Wave reflection in Closed End Wind Instrument

In summary, according to http://newt.phys.unsw.edu.au/jw/flutes.v.clarinets.html, the phase of sound waves in closed end wind instruments does not change when they reflect off the closed end. This is due to the fact that there is nowhere for the "extra" air from the phase inversion to go. However, at the open end, the pressure pulse leaves the tube and creates a partial vacuum, resulting in a phase inversion. The velocity pulse at the closed end does invert, but not at the open end.
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mayer
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Hi, I am a little confused with the phase change that occurs in closed end wind instruments. According to http://newt.phys.unsw.edu.au/jw/flutes.v.clarinets.html, the phase does not change when the sound wave reflects off the closed end of the instrument. I thought that the phase changes by 180 degrees after reflecting off a denser medium?

Thank You
 
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I'm sorry you are not finding help at the moment. Is there any additional information you can share with us?
 
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  • #3
Remember sound waves in a fluid are longitudunal waves, not transverse waves like vibrations of a string.

For the pressure reflection from a closed end, think of it this way: if there is a positive pressure pulse approaching the end, there is more air in the tube than there would be if there was no pulse. So if the phase inverted to give a negative pressure pulse, where is that "extra" air going to end up? There is nowhere for it to go, and the pressure pulse doesn't invert.

At the open end, the pressure pulse leaves the tube and dissipates in the outside air, leaving a partial vacuum behind it - which looks like a negative pressure pulse, or a phase inversion.

Note, the velocity pulse at the closed end does invert. But the velocity doesn't invert at the open end, because the air "in fromt of" the reflected negative pressure pulse is traveling towards the open end, to "fill up" the region of negative pressure as the pressure pulse moves further into the pipe.
 
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  • #4
Ahhh, I see. Well that cleared it up! Thanks to the both of you!
 
  • #5
for your question! I can understand your confusion about the phase change in closed end wind instruments. Let me explain the concept of phase change and its relationship to wave reflection in these instruments.

First, let's define what we mean by phase change. In simple terms, phase change refers to the shift in the position of a wave's crest or trough. In the case of sound waves, it can also refer to the shift in the compressions and rarefactions of the air molecules that make up the wave.

Now, when a sound wave travels through a medium, it causes the particles in the medium to vibrate in a particular direction. When this wave reaches the closed end of a wind instrument, it reflects back in the opposite direction. However, unlike light waves that experience a phase change when reflecting off a denser medium, sound waves do not experience a phase change when reflecting off a closed end.

This is because the closed end of a wind instrument is not a denser medium compared to the air inside the instrument. The air molecules inside the instrument are still the same density as the air outside. Therefore, there is no change in the phase of the sound wave upon reflection.

In fact, the phase of the sound wave remains the same throughout the instrument, except for when it reaches the open end. At the open end, the sound wave is able to escape and continue traveling in a straight line. This change in direction is what causes the phase of the wave to change by 180 degrees.

I hope this explanation has cleared up your confusion about the phase change in closed end wind instruments. It is important to remember that the phase change only occurs when a wave reflects off a denser medium, and in the case of sound waves in wind instruments, this only happens at the open end. Thank you for your question and keep exploring the fascinating world of sound and waves!
 

1. What is wave reflection in closed end wind instruments?

Wave reflection in closed end wind instruments is the phenomenon where sound waves traveling through the instrument are reflected back towards the player when they reach the closed end of the instrument. This results in an interference pattern that affects the overall sound produced.

2. How does wave reflection affect the sound produced by a closed end wind instrument?

Wave reflection can affect the sound produced by a closed end wind instrument in a few ways. It can create standing waves, which can cause certain notes to sound louder or softer. It can also cause interference between the original and reflected waves, resulting in changes to the tone and timbre of the sound produced.

3. Can wave reflection be controlled in closed end wind instruments?

Yes, wave reflection can be controlled in closed end wind instruments through various methods. One way is by adjusting the length of the instrument, such as by using valves or slides, to change the position of the closed end and alter the reflection patterns. Another way is by using materials inside the instrument, such as baffles or tone holes, to absorb or redirect the reflected waves.

4. How does the shape of a closed end wind instrument affect wave reflection?

The shape of a closed end wind instrument can have a significant impact on wave reflection. Instruments with wider diameters or flaring bells will have less reflection because the sound waves have more space to spread out and dissipate. On the other hand, instruments with narrower diameters or cylindrical shapes will have more reflection and a stronger interference pattern.

5. Can wave reflection in closed end wind instruments be beneficial for musicians?

Yes, wave reflection in closed end wind instruments can be beneficial for musicians in certain contexts. For example, it can help create a fuller and more resonant sound in larger ensembles or performance spaces. It can also add complexity and depth to the sound produced, making it more interesting for listeners. However, it can also be a challenge for musicians to control and manage effectively, so understanding and manipulating wave reflection is crucial for achieving the desired sound.

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