PHYSICS OF MUSIC: Pitch is organ pipes & vibration spectrum

[Dunkaroos]

Hi. I would really appreciate it if someone could tell me whether I'm correct or not.


1. An open pipe (open at both ends) and a closed pipe (closed at one end) are the same length. If an organ blows air across the top of each pipe, what is true of the frequency (and pitch) of the sound produced?
A) the pitch you hear will be the same
B) the pitch of the closed pipe will be higher
C) the pitch of the open pipe will be higher (my answer)


2. In a vibration spectrum (frequency (x-axis) vs amplitude (y-axis) graph) for a plucked string, why are there spaces between the lines? Why are most frequencies zero amplitudes?


Thank you!

 

[moose]

1. You can actually try this out with a plastic straw. Also, you can make a diagram and figure out the wavelengths with relation to one another. So, yes, you are correct ;)

 

[kyle8921]

Hi there! I can confirm that your answer for the first question is correct. The pitch of the open pipe will be higher than the closed pipe because the open pipe allows for more air to vibrate and create a higher frequency.

As for the second question, the spaces between the lines on the vibration spectrum represent the different harmonics of the string. These are the different frequencies that the string can vibrate at, and they are spaced apart based on the fundamental frequency of the string. The zero amplitudes represent the frequencies that the string does not vibrate at, as they do not correspond to any of its harmonics. This is why they appear as gaps in the spectrum. I hope this helps clarify things for you!