Transcript Sound Intensity and Resonance

Ch. 13, section 2 – pages 487-493
A. Intensity - rate of energy flow through an area
 energy is transferred from one air molecule to the next
as the wave front travels
 Intensity decreases as distance from the source increases
 Total energy is spread throughout the entire wave front
 Entire wave front expands with distance from the source
B. Intensity and frequency determine which sounds are
audible
 Neither alone give enough information
 Threshold of Hearing – softest sounds that humans
can hear with the unaided ear
 Threshold of Pain – loudest sounds that human ears
can tolerate before pain
 sounds greater than this level produces pain and
ringing in ears and can cause ear damage and hearing
loss especially with prolonged exposure
C. Decibel level (relative intensity)
 Intensity of a sound determines it loudness/volume
 Measured in decibels (dB)
 Relates intensity of a sound to the intensity at the threshold
of hearing
 An increase of 10 decibels doubles the volume
 A logarithmic curve
 See table 13-2 on page 490
 Forced vibrations – energy from one vibrating object is
transferred to another object, causing it to begin to
vibrate
 Example: violin strings / guitar strings
 pluck / strum / bow a string  the vibrations move
through the string to the bridge, to the sound post, to
the body of the instrument, causing the air molecules
next to the body to vibrate and creates a sound wave
 Resonance – condition that exists when the frequency
of vibration from one object matches the natural
frequency of vibration of another object, causing the
second object to vibrate
 The Human Ear – transfers the energy of sound waves in
the air to vibrations in the 3 bones of the middle ear, and
then to the fibers
in the cochlea of
the inner ear,
which
stimulates nerves
to allow us to
hear different
frequencies