Chapter 19: SoundChapter 19: SoundFor those who have ears!For those who have ears!

19.1 Properties of

Sound

19.1 Objectives

Solve problems relating the frequency, wavelength, and velocity of sound.

Demonstrate knowledge of the nature of sound waves and the properties sound shares with other waves.

Define the Doppler shift and identify some of the applications.

What is Sound?

What is sound? Sound is a form of energy, just like electricity and light. Sound is made when air molecules vibrate longitudinally and move in a pattern called waves, or sound waves. They are also referred to as compression or pressure waves.

Think of when you clap your hands, or when you slam the car door shut. That action produces sound waves, which travel to your ears and then to your brain, which says, "I recognize that sound.” For humans, sound most commonly travels through the air. But it can travel through other mediums like water.

What does it look like?

Sound is invisible for the most part. It is heard not seen. There are fun toys that make big air bursts that you can feel But what does sound “look like”?

Since sound needs a medium like air, it cannot travel in a vacuum.

Visualizing Sound

The Speed of Sound

Since sound travels in the medium of air, its speed is fixed. It does however, vary with the temperature of air.

At 0 C, the speed of sound is 331.451 m/s. At 20 C, the speed of sound is 343.371 m/s. At 40 C, the speed of sound is 354.891 m/s.

As a rule of thumb, the speed of sound changes by about 12 m/s for every 20 C of temperature change. The most common value used is 343 m/s.

Sound Measurement

Sound amplitude is measured in decibels (dB). The decibel scale is a logarithmic scale. The sound amplitude is also called sound level or loudness.

Table of sound levelsdB

Jet aircraft, 50 m away 140Threshold of pain 130Threshold of discomfort 120Chainsaw, 1m distance 110Disco, 1 m from speaker 100Diesel truck, 10 m away 90Kerbside of busy road, 5 m 80

Vacuum cleaner, distance 1 m 70Conversational speech, 1m 60Average home 50Quiet library 40Quiet bedroom at night 30Background in TV studio 20Rustling leaf 10Threshold of hearing 0

Spinal Tap: This one goes to 11…

Sound Frequency Ranges

Humans can hear from 20 hz to 20,000 Hz. Other animals have larger ranges.

Species Approximate Range (Hz) human 64-23,000dog 67-45,000 cat 45-64,000 cow 23-35,000 horse 55-33,500 sheep 100-30,000 rabbit 360-42,000 rat 200-76,000 mouse 1,000-91,000 gerbil 100-60,000 guinea pig 54-50,000 hedgehog 250-45,000 raccoon 100-40,000ferret 16-44,000 opossum 500-64,000

Species Approximate Range (Hz) chinchilla 90-22,800bat 2,000-110,000 beluga whale 1,000-123,000elephant 16-12,000 porpoise 75-150,000goldfish 20-3,000 catfish 50-4,000 tuna 50-1,100 bullfrog 100-3,000 tree frog 50-4,000 canary 250-8,000 parakeet 200-8,500 cockatiel 250-8,000 owl 200-12,000 chicken 125-2,000

Sound Speed

Sound Speed - The distance a sound travels in a given time. It is given as the frequency times the wavelength. If the frequency increases then the wavelength must decrease since the speed is constant.

€

υ =ΔdΔt=λ

T= f • λ = 343

m

sec

€

f = frequency =1

T; T = period =

1

f

λ = wavelength

Speed of Sound in Other Media

The speed of sound depends on the media the sound wave travels through.

€

υ vacuum = 0m

sec; υ air = 343

m

sec;

υ water =1,484m

sec; υ iron = 5,120

m

secυ ground > υ air

Echoes

Reflected waves are called echoes and can be used to measure the distance from source to the object. This is how bats, who have poor eyesight and travel at night, navigate.

€

υ =ΔdΔt= 343

m

sec

Sound can also be diffracted. It can bend around barriers.

Sonar

Sonar is reflected sound waves (echoes) that travel through a water media rather than an air media.

€

υwater =Δd

Δt=1,248

m

sec

Doppler Effect

Doppler Shift

Doppler shift: If the sound source is coming towards you at a significant velocity, the sound pitch will get higher. If the sound source is moving away from you then the sound pitch is lowered.

doppler motions

Doppler Shift

Doppler shift: If the sound source is coming towards you at a significant velocity, the sound pitch will get higher. If the sound source is moving away from you then the sound pitch is lowered.

€

fD = fSv + vD( )v − vS( )

€

v = 343m /s;D− sound detector; S − sound source

Doppler Demo

19.2 The Physics of

Music

19.2 Objectives

Demonstate an understanding of resonance, especially as applied to air columns.

Describe the origin of sound.

Explain why there is a variation among instruments and among voices using the terms timbre, resonance, fundamental, harmonic.

Determine why beats occur.

Concept Development Map

Sonance

Latin: sonus (sound) & sonans (to make a noise); a sound; a tune

Related words: Sonic, sonar, sonant, sonata, sonation

Quality or state of being sonant; sonancy

DefinitionsSound Vocabulary

Resonance

Dissonance

Consonance

Re-sonance (again-sound). The act of resounding, being resonant

Sound vibrations are transferred to another object with the same natural frequency of vibration. The two agree.

Con-sonance (with-sound). The act of sounding together; Harmony (different frequency).

Sound vibrations that “fight” With each other. Discord, disharmony.

Dis-sonance (mismatched-sound).

Resonance

Resonance - The tendency of a system to oscillate at maximum amplitude at certain frequencies, known as the system's resonance frequencies (or resonant frequencies). At these frequencies, even small periodic driving forces can produce large amplitude vibrations, because the system stores vibrational energy.

Closed Tube

Open Tube

82 Resonance Demo

83 “Break Step” and Bridges

Pitch and Timbre

Pitch - The musician’s word for frequency of the sound.

Timbre - The tone quality or color of the sound wave generated by the instrument. The extra distortions of the pure sine wave accounts for the unique sound of the human voice, and different instruments.

Beat - An oscillation of wave amplitude caused by the sounding of two nearly identical frequencies. The superposition of the waves makes a slower moving wave.

Timbre

Consonance and Dissonance

Consonance - A pleasant combination of pitches.

Dissonance - A unpleasant combination of pitches. Can be described as “jarring”.

Harmonics and Octaves

Harmonics - Any higher frequency that is a multiple of the original frequency ( f ).

Octave - Two frequencies in a 1:2 ratio.

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e.g. 2 f , 3 f ,4 f ,5 f ,...( )

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e.g. 440Hz&880Hz, 220Hz& 440Hz,...( )

Mr. Mosher’s Band

Trombone - A slide trombone lengthens the instrument’s tube by tube within a tube action.

Guitar - Various frequencies, Harmonics, and Beats can all be demonstrated on the guitar.

Throat - Please don’t ask Mr. Mosher to play his throat!