Download Hearing

Hearing
How hearing works
• First, the ear gathers the compressional
waves.
• Next, the ear amplifies the waves.
• In the ear, the amplified waves are
converted to nerve impulses that travel to
the brain.
• Finally, the brain decodes and interprets
the nerve impulses.
I’m all ears
• Outer Ear -- where
sound waves are
gathered.
• Middle Ear -- where
waves are amplified
• Inner Ear -- converts
waves to nerve
impulses
I’m all ears
• Eardrum -- a tough
membrane about 0.1
mm thick
• Cochlea
– spiral-shaped structure
– Filled with liquid and
tiny hairs
– Convert waves to
impulses
How does it sound?
• Amplitude → Intensity → Volume (Loudness)
– Intensity is the amount of energy that flows through a
wave
• Intensity decreases with distance
– The sound covers more area
– Some of the sound energy is converted to other forms
• Decibels
– Adding decibels is the same as multiplying intensity
– A 50 dB sound is ten times louder than a 40 dB sound
How does it sound?
• Frequency → Pitch → Note
– Remember, frequency is a measure of how many
waves pass by in a second
– Pitch is how high or low a note sounds
• Octaves -- If you go “up” an octave, you double
the frequency
• Ultrasonic and Infrasonic
– Ultrasound → f > 20,000 Hz
– Infrasound → f < 20 Hz
Doppler
• The Doppler Effect -- change in frequency
due to a moving wave source
– Ambulance
– Ice Cream Truck
– Race Car
• It also works for a moving observer and a
stationary source
Doppler
• The Doppler Effect also works for
electromagnetic waves
– Doppler Radar
– Radar Detection (police)
– Used in astronomy to find if objects are
moving towards or away from us