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Metropolitan Community College

Explore the nature of sound waves, loudness versus distance, the human ear, frequency and sound, dB measurements, SPL meter usage, microphone sensitivity, pickup patterns, and more in audio production engineering.

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Metropolitan Community College

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  1. MetropolitanCommunityCollege Audio Video Production Engineering Part 1 Audio This PowerPoint and other resources may be found at: http://faculty.mccneb.edu/ccarlson/vaca1010.htm Rev. 6.4f

  2. Nature of Sound Waves • Sounds in air are commonly produced Vocal cords, Speakers, Instruments, etc. 2

  3. Air particles • As the sound source pushes against air particles they are compressed. • As the sound source moves away they are rarefied. 3

  4. 4

  5. Loudness VS Distance • Loudness follows an Inverse-Square Law • Intensity of sound is inversely proportional to the square of the distance from the source. 5

  6. Sound and Hearing • The Human Ear • Outer Ear • Middle Ear • Inner Ear 6

  7. Labyrinth Pinna Courtesy of Dr. John S. Oghalai Used by permission 7

  8. Courtesy of Dr. John S. Oghalai Used by permission 8

  9. Frequency and Sound 960 Hz • 20 Hz 60 Hz 1920 Hz 120 Hz 3840Hz 240 Hz 7680 Hz 480 Hz 15360 Hz 9

  10. 10

  11. Wavelength & Frequency 11

  12. Amplitude & Phase 12

  13. 13

  14. Decibel • Unit of measure Bel • Based on ratio • Used for both Acoustic and electrical applications 14

  15. dB formulas • Power • dB = 10 log (P1/P0) • Voltage and Acoustic • dB = 20 log (E1/E0) 15

  16. dB as Unit of Measure • Requires a reference • 3 and 10 rule (power) • 6 and 20 rule 16

  17. 3 & 10 and 6 & 20 Rule 17

  18. Add and Subtract dB 18

  19. dB Standards • 0 dBW = 1W • 100W amplifier is 20dBW • 1000W amplifier is 30dBW 19

  20. dB Standards • 0 dBm = 1mw>600 Ohm load (.775 V) • 0 dBu = .775 V • 0 dBv = .775 V • 0 dBV = 1 V 20

  21. Click chart for sound 21

  22. SPL Meter • Microphone Amplifier Meter • A Weighting filter inverse of equal loudness contours • B & C Weighting high end of equal loudness contours 22

  23. Weighting Networks • A weighting 10 – 55 dB • B weighting 55 – 85 dB • C weighting 85 – 140 dB 23

  24. Weighting Chart 24

  25. Loudness of sound (dB) • Threshold of hearing 0 • Normal conversation 60 • City traffic inside car 85 • Sustained exposure results in hearing loss 85-90 • Power Mower 107 25

  26. Loudness of sound (dB) • Rock concert front row 115 • Pain begins 120 • Jet engine @ 100’ 140 • Death of hearing tissue 180 • Loudest sound possible 194 26

  27. dB Meter • Specialized AC Meter with scale calibrated in dB 27

  28. VU Meter • Much the same as dB meter • Calibrated 0VU = __dB • Response peak to average • Analog, LED, Electronic display 28

  29. Noise InducedHearing Loss • Base level 85 dB for 8 hrs • Each 3 db increase 1/2 time • “A” weighting measurement • Most sensitive at 4 KHz • 40 yrs @ 85dB = NIHL 8% 29

  30. 30

  31. End Week 1 • Review Week 2 31

  32. 32

  33. Magnetic Polarity • Like Poles Repel • Unlike Poles Attract 33

  34. 34

  35. Electromagnetic Interference • A Moving magnetic field across a stationary conductor has same effect as a moving conductor in a stationary magnetic field 35

  36. Magnetic field is generated around wires carrying current • Magnetic polarity changes as direction of current flow changes 36

  37. Capacitors • Two metallic plates • Insulated from each other • (insulation called dielectric) 37

  38. 38

  39. Capacitors store electrons • Capacitors behave much like a water tower • Filling the water tower is like charging a capacitor • Using the water is like discharging a capacitor 39

  40. Unit of Measure • The Farad is the unit of measure. Typical values are Micro Farad or Pico Farad. Larger values store more electrons. 40

  41. Capacitor Behavior • Capacitors block DC current and pass AC current 41

  42. Capacitor Behavior 42

  43. Dynamic Capacitor • Microphone Microphone RibbonMicrophone 43

  44. A microphone sensitivity specification tells how much electrical output (in thousandths of a volt or "millivolts") a microphone produces for a certain sound pressure input in dB SPL (usually 94dB SPL) 44

  45. If two microphones are subjected to the same sound pressure level and one puts out a stronger signal (higher voltage), that microphone is said to have higher sensitivity. 45

  46. Microphone Pickup Patterns • Omni-directional: picks up sound from all directions • Directional: picks up sound from one direction • Bi-directional: picks up sound from two directions 46

  47. Pick-up Patterns 47

  48. Polar Pattern 48

  49. Directional Microphones • Directional Microphones called Cardioid, Supercardioid, Hypercardioid 49

  50. Directional Microphones • Proximity effect • Do not “reach” further • Generally do not have as smooth of a response curve as Omni-directional 50

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