Why does a police car siren make such a wailing?
Not always did police cars have sirens. Starting in the 30s the police car siren was developed
The first ones were just ordinary cars which may or may not have had the badge of the police jurisdiction and the precinct number painted on the door. This wasn’t very satisfactory as bystanders and other road users did not really know that the police were in the car. The name of Sirens was taken from Greek mythology. Sirens were figures with beautiful haunting voices that used to lure sailors to their deaths by inducing them to ship wreck their boats on the rock or jump overboard and swim. Odysseus was sorely tempted by sirens and managed not to succumb by tying himself to the mast of his ship. One of the earliest models of a siren as we know them was able to make a noise under water hence the name. A police car siren is not meant to be beautiful and lure you to do something stupid but it is meant to be heard. The usual message it conveys is that a police vehicle is in a hurry and kindly get out of the way.
The original sirens were mechanical devices that worked by the sound being generated by a slotted disk rotating in an airstream. Many of these were hand operated and requited a fair amount of muscle power and arm turning to get going. Electric motors driving sirens have to have very strong starter circuits and if you listen to one of these starting up you will notice the pitch start low and then steadily increase as it speeds up. During that time the electrical current drawn is quite high. An old police car siren has these current problems and is normally wired up with thick low resistance wiring similar to a starter motor.
When small enough sirens were developed for emergency vehicles the ambulances and Fire trucks were the first to get them. However the police were not far behind in getting a specific police car siren. The first had a single pitch and alerted the road user. It was found to be effective when combined with a light beacon, and later with two light beacons and then the lightbar itself. It was quickly found that a two tone police car siren was more effective, rather like a flashing light as opposed to a constant light. The mind picks up a variation in tone far easier that a monotone. So nowadays you will hear a two tone or even a multi-tone emitting from a police car siren.
The modern police car siren is in fact a speaker and amplifier arrangement. A series of sound signals in normally programmed into the amplifier so it can whoop, or wail of scream or whine depending on the requirement of the situation as well as the policies of the city and state. Attached to the amplifier and normally wired under the dash is the control box as well as a microphone which allows the officer to actually have a voice megaphone and give instructions over the siren speakers.
The police car siren speaker should not be mounted on the lightbar or behind the occupants of the car as it could deafen them. It is best mounted in front behind the grill facing forwards. It is also important that the police siren be loud enough to overcome the defenses of the modern car which is designed to be quiet inside, to overcome the effect of telephones and sun woofers that some cars have installed.
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