However, I wonder if you have ever wondered what kind of equipment an air defense siren is? How is the siren sounded? What allows the sound of air defense sirens to travel so far?
(1) How does the air defense siren sound?
In fact, the air defense alarm speaker is not a new product. As early as World War II, this kind of siren that can transmit sound far away has existed. In some old movies, we often see some air defense personnel controlling mechanical air defense. The figure of the siren.
The low-pitched bee-like sound of air defense sirens originally originated from mechanical work. Early anti-aircraft sirens were manually shaken to make the machine run, and then sounded. At the time, the reason why the anti-aircraft siren could make such a loud sound without using electricity was because the anti-aircraft siren had a special internal structure.
The sounding principle of the siren is similar to that of our common diabolo. When rotating, the internal gears will change from large to small, gradually changing from slow rotation to high-speed rotation, which in turn drives the internal ringing wheel. The compressed air is compressed, and then the compressed air is continuously squeezed towards the dense sound window, thereby making a low bee-like sound.
(2) How to distinguish different alarm sounds?
There are three types of air defense warning signals: advance warning, air raid warning and de-alarm. Identifying air defense warnings is the basis for correct protective actions. If the three warning signals are confused, the consequences can be unimaginable.
The pre-alarm sound signal is stipulated as: sound for 36 seconds, stop for 24 seconds, repeat three times as a cycle, and the duration is 3 minutes. Signal.
After hearing the advance warning, citizens should immediately turn off the power switch, turn off the gas, extinguish the fire, carry personal protective equipment and necessary daily necessities, take care of the elderly and children, and enter the civil air defense project or designated hidden areas quickly and orderly.
The sound signal of the air raid siren is stipulated as: sound for 6 seconds, stop for 6 seconds, repeat 15 times as a cycle, and the duration is 3 minutes. A warning signal to sound in the event of an attack on an urban target.
After the citizens hear the air raid siren, all personnel should immediately go to the nearest civil air defense project to hide, except for the staff in various industries (units) who must stick to their posts.
The audible signal for releasing the alarm is stipulated as follows: a long beep sound continuously for 3 minutes. It is characterized by "no interval". It is a warning signal issued when the danger of enemy air strikes has been lifted.
Citizens should return to their homes and work in an organized and orderly manner after hearing that the alarm has been lifted. When the enemy's air strikes cause houses to collapse, fires, casualties, etc., under the unified organization of the unit or community where they are located, actively carry out self-rescue, mutual rescue, firefighting, emergency repairs and other actions to eliminate the consequences of air strikes and restore production and living order as soon as possible. Minimize damage from air strikes.
What we heard on the anniversary of the September 18th Incident was an early warning.
(3) What does an air defense siren Loudspeaker horn look like?
For air defense alarms, we often only hear the sound but don't see the shape. So, what is the alarm like? Where exactly is it installed so that it is so penetrating that it can be heard from every angle of the city?
Modern air defense sirens have been developed into many types and have become an important part of urban air defense systems. As an important combat readiness facility, air defense sirens are usually used for disaster forecasting and emergency notification in case of disaster relief and emergencies, and are used for civil air defense in wartime. means.
Air defense alarm usually uses a combination of wireless and wireless to control the issuance of air defense alarm signals. The control equipment is divided into wired control and wireless control. The power supply system is divided into two types: mains power supply and self-power supply. Currently the main types of alarm facilities are:
electric siren
The electric siren is the main device of the siren by the motor, which converts the mechanical energy into sound. The siren drives the sounding wheel to run at high speed through the motor, 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 generates high-speed and high-pressure for the absorbed air to the window of the fixed wheel. out and resonate.
When the anti-aircraft siren stopped, it was not actually silent, but a low-frequency humming sound due to the inertia of the motor rotor. For example, the pre-alarm says that it sounds for 36 seconds and stops for 24 seconds. In fact, what I hear is that the sound fluctuates high for 36 seconds and low for 24 seconds.
The motor-type air defense alarm is composed of main components such as ringing wheel, fixed wheel, positioning seat, positioning device, stainless steel cover, motor, base, etc. There are two types of discrete and horizontal electric alarms.
1. The beeping wheel: It is the most important part of the alarm, and it runs at a high speed during work to generate a sound source.
2. Fixed wheel: The component that is highly matched with the sounding wheel usually has about 10 sounding windows; the sounding window is equal to the sounding blades of the sounding wheel.
3. Positioning seat: the support for fixing the positioner.
4. Positioning device: The sound window can be automatically closed when the sounding wheel is not working or after the machine is stopped, so as to prevent mice, birds, spiders, and sundries blowing from the air from entering the alarm, which plays the role of protecting the alarm.
5. Stainless steel cover: on the one hand, it has the function of sound reinforcement after sound refraction, and on the other hand, it protects the entire alarm to prevent rainwater from entering the alarm;
6. Electric motor: The power of the siren drives the ringing wheel to rotate and plays a role in sounding.
7. Base: the bracket of the whole alarm.
electric siren
The electro-acoustic siren is composed of the host function and the speaker. Through the electro-acoustic siren terminal, language transmission and shouting can be carried out.
Electric sirens and electro-acoustic sirens mainly cover the main urban area and important target areas, and are the main body of the air defense alarm network.
Multimedia Alarm Terminal
That is, the LED multimedia alarm terminal, which mainly covers residential areas, can not only issue air defense alarm signals, but also release emergency announcements and convenient information through text, voice, images, etc., enriching functions.
motor vehicle
Motorized alarm vehicles focus on covering dead spots and blind spots in the city.
In addition, researchers are actively developing new air defense warning facilities that can be applied to buildings and underground spaces, and gradually establish and improve a multi-method, full-coverage air defense warning network.
Under normal circumstances, an air defense alarm can cover an area of 1 square kilometer, and the civil air defense department will set the alarm according to this distance. However, in the process of sound transmission, it will also be blocked by buildings such as tall buildings. Generally, in urban areas with dense buildings, the installation of alarms is relatively dense; in open spaces, there are relatively few. In addition, squares or schools and other gathering places are the key places to install alarms.
The reason why the air defense siren has a strong "sense of presence" and can be heard clearly in every corner of the city is the result of the cooperation of various and multiple sirens.
