SOUND & THE EAR

Anthony J Greene2 Sound and the Ear 1.Sound Waves A.Frequency: Pitch, Pure Tone. B.Intensity C.Complex Waves and Harmonic Frequencies 2.The Ear A.The Outer Ear B.The Middle Ear C.The Inner Ear i.The Cochlear Membrane ii.Sound Transduction iii.Hearing Loss

Anthony J Greene3 Sound Waves 1.Frequency Wavelength - distance between peaks or compressions Hertz - cycles (1 compression & 1 rarefaction) per second - the major determinant of pitch

Anthony J Greene4 Sound Waves Pure Tones - simple waves Harmonics - complex waves consisting of combinations of pure tones (Fourier analysis) - the quality of tone or its timbre (i.e. the difference between a given note on a trumpet and the same note on a violin) is given by the harmonics

Anthony J Greene5 Sound Waves Pitch and fundamental frequency - in pure tones the pitch is the fundamental frequency - with harmonics added the fundamental frequency is the dominant pure tone

Anthony J Greene6 Sound Waves 2.Intensity Amplitude is measured in Decibels (dB)- the height of the peak, or the amount of compression - determines volume Loudness is the psychological aspect of sound related to perceived intensity or magnitude

Anthony J Greene7 Sound Waves Humans can hear across a wide range of sound intensities –Ratio between faintest and loudest sounds is more than one to one million –In order to describe differences in amplitude, sound levels are measured on a logarithmic scale, in units called decibels (dB) –Relatively small decibel changes can correspond to large physical changes (e.g., increase of 6 dB corresponds to a doubling of the amount of pressure)

Anthony J Greene8 Sound Waves

Anthony J Greene9 Compression Rarefaction Direction of Sound Air Molecules Speaker

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Anthony J Greene12 Harmonics & Fourier Analysis

Anthony J Greene13 Harmonic Frequencies Strings or pipes (trombone, flute organ) all have resonant frequencies. They may vibrate at that frequency or some multiple of it All instruments and voices carry some harmonics and dampen others Length of string or pipe 1f1f 2f 1 octave 3f3f 4f 2 octaves 8f 3 octaves

Anthony J Greene14 Harmonic Frequencies 1f + 3f + 5f + 7f + 9f + …

Anthony J Greene15 Harmonics & Fourier Analysis

Anthony J Greene16 Harmonics & Fourier Analysis Complex sounds can be described by Fourier analysis A mathematical theorem by which any sound can be divided into a set of sine waves. Combining these sine waves will reproduce the original sound. The fundamental frequency is the pitch, and the harmonic frequencies are the timbre. Results can be summarized by a spectrum

Anthony J Greene17 Harmonics & Fourier Analysis

Anthony J Greene18 The Ear Outer Ear Middle Inner Ear Ear

Anthony J Greene19 Outer Ear Pinna - the fleshy part of the ear Channels sound into the auditory canal - which carries the sound to the eardrum tympanic membrane - vibrates in response to vibrations in the air

Anthony J Greene20 Middle Ear Ossicles - the three smallest bones in the human body - malleus (hammer) incus (anvil ), stapes (stirrup ) - transmit sound to the inner ear Eustachian tubes - connects to throat and allows air to enter the middle ear - equalizes the pressure on both sides of the eardrum Conduction Deafness

Anthony J Greene21 Inner Ear

Anthony J Greene22 Inner Ear 1.Semi-Circular Canals 2.The Cochlea Oval Window - the connection point from the stirrup to the inner ear Round Window

Anthony J Greene23 Inner Ear 1.Semi-Circular Canals 2.The Cochlea Oval Window - the connection point from the stirrup to the inner ear Round Window

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Anthony J Greene25 The Cochlea Vestibular canal - wave travels from the oval window towards the end of the cochlea Tympanic canal - wave travels from the end of the cochlea to the round window Reissner's Membrane - separates the vestibular canal from the Cochlear Duct Basilar membrane - vibrates in response to the wave traveling around it - varies in thickness so some areas vibrate best to high pitches and some areas to low pitches Cochlear duct -the third section of the cochlea which contains the Organ of Corti Organ of Corti - the place where physical energy is converted to nerve energy

Anthony J Greene26 The Cochlea

Anthony J Greene27 The Cochlea

Anthony J Greene28 The Cochlea

Anthony J Greene29 Sound Transduction A traveling wave is set up in the vestibular canal The wave causes the Basilar membrane to vibrate - each section is maximally stimulated by a different pitch - serves to sort out differing frequencies In the Organ of Corti hair cells vibrate in response to the vibrations of the Basilar membrane Hair cells transduce the energy into a neural impulse

Anthony J Greene30 Bassilar Membrane

Anthony J Greene31 Basilar Membrane

Anthony J Greene32 Exposure to Loud Noise

Anthony J Greene33 Summary