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Hearing - PowerPoint PPT Presentation


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Hearing. Ear Mechanics. The ear is collects and amplifies sound. Initial receiver is the eardrum. Sensitive to tiny pressure changes Middle ear transmits the sound through bone. Act as levels magnifying force by 40 Inner ear (cochlea) separates pitches. Breaks up superposed waves

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ear mechanics
Ear Mechanics
  • The ear is collects and amplifies sound.
  • Initial receiver is the eardrum.
    • Sensitive to tiny pressure changes
  • Middle ear transmits the sound through bone.
    • Act as levels magnifying force by 40
  • Inner ear (cochlea) separates pitches.
    • Breaks up superposed waves
    • Accurate to better than 1% (0.1% with training)
frequency range
Frequency Range
  • The human ear is sensitive to sounds from 20 Hz – 20 kHz.
  • Maximum sensitivity is from about 3 kHz to 5 kHz with 120 dB range.
  • Sensitivity is much worse at low frequencies.
    • Loudness control for audio equipment boosts bass and treble.
threshold of pain
Threshold of Pain
  • At 120 dB most people feel pain.
    • Rock concert at 4 m.
    • Jet aircraft at 150 m.
  • Eardrums burst at 160 dB.
speaker systems
The sound from a source reaches each ear at a separate time.

Brain uses the time difference to tell direction.

Hard with short wavelength.

Stereo speakers reconstruct timing differences.

Constructive and destructive interference

Speaker Systems
beats
Beats
  • When two wavelengths are at nearly the same frequency the superposed waves create beats.

The separation of peaks is the period T = 1 / f

The difference in frequencies is the beat frequency Df.

The beat period T = 1 / Df.

in tune
A 440 Hz-tuning fork is held near a vibrating piano string. The tuner hears 20 beats in 5 s.

What is the pitch of the piano string?

Will the tuner ever get it tuned perfectly?

The beat frequency is 20 beats / 5 s = 4 Hz.

The piano string could be either at 444 or 436 Hz.

Note: a beat period of 1 min would get a frequency accurate to 0.016 Hz.

In Tune

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