Sound and Hearing

dB = 20log(P1/Po)

P = amplitude of the sound wave

Po = reference pressure = 0.0002 dynes/cm2

Decibels compress the large range of possible pressures into more manageable units

Converts a range of 0.0002 (threshold pressure) to 2,000 (jet at take off) to a range ofr 0 to 140 dB

Decibels

_____________________________________________________Sound SPL (dB)_____________________________________________________Barely audible sound (threshold) 0Leaves rustling 20Quiet residential community 40Average speaking voice 60Loud music from radio/heavy traffic 80Subway 100The Rolling Stones 120Jet engine at takeoff 140_____________________________________________________

0

90

180

270

360

Sine Wave

90° out of phase

180° out of phase

Three primary dimensions of sensations associated with sounds with periodic waveforms

Pitch, loudness and timbre.

Pitch - sensation of "altitude" or "height" of a tone.

Loudness - sensation of "intensity" of a tone.

Timbre - quality of a sound.

Psychological Dimension Associated Physical Dimension

Pitch FrequencyLoudness AmplitudeTimbre Spectrum

Middle Ear

Inner Ear

Organ of Corti

When sound causes the basilar membrane to deflect upward, thereticular membrane moves up and inward causing the stereocilla to bend outward

Auditory Pathways

a. Primary and secondary auditory cortexb. Tonontopic organization - numbers are characteristic frequencies