Using headphones at a sufficiently high volume level may cause temporaryor permanent hearing impairment or deafness. The headphone volume often has to compete with the background noise, especially in loud places such as subway stations, aircraft, and large crowds. Extended periods of exposure to high sound pressure levels created by headphones at high volume settings may be damaging; [19] [20] however, one hearing expert found that "fewer than 5% of users select volume levels and listen frequently enough to risk hearing loss." [21] Some manufacturers of portable music devices have attempted to introduce safety circuitry that limited output volume or warned the user when dangerous volume was being used, but the concept has been rejected by most of the buying public, which favors the personal choice of high volume. Koss introduced the "Safelite" line of cassette players in 1983 with such a warning light. The line was discontinued two years later for lack of interest. contact http://bit.ly/YsuGvw
The government of France has imposed [22] a limit on all music players sold in the country: [22] they must not be capable of producing more than 100dBA (the threshold of hearing damage during extended listening is 80 dB, and the threshold of pain, or theoretically of immediate hearing loss, is 130 dB). [23] Motorcycle and other power-sport riders benefit by wearing foam earplugs when legal to do so to avoid excessive road, engine, and wind noise, but their ability to hear music and intercom speech is enhanced when doing so. The ear can normally detect 1-billionth of an atmosphere of sound pressure level, [24] hence it is incredibly sensitive. At very high sound pressure levels, muscles in the ear tighten the tympanic membrane and this leads to a small change in the geometry of the ossicles and stirrup that results in lower transfer of force to the oval window of the inner ear (the acoustic reflex). [25]
Some studies have found somewhat increased risks for temporary hearing damage from listening to music during strenuous exercise, compared to when listening at rest. [26] A Finnish study [27] recommended that exercisers should set their headphone volumes to half of their normal loudness and only use them for half an hour.
Passive noise canceling headphones can be considered dangerous because of a lack of awareness the listener may have with their environment. Noise cancelling headphones are so effective that a person may not be able to hear oncoming traffic or pay attention to people around them. There is also a general danger that music in headphones can distract the listener and lead to dangerous situations. [28]
The usual way of limiting sound volume on devices driving headphones is by limiting output power. This has the additional undesirable effect of being dependent of the efficiency of the headphones; a device producing the maximum allowed power may not produce adequate volume in low-efficiency high-quality headphones, while possibly reaching dangerous levels in very efficient ones. [citation needed]
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