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Understanding Police Sirens With Amplitude And Frequency

December 02, 2022

When it comes to emergency situations, every second counts. That's why police sirens are designed to immediately grab the attention of civilians with their loud sound. These devices are designed to produce a loud, piercing sound that can be heard from far away. But what makes them so loud? It all has to do with amplitude and frequency. Their relationship with respect to sirens will be examined below.


Role of amplitude and frequency


What is amplitude?

Amplitude is the magnitude of a sound wave, which is measured by its height from the baseline to the crest. The amplitude of a police siren, for example, would determine how loud it is. Therefore a police siren can be deafening or bearable based on its amplitude.


What is the frequency?

Frequency is the number of times a sound wave propagates across a given point in space per second. The more times per second a wave repeats, the higher its frequency and the higher the pitch of the sound it produces. The standard measure of frequency is Hertz (Hz).

One Hz equals one vibration or cycle per second. So, if a siren emits a sound with a frequency of 500 Hz, that means that its sound waves are vibrating at a rate of 500 times per second. 


How amplitude and frequency affect police sirens?

Therefore, amplitude and frequency play different roles in a police siren. For instance, in the famously observed Doppler effect, a passerby hears the pitch or frequency of the siren increase as it draws near them. Similarly, the pitch decreases with respect to another passerby who is standing farther away from the receding vehicle. This is because as the siren draws near, the sound waves get bunched together, thereby increasing their frequency and vice versa. 

Amplitude, on the other hand, remains unchanged in this case. It is more dependent on the energy of the sound source and its effect only dissipates across larger distances.

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