Nowadays, on the roofs of some buildings in the city, we occasionally see some horn-like devices, which are sirens used for civil air defense.
Alarms are divided into three types: electric alarms, electroacoustic alarms, and hand-cranked alarms.
The electric siren speakers are the main device of the siren by the motor, which converts the electrical energy into sound.
The electro-acoustic alarm speaker is composed of a host amplifier and a speaker.
The hand-cranked Air Defense Siren Speaker is a supplementary early warning device for the electric siren and the electro-acoustic siren; the control equipment is divided into two types: wired control and wireless control, and the power supply system is divided into two types: mains power supply and self-power supply.
The amplification equipment includes tweeters and flat speakers. The frequency of the air defense alarm is generally 500±20HZ, and people will feel a little sharp and harsh when they hear it.
The air defense siren is actually a "mechanical wave"
Every September, air defense alarms will be sounded centrally across the country according to regulations. Combined with the sounding of the alarms, some regions and cities will organize urban residents to conduct air defense and disaster prevention drills.
When the air defense siren was tested, the alarm sound was loud and penetrating. This sound was actually a kind of "mechanical wave", which was transmitted from the air defense siren.
The anti-aircraft alarm is driven by a motor to drive the sounding wheel to run at high speed, and the general speed is about 2880r/min; when the motor drives the sounding wheel to rotate, the air enters the sounding wheel from the air inlet on the side, and is discharged from the window of the fixed wheel after high-speed and high-pressure treatment. It resonates, forming a "mechanical wave" that travels through the air.
The "mechanical wave" makes a sound due to the high-frequency "oscillation" of the medium in a certain space. The horn (electromagnetic) in the sound of the air defense siren device converts the adjustable and controllable audio frequency electrical signal through the horn diaphragm (paper cone, etc.) The mechanical vibration that controls the frequency pushes the air in front of it, and transforms it into a "mechanical wave" that can be changed and conveyed to people's ears, that is, the alarm sound that can be heard in every corner of the city.
The loudspeakers of air defense sirens are generally placed very high, and they can be transmitted from a high place down and can be transmitted very far.
Anti-aircraft sirens are generally shrill, piercing, and distinctive through physical design and adjustment controls, and are designed to draw special attention.
Where is the largest air defense siren in the world right now?
At present, the world's largest air defense siren named "Defender" is placed in the Nanjing Massacre Memorial Hall.
"Defender" participated in my country's first National Memorial Day on December 13, 2014, and was incorporated into the National Memorial Day Air Defense Alert System. "Defenders" aims to remind people to remember the historical disaster of the Nanjing Massacre with a piercing siren, to mourn the thousands of innocent compatriots who died, and to remember the unbearable history, so that human tragedies will not be repeated, and world peace will last forever!
The "Defender" air defense siren is a solid "monster", completely domestically developed. Its volume, power and decibel are currently the largest in the world: the diameter of the speaker is 2 meters 6 high, 2 meters wide and 3 meters long. The bell mouth space is enough to lay down 6 strong men with a height of 1.8 meters or more; the operating power reaches 157.5 kilowatts, nearly 30 times higher than that of ordinary air defense sirens; during normal operation, the operator generally needs to operate remotely from 50 meters away. Once tested, the operator stood within 30 meters and heard a sound of 130 decibels, and the skin of the thigh clearly felt a needle-like pain.
The "Defender" air defense siren is generally placed in the commanding heights of the city or in an open place. The siren sound is clear and audible within 30 square kilometers, while the general electroacoustic air defense siren covers less than 5 square kilometers.