Steam whistle
A steam whistle is a device used to produce sound with the aid of live steam, which acts as a vibrating system (compare to train horn). 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 (10) is pulled (usually via a pull cord), 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 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. Railway locomotives, traction engines, and steam ships have traditionally been fitted with a whistle for warning and communication purposes. Large diameter 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. Railway whistles. Steam warning devices have been used on trains since 1833 when George Stephenson invented and patented a steam trumpet for use on the Leicester and Swannington Railway. 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 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 [driver] 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, 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, which delivers dry steam 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. Music. An array of steam whistles arranged to play music is referred to as a calliope. In York, Pennsylvania, 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 horns. 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. Sound pressure level. Whistle sound level varies with several factors: 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  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, Pennsylvania, was entered in the Guinness Book of World Records in 2002 as the loudest steam whistle on record at 124.1dBA from a set  distance 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 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 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, Longview, Washington measured 16 inches diameter x 49 inches in length. The whistle bells of multi-bell chimes used on ocean liners such as the "RMS Titanic" measured 9, 12, and 15 inches diameter. The whistle bells of the Canadian Pacific steamships "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 gong whistle 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 houses 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, 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.