15.2 The Sound of Music

Middle of 19th century German Hermann Helmholtz and English Lord Rayleigh studied how human voices produced sounds studied how instruments produced sounds studied how human ears detected sounds

Sources of Sound Vibrating objects vocal cords –vibrate at air passes them brass instruments –lips of performer vibrate reed instruments –reed vibrates as air is blown across

Open pipes –air column vibrates stringed instruments –string, sound board and air vibrates

Resonance What are the results of just the mouth piece of an instrument? Attach the rest of the instrument are what are the results? It is louder because of resonance

The definition for resonance is to cause a vibration of a natural rate by a vibrating source having the same frequency –piano string vibrates as someone nearby sings –air column in organ vibrates

Closed-pipe resonator When one end of a pipe is closed –organ –slide whistle –flute –large seashell

When a wave travels down the pipe and the back up the waves reinforce each other producing a standing wave

Open-pipe Resonator A tube with both ends open –saxophone –flute –pipe organ overheads

The Quality of Sound The difference is sound from one instrument to another timbre sound quality depending upon both intensity and frequency

Beat is a pulsing variation in loudness because of the superposition of two waves dissonance unpleasant sound consonance a pleasant sound fundamental the lowest note possible harmonics whole number multiplies of the fundamental