# Unit 5, Chapter 15

 Date conversion 12.12.2016 Size 13,76 Kb.

## 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 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 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.