The necessity for a signal sound to inform or warn members of a society is not a recent invention. Even in the Stone Age, drums and animal horns were used to spread messages far and wide. After the discovery of various metals, people began to manufacture signal horns for military use. Instruments like trumpets and trombones are derived from these early horns. As we can see, alarm systems and siren sounds have been part of our society since the dawn of mankind.
The use of alarm bells goes back all the way to the Egyptians and the time of the Pharaos. These so-called plate bells were hung from shelves so that their distinctive sound could be heard from far away. This technique is still being used today, except that plate bells and forged bells have been replaced with cast bells. For many centuries, storm bells and alarm bells were used to warn village and city dwellers from fires and attacking barbarians.
After the Industrialisation, the ambient noise of a mechanised society necessitated a new kind of alarm system. The first sirens were steam-powered pipes used on steamships, because traditional bells were no longer loud enough to overpower the noise of the engines.
WWII Air Raid Alarm Sounds
Thanks to electricity and the invention of the motorised siren, this type of siren was widely adopted before and during the Second World War. The undulating, howling sound of the siren was highly characteristic, which made it an efficient warning signal ahead of air raids. It also became synonymous with the terror of falling bombs -- death dealt from the skies. An entire generation was scarred forever by the sound of the motorised siren.
During the Cold War, sirens were no longer used to warn of air raids. Instead, they became alarm systems for possible nuclear attacks. In Germany, the term 'alert' replaced the previous 'air raid warning'. A shortened, one-minute siren alarm was devised to alert citizens of a possible attack.
In post-WWII England, alarm sirens were assigned a new meaning: alerting people to the threat of a nuclear attack. They were also used to warn people of floods and freak weather, as well as escaped prisoners or highly dangerous mental-health patients.
Alarm Sounds and sound effects at Avosound - Alarm sound are available in a multitude of variations: alarm sounds, alarm sirens, fire alert, fire drill, emergency sirens, siren wail and howling, emergency alarm from fire service and police sirens. In the Second World War, loud and widespread siren wails were generated with pneumatic, electrical or manually operated mechanical alarm systems to warn against air raid. These mechanical alarm sirens are still widely used today for civil protection in many countries. There were different sirens. Air raid alarm is characterized by howling sirens coming in and out. Water alarm due to short, loud alarm blasts. Civil defense alarms are available for earthquakes and disaster alarms, which one hopefully never has to hear. Also a rather unpleasant case of alarm is the ABC alarm. The siren signal of the ABC alarm is like the air raid alarm a rising and declining wailing siren which is repeated.
Sirens and Alarm Bells
Alarm can be triggered by an alarm bell, a mechanical alarm siren or via an electric siren. Alarm systems of cars or alarm systems in case of burglaries usually use electric sirens with electric beeps or hooters to create loud alarm signals. Other alarm systems are produced by the company Klaxon, which have been used for many years in industrial plants. The well-known Klaxon alarm is also a typical sound on submarines, ship sirens or aircraft carriers. Also a user of Klaxon Alarm sirens is the empire. A long long time ago, the empire used the Klaxon horn and sirens as an alarm on the death star.
Further variants of acoustic alarms and signal tones can be found in emergency. Fire alarms, fire alarm sirens, police sirens or sirens from ambulance are differed from country to country. American sirens from police cars are swelling and decaying sirens, while in Europe the two-tone siren is used.
You can find a multitude of alarm sounds and siren blasts at the Avosound online library to preview and download: alarm sirens, sirens, alarm bells and howling air raid siren sounds.
Mechanical Alarm Sounds
Mechanical alarm sirens create a howling noise by rotating a shovel-studded drum within a container that sports openings. The higher the number of the rotor's revolutions, the higher the pitch of the howling. The result is an undulating siren alarm sound. The siren can be operated electrically or manually. These mechanical alarm sirens are widely used all over the world. In the United States, very big and loud mechanical alarm sirens equipped with V8 cylinder motors were used during the Cold War.
In Germany, the mechanical siren is called unit siren E57 (although East Germany and countries of the former Soviet Union used their own type of similar construction during the time of the German Democratic Republic). This alarm siren creates a howling alarm sound that can allegedly be heard across very long distances (it reaches a sound level of 105 dB). In rural areas, the sound of the siren is said to reach 70dB even at a distance of 700m. In cities and industrial areas, these levels can obviously not be reached. One can imagine that the American alarm siren outfitted with a V8 motor was probably quite a bit louder than that.
Pneumatic Alarm Sounds
Pneumatic alarm sirens can create enormous sound pressure and spread it across big distances thanks to the horns mounted on the top of the siren. The construction of pneumatic alarm sirens is different from mechanical sirens. While the mechanical siren creates the airstream with the help of centrifugal forces, the pneumatic alarm siren uses a compressed air canister to pump the airstream into the siren head.
The air-powered alarm siren (pneumatic siren) is easily identified by the horns mounted to the siren's head. Similar to a mechanical siren, the air-powered alarm sirens create their signal by interrupting the air-stream cycle with the help of a perforated disc. The spinning disc inside the siren's head is called a rotor; it is electrically powered. The air-stream is directed through the holes in the rotor and external vents. The spinning motion of the rotor either opens or closes the holes, which creates the sound of the siren that is then directed to several horns. The air-stream that is needed for the operation of the siren is created by an Aerosol canister underneath the siren.
Klaxon Alarm Sounds
Klaxon alarm sirens were often used in the harsh environments of submarines, ships and industrial buildings. It comes as no surprise then that the unique siren sound of the Klaxon can be heard in many movies. A submarine movie without a Klaxon diving alarm is not a real submarine movie!
The Klaxon horn made another famous appearance in George Lucas' Star Wars films. Just one example: Ben Burtt, the sound designer and creator of the Star Wars sounds, used a Klaxon horn for scenes set inside the Death Star.