Beats and Loudness Beats Beats are a special

Beats and Loudness

Beats • Beats are a special case of interference where two tones of slightly different frequencies are heard together. • The vibration of the forks will vary in and out of step, causing both constructive and destructive interference

Beats • The two sound waves and their slightly different frequencies will add into a new wave by the principle of interference • This new wave will have fade in and out as the two original waves go in and out of phase

Beats • Video on beats

Beats • To find the frequency of the beats, you need the difference between the two frequencies creating the beats • f 1 = 230 Hz and f 2 = 233 Hz. The frequency of the beats will be |f 1 – f 2| = |230 Hz – 233 Hz| = 3 Hz

Sound Pressure • Sound level is measured in decibels (d. B) • Sound level depends on the ratio of the pressure of a given sound to pressure of the most faintly heard sound (0 d. B) • Every time the decibels increases by 10, the sound level is multiplied by a factor of 10 • So the difference between 20 and 10 d. B in sound level is 10, and 30 to 10 d. B is 100

Resonance and Pipes • When you play music, you vibrate your lips which vibrates the instrument in resonance. • The length of the air column, the tube of the instrument, determines the resonance frequencies of the vibrating air.

Resonance and Pipes • A resonating tube with one end closed is called a closed-pipe resonator. • The sound wave goes through the pipe and bounces back inverted, creating a standing wave

Resonance and Pipes • A node is when the standing wave crosses itself • An anti-node is where the wave is on the opposite end of itself (crest and trough) • In a closed pipe, the end always has a node • Every 1/4 th wavelength produces either a node or antinode

Resonance and Pipes •

• Do the 3 problems on the worksheet • The Homework is pg 309 1 -4, due Thursday