Unit 5, Chapter 15



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Unit 5, Chapter 15

Unit 5: Waves and Sound

  • Chapter 15 Sound

Chapter 15 Objectives

  • Explain how the pitch, loudness, and speed of sound are related to properties of waves.
  • Describe how sound is created and recorded.
  • Give examples of refraction, diffraction, absorption, and reflection of sound waves.
  • Explain the Doppler effect.
  • Give a practical example of resonance with sound waves.
  • Explain the relationship between the superposition principle and Fourier’s theorem.
  • Describe how the meaning of sound is related to frequency and time.
  • Describe the musical scale, consonance, dissonance, and beats in terms of sound waves.

Chapter 15 Vocabulary Terms

  • pressure
  • frequency
  • pitch
  • superposition principle
  • decibel
  • speaker
  • acoustics
  • microphone
  • fundamental
  • wavelength
  • stereo
  • Doppler effect
  • supersonic frequency
  • spectrum
  • shock wave
  • resonance
  • node
  • antinode
  • dissonance
  • harmonic
  • reverberation
  • note
  • sonogram
  • Fourier’s theorem
  • rhythm
  • musical scale
  • cochlea
  • consonance
  • longitudinal wave
  • beats
  • octave

15.1 Properties of Sound

  • Key Question:
  • What is sound and how do we hear it?
  • *Students read Section 15.1 AFTER Investigation 15.1

15.1 Properties of Sound

  • If you could see the atoms, the difference between high and low pressure is not as great. Here, it is exaggerated.

15.2 The frequency of sound

  • We hear frequencies of sound as having different pitch.
  • A low frequency sound has a low pitch, like the rumble of a big truck.
  • A high-frequency sound has a high pitch, like a whistle or siren.
  • In speech, women have higher fundamental frequencies than men.

15.1 Complex sound

Common Sounds and their Loudness

15.1 Loudness

  • Every increase of 20 dB, means the pressure wave is 10 times greater in amplitude.
  • Logarithmic scale
  • Linear scale
  • Decibels (dB)
  • Amplitude
  • 0
  • 1
  • 20
  • 10
  • 40
  • 100
  • 60
  • 1,000
  • 80
  • 10,000
  • 100
  • 100,000
  • 120
  • 1,000,000

15.1 Sensitivity of the ear

  • How we hear the loudness of sound is affected by the frequency of the sound as well as by the amplitude.
  • The human ear is most sensitive to sounds between 300 and 3,000 Hz.
  • The ear is less sensitive to sounds outside this range.
  • Most of the frequencies that make up speech are between 300 and 3,000 Hz.

15.1 How sound is created

  • The human voice is a complex sound that starts in the larynx, a small structure at the top of your windpipe.
  • The sound that starts in the larynx is changed by passing through openings in the throat and mouth.
  • Different sounds are made by changing both the vibrations in the larynx and the shape of the openings.

15.1 Recording sound

  • A common way to record sound starts with a microphone. A microphone transforms a sound wave into an electrical signal with the same pattern of oscillation.

15.1 Recording sound

  • In modern digital recording, a sensitive circuit converts analog sounds to digital values between 0 and 65,536.

15.1 Recording sound

  • Numbers correspond to the amplitude of the signal and are recorded as data. One second of compact-disk-quality sound is a list of 44,100 numbers.

15.1 Recording sound

  • To play the sound back, the string of numbers is read by a laser and converted into electrical signals again by a second circuit which reverses the process of the previous circuit.

15.1 Recording sound

  • The electrical signal is amplified until it is powerful enough to move the coil in a speaker and reproduce the sound.

15.2 Sound Waves

  • Key Question:
  • Does sound behave like other waves?
  • *Students read Section 15.2 BEFORE Investigation 15.2

15.2 Sound Waves

  • Sound has both frequency (that we hear directly) and wavelength (demonstrated by simple experiments).
  • The speed of sound is frequency times wavelength.
  • Resonance happens with sound.
  • Sound can be reflected, refracted, and absorbed and also shows evidence of interference and diffraction.

15.2 Sound Waves

  • A sound wave is a wave of alternating high-pressure and low-pressure regions of air.

15.2 The wavelength of sound

15.2 The Doppler effect

  • The shift in frequency caused by motion is called the Doppler effect.
  • It occurs when a sound source is moving at speeds less than the speed of sound.

15.2 The speed of sound

  • The speed of sound in air is 343 meters per second (660 miles per hour) at one atmosphere of pressure and room temperature (21°C).
  • An object is subsonic when it is moving slower than sound.

15.2 The speed of sound

  • We use the term supersonic to describe motion at speeds faster than the speed of sound.
  • A shock wave forms where the wave fronts pile up.
  • The pressure change across the shock wave is what causes a very loud sound known as a sonic boom.

15.2 Standing waves and resonance

  • Spaces enclosed by boundaries can create resonance with sound waves.
  • The closed end of a pipe is a closed boundary.
  • An open boundary makes an antinode in the standing wave.
  • Sounds of different frequencies are made by standing waves.
  • A particular sound is selected by designing the length of a vibrating system to be resonant at the desired frequency.

15.2 Sound waves and boundaries

  • Like other waves, sound waves can be reflected by surfaces and refracted as they pass from one material to another.
  • Sound waves reflect from hard surfaces.
  • Soft materials can absorb sound waves.

15.2 Fourier's theorem

  • Fourier’s theorem says any complex wave can be made from a sum of single frequency waves.

15.2 Sound spectrum

  • A complex wave is really a sum of component frequencies.
  • A frequency spectrum is a graph that shows the amplitude of each component frequency in a complex wave.

15.3 Sound, Perception, and Music

  • Key Question:
  • How is musical sound different than other types of sound?
  • *Students read Section 15.3 AFTER Investigation 15.3

15.3 Sound, Perception, and Music

  • A single frequency by itself does not have much meaning.
  • The meaning comes from patterns in many frequencies together.
  • A sonogram is a special kind of graph that shows how loud sound is at different frequencies.
  • Every person’s sonogram is different, even when saying the same word.

15.3 Hearing sound

  • The eardrum vibrates in response to sound waves in the ear canal.
  • The three delicate bones of the inner ear transmit the vibration of the eardrum to the side of the cochlea.
  • The fluid in the spiral of the cochlea vibrates and creates waves that travel up the spiral.

15.3 Sound

  • The nerves near the beginning see a relatively large channel and respond to longer wavelength, low frequency sound.
  • The nerves at the small end of the channel respond to shorter wavelength, higher-frequency sound.

15.3 Music

  • The pitch of a sound is how high or low we hear its frequency. Though pitch and frequency usually mean the same thing, the way we hear a pitch can be affected by the sounds we heard before and after.
  • Rhythm is a regular time pattern in a sound.
  • Music is a combination of sound and rhythm that we find pleasant.
  • Most of the music you listen to is created from a pattern of frequencies called a musical scale.

15.3 Consonance, dissonance, and beats

  • Harmony is the study of how sounds work together to create effects desired by the composer.
  • When we hear more than one frequency of sound and the combination sounds good, we call it consonance.
  • When the combination sounds bad or unsettling, we call it dissonance.

15.3 Consonance, dissonance, and beats

  • Consonance and dissonance are related to beats.
  • When frequencies are far enough apart that there are no beats, we get consonance.
  • When frequencies are too close together, we hear beats that are the cause of dissonance.
  • Beats occur when two frequencies are close, but not exactly the same.

15.3 Harmonics and instruments

  • The same note sounds different when played on different instruments because the sound from an instrument is not a single pure frequency.
  • The variation comes from the harmonics, multiples of the fundamental note.

Application: Sound from a Guitar



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