Chapter 16 Sound

Section 1 - The Nature of Sound Sound - a disturbance that travels through a medium as a longitudinal wave Sounds are created by vibrations. Drum, guitar string, vocal cords Sound waves carry energy through medium (usually air)

The Nature of Sound (con’t.) Sound waves reflect off objects, diffract through narrow openings and around barriers, and interfere with others. Reflection – when they hit a hard surface – Echo (harder and smoother) Diffraction - bending of sound waves around barriers. Can hear around corners, or sounds outside room with door open Interference – Constructive and destructive

The Nature of Sound (con’t.) Speed of sound The speed of sound depends on the elasticity, density, and temperature of the medium the sound travels through. air - 343 m/s (@ 20oC) fresh water - 1,509 m/sec Lead – 1,210 m/s Aluminum – 5,000 m/s Elasticity - ability of a material to bounce back after being disturbed. Very elastic material , particles easily go back to their original positions, more elastic = faster.

The Nature of Sound (con’t.) Density- how much matter, or mass, there is in a given amount of space or volume – denser=Slower Temperature- warmer = faster Speed of sound in air @ 20oC – 343 m/s Speed of sound in air @ 0oC – 330 m/s

Section 2 - Properties of Sound Loudness – describes ones perception of the energy of a sound. The loudness of a sound depends on two factors: the amount of energy it takes to make the sound and the distance from the source of the sound. Larger amplitude of vibration - increase intensity

Properties of Sound (con’t.) Intensity - the amount of energy the wave carries per second through a unit area As one moves away from a sound source, loudness decreases because intensity decreases. (pg 547) Loudness is measured in decibels (dB) Table pg. 548 Each 10-dB increase in loudness represents a tenfold increase in the intensity of the sound.

Properties of Sound (con’t.) Pitch - perception of the frequency of a sound – Low frequency = low pitch Frequency - number of vibrations that occur per second Human hearing range 20 Hz to 20,000 Hz Ultrasound - frequency above human range Infrasound - frequency below human range In music, a pitch is a note. Larynx – (voice box) You change the pitch of your voice with your vocal cords.

Properties of Sound (con’t.) Doppler effect - the apparent change in frequency as a wave source moves in relation to the listener When a sound source moves, the frequency of the waves changes because of the motion of the source adds to the motion of the waves.

Properties of Sound (con’t.) Sonic boom – the release of energy when sounds waves overlap (pg. 551) Sonic Boom Video

Section 3 - Music Music - a set of notes (tones) that combine in patterns that are pleasing Noise - has no pleasing timbre and no identifiable pitch Interference occurs when two or more sound waves interact. The sound quality of musical instruments results from blending a fundamental tone with its overtones. Resonance also plays a role in the sound quality. (Timbre)

Music (con’t) Fundamental Tones and Overtones- A standing wave can only occur at a specific frequencies that are called natural frequencies. Every object has its own natural frequency. Spring demo Fundamental tone- The lowest natural frequency of an object Overtones- The object’s higher natural frequencies Diagram - fundamental frequency and overtones!!!!!!! (page 553)

Music (con’t) Resonance – affects the sound quality of a musical instrument by increasing the loudness of certain overtones. Ex. Opera singer shatters crystal glass

Instruments There are three basic groups of musical instruments: stringed instruments, wind instruments, and percussion instruments. Stringed instruments - strings vibrate, length, thickness, material and tension of string effects frequency. Hollow body increases loudness through resonance. Wind Instruments - players lips vibrate against mouthpiece (reed) creating a vibration. Air column inside instrument vibrates. Length of air column adjusted with valves or slides determines note.

Instruments Percussion Instruments - instruments vibrate when struck. Frequency effected by material used, size of instrument and tension of drum.

Instruments (con’t.) Acoustics - The study of how sounds interact with each other and the environment. Constructive and destructive interference Auditorium design Ear protection - destructive interference Reverberation – Echos of a sound are heard after the sound source stops producing sound waves. Acoustics is used in the design of concert halls to control reverberation and interference.

Instruments (con’t.) Beat - The regular changes in loudness of a sound when two sounds of different frequencies are played together. Piano tuner

Section 4 - How you hear sound The outer ear funnels sound waves, the middle ear transmits the waves inward, and the inner ear converts the sound waves into a form that travels to your brain. Ear Diagram pg. 559 Outer ear - ear canal, eardrum Middle ear - hammer, anvil & stirrup inner ear - cochlea (cavity filled with liquid & 10,000 tiny hairs)

How You Hear Sound (con’t.) Hearing loss caused by injury, infection, (birth defects,) and aging extended exposure to loud sounds Hearing aids amplify sounds and can restore some hearing.

Section 5 – Using Sound Echolocation - use of reflected sound waves to determine distances or to locate objects Some animals, including bats and dolphins, use echolocation to navigate and to find food. Ultrasound technologies such as sonar and ultrasound imaging are used to observe things that cannot be seen directly.

Using Sound (Con’t.) Sonar - a system of detecting reflected sound waves. (sound navigation and ranging) The sonar device measures the amount of time it takes to detect the reflected sound waves. The longer it takes to come back, the further away the object is. Using the speed of sound in the medium the distance is calculated. Calculation example.

Using Sound (Con’t.) Uses of ultrasound & infrasound dog whistle - ultrasound dolphins & whales - echolocation bats - echolocation toothbrush automatic focus camera

sonogram - ultrasound used to look inside human body to diagnose and treat medical conditions