page_title: Noise-induced hearing loss
section_title: Diagnosis
hierarchical_section_title: Noise-induced hearing loss / Diagnosis
caption_attribution_description: English: Example of Notched Audiogram
context_page_description: Noise-induced hearing loss is hearing impairment resulting from exposure to loud sound. People may have a loss of perception of a narrow range of frequencies or impaired perception of sound including sensitivity to sound or ringing in the ears. When exposure to hazards such as noise occur at work and is associated with hearing loss, it is referred to as occupational hearing loss.
  Hearing may deteriorate gradually from chronic and repeated noise exposure or suddenly from exposure to impulse noise, which is a short high intensity noise. In both types, loud sound overstimulates delicate hearing cells, leading to the permanent injury or death of the cells. Once lost this way, hearing cannot be restored in humans.
  There are a variety of prevention strategies available to avoid or reduce hearing loss. Lowering the volume of sound at its source, limiting the time of exposure and physical protection can reduce the impact of excessive noise. If not prevented, hearing loss can be managed through assistive devices and communication strategies.
context_section_description: Both NIHL caused by acoustic trauma and gradually-developed-NIHL can often be characterized by a specific pattern presented in audiological findings. NIHL is generally observed to decrease hearing sensitivity in the higher frequencies, also called an audiometric notch, especially at 4000 Hz, but sometimes at 3000 or 6000 Hz. The symptoms of NIHL are usually presented equally in both ears.
  This typical 4000 Hz notch is due to the transfer function of the ear. As does any object facing a sound, the ear acts as a passive filter, although the inner ear is not an absolute passive filter because the outer hair cells provide active mechanisms. A passive filter is a low pass: the high frequencies are more absorbed by the object because high frequencies impose a higher pace of compression-decompression to the object. The high frequency harmonics of a sound are more harmful to the inner-ear.
  However, not all audiological results from people with NIHL match this typical notch. Often a decline in hearing sensitivity will occur at frequencies other than at the typical 3000–6000 Hz range. Variations arise from differences in people's ear canal resonance, the frequency of the harmful acoustic signal, and the length of exposure. As harmful noise exposure continues, the commonly affected frequencies will broaden to lower frequencies and worsen in severity.
caption: Example audiogram of a notch-shaped high frequency hearing loss.
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