Physics 1240 Thurs 4/6/06Today: tone holes, register and octave keys, begin architectural acousticsNext time: Reverberation and Sabine’s formulaLearning goalsDesign simple flutes/clarinets • Estimate frequencies/pitches of tone holes• Estimate frequencies/pitches of register and octave keys--------------------------------------------------------------------Design a concert hall with good acoustics (next two lectures)• Identify important the important qualities for good room acousticsReview: Categorization of InstrumentsCylindrical pipe open at both ends - flute-type (flute, organ pipe, recorder) – all harmonics present, simple recipe for frequenciesCylindrical pipe closed at one end – clarinet – odd harmonics present, simple recipeConical pipe - oboe, saxophone – all harmonics present, no recipeA large tone hole simply shortens the length of the pipemouthpiece at this endLCT 23.1 A 2m long flute has a large open tone hole at 1.72m. What would be the frequency of the fundamental mode of this configuration?A) 86 HzB) 172 HzC) 200 HzD) none of the abovemouthpiece at this end1.72 mCT 23.2 A 1m long clarinet has a large open tone hole that is 0.14 m from the open end. What would be the frequency of the fundamental mode of this configuration?A) 50 HzB) 100 HzC) 200 HzD) none of the abovemouthpiece at this end1 m0.14 mWhen you “over blow” a flute-type instrument you go up an octaveCT23.3 A flute playing a F=175Hz would play what note if overblown?A) 175 HzB) 350 HzC) 525 HzD) none of the aboveOctave Holes (or Keys), register Holes (or Keys)octave hole hereregister hole hereCT23.4 A clarinet plays a note at 220 Hz with the register key hole closed. What would be the frequency of the note when the register key hole is opened?A) 220 HzB) 440 HzC) 660 HzD) none of the aboveQualities of good concert hall acoustics (common sense things)• Volume• Well distributed sound• Clarity• Low background noise• Envelopment •Performer satisfaction •ReverberationDummy head microphoneNeumann KU 100Two more critical design qualities for exceptional architectural acoustics:Acoustical Intimacy – smaller rooms tend to sound betterSource Width – listeners like differences in the sound going to the left and right earAcoustical Intimacyearly reflections must be present strong short delay, no more than 25 milliseconds apartAcoustical Intimacy and Source width lead to a so-called “shoe box” design for most highly rated concert hallsLong, Tall,
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