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6

$begingroup$

I was having an online conversation about Dungeons and Dragons, and my acquaintance abbreviated "Barbarian Level 17" as Bb17. I took the opportunity to make a joke about how that is similar to musical notation (i.e. B♭₁₇). Then I tried calculating the frequency and wavelength and got:

$$f=3.8 text{ }GHz$$
$$λ=87.5 text{ }μm$$

Can a compression wave (not sure you could even call it sound at that point) have such a high frequency? Does anything happen when it does?

acoustics

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edited 8 hours ago

David Coffron

asked 9 hours ago

David CoffronDavid Coffron

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6

$begingroup$

I was having an online conversation about Dungeons and Dragons, and my acquaintance abbreviated "Barbarian Level 17" as Bb17. I took the opportunity to make a joke about how that is similar to musical notation (i.e. B♭₁₇). Then I tried calculating the frequency and wavelength and got:

$$f=3.8 text{ }GHz$$
$$λ=87.5 text{ }μm$$

Can a compression wave (not sure you could even call it sound at that point) have such a high frequency? Does anything happen when it does?

acoustics

share|cite|improve this question

edited 8 hours ago

David Coffron

asked 9 hours ago

David CoffronDavid Coffron

13055 bronze badges

New contributor

David Coffron is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

add a comment | 

$begingroup$

I was having an online conversation about Dungeons and Dragons, and my acquaintance abbreviated "Barbarian Level 17" as Bb17. I took the opportunity to make a joke about how that is similar to musical notation (i.e. B♭₁₇). Then I tried calculating the frequency and wavelength and got:

$$f=3.8 text{ }GHz$$
$$λ=87.5 text{ }μm$$

Can a compression wave (not sure you could even call it sound at that point) have such a high frequency? Does anything happen when it does?

acoustics

share|cite|improve this question

edited 8 hours ago

David Coffron

asked 9 hours ago

David CoffronDavid Coffron

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David Coffron is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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share|cite|improve this question

edited 8 hours ago

David Coffron

asked 9 hours ago

David CoffronDavid Coffron

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share|cite|improve this question

edited 8 hours ago

David Coffron

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asked 9 hours ago

David CoffronDavid Coffron

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3 Answers
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2

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When we think of air as a continuous medium that can support waves, we have to assume that the scale of spatial variation in macroscopic quantities (like pressure, density, etc.) is significantly higher than the mean free path of the molecules. To within an order of magnitude, the mean free path of air molecules is around 0.1 µm, which is still a few orders of magnitude smaller than the wavelengths you're looking at. So treating this as a sound wave is probably still fine.

It's also worth noting that acoustic microscopy uses sound waves with frequencies up to a few GHz, not too far off from what you're talking about. However, we're usually talking about waves in solids or liquids in this case; in air, waves of high frequencies like this are quickly attenuated as they propagate.

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answered 8 hours ago

Michael SeifertMichael Seifert

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0

$begingroup$

Yes, no problem in principle.

The limit for wavelengths is the interatomic distance. The cut-off frequencies for phonons in solids are about $10^{13}$ Hz.

In gases, attenuation goes up a lot a short wavelengths. This paper says that attenuation in air is 80 000 dB/m (for $f = 20$ MHz): http://acoustics.ippt.pan.pl/index.php/aa/article/viewFile/555/486

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answered 8 hours ago

PieterPieter

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-1

$begingroup$

It's called ultrasonic because most people cannot hear it (this particular frequency is way over the typical audible threshold of 20,000Hz). You could also call it an overtone in a more musical nomenclature. This sound would resolve smaller features than larger waves, so you can use it to generate higher resolution images as in ultrasound or with a hypothetical creature in D&D with ultrasonic echolocation (animals typical echolocate in the range 40-140kHz).

share|cite|improve this answer

answered 7 hours ago

guitarphishguitarphish

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$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  This doesn't seem to address my question. Welcome to StackExchange; I'm not super familiar with the Physics stack, but their tour could shed some basic light on what kind of answers are expected here. My question isn't about what class of sound this would be, but on the physical implications of such an occurrence. In any case, it's a pleasure to meet you and I hope to see you around.
  $endgroup$
  – David Coffron
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I can delete my answer if you don't like it. The other answers also do not talk about phonons, which are quantum quasi-particles of sound that are much smaller than the scales being talked about. en.wikipedia.org/wiki/Phonon
  $endgroup$
  – guitarphish
  7 hours ago
  

  
  
  
  

add a comment | 

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2

$begingroup$

When we think of air as a continuous medium that can support waves, we have to assume that the scale of spatial variation in macroscopic quantities (like pressure, density, etc.) is significantly higher than the mean free path of the molecules. To within an order of magnitude, the mean free path of air molecules is around 0.1 µm, which is still a few orders of magnitude smaller than the wavelengths you're looking at. So treating this as a sound wave is probably still fine.

It's also worth noting that acoustic microscopy uses sound waves with frequencies up to a few GHz, not too far off from what you're talking about. However, we're usually talking about waves in solids or liquids in this case; in air, waves of high frequencies like this are quickly attenuated as they propagate.

share|cite|improve this answer

answered 8 hours ago

Michael SeifertMichael Seifert

17.3k22 gold badges3333 silver badges6060 bronze badges

$endgroup$

add a comment | 

2

$begingroup$

When we think of air as a continuous medium that can support waves, we have to assume that the scale of spatial variation in macroscopic quantities (like pressure, density, etc.) is significantly higher than the mean free path of the molecules. To within an order of magnitude, the mean free path of air molecules is around 0.1 µm, which is still a few orders of magnitude smaller than the wavelengths you're looking at. So treating this as a sound wave is probably still fine.

It's also worth noting that acoustic microscopy uses sound waves with frequencies up to a few GHz, not too far off from what you're talking about. However, we're usually talking about waves in solids or liquids in this case; in air, waves of high frequencies like this are quickly attenuated as they propagate.

share|cite|improve this answer

answered 8 hours ago

Michael SeifertMichael Seifert

17.3k22 gold badges3333 silver badges6060 bronze badges

$endgroup$

add a comment | 

$begingroup$

When we think of air as a continuous medium that can support waves, we have to assume that the scale of spatial variation in macroscopic quantities (like pressure, density, etc.) is significantly higher than the mean free path of the molecules. To within an order of magnitude, the mean free path of air molecules is around 0.1 µm, which is still a few orders of magnitude smaller than the wavelengths you're looking at. So treating this as a sound wave is probably still fine.

It's also worth noting that acoustic microscopy uses sound waves with frequencies up to a few GHz, not too far off from what you're talking about. However, we're usually talking about waves in solids or liquids in this case; in air, waves of high frequencies like this are quickly attenuated as they propagate.

share|cite|improve this answer

answered 8 hours ago

Michael SeifertMichael Seifert

17.3k22 gold badges3333 silver badges6060 bronze badges

$endgroup$

share|cite|improve this answer

answered 8 hours ago

Michael SeifertMichael Seifert

17.3k22 gold badges3333 silver badges6060 bronze badges

answered 8 hours ago

Michael SeifertMichael Seifert

17.3k22 gold badges3333 silver badges6060 bronze badges

answered 8 hours ago

Michael SeifertMichael Seifert

17.3k22 gold badges3333 silver badges6060 bronze badges

0

$begingroup$

Yes, no problem in principle.

The limit for wavelengths is the interatomic distance. The cut-off frequencies for phonons in solids are about $10^{13}$ Hz.

In gases, attenuation goes up a lot a short wavelengths. This paper says that attenuation in air is 80 000 dB/m (for $f = 20$ MHz): http://acoustics.ippt.pan.pl/index.php/aa/article/viewFile/555/486

share|cite|improve this answer

answered 8 hours ago

PieterPieter

9,80033 gold badges1818 silver badges3939 bronze badges

$endgroup$

add a comment | 

0

$begingroup$

Yes, no problem in principle.

The limit for wavelengths is the interatomic distance. The cut-off frequencies for phonons in solids are about $10^{13}$ Hz.

In gases, attenuation goes up a lot a short wavelengths. This paper says that attenuation in air is 80 000 dB/m (for $f = 20$ MHz): http://acoustics.ippt.pan.pl/index.php/aa/article/viewFile/555/486

share|cite|improve this answer

answered 8 hours ago

PieterPieter

9,80033 gold badges1818 silver badges3939 bronze badges

$endgroup$

add a comment | 

$begingroup$

Yes, no problem in principle.

The limit for wavelengths is the interatomic distance. The cut-off frequencies for phonons in solids are about $10^{13}$ Hz.

In gases, attenuation goes up a lot a short wavelengths. This paper says that attenuation in air is 80 000 dB/m (for $f = 20$ MHz): http://acoustics.ippt.pan.pl/index.php/aa/article/viewFile/555/486

share|cite|improve this answer

answered 8 hours ago

PieterPieter

9,80033 gold badges1818 silver badges3939 bronze badges

$endgroup$

share|cite|improve this answer

answered 8 hours ago

PieterPieter

9,80033 gold badges1818 silver badges3939 bronze badges

answered 8 hours ago

PieterPieter

9,80033 gold badges1818 silver badges3939 bronze badges

answered 8 hours ago

PieterPieter

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-1

$begingroup$

It's called ultrasonic because most people cannot hear it (this particular frequency is way over the typical audible threshold of 20,000Hz). You could also call it an overtone in a more musical nomenclature. This sound would resolve smaller features than larger waves, so you can use it to generate higher resolution images as in ultrasound or with a hypothetical creature in D&D with ultrasonic echolocation (animals typical echolocate in the range 40-140kHz).

share|cite|improve this answer

answered 7 hours ago

guitarphishguitarphish

1111 bronze badge

New contributor

guitarphish is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  This doesn't seem to address my question. Welcome to StackExchange; I'm not super familiar with the Physics stack, but their tour could shed some basic light on what kind of answers are expected here. My question isn't about what class of sound this would be, but on the physical implications of such an occurrence. In any case, it's a pleasure to meet you and I hope to see you around.
  $endgroup$
  – David Coffron
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I can delete my answer if you don't like it. The other answers also do not talk about phonons, which are quantum quasi-particles of sound that are much smaller than the scales being talked about. en.wikipedia.org/wiki/Phonon
  $endgroup$
  – guitarphish
  7 hours ago
  

  
  
  
  

add a comment | 

-1

$begingroup$

It's called ultrasonic because most people cannot hear it (this particular frequency is way over the typical audible threshold of 20,000Hz). You could also call it an overtone in a more musical nomenclature. This sound would resolve smaller features than larger waves, so you can use it to generate higher resolution images as in ultrasound or with a hypothetical creature in D&D with ultrasonic echolocation (animals typical echolocate in the range 40-140kHz).

share|cite|improve this answer

answered 7 hours ago

guitarphishguitarphish

1111 bronze badge

New contributor

guitarphish is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

$endgroup$

• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  $begingroup$
  This doesn't seem to address my question. Welcome to StackExchange; I'm not super familiar with the Physics stack, but their tour could shed some basic light on what kind of answers are expected here. My question isn't about what class of sound this would be, but on the physical implications of such an occurrence. In any case, it's a pleasure to meet you and I hope to see you around.
  $endgroup$
  – David Coffron
  7 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  $begingroup$
  I can delete my answer if you don't like it. The other answers also do not talk about phonons, which are quantum quasi-particles of sound that are much smaller than the scales being talked about. en.wikipedia.org/wiki/Phonon
  $endgroup$
  – guitarphish
  7 hours ago
  

  
  
  
  

add a comment | 

$begingroup$

It's called ultrasonic because most people cannot hear it (this particular frequency is way over the typical audible threshold of 20,000Hz). You could also call it an overtone in a more musical nomenclature. This sound would resolve smaller features than larger waves, so you can use it to generate higher resolution images as in ultrasound or with a hypothetical creature in D&D with ultrasonic echolocation (animals typical echolocate in the range 40-140kHz).

share|cite|improve this answer

answered 7 hours ago

guitarphishguitarphish

1111 bronze badge

New contributor

guitarphish is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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share|cite|improve this answer

answered 7 hours ago

guitarphishguitarphish

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answered 7 hours ago

guitarphishguitarphish

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answered 7 hours ago

guitarphishguitarphish

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