2014 Inner Ear Physiology

Critical facts iconHuman audiogram

Absolute intensity audiogram
Relative intensity audiogram
  • this graph is plotted using absolute intensity levels (dB SPL)

  • at birth, humans can hear frequencies between 100 Hz and 20 kHz

  • at each frequency, it is possible to define the minimum intensity that is detectable (this intensity will be different for different people) - this intensity is called THRESHOLD
    • the lower black line on this graph represents the average threshold at each frequency
    • the threshold at 2 kHz was used to define 0 dB SPL

  • the mass of the ossicles limits high frequency transmission, therefore frequencies above 5 kHz have higher thresholds than lower frequencies

  • similarly, the stiffness of the air in the middle ear cavity limits low frequency transmission, therefore frequencies below 1 kHz also have higher thresholds

  • very intense sounds are painful; the pain threshold is typically between 110 and 140 dB SPL (depending on frequency)
  • clinically, thresholds are typically reported in relative, rather than absolute, terms (dB HL)

  • based on data averaged from many normal individuals, each audiology facility will determine what their "normal" threshold is at each frequency (large blue dots on both graphs), and this intensity is set at 0 dB HL

  • of most concern to people (including clinicians) is the ability to perceive speech, and this falls into a relatively restricted range of frequencies and intensities (shaded blue area) - consonants have higher frequency components than vowels, which is an important consideration in the discussion of otitis media and otosclerosis as well as sensorineural hearing loss and presbycusis

  • also shown on this graph are the relative intensities of various sounds if they were presented at a very short distance from your external ear

Email: Dr. Janet Fitzakerley | ©2014 University of Minnesota Medical School Duluth | Last modified: 15-feb-14 9:04 PM