HearingEar MechanicsFrequency RangeThreshold of PainSpeaker SystemsBeatsIn TuneHearingHearingEar MechanicsEar MechanicsThe ear is collects and amplifies sound.The ear is collects and amplifies sound.Initial receiver is the eardrum.Initial receiver is the eardrum.•Sensitive to tiny pressure changesSensitive to tiny pressure changesMiddle ear transmits the sound through bone.Middle ear transmits the sound through bone.•Act as levels magnifying force by 40Act as levels magnifying force by 40Inner ear (cochlea) separates pitches.Inner ear (cochlea) separates pitches.•Breaks up superposed wavesBreaks up superposed waves•Accurate to better than 1% (0.1% with training)Accurate to better than 1% (0.1% with training)Frequency RangeFrequency RangeThe human ear is sensitive to The human ear is sensitive to sounds from 20 Hz – 20 kHz.sounds from 20 Hz – 20 kHz.Maximum sensitivity is from Maximum sensitivity is from about 3 kHz to 5 kHz with 120 about 3 kHz to 5 kHz with 120 dB range.dB range.Sensitivity is much worse at Sensitivity is much worse at low frequencies.low frequencies.•Loudness control for audio Loudness control for audio equipment boosts bass and equipment boosts bass and treble.treble.Threshold of PainThreshold of PainAt 120 dB most people feel At 120 dB most people feel pain.pain.•Rock concert at 4 m.Rock concert at 4 m.•Jet aircraft at 150 m.Jet aircraft at 150 m.Eardrums burst at 160 dB.Eardrums burst at 160 dB.Speaker SystemsSpeaker SystemsThe sound from a source The sound from a source reaches each ear at a reaches each ear at a separate time.separate time.•Brain uses the time Brain uses the time difference to tell direction.difference to tell direction.•Hard with short wavelength.Hard with short wavelength.Stereo speakers reconstruct Stereo speakers reconstruct timing differences. timing differences. •Constructive and destructive Constructive and destructive interferenceinterferenceBeatsBeatsWhen two wavelengths are at nearly the same When two wavelengths are at nearly the same frequency the superposed waves create beats.frequency the superposed waves create beats.The separation of peaks is the period T = 1 / fThe difference in frequencies is the beat frequency f. The beat period T = 1 / f .In TuneIn TuneA 440 Hz-tuning fork is held A 440 Hz-tuning fork is held near a vibrating piano string. near a vibrating piano string. The tuner hears 20 beats in The tuner hears 20 beats in 5 s.5 s.What is the pitch of the piano What is the pitch of the piano string?string?Will the tuner ever get it Will the tuner ever get it tuned perfectly?tuned perfectly?The beat frequency is 20 The beat frequency is 20 beats / 5 s = 4 Hz.beats / 5 s = 4 Hz.The piano string could be The piano string could be either at 444 or 436 Hz.either at 444 or 436 Hz.Note: a beat period of 1 min Note: a beat period of 1 min would get a frequency would get a frequency accurate to 0.016 Hz.accurate to 0.016
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