Earphones are contained within devices such as headsets, headphones, handsets, earbuds and inset earphones and have the potential to produce sound levels that can harm or cause discomfort to the listener of these devices. Harm such as the loss of hearing sensitivity can occur as a result of either excessive short-term exposure or long-term exposure to sound. Other hearing dysfunctions that may result from excessive exposure to sound include tinnitus, reduced speech understanding, hyperacusis and ear pain, the later two in particular have been observed to result from short-term exposure. Short-term exposure which is perceived by the listener to be loud and abrupt may result in symptoms affecting other parts of the body such as pain/ache within the head and/or neck. Injury resulting from short-term exposure to sound, which is perceived as being both loud and abrupt, has been described as an acoustic shock injury.
To reduce the occurrence and severity of injury to the listener methods of limiting the short-term and long-term sound exposure have been developed. These include the suppression of sounds known to cause injury, known as shriek rejection as well as broadband and frequency specific level control with a variety of response times. Methods of monitoring and recording the short-term and long-term exposure of a listener have also been developed. Devices have been developed to control the long-term sound exposure of a listener based on an estimate of the long-term exposure. One device predicts the future long-term sound exposure from past estimates of sound exposure combined with data on the anticipated use which it uses to control the current amplification of the signal.
Many of the injuries to users of earphones have resulted from short-term exposure and therefore long-term level control and recording offers nothing in the prevention of this injury or furthers the understanding of it.