Sound and Hearing

Sound Waves

• Sound waves are mechanical and longitudinal waves

• What does this tell you about sound waves?

Sound waves need a material (medium) to travel through

Sound waves travel as a series of compressions and rarefactions

Properties of SoundSpeed

• In air at room temperature, sound travels around 340 m/s– About 765 mi/hr

• Sound generally travels fastest in solids and slowest in gases. Why?

Particles collide most often – energy is transferred the fastest

Particles collide least often – energy is transferred the

slowest

Properties of SoundSpeed

• In air at room temperature, sound travels around 340 m/s

• Sound generally travels fastest in solids and slowest in gases. Why?

• Sound will also travel faster in materials as the temperature of a substance increases. Why?

As the temperature of a substance increases, the speed of the particles increases, so particles (of any state of matter) collide more often, so energy is transferred faster

Properties of SoundIntensity (& Volume)

• Intensity is the rate that energy flows through a given area– Rate = a measurement over a specific period

of time or “per time”– What area are people most concerned with?

• Intensity depends on the wave’s amplitude and distance from the sound source– Why?

• Measured in decibels (dB)

Properties of SoundPitch

• What a wave “sounds like” to a person

• Pitch is based on the frequency of the wave– High frequency = high pitch– Low frequency = low pitch

• Pitch (how a sound is perceived by an individual) depends on factors like age, health, previous damage, heredity

Ultrasound

• Waves at frequencies higher than most humans can hear– Generally >20,000 Hz

• Applications for Ultrasound Waves– Sonar: technique for determining the distance

to an object through water– Imaging: Looking at reflected waves and

based on the reflections, a detailed picture of an object can be produced

Doppler Effect

• A change in the frequency of a wave caused by the motion of a sound source or the motion of the listener (or both)– As the distance between the source and

the listener decreases, pitch increases– As the distance between the source and

the listener increases, pitch decreases

Sound and Music

• Musical Instruments vary the frequency of the waves it produces by changing the wavelength of standing waves

• Resonance: Sound waves cause other items to vibrate, which greatly increases the amplitude of the waves produced, which increases the volume

Hearing and the Structure of the Ear

• Outer Ear: Funnels sound down ear canal; waves strike eardrum and eardrum vibrates at same frequency as wave

• Middle Ear: contains three bones (hammer, anvil, stirrup) that act as “amplifiers”

• Inner Ear: Tiny, hair-like projections send electrical impulse through nerves to the brain

Recording & Reproducing Sound

• Sound is recorded by converting sound waves into electrical signals that can be processed and stored

• Sound is reproduced by converting electrical signals back into mechanical, longitudinal waves (using a speaker)

Changing the Wavelength