Wave reflection in Closed End Wind Instrument

[mayer]

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

 

[Greg Bernhardt]

I'm sorry you are not finding help at the moment. Is there any additional information you can share with us?

 

[AlephZero]

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.

 

[mayer]

Ahhh, I see. Well that cleared it up! Thanks to the both of you!