Chapter 4 PHYSICS OF HEARING by Tsion.pptx - Chapter 4...

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Chapter 4Physics of HearingBy Tsion S.1
OutlinePhysics of HearingSoundPhysics of soundSpeed, frequency & wavelength of sound waveThe EarCochlear implants2
SoundSound-adisturbancewhichpropagatesthroughanelasticmaterialat a speed which is characteristic of that material.Sound is usually caused by radiation from a solid vibratingsurface or fluid disturbances. A sound wave is a mechanical wave thatmoves through a medium as particles in the medium are displacedrelative to each other.3
SoundHearing is the perception of sound.Sound has more application.Sound: the disturbances of matter that istransmitted from the source outward.Sound is a wave.It is disturbance of atoms, and mostsounds are periodic.4
SoundEg: Vibration of strings, as the strings goes back and forth some of the energieswill be transferred to the air molecules as thermal. But a small fraction of energywill be compressing and expanding the surrounding air molecules creating higherand lower local pressures.compression = high pressure regions rarefactions = low pressure regions.Disturbances => sound5
SoundAfter many vibrations, there willbe many pressure variationsaway from the source• The amplitude of the wavedecreases going away form thesource:• The energy of the wave spreadwider and wider area.• During compression andrarefaction thermal energy istransferred which makes thedisturbance more random thermalmotions.6
Physics of Sound=>Sound wave can be modeled mathematically as some mechanical dynamicsystems.7
Physics of SoundIt is preferable to write the equation in a single sinusoid,x = Csin(wt + ø)where: C is composite amplitude of A&B ø is phase• Conventionally, single sinusoidal wave is used to represent sound wave.•Undertheseconditionstheinitialvelocityiszero.Substituting the initial conditions into the equation, phase shift is 90◦ =>x = Ccosωt.8
Speed, frequency and wavelengthSound travels at a certain speed, with certain properties likefrequency and wavelength• Frequency of a sound can be sensed as pitch.• High pitch means very rapid oscillation .9
Speed, frequency and wavelengthSpeed of sound have frequency inaudible range(20Hz to 20K Hz),Speed of sound isVw= fλ10
Speed, frequency and wavelengthThe speed of sound isaffected by temperature of the medium,Eg: the speed ofsound in air at temperature T11
Speed, wavelength and frequencyAt almost constant speed:Lower speaker: wooferUpper speaker: tweeterEx: calculate the wavelengths ofsound wave at the extreme endsof the audible range 20 & 20KHzin the air medium at 30 oC.[331m/s is speed of sound in air]12
How do headphones work?.13
Sound intensity and levelInquiettime,youmayhearyourbloodpulsingthroughyourears.

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