15.3 Sound, Perception, and Music

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. 2

Chapter 15 Vocabulary Terms acoustics beats cochlea consonance decibel dissonance Doppler effect Fourier’s theorem frequency spectrum microphone musical scale note octave pitch pressure reverberation rhythm shock wave sonogram speaker stereo subsonic supersonic

Inv 15.3 Sound, Perception, and Music Investigation Key Question: How is musical sound different than other types of sound? 4

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 Patterns of frequency The brighter the sonogram, the louder the sound is at that frequency.

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.

Sound from a Guitar The sound of an acoustic guitar is shaped by sound waves bouncing around inside the guitar, as well as the vibration of the top. Because the shape of the guitar is irregular, there are many resonances. In general, large-bodied guitars have stronger long-wavelength, low-frequency sounds, and are louder. Small-bodied acoustic guitars often lack low frequencies in their range of sounds.