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Exam 1997 Question 5

"Explain the difference between sound intensities measured in dBSPL and in dBHL. Describe the procedure by which a pure-tone audiogram is measured for a listener. Why is the ear more sensitive to pure tones with frequencies between 1000Hz and 4000Hz?"

20 things you should mention:

  • Measures
    • dBSPL is absolute intensity measure
    • re: 20 ÁPa
    • same reference at all frequencies
    • dBHL is relative measure
    • re: ISO standard values
    • of threshold of audibility
    • of young, normally hearing adults
    • different at different frequencies
  • Pure-tone audiogram
    • in quiet room
    • over headphones (typically)
    • present pure tones
    • step in level down to threshold
    • signal from listener
    • 10dB down 5dB up
    • repeat until consistent result
    • convert threshold in SPL to HL
    • HL = SPL - ISO
  • Greater sensitivity
    • resonances in external auditory meatus
    • typical frequency response
    • resonance in ossicular chain

© 2000 Mark Huckvale University College London