar frequency to a partial mouth organ whistle of the same mouth area and same overall resonator length (aperture to ceiling), despite an immensely different cut-up. (Cut-up is the distance between the steam aperture and the upper lip of the mouth.) This suggests that ''effective'' cut-up is determined by proximity of the oscillating gas column to the steam jet rather than by the distance between the upper mouth lip and the steam aperture. *Steam aperture width – Frequency may ''rise'' as steam aperture width ''declines'' and the slope of the frequency/pressure curve may vary with aperture width. *Gas composition – The frequency of a whistle driven by steam is typically higher than that of a whistle driven by
compressed air Compressed air is air kept under a pressure that is greater than atmospheric pressure. Compressed air is an important medium for transfer of energy in industrial processes, and is used for power tools such as air hammers, drills, wrenches, and o ...
at the same pressure. This frequency difference is caused by the greater
speed of sound The speed of sound is the distance travelled per unit of time by a sound wave as it propagates through an elastic medium. At , the speed of sound in air is about , or one kilometre in or one mile in . It depends strongly on temperature as w ...
in steam, which is less dense than air. The magnitude of the frequency difference can vary because the speed of sound is influenced by air temperature and by steam quality. Also, the more squat the whistle, the more sensitive it is to the difference in gas flow rate between steam and air that occurs at a fixed blowing pressure. Data from 14 whistles (34 resonant chambers) sounded under a variety of field conditions showed a wide range of frequency differences between steam and air (5 - 43 percent higher frequency on steam). Very elongate whistles, which are fairly resistant to gas flow differences, sounded a frequency 18 - 22 percent higher on steam (about three semitones).


Sound pressure level

Whistle sound level varies with several factors: *Blowing pressure – Sound level increases as blowing pressure is raised, column 5, lines 29-31 although there may be an optimum pressure at which sound level peaks. *Aspect ratio – Sound level increases as whistle length is reduced, increasing frequency. For example, depressing the piston of a variable-pitch steam whistle changed the frequency from 333 Hz to 753 Hz and raised the sound pressure level from 116 dBC to 123 dBC. That five-fold difference in the square of the frequency resulted in a five-fold difference in sound intensity.Barry, Harry and Peter Ommundsen (2015). "Whistle sound levels revisited." ''Horn and Whistle'' (133):4-5. Sound level also increases as whistle cross-sectional area is increased. Burrows, 1957, US2784693, column 5, lines 30-34 A sample of 12 single-note whistles ranging in size from one-inch diameter to 12-inches diameter showed a relationship between sound intensity and the square of the cross-sectional area (when differences in frequency were taken into account). In other words, relative whistle sound intensity can be estimated using the square of the cross-sectional area divided by the square of the wavelength. For example, the sound intensity from a whistle bell of 6-inch diameter x 7.5-inch length (113 dBC) was 10x that of a 2 x 4-inch whistle (103 dBC) and twice that of a (lower frequency) 10 x 40-inch whistle (110 dBC). These whistles were sounded on compressed air at 125 pounds per square inch gauge pressure (862 Kilopascals) and sound levels were recorded at 100 feet distance. Elongate organ whistles may exhibit disproportionately high sound levels due to their strong higher frequency overtones. At a separate venue a 20-inch diameter Ultrawhistle (ring-shaped whistle) operating at 15 pounds per square inch gauge pressure (103.4 kilopascals) produced 124 dBC at 100 feet. It is unknown how the sound level of this whistle would compare to that of a conventional whistle of the same frequency and resonant chamber area. By comparison, a Bell-Chrysler
air raid siren A civil defense siren, also known as an air-raid siren or tornado siren, is a siren used to provide an emergency population warning to the general population of approaching danger. It is sometimes sounded again to indicate the danger has pa ...
generates 138 dBC at 100 feet. The sound level of a Levavasseur toroidal whistle is enhanced by about 10 decibels by a secondary cavity parallel to the
resonant cavity A resonator is a device or system that exhibits resonance or resonant behavior. That is, it naturally oscillates with greater amplitude at some frequencies, called resonant frequencies, than at other frequencies. The oscillations in a resonato ...
, the former creating a
vortex In fluid dynamics, a vortex ( : vortices or vortexes) is a region in a fluid in which the flow revolves around an axis line, which may be straight or curved. Vortices form in stirred fluids, and may be observed in smoke rings, whirlpools in th ...
that augments the
oscillation Oscillation is the repetitive or periodic variation, typically in time, of some measure about a central value (often a point of equilibrium) or between two or more different states. Familiar examples of oscillation include a swinging pendulum ...
s of the jet driving the whistle. *Steam aperture width – If gas flow is restricted by the area of the steam aperture, widening the aperture will increase the sound level for a fixed blowing pressure. Enlarging the steam aperture can compensate for the loss of sound output if pressure is reduced. It has been known since at least the 1830s that whistles can be modified for low pressure operation and still achieve a high sound level. Data on the compensatory relationship between pressure and aperture size are scant, but tests on compressed air indicate that a halving of absolute pressure requires that the aperture size be at least doubled in width to maintain the original sound level, and aperture width in some antique whistle arrays increases with diameter (aperture area thus increasing with whistle cross-sectional area) for whistles of the same scale. Applying the physics of high pressure jets exiting circular apertures, a doubling of velocity and gas concentration at a fixed point in the whistle mouth would require a quadrupling of either aperture area or absolute pressure. (A quartering of absolute pressure would be compensated by a quadrupling of aperture area—the velocity decay constant increases approximately with the square root of absolute pressure in the normal whistle-blowing pressure range.) In reality, trading pressure loss for greater aperture area may be less efficient as pressure-dependent adjustments occur to virtual origin displacement. Quadrupling the width of an organ pipe aperture at a fixed blowing pressure resulted in somewhat less than a doubling of velocity at the flue exit. *Steam aperture profile – Gas flow rate (and thus sound level) is set not only by aperture area and blowing pressure, but also by aperture geometry.
Friction Friction is the force resisting the relative motion of solid surfaces, fluid layers, and material elements sliding against each other. There are several types of friction: *Dry friction is a force that opposes the relative lateral motion of t ...
and
turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
influence the flow rate, and are accounted for by a
discharge coefficient In a nozzle or other constriction, the discharge coefficient (also known as coefficient of discharge or efflux coefficient) is the ratio of the actual discharge to the ideal discharge,Sam Mannan, Frank P. Lee, ''Lee's Loss Prevention in the Process ...
. A mean estimate of the discharge coefficient from whistle field tests is 0.72 (range 0.69 - 0.74). *Mouth vertical length (“cut-up”) – The mouth length (cut-up) that provides the highest sound level at a fixed blowing pressure varies with whistle scale, and some makers of multi-tone whistles therefore cut a mouth height unique to the scale of each resonant chamber, maximizing sound output of the whistle. Ideal cut-up for whistles of a fixed diameter and aperture width (including single-bell chime compartments) at a fixed blowing pressure appears to vary approximately with the square root of effective length.
Antique An antique ( la, antiquus; 'old', 'ancient') is an item perceived as having value because of its aesthetic or historical significance, and often defined as at least 100 years old (or some other limit), although the term is often used loosely ...
whistle makers commonly used a compromise mouth area of about 1.4x whistle cross-sectional area. If a whistle is driven to its maximum sound level with the mouth area set equal to the whistle cross-sectional area, it may be possible to increase the sound level by further increasing the mouth area. . *Frequency and distance –
Sound pressure Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophone ...
level decreases by half (six decibels) with each doubling of distance due to divergence from the source, an
inversely proportional In mathematics, two sequences of numbers, often experimental data, are proportional or directly proportional if their corresponding elements have a constant ratio, which is called the coefficient of proportionality or proportionality constan ...
relationship. (Distinct from the
inverse square law In science, an inverse-square law is any scientific law stating that a specified physical quantity is inversely proportional to the square of the distance from the source of that physical quantity. The fundamental cause for this can be understoo ...
, applicable to sound intensity, rather than pressure.) Sound pressure level also decreases due to atmospheric absorption, which is strongly dependent upon frequency, lower frequencies traveling farthest. For example, a 1000 Hz whistle has an atmospheric attenuation coefficient one half that of a 2000 Hz whistle (calculated for 50 percent
relative humidity Humidity is the concentration of water vapor present in the air. Water vapor, the gaseous state of water, is generally invisible to the human eye. Humidity indicates the likelihood for precipitation, dew, or fog to be present. Humidity depe ...
at 20 degrees Celsius). This means that in addition to divergent sound dampening, there would be a loss of 0.5 decibel per 100 meters from the 1000 Hz whistle and 1.0 decibel per 100 meters for the 2000 Hz whistle. Additional factors affecting
sound propagation 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 ...
include barriers, atmospheric temperature gradients, and "ground effects.”Piercy, J.E. and Tony F.W. Embleton (1979). Sound propagation in the open air. In: Harris, Cyril M. Handbook of Noise Control, Second Edition. New York: McGraw-Hill.


Terminology

Acoustic length or effective length is the quarter wavelength generated by the whistle. It is calculated as one quarter the ratio of speed of sound to the whistle's frequency. Acoustic length may differ from the whistle's physical length, also termed geometric length. depending upon mouth configuration, etc. The end correction is the difference between the acoustic length and the physical length above the mouth. The end correction is a function of diameter whereas the ratio of acoustic length to physical length is a function of scale. These calculations are useful in whistle design to obtain a desired sounding frequency. Working length in early usage meant whistle acoustic length, i.e., the effective length of the ''working'' whistle, but recently has been used for physical length including the mouth.


Loudest and largest whistles

Loudness In acoustics, loudness is the subjectivity, subjective perception of sound pressure. More formally, it is defined as, "That attribute of auditory sensation in terms of which sounds can be ordered on a scale extending from quiet to loud". The rel ...
is a subjective perception that is influenced by sound pressure level, sound duration, and sound frequency. High sound pressure level potential has been claimed for the whistles of Vladimir Gavreau, who tested whistles as large as 1.5 meter (59-inch) diameter (37 Hz). A 20-inch diameter ring-shaped whistle (“Ultrawhistle”) patented and produced by Richard Weisenberger sounded 124 decibels at 100 feet. The variable pitch steam whistle at the New York Wire Company in
York York is a cathedral city with Roman origins, sited at the confluence of the rivers Ouse and Foss in North Yorkshire, England. It is the historic county town of Yorkshire. The city has many historic buildings and other structures, such as a ...
,
Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
, was entered in the
Guinness Book of World Records ''Guinness World Records'', known from its inception in 1955 until 1999 as ''The Guinness Book of Records'' and in previous United States editions as ''The Guinness Book of World Records'', is a reference book published annually, listing world ...
in 2002 as the loudest steam whistle on record at 124.1dBA from used by Guinness. The York whistle was also measured at 134.1 decibels from a distance of 23-feet. A fire-warning whistle supplied to a Canadian
saw mill A sawmill (saw mill, saw-mill) or lumber mill is a facility where logs are cut into lumber. Modern sawmills use a motorized saw to cut logs lengthwise to make long pieces, and crosswise to length depending on standard or custom sizes ( dimens ...
by the Eaton, Cole, and Burnham Company in 1882 measured 20 inches in diameter, four feet nine inches from bowl to ornament, and weighed 400 pounds. The spindle supporting the whistle bell measured 3.5 inches diameter and the whistle was supplied by a four-inch feed pipe. Other records of large whistles include an 1893 account of U.S. President
Grover Cleveland Stephen Grover Cleveland (March 18, 1837June 24, 1908) was an American lawyer and politician who served as the 22nd and 24th president of the United States from 1885 to 1889 and from 1893 to 1897. Cleveland is the only president in American ...
activating the “largest steam whistle in the world,” said to be “five feet” at the Chicago World's Fair. The sounding chamber of a whistle installed at the 1924
Long-Bell Lumber Company In 1887, Robert A. Long and Victor Bell formed the Long-Bell Lumber Company in Columbus, Kansas. The Long-Bell Lumber Company branched out using balanced vertical integration to control all aspects of lumber from the sawmills to the retail lumber ...
,
Longview, Washington Longview is a city in Cowlitz County, Washington, United States. It is the principal city of the Longview, Washington Metropolitan Statistical Area, which encompasses all of Cowlitz County. Longview's population was 37,818 at the time of the 2 ...
measured 16 inches diameter x 49 inches in length. The whistle bells of multi-bell chimes used on
ocean liner An ocean liner is a passenger ship primarily used as a form of transportation across seas or oceans. Ocean liners may also carry cargo or mail, and may sometimes be used for other purposes (such as for pleasure cruises or as hospital ships). Ca ...
s such as the ''
RMS Titanic RMS ''Titanic'' was a British passenger liner, operated by the White Star Line, which sank in the North Atlantic Ocean on 15 April 1912 after striking an iceberg during her maiden voyage from Southampton, England, to New York City, United ...
'' measured 9, 12, and 15 inches diameter. The whistle bells of the
Canadian Pacific The Canadian Pacific Railway (french: Chemin de fer Canadien Pacifique) , also known simply as CPR or Canadian Pacific and formerly as CP Rail (1968–1996), is a Canadian Class I railway incorporated in 1881. The railway is owned by Canadi ...
steamship A steamship, often referred to as a steamer, is a type of steam-powered vessel, typically ocean-faring and seaworthy, that is propelled by one or more steam engines that typically move (turn) propellers or paddlewheels. The first steamships ...
s ''Assiniboia'' and '' Keewatin'' measured 12 inches in diameter and that of the Keewatin measured 60 inches in length. A multi-bell chime whistle installed at the Standard Sanitary Manufacturing Company in 1926 was composed of five separate whistle bells measuring 5 x15, 7 x 21, 8x 24, 10 x 30, and 12 x36 inches, all plumbed to a five-inch steam pipe. The Union Water Meter Company of Worcester Massachusetts produced a composed of three bells, 8 x 9-3/4, 12 x 15, and 12 x 25 inches. Twelve-inch diameter steam whistles were commonly used at
light house A lighthouse is a tower, building, or other type of physical structure designed to emit light from a system of lamps and lenses and to serve as a beacon for navigational aid, for maritime pilots at sea or on inland waterways. Lighthouses mar ...
s in the 19th century. It has been claimed that the sound level of an Ultrawhistle would be significantly greater than that of a conventional whistle,For example, Weisenberger, Richard (1986). Build an eight inch super whistle: an introduction to the toroidal whistle. Horn and Whistle 25:4-6. but comparative tests of large whistles have not been undertaken. Tests of small Ultrawhistles have not shown higher sound levels compared to conventional whistles of the same diameter.


See also

*
Train whistle A train whistle or air whistle (originally referred to as a steam trumpet) is an audible signaling device on a steam locomotive, used to warn that the train is approaching, and to communicate with rail workers. Modern diesel and electric locomot ...


References


Further reading

* {{DEFAULTSORT:Steam Whistle Sound production Steam power Whistles