Key Terms
Sound
A disturbance of matter transmitted outward from its source. It is a wave.
Pitch
Perception of frequency. Loudness: perception of intensity; also affected by frequency.
Speed depends on two things
Rigidity (or compressibility) and density.
Formula for air
V = 331 x sqrt(T / 273 K), where T is in kelvin.
Intensity (I)
Power per unit area carried by a wave. I = P / A Units: W/m^2
Sound intensity level (beta) in decibels
Beta = 10 x log(I / I_0)
Doppler effect
An alteration in observed frequency due to relative motion between source and observer. Doppler shift: the actual numeri
Bow wake
The same phenomenon for any wave when the source exceeds wave speed. V-shaped water wake behind a boat is a bow wake.
Resonance
Driven oscillation at a system's natural frequency. Energy transfers rapidly at resonance; amplitude grows until the sys
Antinode
Point of maximum displacement. Occurs at open ends of tubes (motion unconstrained).
Resonant frequencies
F_n = n x (v / 2L), where n = 1, 2, 3, 4 ... (ALL integers)
Fundamental
Lowest resonant frequency (first harmonic). Overtones: all resonant frequencies above the fundamental.
Normal range
20 Hz to 20,000 Hz (20 kHz). Below 20 Hz = infrasound (can sometimes be felt, not heard).
Dogs
Up to 30,000 Hz. Bats and dolphins: up to 100,000 Hz.
Presbycusis
Age-related hearing loss; progressively worse at higher frequencies.