Diffraction of Sound Waves Through Slit

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Discussion Overview

The discussion centers around the diffraction of sound waves through a slit, specifically a 2m opening behind a curtain, and the implications of using Fraunhofer's Single Slit equation, typically applied to light waves, for sound waves. Participants explore the effects of different frequencies played by a piano and the resulting sound behavior in a concert hall environment.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the applicability of Fraunhofer's Single Slit equation to sound waves, given its origin in light wave theory.
  • Another participant notes that the curtain may not act as a complete barrier and that the sound waves may not be plane waves at the opening.
  • There is a discussion about how reflections off walls in a concert hall may allow certain frequencies to reach points that would otherwise be outside the direct diffraction pattern.
  • One participant suggests that achieving minima with sound waves is challenging and proposes experimentation with two speakers and sine waves.
  • A question is raised about quantifying the loss in sound intensity as it travels and reflects in the concert hall.
  • A later reply indicates that numerical simulations may be necessary for accurate modeling, as the typical 1/r² dependence may not apply effectively in this scenario.

Areas of Agreement / Disagreement

Participants express varying views on the applicability of diffraction equations to sound waves, the impact of reflections, and the challenges of quantifying sound intensity loss. No consensus is reached on these points, and multiple competing views remain.

Contextual Notes

Participants acknowledge limitations such as the non-ideal nature of the curtain and the complexity of sound sources like a piano, which may affect the outcomes of their discussions.

Who May Find This Useful

This discussion may be of interest to those studying acoustics, sound engineering, or related fields, particularly in the context of sound wave behavior in large spaces.

gex
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Hi there,

I have a scenario in which different frequencies will be played behind a curtain with a 2m opening. I would like to calculate the angle of diffraction for different frequencies played by the piano. One equation that I came across through research is Fraunhofer's Single Slit equation. (http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html) I am just curious as to whether I can apply this to sound even though it was developed for light waves.

-Thank you in advance.
 
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Formulas apply, yes. Notes:
the curtain probably isn't a 100% barrier...
the waves at the 2 m opening will probably not be all that plane waves
echos and other acoustics will smear out the results
 
Thank you for your response BvU, so to clarify, even though a certain frequency might not diffract far enough to reach a certain point on the concert hall, its reflections off of walls will cause it to eventually reach that point?
 
Yes. In agreement with practical experience, I would say. It takes an effort to achieve minima with sound waves: best bet is two speakers and a sine wave. A curtain with an opening is far from ideal. And a piano is a complicated source. But: experiment ! Who knows.
 
Cool! Thanks a lot for your help BvU, but if you don't mind I have one more question. Is it possible to quantify the loss in sound intensity as it travels to the back of the concert hall and gets reflected back?
 
My estimate is you have to turn to numerical simulations rather soon. Don't think the usual 1/r^2 dependence of spherically expanding waves (i.e. from a point source) is practically useful.
Note that the section on acoustics doesn't even mention diffraction... (but the encompassing sound section does...)
 
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Perfect, thanks a lot for all your help BvU! :wink:
 

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