Standing Waves in Air Columns (9/22)

what are standing waves?

2+ waves with the same frequency and amplitude moving in opposite directions are superimposed

why do we study standing waves in air columns or tubes?

both the vocal tract and ear canal are tubes with one end open and one end closed

T [does/does not change] as harmonics are added to a sine wave

does not

what is the missing fundamental/virtual pitch?

if you are listening to a series of frequencies of 200 Hz, 300 Hz, 400 Hz, etc. your ear-brain system will ALSO perceive a single note of 100 Hz even if the 100 Hz fundamental is missing

what phenomena allows you to perceive a person’s voice even if the phone speaker does not produce frequencies below 300 Hz

missing fundamental/virtual pitch

a [node/antinode] will always form at a fixed end

node

if a 200 Hz frequency is made over the opening of a bottle and an antinode forms right over the opening of a tube, that means that 200 Hz….

is that bottle’s resonant frequency

if a frequency is played over a bottle and a very light sound occurs, what physically is happening?

a point between a node and antinode is forming right at the opening of the bottle = not the bottle’s resonant frequency

if the end of a string is not fixed, a node will [always/never] form there

never

tubes open at one end can produce [odd/even] harmonics

odd

tubes closed at both ends can produce [odd/even] harmonics

odd and even

tubes open at both ends can produce [odd/even] harmonics

both odd and even

a tube open at both ends can’t have [nodes/antinodes] at either end

nodes

what are the formulas for tubes that are closed on one end?

λ = 4L, f₁= v/λ = v/4L 

what is the velocity of sound in air?

340 m/s

what are the formulas for tubes that are open on both ends (or closed on both ends)?

λ = 2L, f₁ = v/λ = v/2L

if you take a tube with one open end and one closed end and make it so that both ends are open, what happens to the frequency?

it doubles

if you take a tube that is open on both ends and close one end, what happens to the frequency of the first harmonic? 

it will halve

why are our ears most sensitive to the frequency region between 3-4k?

L of human ear canal = 0.025 m

f1 = v/4L = 340/(4×0.025) = 3400

about 3400 Hz is the resonant frequency of the human ear canal, so sounds will appear largest at 3000-4000 Hz

tube length and fundamental frequency are [inversely/directly] proportional to each other

inversely

as the length of a tube increases, the fundamental frequency will [increase/decrease]

decrease

what are the 3 reasons that male voices are lower than female voices?

Male vocal tracts are longer, male vocal folds are longer, and male vocal folds are thicker