Casablanca Sound Library | Alarm Sounds | 3 Siren Sound Effects

Siren Sounds

You will find them on pylons and rooftops, in industrial quarters, prisons and even on beaches. Alarm sirens are installed around the world to warn about potential threats and dangers. For some, the sound of a siren is an everyday reminder that work is over; to others, sirens are a nuisance -- particularly if they are being tested frequently (and if they happen to be installed next to your home).While the main purpose of sirens is to save lives, they can also become a symbol of death and destruction during wartime. For victims of war, the unnerving sound of an alarm siren is a harbinger of terror, deeply ingrained in their traumatised souls.

Alarm Siren - Types and Construction

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.

Air Raid Siren Sound

In England, each village and city had its own network of sirens. Some of them were electrical (e.g. the famous brand Klaxon) while others were manually operated (particularly in rural areas).

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.

Mechanical Air Raid Siren Sound

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.

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 Siren

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.

Electric Sirens

Electric alarm sirens are not only used in household alarm systems or fire alarms, they are also quite common in civil defence structures (although in larger versions). Electric alarm sirens create the siren signal with the help of a loudspeaker and an amplifier. A horn directs the siren sound into whatever direction is desired. Electric sirens come with the benefit of having few mechanical parts that need maintenance (except for the loudspeaker). These sirens are therefore much lighter than their mechanical counterparts. Thanks to the electric transmission of the siren signal, undulating sounds can be created. It is also possible to use the siren as a public-address system.