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Bel

Bel. One Bel = log (I 1 /I 0 ), where I 1 is the absolute measured power, and I 0 is a reference power. Reference used is usually the least sound level that can be detected. Normal human hearing in terms of bels. Least amount of sound power that can be detected: 0 bel

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Bel

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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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