NPB 100 Lecture Notes - Lecture 14: Sine Wave, Basilar Membrane, Tectorial Membrane
13 Feb 2018
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Sound: sound = air pressure waves, amplitude = loudness, humans: 100 to 20,000hz. Sine waves: sine waves are in some respects the simplest signal, sine wave in sound pressure is a pure tone, sine waves can differ only in: amplitude, frequency, and phase. Sound pressure level (spl: spl = 20 log ptest/ preference, preference = sound that is just noticeable (20 un/mm2, loudness expressed in decibel (db)- log scale. Just-noticeable difference between two tones increases logarithmically as tones get louder (easier to tell 2 soft tones apart than 2 loud tones: normal conversation: 65 decibel, rock band 110 decibels. Impedance mismatch from air to tissue: 0. 1% of energy absorbed by tympanic membrane with large area, is focused on a small area of oval window. This boosts the pressure 200-fold. (like getting stepped on by a spiked heel: 99% of sound in air is reflected from tympanic membrane (high impedance medium)
