1. When Intensity doubles
    ouput level is increased by 3
  2. When pressure is doubled
    output level is increased by 6
  3. Purpose of sound measurement
    • 1. To calibrate audiometers
    • 2. Assess background levels in audiometric test rooms
    • 3. Identify hazardous noise exposure levels
  4. Sound level meter (SLM)
    • • Picks up sounds of all frequencies within a certain range
    • • Determines the magnitude of the sound in dB SPL
  5. Linear Setting
    SLM measures overall SPL of sounds picked up by the microphone
  6. Weighting Fliters
    De-emphasizes low frequency sounds
  7. octave-band analyzer
    • – Set of selectable Band-Pass filters
    • – Used to determine dB present for a given frequency bandwidth
  8. C-weighting
    Practically linear, virtually no weighting of spectrum in the greatest part of the audible range
  9. B-weighting
    some reduction of sound level at very low and very high frequencies
  10. A-weighting
    • dramatic reduction of low frequency sound level
    • – e.g., sounds of 100 Hz are reduced by about 20 dB
  11. Weighting Networks
    • A and C scales are most commonly used in noise measurement
    • A scale used to measure speech sound-closest to human hearing
  12. Decible
    • a relative measure of sound level
    • – There is always a reference value
    • – Intensities/Pressure are compared to a standard reference value in the form of a ratio or fraction
    • – Physical magnitudes are stated in relation to a value that has meaning to us• See next slide for example
  13. Equal ratios
    become equal intervals on logarithmic scale
Card Set
unit 3