16.2: Intensity and sound level (2023)

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Summary of Intensity sound intensity human perception of sounds wave properties the human ear decibel key points key terms Videos
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    learning goals

    • Calculate the sound intensity from the power

    Summary of Intensity

    Sound intensity is the power per unit area carried by a wave. Power is the rate at which energy is transferred from a wave.

    Sound intensity and decibels

    The equation used to calculate this intensity I is: I\(\mathrm{I=\frac{P}{A}}\) where P is the power flowing through the area A. The SI unit for intensity is the watt per square meter or Wm2Wm2. This is the general intensity formula, but let's look at it from a solid perspective.

    (Video) 14.2 Sound Intensity and Intensity Level

    sound intensity

    The intensity of the sound can be determined from the following equation: \(\mathrm{I=\frac{Δp^2}{2ρv_w}}\). Δp - pressure or amplitude changeρ - density of the material through which the sound is propagatingvC– Observed speed of sound. Now we have a way to calculate the sound intensity, so let's talk about the observed intensity. The change in pressure, the amplitude, is proportional to the intensity, so it's safe to say that the more your sound wave vibrates, the more intense your sound will be. This illustration shows this concept.

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    16.2: Intensity and sound level (2)

    sound intensity: Diagrams of overpressures in two sound waves of different intensities. The loudest sound is produced by a source that has larger amplitude vibrations and greater maximum and minimum pressure. Because the pressure is greater at the loudest sound, it can exert greater forces on the objects it encounters.

    While units of sound intensity are technically watts per square meter, they are much more commonly known as decibels, dB. A decibel is a ratio of the observed amplitude or volume level to a reference, which is 0 dB. The equation for this is: \(\mathrm{β=10 \log 10} \frac{I}{I_0}B}\)–Decibel level I - observed intensity I0– reference intensity. For more information about decibels, see Decibel Atom.

    As a guide to intensity levels, below is a list of some of the different intensities:

    • 0 dB, yo = 1 × 10-12–> Human hearing threshold
    • 10 dB, yo = 1 × 10-11–> rustling of leaves
    • 60 dB, yo = 1 × 10-6-> normal conversation
    • 100 dB, yo = 1 × 10-2–> Loud sirens
    • 160 dB, yo = 1 × 104-> Your eardrum has just burst

    human perception of sounds

    The study of the human perception of sound is called psychoacoustics.

    (Video) Sound: Crash Course Physics #18

    to develop skills

    • Explain how humans perceive frequency.

    The study of the human perception of sound is called psychoacoustics. Many factors influence hearing, including wave characteristics, sensory and brain processes. First, the wave must be generated and have a specific wavelength and frequency. The sound wave then reaches the human ear and is processed by many areas. Eventually, the sound wave passes through the ear and reaches the human brain, where more happens. You may think that you hear sounds right away, but actually it goes through many steps first.

    wave properties

    We won't go into too much detail about the physical properties of the wave as they are beyond the scope of this atom, but remember:

    • Humans perceive frequency as pitch;
    • The intensity of the sound is the amplitude;
    • Humans can only hear a specific range of sounds, typically 20 Hz to 20,000 Hz;
    • The factors that affect a sound are its intensity, frequency, and overtones (which are like interference or background noise).
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    the human ear

    The human ear consists of three main sections as shown in:

    16.2: Intensity and sound level (3)

    (Video) 16.3 Sound Intensity

    the human ear: A detailed diagram of the human ear.

    1. the outer ear
    2. the middle ear
    3. the inner ear

    Let's start where a sound wave would begin and follow it on its journey from the outside of the ear to the brain. When you look into someone's ear, all you really see is the pinna, the outermost part of the ear. Collect and concentrate the sound wave. The wave then travels through the ear canal to the eardrum. Sound waves cause the eardrum to vibrate. So we're in the middle ear, which is made up of three very, very small bones: the malleus, the incus, and the stirrup. These can also be called hammer, anvil or stirrup. These three bones transmit the signal to the elliptical window. This is the beginning of the inner ear. Sound waves are then directed from the elliptical window through the semicircular canals of the inner ear, the cochlea, and the fluid-filled auditory nerve. This fluid allows the body to sense movement and maintain balance. Your cochlea is shaped like a snail and lined with tiny hairs. Depending on the frequency, these hairs vibrate differently. These vibrations deliver electrical impulses to the auditory nerve and are then sent to your brain where they are perceived as sound. So while this seems to be happening fairly quickly, sound waves have a long way to go before you hear anything!

    decibel

    The decibel is a logarithmic unit used to quantify sound levels by comparing a physical quantity to a reference level.

    to develop skills

    • Identify how the decibel is quantified in acoustics

    The decibel, dB, is commonly used to quantify sound levels, although it is not a unit of sound but a unit of pressure. The decibel is a logarithmic unit that represents the relationship between a physical quantity and a reference level. It's a tenth Bel, named after the inventor of the telephone, Alexander Graham Bell. The word decibel comes from the prefix deci, which is 1/10 of the word before it. For more information about unit conversions, see Atomic Unit Conversions. While the decibel can be used to talk about many different topics, in this atom we cover its use in acoustics and sound level.

    In acoustics, the decibel is quantized relative to a reference defined at a sound pressure level of 20 micropascals, called 0 dB. This reference level is a typical threshold of human auditory perception. The following equation is used to calculate the sound pressure level or amplitude: \(\mathrm{amplitude[dB]=20 \log 10}\frac{s}{s_o}}\)sÖis the reference pressure, which is 20 micropascals or 0 dB, and s is the observed sound pressure. The human ear has a standard sound threshold of 120 dB, which is about 10 logarithmically12. This is a standard threshold, but it is also frequency dependent. Loudness is a frequency-related measure of sound intensity and is referred to as the A-weighted decibel, dB(A) or Fon. This figure shows the Fletcher-Munson diagram showing the different sound frequencies and decibels perceived as the same by the human ear.

    (Video) 16.2 The Speed of Sound

    16.2: Intensity and sound level (4)

    The Fletcher-Munson letter: Intensity conformed to Fletcher-Munson contours. The phones are labeled in blue.

    key points

    • The intensity of the sound can be determined from the following equation: \(\mathrm{I=\frac{Δp^2}{2ρv_w}}\). Δp – change in pressure or amplitude ρ – density of the material through which the sound is propagating vC– Observed speed of sound.
    • The greater the vibration of the sound wave, the more intense the tone.
    • While units of sound intensity are technically watts per square meter, they are much more commonly known as decibels, dB.
    • Humans perceive frequency as pitch. Sound intensity is what humans can hear and is usually just a specific range of sounds, typically 20Hz to 20,000Hz. The factors that go into a sound are its intensity, frequency and harmonics (which are like interference or noise). .
    • Your ear is made up of three main sections: the inner, middle, and outer ear.
    • Your cochlea, located in your inner ear, not only transmits sound waves to your brain, but also contains a fluid that helps humans balance.
    • In acoustics, the decibel is quantized relative to a reference defined at a sound pressure level of 20 micropascals, called 0 dB.
    • The following equation is used to calculate the sound pressure level or amplitude: \(\mathrm{amplitude[dB]=20 \log_{10} \frac{s}{s_o}}\). \(\mathrm{s_o}\) is the reference pressure, which is 20 micropascals or 0 dB, and s is the observed sound pressure.
    • The human ear has a standard sound threshold of 120 dB, which is approximately 1012 logarithmically. This is a standard threshold, but it is also frequency dependent. Loudness is a frequency-related measure of sound intensity and is referred to as the A-weighted decibel, dB(A) or Fon.

    key terms

    • decibel: A common measure of sound intensity, which is one tenth of a bel on the logarithmic intensity scale. It is defined as \(\mathrm{dB=10 \log_{10}(P_1/P_2)}\), where \(\mathrm{P_1}\) and \(\mathrm{P_2}\) are the relative powers of the sound
    • Amplitude: The maximum absolute value of a variable quantity.
    • eardrum: A thin membrane that separates the outer ear from the middle ear and transmits sound from the air to the hammer.
    • SnailThe complex, helical, tapered conical cavity of the inner ear where sound vibrations are converted into nerve impulses.
    • Telephone: Unit of apparent loudness, numerically equal to the intensity in decibels of a 1000 Hertz tone considered to be as loud as the tone being measured.

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