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Lesson 3 - Logs and Levels

Lesson 3 - Logs and Levels. Math Prereqs. Examples. Without using your calculator, find the following: (log 10 (2) = 0.30) log 10 (10 -3 ) = log 10 (1 x 10 12 ) = log 10 (2 x 10 12 ) = log 10 (200) = log 10 (200) - log 10 (10) = log 10 (2 10 ) =. -3, 12, 3.6, 2.3, 1.3, 3.

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Lesson 3 - Logs and Levels

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  1. Lesson 3 - Logs and Levels Math Prereqs

  2. Examples • Without using your calculator, find the following: (log10(2) = 0.30) • log10(10-3) = • log10(1 x 1012) = • log10(2 x 1012) = • log10(200) = • log10(200) - log10(10) = • log10(210) = -3, 12, 3.6, 2.3, 1.3, 3

  3. Pitch is frequency Middle C on the piano has a frequency of 262 Hz. What is the wavelength (in air)? 1.3 m

  4. Intensity of sound • Loudness – intensity of the wave. Energy transported by a wave per unit time across a unit area perpendicular to the energy flow.

  5. Sound Level - Decibel

  6. Why the decibel? • Ears judge loudness on a logarithmic vice linear scale • Alexander Graham Bell • deci = • 1 bel = 10 decibel

  7. Reference Level Conventions

  8. Historical Reference • 1 microbar • 1 bar = 1 x 105 Pa • 1 mbar = 1 x 105mPa • So to convert from intensity levels referenced to 1 mbar to intensity levels referenced to 1 mPa, simply add 100 dB

  9. Sound Pressure Level Mean Squared Quantities: Power, Energy, Intensity “Intensity Level” Root Mean Squared Quantities: Voltage, Current, Pressure “Sound Pressure Level”

  10. Subtracting Intensity Levels

  11. Two Submarines • If a noisy sub was emitting a source level of 140 dB and a quiet sub was emitting a source level of 80 dB, • What is the difference in noise levels? • what does this mean in terms of relative intensity and acoustic pressure?

  12. Adding Levels

  13. Total Noise • On a particular day, noise from shipping is 53 dB and noise from rain and biologics is 50 dB. What is the total noise level from the two sources?

  14. Adding Equal Noise Levels • Two transducers are both transmitting a source intensity level of 90 dB. What is the total source intensity level?

  15. Two Submarines • If a noisy sub was emitting a source level of 140 dB and a quiet sub was emitting a source level of 80 dB, what is the total noise from the two submarines?

  16. Backups

  17. Reference Values Air: Water:

  18. Sound Pressure Level

  19. Subtracting Intensity Levels

  20. Addition

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