1 GENERAL
LK-STH21-2 siren is an omnidirectional, single-tone alarm siren that is capable of producing high intensity and distinctive sound that is readily distinctive from other warning signals such as vehicle sirens over a large area. The high efficiency of LK-STH21-2 siren enables them to produce a high sound level while making moderate demands on the power source.
2 SIREN DESCIPTION
LK-STH21-2 siren consists of two major assemblies: the Motor Assembly, the Intake Tube Assembly.
The Motor Assembly consists of a vertically installed motor having a drive shaft that extends from each end. A stator and rotor are mounted on each end of the motor. The stators are attached to the motor housing and the rotors are mounted on the drive shaft concentric to the stators. Each rotor-stator combination contains a different number of ports. As the motor rotates the rotors, air is drawn through the upper and lower intake tubes and passes through the rotor and stator ports in pulses. These pulses are produced because the rotor alternately opens and closes the stator ports. The pulses of air produce sound at a frequency that is dependent on the instantaneous rotational speed of the rotor, and number of ports in each rotor and stator. Ten megaphonic horns are attached to the stators, one at each port, to project the sound to the surrounding area.
3 SIGNAL DESCRIPTION
LK-STH21-2 siren is capable of producing a steady single-tone and a wailing single-tone signal. The frequency of the tones that comprise these signals have a ratio of 5.5:5. For example, if the frequency of the higher pitched tone at a given time is 560Hz, the frequency of the lower pitched tone is 500Hz. Both tones in each of the signals are produced simultaneously, lending a very distinctive sound to the siren warning signals. The steady signal is usually used as a Civil Defense "Alert" signal and the wailing signal is usually used as a Civil Defense "Attack” signal.
