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Open-End Air Columns Standing Waves.

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Presentation on theme: "Open-End Air Columns Standing Waves."— Presentation transcript:

1 Open-End Air Columns Standing Waves

2 Review of Fundamental Frequency and Harmonics
A standing wave is the result of the interference of two waves! 1st Harmonic or Fundamental Frequency: Wavelength = 2L

3 Review Continued 2nd Harmonic Wavelength= L

4 Harmonics Continued 3rd Harmonic * L = 3/2λ λ=2/3 L
Where L is the string length

5 CHART OF HARMONICS Harmonic# # ofWavesin String # ofNodes
# ofAnti-nodes Length-WavelengthRelationship 1 1/2 2 Wavelength = (2/1)*L 1 or 2/2 3 Wavelength = (2/2)*L 3/2 4 Wavelength = (2/3)*L 2 or 4/2 5 Wavelength = (2/4)*L 5/2 6 Wavelength = (2/5)*L

6 Open-End Air Columns Most instruments consist of an air column.
Tone is determined by a standing wave inside the instrument. An open-end air column has two open ends like a flute. In open-end air columns there are anti-nodes ALWAYS at the open ends of the instrument or column. How many waves are in this?

7 1st Harmonic Continued There is ½ wave in the first harmonic
The distance between the anti-nodes is equivalent to ½ a wavelength. The length of the air column is equal to ½ of the wavelength for the first harmonic.

8 2nd Harmonic 2nd harmonic can be produced when another node and anti-node is added, for a total of 3 antinodes and 2 nodes. There is one full wave in the column. One full wave is twice as many waves as in the first harmonic. That means that there are twice as many waves in the same amount of space. This means that the frequency is double that of the first harmonic.

9 Describe the Third Harmonic
How many nodes? 3 How many anti-nodes? 4 How many waves? 1.5 waves What is the frequency compared to the fundamental? 3 Times the frequency.

10 Harm.# # of Waves in Air Column # of Nodes # of Antinodes
Length-WavelengthRelationship 1 1/2 2 Wavelength = (2/1)*L 1 or 2/2 3 Wavelength = (2/2)*L 3/2 4 Wavelength = (2/3)*L 2 or 4/2 5 Wavelength = (2/4)*L 5/2 6 Wavelength = (2/5)*L

11 Determine the length of an open-end air column required to produce a fundamental frequency (1st harmonic) of 480 Hz. The speed of waves in air is known to be 340 m/s. speed = frequency • wavelength = speed / frequency wavelength = (340 m/s) / (480 Hz) wavelength = m   Length = (1/2) • Wavelength Length = m

12 Example: Stan Dinghwaives is playing his open-end pipe. The frequency of the second harmonic is 880 Hz (a pitch of A5). The speed of sound through the pipe is 350 m/sec. Find the frequency of the first harmonic and the length of the pipe. We know that the frequency will be half of the second harmonic. F=440Hz. Λ=v/f=(350m/s)/(440Hz) = m L = 0.5 * λ = m

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