Sound waves are the foundation of all music and audio. They have specific physical properties that determine how we perceive sound. Understanding these properties is crucial for anyone working with audio or creating electronic music.

Wavelength, frequency, and amplitude are key characteristics of sound waves. These properties influence pitch, loudness, and timbre. Sound waves travel through different mediums at varying speeds, affecting how we hear and experience sound in different environments.

Physical Properties of Sound Waves

Characteristics of sound waves

• Wavelength measures the distance between two corresponding points on adjacent waves (crest to crest or trough to trough) in meters (m) or feet (ft)
  • Longer wavelengths correspond to lower frequencies and lower pitch sounds (bass notes)
  • Shorter wavelengths correspond to higher frequencies and higher pitch sounds (treble notes)
• Frequency quantifies the number of wave cycles passing a fixed point per second, measured in Hertz (Hz)
  • Higher frequencies (1000 Hz) correspond to shorter wavelengths and higher pitch sounds
  • Lower frequencies (100 Hz) correspond to longer wavelengths and lower pitch sounds
• Amplitude determines the maximum displacement of a wave from its equilibrium position, measured in decibels (dB)
  • Higher amplitudes result in louder sounds (jet engine)
  • Lower amplitudes result in quieter sounds (whisper)

Sound propagation through mediums

• Sound waves require a medium (air, water, solid materials) to propagate and cannot travel through a vacuum (outer space)
• Speed of sound varies depending on the medium's properties
  • Air: approximately 343 m/s at room temperature (20°C)
  • Water: approximately 1,480 m/s, about 4.3 times faster than in air
  • Solid materials: varies based on the material's density and elasticity (steel: ~5,100 m/s, wood: ~3,500 m/s)
• Sound waves transfer energy through the medium by causing particles to oscillate
  • Particles compress and expand, creating areas of high (compressions) and low (rarefactions) pressure that propagate the wave

Types of Sound Waves and Their Properties

Longitudinal vs transverse waves

• Longitudinal waves have particles oscillating parallel to the direction of wave propagation
  • Compressions and rarefactions occur along the direction of travel
  • Examples include sound waves in air and water
• Transverse waves have particles oscillating perpendicular to the direction of wave propagation
  • Crests (high points) and troughs (low points) occur perpendicular to the direction of travel
  • Examples include waves on a string and electromagnetic waves (light)
• Sound waves are primarily longitudinal waves, but transverse waves can occur in solid materials due to shear stress

Wave properties and sound perception

• Pitch is determined by the frequency of the sound wave
  1. Higher frequencies (2000 Hz) are perceived as higher pitch sounds (soprano voice)
  2. Lower frequencies (200 Hz) are perceived as lower pitch sounds (bass guitar)
  • Relationship: $pitch \propto frequency$
• Loudness is determined by the amplitude of the sound wave
  1. Higher amplitudes (120 dB) are perceived as louder sounds (thunder)
  2. Lower amplitudes (20 dB) are perceived as quieter sounds (rustling leaves)
  • Relationship: $loudness \propto amplitude$
• Timbre is the characteristic quality of a sound that distinguishes it from other sounds with the same pitch and loudness
  • Determined by the harmonics (integer multiples of the fundamental frequency) present in the sound wave
  • Allows differentiation between instruments playing the same note (piano vs guitar playing middle C)