Why does the sound of a siren sound higher when it's close and lower as it moves away?

Answer 1

When source of sound is far away, the sound energy is dissipated while reaching us. That is its amplitude decreases. When it is nearer sound energy falling in our ear is large (amplitude is large) and hence volume of sound heard is high.

The above phenomenon is when the source of sound is stationary. But when the source is moving toward or away from us, other than the above the pitch (frequency) of sound varies.

This is because we determine the pitch of sound by the number of waves falling in our ear and not by the actual number of waves emitted by the source.

Suppose that the siren is sending a pulse of sound every second and is moving away from us. It takes some time for the first pulse to reach us when the siren is some distant away from us. The second pulse has to travel some more distance to reach us than the first pulse, because the source has moved some distance during this time.

Thus the number of waves falling in our ear drum has decrease and hence the pitch is also decreased.

Answer 2

It is called the "doppler effect" Since the siren is moving, so are the sound waves coming from it. the sound waves reach our ears faster when the object approaches making the sound higher since the waves are closer together. As it moves away, the sound lowers since the sound waves are farther apart

Answer 3

because of the doppler effect, the car it is on is moving in one direction and the sound waves it emits are going in all directions, so the forward movement causes the waves in front of the car to bunch up and become higher pitched as it is coming toward you. Then, the waves in back of the car become more spread out, causing a lower tone as the car is moving away from you.

Answer 4

easy, for example, if you step up to a speaker, you could get deak, it is just like being near a siren. When you get close, it is louder becasue of the waves, and when you get farther away, it is softer becasue you are moving away from the sound.

Answer 5

i forget the technical name for it, i learned it in physics (i hated that class). anyway, it has something to do with the distance that the sound has to travel....for instance, lower pitches can be heard from further distances than higher pitches, and higher pitches have a higher volume than lower pitches; therefore when a sound is nearer to you, you are more likely to hear the higher pitches, and when it's further from you to hear the lower pitches. oh yah, the dopplar effect....i think that's it.

Answer 6

Because the sound waves are being compressed as it moves toward you and drawn out as it passes.

Answer 7

soundwaves dissipate over space. the longer the waves are the weaker they become. as the siren grows closer there is less and less space for the waves to dissipate.

Answer 8

this pitch shift is know as the doppler effect....the sound is traveling......buit so is the siren itself.....just like when an airplane flys by

Answer 9

It is because of the Doppler Effect. Read about it here: http://en.wikipedia.org/wiki/Doppler_effect

Answer 10

because the sound waves are closer