1.1 Fundamentals of sound and acoustics

Sound waves are mechanical vibrations that travel through matter, transferring energy via particle oscillations. They're characterized by alternating compressions and rarefactions, requiring a physical medium to propagate. Unlike electromagnetic waves, sound can't travel through a vacuum.

Key properties of sound waves include frequency (pitch), wavelength, speed, and amplitude (loudness). The relationship between these factors is crucial for understanding sound behavior. Longitudinal waves, where particles move parallel to the wave direction, are typical for sound in gases and liquids.

Fundamentals of Sound and Acoustics

Nature of sound as mechanical wave

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• Sound propagates through physical medium transferring energy via particle oscillations (air, water, solids)
• Vibrations of particles in medium cause alternating compressions and rarefactions
• Requires physical medium unlike electromagnetic waves cannot travel through vacuum
• Classified as pressure wave due to alternating high and low pressure regions

Key properties of sound waves

• Frequency determines pitch perception measured in Hertz (Hz) number of oscillations per second
• Wavelength distance between consecutive peaks inversely proportional to frequency
• Speed of sound relationship $c = f \lambda$ (c: speed, f: frequency, λ: wavelength)
• Amplitude maximum particle displacement from equilibrium affects perceived loudness
• Sound pressure level measured in decibels (dB) logarithmic scale of intensity

Longitudinal vs transverse waves

• Longitudinal waves particle motion parallel to propagation direction (sound in air, water)
• Transverse waves particle motion perpendicular to propagation (waves on string, light)
• Media support:
  • Gases and liquids only longitudinal waves
  • Solids both longitudinal and transverse waves

Relationships in sound propagation

• Sound pressure local deviation from ambient pressure measured in Pascals (Pa)
• Particle velocity vector quantity describing speed and direction of particle oscillation
• Acoustic impedance medium's resistance to sound wave propagation $Z = p / v$ (Z: impedance, p: pressure, v: velocity)
• Plane waves pressure and particle velocity in phase
• Impedance crucial for understanding energy transfer reflection and transmission at boundaries