Sound W

aves

• Production–Vibrating Objects

•Tuning fork–Compression

–Rarefaction

•What type of wave is sound?

Sound W

aves

• Characteristics–Pitch

• Shepard tone (auditory illusion)Superposition of waves an octave apart. Makes it sound like the pitch is constantly increasing.

• Doppler Effect

–Human Hearing–20-20,000 Hz

• Infrasonic• Ultrasonic ‘Stealth tones’

Intensity

• Relationship between distance from source and intensity?

• Relative intensity (loudness)–Decibels (dB)

• Logarithmic scale

• 10dB 20dB increase of 10X

24

PowerIntensity

rπ=

Intensity (W/m2) Decibel level (dB) Examples

1.0x10-12 0 Threshold of hearing1.0x10-11 10 Rustling leaves1.0x10-10 20 Quiet whisper1.0x10-9 30 Whisper1.0x10-8 40 Mosquito buzzing1.0x10-7 50 Normal conversation1.0x10-6 60 Air conditioning at 6 m1.0x10-5 70 Vacuum cleaner1.0x10-4 80 Busy traffic, alarm clock1.0x10-3 90 Lawn mower1.0x10-2 100 Subway, power motor1.0x10-1 110 Auto horn at 1m1.0x100 120 Threshold of pain1.0x101 130 Thunderclap, machine gun1.0x103 150 Nearby jet engine

Other S

tuff

• Natural Frequency–Resonance

• Tacoma Narrows Bridge• Beats

–Difference in the frequency

• Hearing–Eardrum–Hammer, anvil, stirrup–Cochlea–Auditory nerve

Other S

tuff

• Natural Frequency–Resonance

• Tacoma Narrows Bridge• Beats

–Difference in the frequency

• Hearing–Eardrum–Hammer, anvil, stirrup–Cochlea–Auditory nerve