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Understanding Sound Measurement: Bel, Decibel & Intensity Levels

Learn about Bel, Decibel, Intensity Levels, and how sound power and pressure are measured in dB. Explore the basics of sound intensity, pressure levels, and their relevance to human hearing and ear damage.

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Understanding Sound Measurement: Bel, Decibel & Intensity Levels

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  1. Bel One Bel = log (I1/I0), where I1 is the absolute measured power, and I0 is a reference power. Reference used is usually the least sound level that can be detected.

  2. Normal human hearing in terms of bels • Least amount of sound power that can be detected: 0 bel • Sounds that are damaging to the ear: 14 bels

  3. Decibel (dB) One Decibel = one-tenth of a Bel, i.e. 1 Bel = 10 Decibels Therefore dB = 10 log (I1/I0)

  4. Normal human hearing in terms of decibels • Least amount of sound power that can be detected: 0 dB • Sounds that are damaging to the ear: 140 dB

  5. Intensity expressed in terms of power with a reference power of 10-12 W/m2 or 10-16 W/cm2 is called INTENSITY LEVEL (dB IL) INTENSITY LEVEL

  6. Pressure and Intensity • Pressure  Square root of Intensity P  I OR P2  I

  7. Normal human hearing in terms of pressure • Least amount of sound pressure that can be detected: 0.0002 dynes/cm2, or 20µPa (20 x 10-6 Pa) • Sounds that are damaging to the ear: 2 x 108µPa

  8. Decibel: Expressed in terms of pressure Decibel = 20 log (p1/p0) where p1 is the absolute pressure of sound p0 is the reference pressure

  9. SOUND PRESSURE LEVEL Intensity expressed in terms of pressure with a reference pressure of 20 micropascals (20 µPa) or 0.0002 dynes/cm2is called SOUND PRESSURE LEVEL (dB SPL) One µPa = 10-6 pascals

  10. Decibel questions • Two types of questions: • What is the intensity in dB IL or dB SPL of a sound with an absolute power of X w/m2 or absolute pressure of X µPa? • What is the absolute power or pressure of a sound with an intensity of X dB IL or X dB SPL?

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