1Phys 1240: Sound and MusicLAST: spectraTODAY: spectra and wind instrumentsNEXT: AM/FM, wind instruments andvoiceReading:14.1-3No office hours for SJP Thurs AM(email me for another time!)FCQCT Ex_capaShould the due date of thecurrent CAPA set (#9, dueThursday) be extended?A) Yes, till next TuesdayB) Yes, till next Thursday(note! Final is on Saturday)C) No, keep it as is (but thisshould be the last CAPA)D) No, keep it as is (and haveone more CAPA)Ampl.frequencyf12f13f1f1(medium)2f1(small)3f1(big)Example from last time:Frequency SPECTRUM:?Ampl.frequencyf12f13f1f1(medium)2f1(small)3f1(big)Example from last time:Frequency SPECTRUM:2Consider the following waveforms:Which of the following are true: i) Both have the same fundamentalfrequency ii) Both have the same frequencyspectra.A) i and ii are trueB) i and ii are falseC) i is true, ii is falseD) i is false, ii is trueCt8.1.1A violin has fundamental frequency f1.I bow it 1/3 of the way down the string.Which of the following frequencyspectra is more likely?Ct8.2.2bAf1amplitudeBf1amplitudeCf1amplitude6f16f16f1f12f13f13f16f13Wind instrumentsOpen pipes (open at BOTH ends)Easy to get overpressure in middle(Ends are just open atmosphere…) LOpen tubesoverpressureLOpen tubesoverpressureLCT 12.1. 1How will the harmonics of anopen tube compare with those ofa stringed instrument(with the same fundamental?)A) Totally different frequenciesB) The same frequencies4Open tubesoverpressureN=2, the 2nd harmonic in the tubeLPressure waves “fit” in theopen tuben (λ/2) = LSince f λ = v,fn= n (v/2L)Usual harmonics -same modes as a string!CT 12.1.1bWhat is “v” in the formulaf λ = v for an open pipe?A) The speed of sound, 344 m/sB) some other speed.CT 12.1.1dThe speed of sound in helium gas isconsiderably higher than 344 m/s.If I fill a tube with helium, what willhappen to the fundamental toneproduced by that tube?A) Goes up in pitchB) Goes down in pitchC) Stays about the same5CT 12.1.1cThe air in an open pipe is in the n=2mode (shown above).A small speck of dust is located 1/2 ofthe way down the pipe.What does the dust do ?A) Wiggles up and down (towards /away from wall of tube)B) Wiggles back and forth (left/right, along the tube…)C) Sit still at center of the pipeD) Something
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