Course:PHYS341/2018/Calendar/Lecture 16
Phys341 Lecture 16: Summary and web references
2018.02.07
Textbook 12.1-12.3
Slide List
- Quiz - A pipe 34.4 cm long plays at what frequencies (approximately)?
- 1000, 2000, 3000 Hz... with open ends; 500, 1500, 2500 Hz... with one closed end
- 500 , 1500, 2500 Hz... with open ends; 1000, 2000, 3000 Hz... with one closed end
- 500, 1000, 1500 Hz... with open ends; 1000, 3000, 5000 Hz... with one closed end
- 500, 1000, 1500 Hz... with open ends; 250, 750, 1250 Hz... with one closed end
- 250, 750, 1250 Hz... with open ends; 500, 1000, 1500 Hz... with one closed end
- 250, 500, 750 Hz... with open ends; 500, 1500, 2500 Hz... with one closed end
- The fundamental frequency of the acrylic tube used in class is 215 Hz
- = (344 m/s)/(2)(215 Hz) = 0.80 m, 80 cm
- But: the tube is only 74 cm long.
- The standing wave is leaking beyond the confines of the tube (3 cm at either end).
- The wavelength is longer than the simple theory predicts.
- This is why we can hear sound radiation from an open tube.
- Radiation from the end of a pipe or cavity
- With an open end, sound is radiated to the environment: we have the makings of a musical instrument.
- Edge tones (a.k.a. air reeds)
- Modes in real air-reed instruments
- You cannot drive a standing wave precisely at a node.
- Wavelengths in a real pipe driven by blowing are longer than the simple theory predicts.
- Fundamental frequency also varies with how hard you blow (pitch “bending”).
- Karman vortex street (ignore math, look at images and videos) https://en.wikipedia.org/wiki/K%C3%A1rm%C3%A1n_vortex_street