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Please excuse my terminologies if they are not accurate as I am not an expert in physics.

For the sake of my question, if I may, I would simplistically call "ultrasonic sound" the sound that human cannot hear, and only some animals such as dogs/cats/whales can hear. "Normal sound" is the sound that both human and dog can hear.

For example, here is the link to wikipedia that describes the hearing ranges of human and some animals such as dogs/cats/whales : https://en.wikipedia.org/wiki/Hearing_range#In_animals

I know that "normal sound" can travel, bounce back and forth from many hard surfaces, and have echos. Does "ultrasonic sound" behave the same way ?


For example, if both "Ultrasonic sound" and "human audible sound" are traveling through a normal residential wooden fence, do they both make it equally well to the other side ?

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2 Answers 2

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Ultrasound and human-audible sound are governed by the same physicals laws, so there are no fundamental differences.

Ultrasound just has higher frequencies and smaller wavelength. That manifests itself the same way as it does for different audible frequencies (bass vs treble).

For examples:

  1. The higher the frequency, the higher is absorption in air
  2. The smaller the wavelength, the smaller the object the sound interacts with and the more it haves like "light beams", i.e specular reflection instead of diffuse reflection

Does "ultrasonic sound" behave the same way ?

Yes.

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  • $\begingroup$ If both "Ultrasonic sound" and "human audible sound" are traveling through a normal residential wooden fence, do they both make it equally well to the other side ? $\endgroup$ Jul 5, 2022 at 22:35
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    $\begingroup$ Depends on the details (fence construction, nearby objects, relative location, directivity, etc) but in most cases lower frequencies pass better than higher frequencies. $\endgroup$
    – Hilmar
    Jul 6, 2022 at 11:50
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Sound spectrum, from low frequency to high frequency, is a continuous spectrum.

Over the entire span of the frequency spectrum there is gradual change of properties.


Propagating sound is propagating (longitudinal) waves of compression and rarefaction of air. As we know, when air is compressed it heats up. So the temperature of the air is non-uniform, in accordance with the oscillation pattern. The temperature difference is minute, but there is an audible effect that arises from it.

The shorter the wavelength of the sound, the more opportunity is for the heat to spread. The effect of this spreading is that the energy of the pressure oscillation dissipates to evenly distributed heat. What that means is that high frequency sound has a noticably faster rate of dissipation of sound energy to heat.

For instance, when a lightning strike is relatively close by then the explosive sound that is produced sounds like a harsh crack. It sounds as if a giant whip is cracked. The harshness of the sound arises from high frequency components in the sound.

When a lightning strike occurs many kilometers away the sound that reaches you, eventually, sounds like low pitched rumbling. Over the length of the kilometers of travel all the high frequency components have dissipated to heat. The lower the frequency, the further it can travel. So, over a distance of many kilometers only the lowest frequencies make it to your ears.


This trend of higher sound frequencies dissipating to heat faster continues with Ultrasonic sound.

In that sense 'Ultrasonic sound' is in fact different, but the difference correlates with the frequency of the sound produced; not with whether the sound is audible to humans or not

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  • $\begingroup$ If both "Ultrasonic sound" and "human audible sound" are traveling through a normal residential wooden fence, do they both make it equally well to the other side ? $\endgroup$ Jul 5, 2022 at 22:35

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