Siren

siren

1. a device for emitting a loud wailing sound, esp as a warning or signal, typically consisting of a rotating perforated metal drum through which air or steam is passed under pressure

2. Greek myth one of several sea nymphs whose seductive singing was believed to lure sailors to destruction on the rocks the nymphs inhabited

3. any aquatic eel-like salamander of the North American family Sirenidae, having external gills, no hind limbs, and reduced forelimbs

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

siren

[′sī·rən]

(engineering acoustics)

An apparatus for generating sound by the mechanical interruption of the flow of fluid (usually air) by a perforated disk or cylinder.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

siren

half-woman, half-bird, enticed seamen to their death with song. [Gk. Myth.: Benét, 934]

See: Monsters

Allusions—Cultural, Literary, Biblical, and Historical: A Thematic Dictionary. Copyright 2008 The Gale Group, Inc. All rights reserved.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Siren

 

in ancient Greek mythology, a half-bird, half-woman. According to Homer’s Odyssey, the sirens used their enchanting voices to lure sailors to rocky shores, against which the sailors’ ships were smashed. In order to save his ship, Odysseus stopped his companions’ ears with wax and ordered himself tied to the mast. Similarly, Orpheus’ persuasive voice overcame the allure of the sirens and saved the Argonauts from death.

The ancient Greeks also believed that the sirens were associated with an underground kingdom, and as a result, the sirens were often depicted on gravestones. The most common type of sirens in ancient Greek art were creatures with the head and chest of a woman and the body of a bird. Figuratively, the term “siren” refers to a beautiful and seductive woman with an enchanting voice.

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Siren

 

an acoustic radiator whose operation is based on the periodic interruption of a stream of gas or liquid. Liquid sirens do not differ in principle from gas sirens, but they are used comparatively rarely because of the difficulty in designing a mechanism for radiation into a medium with a high acoustic resistance.

Sirens are classified according to the principle of operation as dynamic (rotating) and pulsating. Dynamic sirens are the most widely used type and are subdivided into axial and radial sirens (Figure 1). In an axial siren the air stream coincides with the axis of rotation; in a radial siren the air stream is directed along a radius perpendicular to the axis. In axial sirens a perforated disk—the rotor—rotates relative to a stationary disk—the stator. In radial sirens the rotor and the stator are two coaxial, usually cylindrical, surfaces. The rotor is rotated by an electric motor or by a small gas turbine. Air from a chamber enters under pressure through the apertures in the rotor and stator and is periodically interrupted. The frequency of air pulsations f is determined by the number of apertures in the rotor or stator m and by the number of rotor revolutions per minute N:f= mN/60 hertz (Hz). The frequency f is the fundamental frequency in the sound spectrum being radiated by the siren. The frequency range of sirens used in actual practice ranges from 200-300 Hz to 80-100 kilohertz (kHz); however, some sirens operate at frequencies up to 600 kHz. The power rating of a siren may be as high as tens of kilowatts.

Figure 1. Siren mechanisms: (a) axial siren, (b) radial siren; (1) rotor, (2) electric motor, (3) stator, (4) directional horn, (5) sound reflector, (6) air chamber

Dynamic air sirens are used for signaling, as in alarm and signal sirens, and for various technological purposes, including the coagulation of finely dispersed aerosols, defoaming, the precipitation of fogs, and the acceleration of heat-exchange and mass-exchange processes.

REFERENCES

Bergmann, L. Ul’trazvuk i ego primenenie ν nauke i lekhnike, 2nd ed. Moscow, 1957. (Translated from German.)
Crawford, A. E. Ul’trazvukovaia tekhnika. Moscow, 1958. (Translated from English.)
Veller, V. A., and B. I. Stepanov. “Ul’trazvukovye sireny s privodom ot elektrodvigatelia.” Akusticheskii zhurnal, 1963, vol. 9, no. 3.

IU. IA. BORISOV [23–1333–]

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.