Fluids and Media (carrying displacement and/or pressure waves)
3D filled volumes: air (bomb blast), underwater
(sofar channel), earth (seismic waves)
3D elastic structures: buildings (ditto -- seismic)
2D surface waves and plate vibration: water, wood,
metal, membranes, earth surface
1D strings and columns: violin strings, bungee,
different piano strings, trees, air & water columns
Propagation of Sound Waves in nD Fluids or Elastic Materials
Free space: 1/r^2 attenuation, spectral damping
over distance, spectral time smear over distance
Partially enclosed spaces and waveguides: end reflections,
boundary absorption
Coupled waveguides: energy transfer between them,
radiation from ends
Fully enclosed spaces
Aperiodic Sound Sources (in free space, no waveguides)
Impulses (explosions, hand clap, balloon burst)
Free turbulence (wind, water, bowed desktop computers,
frictional motion)
Periodic Sound Sources from Mechanical Resonators
(with waveguides whose time delays match those of hearing range)
Impusively excited media (popped, struck, plucked)
-- externally applied momentary excitation
Mechanically-driven passive system (buzzed string,
voice) -- non-entrained, secondary excitation
where pitch is independent of resonator [vocal tract]
Mechanically-driven active system (blown, bowed)
-- entrained near-DC external energy source
excites system through coupled non-linear gating [glottis]
(always some identifiable non-linear means which
converts flow to vibration)
Resonator Extras:
Passive non-linear alterations (sitar, cymbal, gong,
non-uniform string)
Sympathetic excitation from another sound source
(tubes, strings) -- coupling via air or boundaries
(can include feedback, and can become self-sustained
active system with electronic amplification)
Fixed Resonator Complexes (instrument bodies)
Ttime-varying Resonator Complexes (vowels)
Entrained turbulence (whistling resonators, pulsed
noise when coupled to drive mechanisms)
Environmental Resonators:
(time delays are below hearing range, > 50 msec., e.g., large nD volumes,
elastic complexes)
Impusively excited medium (thunder, earthquakes,
knocking on a tree)
Mechanically Driven medium (helicopters, drilling
a building)
Sympathetically excited by another sound source(3D
= reverberation
chamber, 2D = echoes, plate reverb, 1D = viaduct comb filter, flutter
echoes)
[measure speed of sound]
[question: what's the biggest sound you ever heard?]
[contribute a sound to analyze]
[question: think of visible waves, waves that you can feel]
[view bow motion]
[test reverb from convolution]
[guess the type of instrument from world collection CD]