Why does an open ended column reflect sound?

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Discussion Overview

The discussion centers around the phenomenon of sound wave reflection in open-ended columns, such as those found in musical instruments and the human vocal tract. Participants explore the mechanisms behind the reflection of sound waves at the open end of the column and the implications of impedance mismatch.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant questions why sound waves are reflected at the open end of a column, noting that it does not seem to have a solid boundary to bounce against.
  • Another participant introduces the concept of impedance mismatch, suggesting that pressure variations at the end of the column interact with a larger mass of air, leading to reflection.
  • A participant requests further clarification on the explanation of sound wave reflection.
  • Another participant explains that changes in the shape or end of the pipe alter the pressure and velocity ratio of the moving gas, resulting in energy being reflected back. They also draw a parallel to radar technology and mention echoes in long pipes.
  • A participant notes that preventing reflection requires matching the conditions at the open end to those of an identical pipe extension.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and seek clarification, indicating that there is no consensus on the explanation of sound wave reflection at the open end of the column. Multiple perspectives on the mechanisms involved are presented.

Contextual Notes

Some assumptions regarding the nature of sound wave behavior and the conditions necessary to prevent reflection remain unresolved. The discussion does not fully explore the mathematical or physical principles underlying the concepts presented.

Who May Find This Useful

This discussion may be of interest to individuals studying acoustics, sound wave behavior, or those involved in the design of musical instruments and audio equipment.

BigMacnFries
I am reading about how sound waves traveling down a column that is open at one end (clarinet, vocal tract etc). Apparently when they reach the open end some are reflected and interfere constructively or destructivly with subsequent waves in the column. My question is why are the sound waves reflected at all at the end of the column, its not like there is a thick solid to bounce against.
Thanks
 
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In effect there is an impedance mismatch at the end of the column. Basically, it means that the pressure variations at the end of the column end up pushing and pulling a noticeably larger mass of air.
 
Can you please explain more, I don't understand. Thanks
 
BigMacnFries said:
Can you please explain more, I don't understand. Thanks

Whenever the pipe changes shape or ends, the pressue and velocity ratio
of the moving gass changes. At such a change there will always be
some energy reflected backward. In free space this is how radars work,
and in pipes this is why you hear strange echoes from very long pipes.

The only way to prevent a reflection is to have the open end presented
with the same conditions as occurr when you place another identical pipe
to the end, i.e. extending the pipe.
 
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Link was excellent, thanks Tide
 

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