Sound Wave Attenuation: Why Does Water Attenuate More?

In summary, the difference in speed of sound waves between water and air is due to the greater bulk modulus of water. However, the attenuation of sound in water is much less than in air due to the impedance mismatch between water and our ears, which evolved to match sound in air. This is why whale song can be heard over huge distances, as the whales adapted to living in the water and their ears are better suited to detecting sound in this medium.
  • #1
silversurf
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Why does water attenuate sound waves more than air? Is it because of it's bulk modulus? This is what I understand. Speed through a medium is determined by the elastic component over the inertial component. Since water has a much greater bulk modulus (elastic component) than air, it makes the wave travel faster in water. What I don't understand is how is it that the speed is faster yet it's attenuation is also greater. Since a sound wave travels faster through water than air shouldn't it also be more resistant to attenuation?
 
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  • #2
hi silversurf

you are coming from an incorrect assumption

attenuation of sound in water is much less than in air for a given freq

here's just one example from some tables

Attn in Air dB/km @ 1kHz = 14dB/km @ 10% RH; 5.3 dB/km @ 90% RH ( Relative Humidity)

Attn in seawater dB/km @ 1kHz = 0.07 dB/ km @ 0 deg C 0.05 dB/km @ 30 deg C

http://www.kayelaby.npl.co.uk/general_physics/2_4/2_4_1.html

hence why whale song can be heard over huge distancescheers
Dave
 
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  • #3
davenn said:
hence why whale song can be heard over huge distances

that's why the whales left the land, to live in the water! :wink:
 
  • #4
tiny-tim said:
that's why the whales left the land, to live in the water! :wink:

haha :smile:


D
 
  • #5
silversurf said:
Why does water attenuate sound waves more than air? Is it because of it's bulk modulus? This is what I understand. Speed through a medium is determined by the elastic component over the inertial component. Since water has a much greater bulk modulus (elastic component) than air, it makes the wave travel faster in water. What I don't understand is how is it that the speed is faster yet it's attenuation is also greater. Since a sound wave travels faster through water than air shouldn't it also be more resistant to attenuation?

It is true that water attenuates the level of sound that you can hear, when you are immersed in water. This is not due to losses in the transmission through the water but in how well the sound power is matched from the source into the water medium and then how well it is matched to your ears.
You mention modulus. This (and the density), affects the impedance of sound waves in a medium (high in water and low in air). Your ears evolved to match sound in air, using very flimsy diaphragms and tiny levers (the ossicles). The displacement in air (for a given power level) is much greater than that in water and the movement at the entrance to the cochlea will be very much less for waterborne sound. I imagine that dolphins have a similar problem hearing sound when they are out in the air - for the converse reason.
 
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1. What is sound wave attenuation?

Sound wave attenuation refers to the decrease in intensity or amplitude of a sound wave as it travels through a medium. This can be caused by various factors such as distance, temperature, and the properties of the medium itself.

2. How does water attenuate sound waves?

Water attenuates sound waves due to its high density and viscosity. As sound waves travel through water, they encounter resistance from the water molecules, causing them to lose energy and decrease in intensity.

3. Why does water attenuate more than air?

Water attenuates more than air because it is a denser and more viscous medium. This means that there are more molecules present to absorb and dissipate the energy of the sound waves, resulting in a greater decrease in intensity.

4. What factors can affect the rate of sound wave attenuation in water?

The rate of sound wave attenuation in water can be affected by various factors such as the temperature, salinity, and depth of the water. Higher temperatures and salinity can decrease the rate of attenuation, while greater depths can increase it.

5. How does sound wave attenuation in water impact marine life?

The attenuation of sound waves in water can have significant impacts on marine life. It can affect the communication, navigation, and behavior of marine animals, as well as their ability to detect predators and prey. Excessive noise from human activities can also cause stress and harm to marine animals.

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