EES 0836 Lecture Notes - Lecture 42: Fundamental Frequency, Spectral Density, Rarefaction
3 Apr 2016
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Lecture - 42: eardrum can"t be wiggled faster than about 20 khz. Just like trying to wiggle resonant system too fast produces no significant motion: sensitivity of the human ear, we can hear sounds with frequencies ranging from 20 hz to 20,000 hz. An impressive range of three decades (logarithmically) Compare this to vision, with less than one octave: _localization of sound, at low frequencies (< 1000 hz), detect phase difference. Wave crest hits one ear before the other. Shadowing not very effective because of diffraction: at high frequencies (> 4000 hz), use relative intensity in both ears. Even with one ear, can tell front vs. back at high freq: speakers: inverse eardrums, speakers vibrate and push on the air. Pulling back creates rarefaction: speaker must execute complex motion according to desired waveform, speaker is driven via solenoid idea: Electrical signal (ac) is sent into coil that surrounds a permanent magnet attached to speaker cone.
