Download Biomechanics of hearing

Biomechanics of hearing BML 770 -­‐ Dinesh Kalyanasundaram 1 BML 770 -­‐ Dinesh Kalyanasundaram 2 Hearing •  Ear and Nervous system enables hearing –  Ear is the receiving and sensing part –  Brain is the recogniCon part (auditory cortex) Sound is processed in different regions of the auditory cortex on both sides of the brain. However, for most people, the leM side is specialized for perceiving and producing speech. Damage to the leM auditory cortex, such as from a stroke, can leave someone able to hear but unable to understand language. BML 770 -­‐ Dinesh Kalyanasundaram 3 CriCcal Features of the ear •  The audible frequency range, roughly 20 Hz -­‐ 20 kHz. •  The human ear can respond to minute pressure variaCons in the air in the range. •  It is capable of detecCng pressure variaCons of less than one billionth of atmospheric pressure. BML 770 -­‐ Dinesh Kalyanasundaram 4 Wavelength CalculaCon •  Frequency = speed of sound/ wavelength –  20 Hz = 330 m/s / wavelength (L) Wavelength (L) = 16.5 m –  20 kHz = 330 m/s / wavelength (s) Wavelength (s) = 16.5 mm Speed of air 330 m/s at 0 deg C Speed of air 340 m/s at 20 deg C BML 770 -­‐ Dinesh Kalyanasundaram 5 Standing Waves in a Open/ Closed Channel BML 770 -­‐ Dinesh Kalyanasundaram 6 Harmonics of an open channel BML 770 -­‐ Dinesh Kalyanasundaram 7 Harmonics of an Closed/Open channel BML 770 -­‐ Dinesh Kalyanasundaram 8 Intensity Vs Frequency BML 770 -­‐ Dinesh Kalyanasundaram 9 Phon The phon is a unit of loudness level for pure tones. Its purpose is to compensate for the effect of frequency on the perceived loudness of tones. BML 770 -­‐ Dinesh Kalyanasundaram 10 Measurement units •  Decibel: The decibel ( dB) is used to measure sound level, but it is also widely used in electronics, signals and communicaCon. The dB is a logarithmic way of dscribing a raCo. The raCo may be power, sound pressure, voltage or intensity or several other things. 10 log (P2/P1) dB or 20 log (p2/p1) dB P == Power And p== pressure BML 770 -­‐ Dinesh Kalyanasundaram 11 Sources of Sound Shockwave (distorted sound waves > 1 atm; waveform valleys are clipped at zero pressure) Stun grenade Threshold of pain Loudest human voice at 1 inch Traffic on a busy roadway at 10 m Hearing damage (over long-­‐term exposure, need not be conCnuous) Passenger car at 10 m TV (set at home level) at 1 m Pa dB >101,325 >194 6,000–20,000 170–180 63-­‐200 130-­‐140 110 135 0.2-­‐0.632 80-­‐90 0.365 85 (2–20)×10−2 60-­‐80 2×10−2 60 Washing machine, dishwasher Normal conversaCon at 1 m Very calm room Light leaf rustling, calm breathing Auditory threshold at 1 kHz 42–53 (2–20)×10−3 40-­‐60 (2–6.32)×10−4 20-­‐30 6.32×10−5 10 2×10−5 0 BML 770 -­‐ Dinesh Kalyanasundaram 12 CriCcal Features of the ear •  Threshold of hearing – 135 dB BML 770 -­‐ Dinesh Kalyanasundaram 13 Parts of the receiving sensor •  Three main parts –  Outer ear consists of the pinna, and the ear canal –  Middle ear consisCng of eardrum (tympanic membrane), malleus, incus and the stapes (Eustachian tube connects to the middle ear) –  Inner ear consisCng of the cochlea, vesCbular canals and the auditory nerve BML 770 -­‐ Dinesh Kalyanasundaram 14 Outer Ear •  The pinna is made up of a frame of carClage that is covered with skin. •  The pinna has obvious folds, elevaCons, depressions and a prominent bowl – a fairly universal shape among all people. •  The pinna acts as a funnel to collect and direct sound down the ear canal. •  It also serves to enhance some sounds through its resonance characterisCcs. Finally, it helps us to appreciate front-­‐back sound localiza6on. •  The other structure of the outer ear is the external ear canal. •  The outer two-­‐thirds of this canal has a carClaginous framework, and the inner one-­‐
third is bony. •  The ear canal is curved, almost "S" shaped and averages about 1 inch in length in adults. •  The skin of ear canal has hairs and glands that produce wax called cerumen. •  This hair and cerumen serve a protecCve funcCon for the ear canal. In addiCon, cerumen helps to lubricate the skin and keep it moist. BML 770 -­‐ Dinesh Kalyanasundaram 15 BML 770 -­‐ Dinesh Kalyanasundaram 16 Middle Ear •  The tympanic membrane (or the eardrum) is a thin and delicate membrane stretched across the enCre inner end of the ear canal separaCng the environment from the middle ear. •  The vibratory moCons are transmiied to ossicles or the ossicular chain. •  This ossicular chain arCculates with the tympanic membrane through the lateral most bone called the malleus (hammer). •  The malleus then sends the mechanical vibraCons to the incus (anvil), which in turn communicates with the inner most ossicle called the stapes (sCrrup). •  These are the three smallest bones in the body, and, like the tympanic membrane, they never stop moving because they are constantly bombarded with sound, even while we're sleeping! BML 770 -­‐ Dinesh Kalyanasundaram 17 MoCon of Middle Ear under oscillaCons BML 770 -­‐ Dinesh Kalyanasundaram 18 Middle and Inner Ear TM – Tympanic membrane Enlarged View BML 770 -­‐ Dinesh Kalyanasundaram Malleus is connected to the tympanic membrane all along the line 19 Curved Membrane theory – Tympanic membrane BML 770 -­‐ Dinesh Kalyanasundaram 20 OscillaCons of the Middle Ear BML 770 -­‐ Dinesh Kalyanasundaram 21 OscillaCons of the Middle Ear BML 770 -­‐ Dinesh Kalyanasundaram 22 OscillaCons of the Middle Ear BML 770 -­‐ Dinesh Kalyanasundaram 23 OscillaCons of the Middle Ear BML 770 -­‐ Dinesh Kalyanasundaram 24 Different modes of oscillaCon of the malleus, and incus w.r.t. frequency OscillaCons of the Middle Ear BML 770 -­‐ Dinesh Kalyanasundaram 25 Umbo displacement at 3 kHz BML 770 -­‐ Dinesh Kalyanasundaram 26 ConnecCon between tympanic membrane and malleus BML 770 -­‐ Dinesh Kalyanasundaram 27 VibraCon of the tympanic membrane “Wave moCon on the surface of the human tympanic membrane: Holographic measurement and modeling analysis”, Cheng et al, J. Ac. So. Am., 2013. BML 770 -­‐ Dinesh Kalyanasundaram 28 VibraCon of the tympanic membrane “Wave moCon on the surface of the human tympanic membrane: Holographic measurement and modeling analysis”, Cheng et al, J. Ac. So. Am., 2013. BML 770 -­‐ Dinesh Kalyanasundaram 29 OscillaCons of the Middle Ear BML 770 -­‐ Dinesh Kalyanasundaram 30 BML 770 -­‐ Dinesh Kalyanasundaram 32 VibraCons of the Cochlea w.r.t. frequency BML 770 -­‐ Dinesh Kalyanasundaram 34 VibraCons of the Cochlea w.r.t. frequency BML 770 -­‐ Dinesh Kalyanasundaram 36