Sounds of a Police Car Siren
A siren is essentially a gadget used for making noise to alert the public of some impending danger. Sirens are used in numerous different situations. There are the civil defense sirens used in case of air-raids or impending tornados, police sirens, and sirens used on ambulances or fire trucks.
Basically, there are two types of sirens in existence - pneumatic and electronic. All traditional sirens used to be pneumatic and they generally had much higher energy requirements. A police siren now mostly makes use of the electronic siren, but some police cars may make use of both types in their cars. The prevailing police siren has a greater variety of sound choices and the officers can select sounds depending on their needs. Whereas in the past, the most common sounds were the wail and the yelp, now the hi-lo, air-horn, and fast siren sounds are also available.
It was in the early 1970s that these new sirens were introduced to take care of an increasing problem. When officers approached the same intersection using the same frequencies, they often could not hear each other. A phenomenon called the wash-out effect would occur, causing the two sirens to cancel each other out. This effect had the potential of causing crashes. Thus the police siren that uses a variety of patterns and frequencies was necessary.
The yelp is the electronic version of the yodel and is good for gaining attention at intersections. It is also used during chases. The wail is a more traditional sound; it sounds similar to the old windup police siren. The hi-lo siren is also called “European” because it brings to mind the police chases most commonly heard and seen in French and Italian movies. The air-horn is a favorite when intersections need to be cleared of pedestrians and the fast police siren gives the impression of an asteroid blaster in a video game.
Each time the distinctive invasive yowl of a police siren is heard, one can be sure that a police officer made a deliberate, perhaps even artistic, choice. There are no rules or guidelines as to which sound is chosen, the decision is totally subjective. The officers are just told to mix up the sirens so no two police cars have the exact pattern causing a wash-out.
Each officer has their own method of how to get a speeding vehicle to stop. A majority of the highway officers just hit the air horn, while others like to start with the less intimidating sounds and increase to the more aggressive ones until they have gone through the whole dash-mounted keyboard controlling the sounds. Then there are times when sirens make no difference no matter what the sound is; for instance, someone attempting to flee may not respond at all.
There are, however, situations when a siren is just not heard. Summers with the windows up, air-conditioners on full blast, and music blaring present their own set of challenges. The elderly also tend to be a bit tricky. Joggers, bikers, and iPod users who are too focused on what they are listening to, pay little attention to sirens. In the more congested areas of a city, where there are horns, other sirens, cell phones and honking, a police siren is very often not heard.
