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Chapter 5 Notes - Hearing Sound Human Ear Concepts Sound...

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1 PHYS 1L03, Winter 2010, McMaster University, R. Nejat Hearing Sound, Human Ear Concepts: Sound loudness and Human ear sensitivity Waves, sound waves Standing waves, sound waves in tubes Resonance Human Ear, Ear structure Functions of different parts of human ear Chapter 17 Pages: 527-539, 540-548,550-556 PHYS 1L03, Winter 2010, McMaster University, R. Nejat Sound and Hearing • Questions: What is sound? What is hearing? How does our auditory system work? PHYS 1L03, Winter 2010, McMaster University, R. Nejat Sound What is Sound? –Is it a variation in air pressure? –Is it a variation in air density? –Is it a variation in air molecule’s position? –Is it a vibration? –Is it an oscillation? –Is it a wave? • What kind of wave is it? –What is wave? PHYS 1L03, Winter 2010, McMaster University, R. Nejat Sound Sound is: – the fluctuations in air pressure that can be detected by our auditory system , the ear. – is the sequence of compressions and rarefactions , a vibration , that is transmitted through air, or another medium, at a characteristic speed. – is a wave, a longitudinal wave; is a mechanical wave , which travels through some medium; it can not travel through vacuum. PHYS 1L03, Winter 2010, McMaster University, R. Nejat Sound and Hearing Hearing: What is hearing? Which part of the body performs this task (hearing)? –How does it do that? PHYS 1L03, Winter 2010, McMaster University, R. Nejat Sound and Hearing Hearing is: –the ability to perceive sound by receiving the air pressure fluctuations (vibrations in the air), transducing them into nervous impulses and transmitting the impulses to the central nervous system. The ear performs this task. –A transducer is any device which converts one type of energy (sound) into another (electrical).
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2 PHYS 1L03, Winter 2010, McMaster University, R. Nejat The ear functions as a biological transducer. – It turns sound energy into mechanical energy, and the into electrical impulses. – The ear has inner , middle , and oute r sections Sound and Hearing PHYS 1L03, Winter 2010, McMaster University, R. Nejat The Ear Outer Middle Inner PHYS 1L03, Winter 2010, McMaster University, R. Nejat The Human Ear The ear is a very sensitive device, –sensing vibration amplitudes as small as 10 -8 cm, • roughly the size of a single Hydrogen atom. Changes in sound intensity (amplitude) are perceived as changes in sound loudness . However, sound loudness is subjective . –It does not correlate in a simple way with intensity. PHYS 1L03, Winter 2010, McMaster University, R. Nejat Loudness and sensitivity Sound Loudness is a function of both sound frequency and intensity . The sensitivity of the ear varies with sound frequency ( also known as “pitch”). The ear is: – less sensitive at very low and very high frequencies – most sensitive in the range of 40 Hz to 3 kHz • You may check your headphones (usually they can emit sound in the range of 20 Hz – 20 kHz).
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