Do soap bubbles reflect sound?

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Discussion Overview

The discussion centers around the acoustic properties of soap bubbles, specifically whether they reflect sound and how their structure affects sound reflection. Participants explore theoretical and practical implications, considering both classical physics and real-world observations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant notes that bats do not seem to notice soap bubbles, prompting the question of sound reflection.
  • Another participant suggests that soap bubbles likely reflect sound only weakly due to their elastic nature, which absorbs sound rather than reflecting it, and that any reflected sound may be below the sensitivity of bats' hearing.
  • A different viewpoint introduces a classical physics perspective, stating that the reflection coefficient can be calculated using acoustic impedance, indicating a potential for high reflection due to the impedance mismatch between air and water.
  • Another participant counters that the thinness of the soapy water film relative to its width must be considered, as it affects how sound interacts with the film, similar to how different materials reflect sound differently.
  • A participant recalls an article about a recording studio that utilized plastic foam bubbles to minimize sound reflection, suggesting practical applications of bubble-like structures in acoustics.

Areas of Agreement / Disagreement

Participants express differing views on the extent to which soap bubbles reflect sound, with some emphasizing absorption and others focusing on theoretical reflection based on impedance. The discussion remains unresolved with multiple competing perspectives.

Contextual Notes

There are limitations in the discussion regarding the assumptions made about the acoustic properties of soap bubbles, the dependence on definitions of sound reflection, and the lack of detailed mathematical treatment of the reflection coefficient in this specific context.

spareine
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Bats in my garden do not seem to notice soap bubbles. Do soap bubbles reflect sound?
 
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Probably only very weakly since soap bubbles are elastic and will absorb a lot of sound rather than reflecting it.
Any sound which does reflect is probably beneath the bat's hearing sensitivity
 
On the other hand, according to classical physics the reflection coefficient is R = (Z1-Z2)2 / (Z1+Z2)2, where Z=ρc is acoustic impedance and Zair<<Zwater. That implies R≈1 due to the huge impedance mismatch.
 
But since the soapy water film is much thinner than it is wide, one has to take into account the kinematics of the film and air resistance on the film as it vibrates. For similar reasons a thick wood panel will reflect much more sound than a sheet of facial tissue will.
 
I remember an article about a recording studio (I forget where).
The idea was that studio setup would as best as possible capture instruments and vocals with minimal complication from sound reflection.
The solution was covering most of walls and ceiling with plastic foam bubbles.
 

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