Phys 1240: Sound and MusicLAST: harmonics, perception andearsTODAY: ears, and spectraNEXT: more on spectraReading: Catch up! (There IS aTues online particip, as always)surveyClass (lectures): 82% helpful6% NOT helpfulCAPA: 73% helpful 15% NOT helpfulLong Ans: 40/40Book: 35/40MIDDLEOUTER INNERCT 6.1.1Why have a middle ear?A) To provide an amplifier ofpressure wavesB) To better couple pressurewaves from “air” medium to“liquid” mediumC) To protect the inner ear fromextremely loud soundsD) To maintain the tympanicmembrane (eardrum) inproper equilibriumE) More than one of the aboveCT 6.1.1aThe eardrum is ~ 20 times larger than the ovalwindow. Assume force is same on either end of theconnecting bones (“ossicles”)The pressure on the oval window is…A) 20 times larger B) 20 times smallerC) 400 times larger D) 400 times smallerE) same… …than on eardrumCT 6.1.1bOssicles are a LEVERMalleus (<-> eardrum) moves 30% morethan stapes (<-> oval window)⇒force on the oval window is “30%” morethan force of eardrum. (WHY?)Conclusion:Pressure on oval window is…A) MORE than what we just figuredB) SAME as what we just figuredC) LESS than what we just figuredCT 6.1.1cOssicles are a LEVERThe stapes exerts about 1.3 times the force onthe oval window as the eardrum does on themalleus. If the eardrum is 10x the surface are asthe oval window, then the ratio of Povalwindow/Peardrum will bea)0.13b)1.3c)13d)130e)Something elseInner earBasilar membranePlace Theoryhair cellsAnt(holding microgear)On which a “hair cell” is superposedCT 6.1.2What physical mechanism mosthelps you perceive “pitch”A) Direct coupling of vibration rateof hair cells to signal strengthB) Location of vibrating hair cellscarries frequency informationC) Amplitude of vibration of haircell carries frequency infoD) Entirely done at the level of“brain signal processing”CT 6.2.1A factoid question!Prolonged exposure to roughlywhat “threshold” level of decibelswill cause gradual hearing loss?A) Any level, given long enoughexposureB) 70 dB or higherC) 90 dB or higherD) 110 dB or higherE) 130 dB or higher• 90 Decibels Prolongedexposure to any noise above90 decibels can cause gradualhearing loss.• 100 Decibels No more than 15minutes unprotected exposurerecommended.• 110 Decibels Regularexposure of more than 1minuterisks permanent hearing loss.Boulder ordinances• Moving vehicles: 80 dBA (at 25 ft)• Residential, 7 AM-11 PM: 55 dBA 11 PM - 7 AM : 50 dBA (at closer of: property line or 25 ft)!!???Hearing loss• Presbycusisold age,worse for men,high frequencies first,exposure to noise hastens• Many others (infection, injury,…)10 Million Americans have Noise InducedHearing Loss (the majority <65 yrs old)28 Million Americans have significanthearing loss. (# climbing rapidly)Frequency ranges for typical music,from 20’s to ‘00’s.Green Edith Piaf 1937Red = Led Zeppelin 1971Blue = ColdPlay 2001Timbre and instrumentrecognitionFocused on pitch and loudness.Next: TIMBRE. “character”• Different frequencies• Complex waveformsAlso:• Attack and decay• Incidental noisesHarmonics on a string! fn= n " f1You usually hear several of theseHarmonics simultaneously.Which ones are present (and how strong) does NOT (much)impact “pitch” you hear, But => BIG impact on the TIMBRE (“character”) of sound.f1Amplitude A1f2 =2f1Amplitude A2f3 =3f1Amplitude A3(Rather small)(Rather
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