~ Nature of Sound ~ 1. What is sound? 2. Human Hearing 3. Properties of Sound 4. Interactions of Sound 5. Sound Quality
I. WHAT IS SOUND?
I. WHAT IS SOUND? A Sound wave is a LONGITUDINAL WAVE caused by vibrations of particles back and forth through a medium. Sound waves are mechanical waves and NEED A MEDIUM TO TRAVEL Sound waves travel in all directions from the source
II. Human Hearing
converted to nerve impulses in cochlea II.Human Hearing sound wave vibrates ear drum amplified by bones converted to nerve impulses in cochlea
http://www.hearingusa.com/ears01.mov
III. Properties of Sound
A. SPEED OF SOUND 345 m/s in air at 20°C Depends on: Type of medium travels better through liquids and solids can’t travel through a vacuum Temperature of medium travels faster at higher temps
http://www.stmary.ws/highschool/physics/home/notes/waves/CharacteristicsPeriodicWaves.htm
B. PITCH Pitch highness or lowness of a sound depends on frequency of sound wave human range: 20 - 20,000 Hz ultrasonic waves subsonic waves
C. LOUDNESS Loudness volume of sound depends on energy (amplitude) of sound wave measured in decibels (dB)
Loudness measured in Decibels DECIBEL SCALE 120 110 100 80 70 40 18 10
D. DOPPLER EFFECT Have you ever noticed how the sound of a police car siren changes as it moves past you? The changes in pitch you hear are due to a phenomenon known as the Doppler effect. Look at the illustration of the police car to answer these questions. The police car has passed the woman standing on the sidewalk, but has not yet passed the man. Which observer hears the siren at a higher pitch—the woman or the man?
D.DOPPLER EFFECT moving toward you - pitch sounds higher change in wavelength due to the motion of the source. As the source moves, the waves become bunched up and the pitch (frequency) of the sound changes. moving toward you - pitch sounds higher moving away from you - pitch sounds lower
Doppler Effect http://www.fearofphysics.com/Sound/doppler.html
Doppler Effect http://www.colorado.edu/physics/2000/applets/doppler.html http://www.pbs.org/wgbh/nova/universe/moving.html
IV. INTERACTIONS OF SOUND Reflection Interference Resonance
A. REFLECTIONS OF SOUND WAVES Reflections of sound waves are called echos! Sound waves reflect best off smooth, hard surfaces ECHOLOCATION USE OF REFLECTED SOUND WAVES TO FIND OBJECTS
Ultrasonic waves are used to see with sound using reflection! Ultrasonic waves - above 20,000 Hz SONAR “Sound Navigation Ranging” Medical Imaging
B. Interference Interference When 2 or more waves overlap Constructive - louder Destructive - softer
SONIC BOOM When a jet plane reaches the speed of sound, the sound waves in front of the jet combine by constructive interference. The result is a high density compression (high amplitude) compression called the sound barrier.
WATCH THESE VIDEOS! http://www.youtube.com/watch?v=-d9A2oq1N38&feature=related http://www.youtube.com/watch?v=QjpikTn2qAk&feature=related
C. RESONANCE Forced Vibration when one vibrating object forces another object to vibrate at the same frequency results in a louder sound because a greater surface area is vibrating used in guitars, pianos, etc.
= Resonance = Resonance special case of forced vibration object is induced to vibrate at its natural frequency http://www.youtube.com/watch?v=17tqXgvCN0E
The Tacoma Narrows Bridge Disaster = Resonance = “Galloping Gertie” The Tacoma Narrows Bridge Disaster http://www.youtube.com/watch?v=j-zczJXSxnw&feature=related Wind through a narrow waterway caused the bridge to vibrate until it reached its natural frequency.
= Resonance = Beats variations in sound intensity produced by 2 slightly different frequencies both constructive and destructive interference occur
V. Sound Quality
A. Music vs. Noise Music Noise specific pitches and sound quality regular pattern Noise no definite pitch no set pattern
Anechoic chamber - designed to eliminate reverberation. B. ACOUSTIC Acoustics the study of sound Reverberation echo effect produced by the reflection of sound Anechoic chamber - designed to eliminate reverberation.