Sound Characteristics Loudness Amplitude Pitch frequency Wave Formulas

Sound

Characteristics • Loudness --> Amplitude • Pitch -->frequency

Wave Formulas

Speed of Sound • The speed of sound in air changes with temperature. • The speed at 0 o. C is 331 m/s for dry air • It increase by 0. 6 m/s for each degree Celsius above zero.

Echoes • An echo is a reflected sound wave • An echo is sent from and detected at the same location • An echo must travel the distance to the barrier two times to get back to the detector

Doppler Effect • • • v = velocity of sound in air vs = velocity of source (toward is +) vd = velocity of detector (toward is +) f = frequency emitted f ' = frequency detected

Sound Intensity 1 E -12 W/m 2 • = decibels (d. B) • P = Power of source (watts) • I = intensity (W/m 2) • R= distance from source (m) • Io = 10 -12 W/m 2 threshold of hearing

Concepts • A 20 d. B increase = 10 times the pressure • A 10 d. B increase = twice the loudness

Remember units! • • • Frequency -- Hertz (cycles/sec) Period -- seconds Wavelength -- meters Wave speed -- m/s Intensity -- W/m 2 Sound intensity level -- decibels (d. B)

Harmonics and Overtones st 1 nd 2 harmonic = fundamental (f 1) frequency harmonic = st 1 overtone (f 2) 3 rd harmonic = 2 nd overtone (f 3) 4 th harmonic = 3 rd overtone (f 4) and so on. . .

Resonance and Fundamental Frequency in air columns (tubes) • Open ends have an antinode • Closed ends have a node • fundamental frequency is lowest frequency possible (lowest frequency longest wavelength) • use length of pipe to calculate wavelength by relating the length to the number of wavelengths formed

Resonance in air columns (tubes) Remember: open end antinode, closed end node • Fundamental frequency (1 st harmonic) has 1 node • 1 st overtone (2 nd harmonic)-2 nodes • 2 nd overtone (3 rd harmonic)-3 nodes • and so on … • Assume speed of sound in air to be 343 m/s unless told otherwise (i. e. sound not in air or you are given a specific temp of air).

Resonance on Strings • Fundamental frequency has ONE antinode (L = /2) (or segment) • 2 nd harmonic (1 st overtone) – 2 antinodes (L = ) (or segments) • 3 rd harmonic (2 nd overtone) - 3 antinodes ( L = 3 /2) (or segments) • 4 th harmonic (3 rd overtone) - 4 antinodes ( L = 2 ) (or segments) • and so on…

Beats • Beats occur due to interference patterns between sound waves of different frequencies. • Sounds with frequencies separated by 7 Hertz or less will produce beats that can be detected by the human ear.