Introduction to Sound Waves

Introduction to Sound Waves

• Sound is a vibration that propagates as an acoustic wave through a transmission medium (gas, liquid, or solid).
• Audible sound frequencies range from 20 Hz to 20 kHz.
• Sound waves in air, at atmospheric pressure, have wavelengths from 17 meters to 1.7 centimeters.
• Frequencies above 20 kHz are called ultrasound and are not audible to humans.
• Frequencies below 20 Hz are called infrasound.

Definition of Sound

• Sound is defined as oscillations in pressure, stress, particle displacement, and particle velocity, propagated in a medium with internal forces (e.g., elastic or viscous), or the superposition of such propagated oscillation.
• The particles of the medium do not travel with the sound wave; the vibrations of particles transport the vibrations, but the average position of particles remains unchanged.

Sound Generation and Frequency

• Sound waves are generated by a vibrating sound source, such as a speaker diaphragm.
• Frequency is the number of oscillations per second and is measured in Hertz (Hz).
• Audible sounds range from 20 Hz to 20 kHz.
• Speed of sound (C) = wavelength (λ) * frequency (f)

Wavelength

• Wavelength (λ ) is the distance over which a wave property repeats itself.

Factors Affecting Speed of Sound

• Physical properties and ambient conditions affect the speed of sound.
• In 20°C air, sound speed is approximately 343 m/s (1,230 km/h) using the formula: v [m/s] = 331 + 0.6 T[°C]
• The speed of sound in gases depends on temperature.

Ultrasound

• Ultrasound refers to sound frequencies above 20 kHz.
• Diagnostic applications use frequencies between 1 MHz and 30 MHz.
• Manufacturers strive for higher frequencies (better resolution) while maintaining adequate visualization depth.

Wave Types

• Sound can propagate as longitudinal waves in air, water, and solids.
• Sound can also propagate as transverse waves in solids.
• Longitudinal plane wave
• Transverse plane wave

Sound Propagation Behavior

• The behavior of sound propagation is affected by:

  • Density and pressure of the medium
  • Motion of the medium
  • Viscosity of the medium

• A complex relationship between density, pressure, and temperature of the medium determines the speed of sound.

• Motion of medium

  • Increases speed if sound and wind are in the same direction.
  • Decreases speed if sound and wind are in opposite directions.

• Medium viscosity determines the rate of sound attenuation. For many media (air or water), attenuation due to viscosity is negligible.

General Properties

• Sound can travel through all forms of matter (gases, liquids, solids, plasmas)
• Sound cannot travel through a vacuum.
• Sound waves are often simplified to sinusoidal plane waves characterized by frequency, wavelength, amplitude/intensity, speed of sound, and direction.

This quiz explores the fundamental concepts of sound waves, including their definitions, properties, and generation. You'll learn about frequencies, the range of audible sounds, and the behavior of sound in different mediums. Test your knowledge on how sound is characterized and transmitted.