Longitudinal Standing Waves and Harmonic Series in Open and Closed Tubes Physics of Music, Spring 2016
Key terms Bernoulli’s Equation Pressure vs. velocity Compression vs. rarefaction Open vs. Closed Tubes Node vs. anti-node Even and Odd harmonics Kundt’s Tube Rubens’ Tube
Standing Waves
Analogy: Longitudinal to Transverse Waves Pressure waves are sine waves too!
Longitudinal Standing Waves Animation courtesy of Dan Russsell, Grad Prog Acoustics, Penn State
What causes the oscillation? FippleReed
Fire It Up: Rubens’ Tube Other good videos: (Utah’s tube, detailed explanation) (Portland rubens’ tube, good music) (Brazil, fun starts about 6’30”, really good music) (cycles through resonance frequencies, turn your sound off, you don’t go crazy)
Kundt’s Tube: Standing waves in wind instruments
P + ½ V 2 = constant Bernoulli’s Equation for Fluids Pressure goes up, velocity goes down (and vice-versa) Energy divided random and chaotic pressure mass density velocity
Time for Reflection Phase ChangeNo Phase Change
Open Tube Pressure nodes: Openings always “clamped” at ~P atm (Velocity antinodes)
Closed Tube Pressure anti-node (Velocity node) Pressure node (Velocity anti-node)
Harmonics: Velocity vs Pressure Open tubes Closed-open tubes
Closed Tubes
Harmonic Scale Flute (open, all harmonics) Clarinet (closed, missing even harmonics)
Brass Instruments How the valves on a trumpet work? Why does pushing down a valve change the note that sounds?
Top Brass
Fire It Up: Rubens’ Tube Other good videos: (Utah’s tube, detailed explanation) (Portland rubens’ tube, good music) (Brazil, fun starts about 6’30”, really good music) (cycles through resonance frequencies, turn your sound off, you don’t go crazy)
The Fipple: Divides Airstream
Sources Univ. of New South Wales Acoustics Research Group: (Kundt’s Tube)
Condenser Microphone
Harmonic Series Open-Open Open-Closed
Acoustic Impedance Z = P/V How much pressure it takes to induce a certain amount of air to flow