Why sound produced by rapids varies in pitch based on height

In summary: Is it frequency dependant?In summary, the sound produced by the rapids varied in pitch depending on how high up I was. I think this could be because high frequencies are more directional and are blocked by terrain between me and (at least part of) the rapids.
  • #1
BenWinchester
1
0
The other day I was at a river listening to some rapids.
The sound produced by the rapids appeared to vary in pitch depending on how high up I was (squatting down to the ground and standing up produced about a fifth in the variation of the pitch); and I can't think why it should be?
Many Thanks
 
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  • #2
Odd! Which direction? Also, being rapids I presume there was some surrounding walls or bluffs, correct? Could you describe the topology? I'm not saying that is the cause, but it is something to consider. Location dependent sound suggests reflecting surfaces to me, and the hardness, shape, and texture of a reflecting surface can certainly affect the quality of the sound.
 
  • #3
A couple of possibilities come to mind and the sound may be influenced by a combination of these and other factors:
1) The vibrations of the rapids may be transmitted through the ground and the closer you get to the ground the more those frequencies are heard. So if the Earth responds to different frequencies than the air, it would sound different.
2) High frequencies are much more directional and "line-of-sight" than low frequencies. So the high frequencies may be blocked by terrain between you and (at least part of) the rapids.
 
  • #4
doppler effect maybe? when you are standing you are at a greater distance than when you are crouching?
 
  • #5
I believe you'll find that the attenuation by air of sound is frequency dependent. If you place your ear really close to trickling water or a TV speaker you can discern higher frequencies than when you are a metre away; all the frequencies are louder because you are close to the source of the sound, but the upper frequency content appears even louder still when you get closer.

This graph illustrates how the higher tones suffer higher attenuation:

1300px-Atmospheric_sound_absorption_coefficient_2.svg.png

https://en.m.wikibooks.org/wiki/Engineering_Acoustics/Outdoor_Sound_Propagation
 
  • #6
CORRECTION: @NascentOxygen has questioned this and I think I agree with him.
There could also be a temperature effect. The air near the ground may have a different temperature and the sound frequency might change.
 
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  • #7
FactChecker said:
There could also be a temperature effect. The air near the ground may have a different temperature and the sound frequency might change.
That doesn't seem right. How could temperature bring a frequency change after the sound is generated?
 
  • #8
NascentOxygen said:
That doesn't seem right. How could temperature bring a frequency change after the sound is generated?
I think you are right.
 
  • #9
When you pour liquid into a drinking glass, the resonant pitch starts out low, and increases as the glass fills up.
 
  • #10

1. Why does the sound produced by rapids vary in pitch based on height?

The sound produced by rapids varies in pitch based on height because of the changing speed of the water as it flows down the river. As the water falls from a higher height, it gains more kinetic energy and moves faster, causing the pitch of the sound to increase. On the other hand, as the water falls from a lower height, it has less kinetic energy and moves slower, resulting in a lower pitch sound.

2. How does the height of rapids affect the pitch of the sound?

The height of rapids directly affects the pitch of the sound produced. The higher the rapids, the higher the pitch of the sound, and the lower the rapids, the lower the pitch of the sound. This is because the height determines the speed of the water, which in turn affects the frequency and pitch of the sound waves produced.

3. Is there a specific pattern or relationship between the height of rapids and the pitch of the sound?

Yes, there is a direct relationship between the height of rapids and the pitch of the sound. As the height of the rapids increases, the pitch of the sound also increases. This can be observed in any river or waterfall where the sound becomes higher pitched as the water flows down from a higher height.

4. Can the pitch of the sound produced by rapids be manipulated by changing the height of the rapids?

Yes, the pitch of the sound produced by rapids can be manipulated by changing the height of the rapids. If the height is increased, the pitch will also increase, and if the height is decreased, the pitch will decrease. This is because the speed and frequency of the water are directly related to the pitch of the sound waves produced.

5. Are there any other factors besides height that can affect the pitch of the sound produced by rapids?

Yes, there are other factors that can affect the pitch of the sound produced by rapids, such as the volume and speed of the water, the shape and size of the rocks in the river, and the surrounding environment. These factors can all contribute to the variations in pitch that can be heard in the sound produced by rapids.

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