Sound Frequencies 5.3

Sound Frequencies

Introduction to Sound Waves

  • Sound waves are introduced into a medium by a vibrating object.

    • Examples of vibrating objects include:

      • Vocal cords of a person.

      • Strings on musical instruments like guitar or violin.

  • Particles of the medium vibrate at a given frequency when a wave passes through.

Frequency Definition

  • Frequency: Refers to how often the particles vibrate when a wave passes through the medium.

    • Common unit for frequency: Hertz (Hz)

      • 1 Hertz = 1 vibration per second.

Nature of Sound Waves

  • Sound is also a pressure wave.

    • Detectors can measure changes in pressure, resulting in visual oscillations of high and low pressure.

      • Compressions: High pressure points in sound waves.

      • Rarefactions: Low pressure points in sound waves.

  • Frequency is determined by the number of vibrations, compressions, or rarefactions per unit of time.

  • Frequency directly affects pitch and perception of sound.

Human Hearing Range

  • Humans can detect sound waves from:

    • 20 Hz (lower limit) to 20,000 Hz (upper limit).

  • Infrasound: Frequencies below 20 Hz (inaudible to humans).

  • Ultrasound: Frequencies above 20,000 Hz (also inaudible).

Animal Hearing Abilities

  • Different animals have varying detection abilities for sound frequencies:

    • Dogs: Can hear up to 45,000 Hz (higher pitched sounds).

    • Bats: Can detect up to 20,000 Hz (used for navigation and hunting).

    • Elephants: Can detect infrasound, hearing as low as 5 Hz.

Pitch of Sound

  • The perception of frequency relates to pitch:

    • High-pitched sounds: Higher frequencies.

    • Low-pitched sounds: Lower frequencies.

  • Musically trained individuals use frequency and pitch to create music.

Musical Frequencies

  • Octaves: Series of eight notes between two notes.

    • Example with the C scale:

      • Lower C and the next higher C.

      • Higher C has twice the frequency of the lower C.

    • This creates a 2:1 ratio between notes of an octave.

Harmonics in Music

  • Harmonics: Waves with frequencies that are positive integer multiples of the original wave.

    • Original wave: Frequency = n.

    • Second harmonic: Frequency = 2n.

    • Third harmonic: Frequency = 3n, and so on.

  • Harmonics create harmony when used together in music.

    • The original wave is referred to as the first harmonic, with subsequent waves being the second, third, fourth harmonic, etc.