Sound Waves

Sound Waves• mechanical, longitudinal waves– require a medium• may pass through solids, liquids, or gases

– medium particles move parallel to the motion of the wave

– has compressions and rarefactions

Speed of Sound• about 342 m/s in air– changes with temperature

• much slower than light– speed of light = 300,000,000 m/s

Loudness or Intensity• Sound Simulator• amplitude (energy) of a wave• describes how loud or soft a sound is• measured in decibels

Sound Decibels (db)

Threshold of hearing for human 0Whisper 10-20

Average Home 40-50Car 40-50

Conversation 60-70Urban Background noise 70-80

Loud Music 90-100Threshold of Pain 120

Jet airplane engine 170Threshold of death 180

Loudness or Intensity

• Soft– Low energy

• Loud– High energy

Pitch• Sound Simulator• frequency of a wave– measured in Hertz

• how high or low a sound is

Pitch• Low f, low pitch– Large wavelength

• High f, high pitch– Small wavelength

Pitch & Human Hearing• Humans hear between 20-20,000 Hz– Ultrasound – too high f for humans to hear– Infrasound – too low f for humans to hear

Doppler Effect

Doppler Effect• as a sound producing object approaches a

receiver (listener) the sound’s pitch increases (high f)– the waves appear to sound higher

Doppler Effect• as the object moves away, the pitch drops

(low f)– the sounds appears to sound lower

Doppler Effect• occurs for other types of waves as well, but is

easiest to relate to sound waves

Doppler Effect• Used to:– Predict weather– Tell instant speed of

moving objects– Track galaxies

St. Nazianz storm May 12, 2000. Caused some schools to be

extended.

1999Oklahoma City F 5 Tornado

Acoustics• How sound interacts with surroundings

Why does sound travel a long distance over water? •Sound waves bounce off the flat surface of a lake•Sound waves refract off of warm air over a lake

Warm Air

Cool Air

Reflection

Refraction

Room and Building Acoustics• Sound behavior in a room depends on many

factors:– Volume– Shape of room– Echo patterns

Room and Building Acoustics

Room and Building Acoustics

Room and Building Acoustics• Construction Material– Energy absorbing: foam, wood, carpet– Energy reflecting: metal, concrete

Room and Building Acoustics• Audience layout• Furnishing• Source of Sound