Have you ever noticed that a police siren sounds different from that of an ambulance or a fire engine? Also, if you ever travel abroad, you may notice that the sound of sirens is different over there from the ones you are used to. So what is that all about? It seems that it is essential for both emergency services and for road users to be able to tell immediately what type of emergency is unfolding. The exact sound itself is just something that every country has decided for themselves. The history of sirens is actually very interesting as well, let’s take a closer look at that.
As with almost everything in the world today, the origins of the siren can be traced back to ancient Greek mythology. This is where the word “siren” comes from. The siren is the creature we now know as the mermaid. Her song was designed to entice sailors to come towards them. If they would, they would be engulfed by the sirens, never to be seen again. The word has since continued to be associated with a temptation that is fraught with danger. Interestingly, however, according to Greek mythology, hearing a siren means that you are being pulled into danger. Nowadays, hearing a siren means you need to move away from danger.
History of Sirens
It wasn’t until the early 19th century that real sirens were becoming more commonplace. Before those times, emergency services – which was, in effect, only the fire department – would have bells attached to their handcarts. In the early 19th century, just before the start of the industrial revolution, sirens were complicated constructions made of a number of pneumatic tubes as well as two separate discs. One disc was rotated and the other one was perforated. Air would flow from the tube to the perforated disc and the other disc would rotate. It didn’t take long for this system to change and slotted cylinders were used instead. Afterwards, sirens started to use electro-plating hangers. Interestingly enough, the sirens we know today are very much unchanged from these designs.
Three Types of Sirens
There are three main types of sirens. The first is the pneumatic version, which is pretty much the same as the old versions from the 19th century. The downside of these sirens is that they have very high energy requirements. In today’s day and age, having anything that uses a lot of energy is a big no-no, because we have to consider the environment. That, and the fact that high energy usage means that we have to buy additional electricity or fuel and nobody can afford that anymore.
The second type is the electronic siren. These use a range of synthesized sounds and the combine oscillators, sound modulators and amplifiers. This is the most commonly used siren that you will see nowadays. Most police cars, however, have both types of sirens and policemen do like to use both alternately.
The last type is the European siren. The Europeans seem to have developed a model that is in between the pneumatic and the electronic siren. This is called and electro-mechanic siren. With these sirens, two sets of air horns are used that have high and low pitches. An air compressor is also installed and this switches between the first and second set of air horns. This causes the siren sound to alternate between a high pitch and a low pitch. This is the first type of siren that was developed specifically to create a pattern. Plus, they are low in energy use so actually very useful.
Next time you hear a fire alarm go off, you will know how it is produced. Grab your extinguisher for home and get to safety.