Phys 1240: Sound and MusicLAST: wind instrumentsTODAY: wind instruments (+ AM/FM)NEXT: J. Merkel on “sound in thestudio”No new reading!CAPA #9 due next TuesdayChris and David’s office hoursaccordingly rescheduled:Chris Tuesday (usual time, 2-4)David Tuesday (usual time, 4-6)Open tubesoverpressureLPressure waves “fit” in theopen tuben (λ/2) = LSince f λ = v,fn= n (v/2L)Usual harmonics -same modes as a string!real tubes - end effectoverpressureOuter node is a bit outside tube(about 0.3 * diameter)LCT 12.1.2If you double the diameter of a longorgan pipe, what happens to thefundamental you hear?A) Goes down by an octaveB) Goes down, but way less than anoctaveC) Goes up, by an octaveD) Goes up, but way less than anoctaveE) Something elsereal tubes - shapeHigher modes reach different distances out - => not quite pure harmonics!overpressureLClosed tubes(closed on one end)overpressureClosed end: antinodeopen end:nodeLClosed tubes(closed on one end)overpressureClosed end: antinodeopen end:nodeLCT 12.1.3What is the wavelength of the fundamental (shown above) in a closed tube?A) λ=L B) λ=2LC) λ=4L D) λ=L/2E) λ=L/4LCT 12.1.3What is the wavelength of the fundamental (shown above) in a closed tube?A) λ=L B) λ=2LC) λ=4L D) λ=L/2E) λ=L/4LDraw the next higher mode (zeroat right end, antinode at left, oneextra node in middle)overpressureClosed end: antinodeopen end:nodeLDraw the next higher mode (zeroat right end, antinode at left, oneextra node in middle)overpressureClosed end: antinodeopen end:nodeLCT 12.1.4What is the wavelength of thestanding wave (shown above) in a closed tube?A) λ=L B) λ=L/2C) λ=3L/4 D) λ=4L/3E) Something elseLPressure waves “fit” in theclosed tube differently:(odd n) (λ/4) = LSince f λ = v,fn= (odd n) (v/4L)Lower fundamentalMissing harmonicsCT 12.1.4A clarinet is basically sealed at one end (you blow into a very narrow hole), but open at the otherA flute is open at both ends. If you have a clarinet and fluteof equal lengths, and play the fundamental…A)The flute will sound lowerB)The clarinet will sound lowerC)They will have identical pitchA flute playing its lowest note isshown in spectrum “A”.Which spectrum below best matchesthat of a clarinet (of equal length)playing i ts lowest note?CT12.1.4bAf1amplitudeBf1amplitudeCf1amplitude6f16f16f1Df1amplitude6f1E) None of these looks right.Remember the dust speckexample from last time:overpressureN=1, the fundamental in the tubeDisplacement (not pressure) graphs.Case 1: open tubesdisplacementLDisplacement (not pressure) graphs.Case 1: open tubesdisplacementLdisplacement graphs:• Displacement is longitudinal(despite the graph going “up”)• Pressure nodes <=>displacement antinodes(and vice versa)AM -Amplitude ModulationcarriersignalFM-Frequency modulationCT 8.3.1Under cover of night, a Girl scoutsignals her friends on a distant hillby alternately dimming andbrightening her flashlight. Thissignal is most accurately describedas..A: Frequency modulation.B: Amplitude modulation.CT 8.3.2Musicians refer to tremolo whenthe loudness fluctuates while thepitch remains unchanged. Is this anexample of…A: Frequency modulation.B: Amplitude modulation.CT 8.3.2bMusicians refer to vibrato when thepitch is wiggled up and down as yousing. Is this an example of…A: Frequency modulation.B: Amplitude modulation.Violinists can make “excursions”of .2 semitones, 6 times/sec.0.2 semitones-> strength of the modulation6 Hz -> “signal frequency”440 Hz -> “carrier frequency”CT 8.3.3We say that "concert A" correspondsto a frequency of 440 Hz.Does that mean that a flute playingconcert A is emitting low frequencyelectromagnetic radiation which we"hear"?A: Yes, sound is an electromagneticwave.B: No, sound is not anelectromagnetic
View Full Document
Unlocking...