Headphones may be used to prevent other people from hearing the sound either for privacy or to prevent disturbance, as in listening in a public library. They can also provide a level of sound fidelity greater than loudspeakers of similar cost. Part of their ability to do so comes from the lack of any need to perform room correction treatments with headphones. High quality headphones can have an extremely flat low-frequency response down to 20 Hz within 3dB. However, rated frequency response distortion figures do not provide information on what character the sound reproduced at that frequency will be. Marketed claims such as 'frequency response 4 Hz to 20 kHz' are usually overstatements; the product's response at frequencies lower than 20 Hz is typically very small. [3]
Headphones are also useful for video games that use 3D positional audio processing algorithms, as they allow players to better judge the position of an off-screen sound source (such as the footsteps of an opponent).
Although modern headphones have been particularly widely sold and used for listening to stereo recordings since the release of the Walkman, there is subjective debate regarding the nature of their reproduction of stereo sound. Stereo recordings represent the position of horizontal depth cues (stereo separation) via volume differences of the sound in question between the two channels. When the sounds from two speakers mix, they create the phase difference the brain uses to locate direction. Through most headphones, because the right and left channels do not combine in this manner, the illusion of the phantom center can be perceived as lost. Hard panned sounds will also only be heard only in one ear rather than from one side. This latter point is of particular importance for earlier stereo recordings which were less sophisticated, sometimes playing vocals through one channel and music through the other.
Binaural recordings use a different microphone technique to encode direction directly as phase, with very little amplitude difference (except above 2 kHz) often using a dummy head, and can produce a surprisingly life-like spatial impression through headphones. Commercial recordings almost always use stereo recording, because historically loudspeaker listening has been more popular than headphone listening. It is possible to change the spatial effects of stereo sound on headphones to better approximate the presentation of speaker reproduction by using frequency-dependent cross-feed between the channels, or—better still—a Blumlein shuffler (a custom EQ employed to augment the low-frequency content of the difference information in a stereo signal). While cross-feed can reduce the unpleasantness that some listeners find with hard panned stereo in headphones, the use of a dummy head during recording, with artificial pinnae, can allow on playback through headphones, the experience of hearing the performance as though situated in the position of the dummy head. Optimal sound is achieved when the dummy head matches the listener's head, since pinnae vary greatly in size and shape.
Headsets can have ergonomic benefits over traditional telephone handsets. They allow call center agents to maintain better posture instead of tilting their head sideways to cradle a handset.[4]
Over time, headphone cables fail. The common scenario in which a replacement might need to be purchased is the physical breakdown of copper wiring at junction points on the cord (at the TRS jack, or at the point of connection to the headphone). These are the sites of greatest and most stressful motion on a cord and so they are typically fitted with some kind of strain relief.
Dangers and volume solutions
Using headphones at a sufficiently high volume level can cause temporary or permanent hearing impairment or deafness due to an effect called "masking." The headphone volume has to compete with the background noise, especially in excessively loud places such as subway stations, aircraft, and large crowds. This leads to the disappearance of the normal pain associated with higher levels of volumes. Extended periods of the excessively loud volume may be damaging;[5][6] however, one hearing expert found that "fewer than 5% of users select volume levels and listen frequently enough to risk hearing loss."[7] 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.
The government of France has imposed[8] a limit on all music players sold in the country[8]: they must not be capable of producing more than 100dBA (the threshold of hearing damage during extended listening is 80dB, and the threshold of pain, or theoretically of immediate hearing loss, is 130dB). Many users[who?] decry this as an infringement on personal choice, and use third-party options to reverse the volume limits placed on such devices. Still, other users welcome the government's pro-health stance.
Canalphones and in-ear monitors have been described as being less likely to cause hearing impairment in noisy environments because much of the external noise is physically blocked out due to the noise isolation properties of the in-ear seal. This allows the user to listen at lower volume levels. However, the user can still choose to listen at dangerously high levels.
Other risks arise from the reduced awareness of external sounds—some jurisdictions regulate the use of headphones while driving vehicles, usually limiting the use of earphones to a single ear. The complete isolation from outside noise can be a hazard in itself, as a user could miss the sound of a car horn and walk into traffic with fatal consequences. Losing situational awareness can also lead to theft, particularly in busy environments where bumping into another person would be ignored, e.g., subway stations.
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 actually enhanced when doing so. The ear can normally detect 1-billionth of an atmosphere of sound pressure level[9], 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. Since earplugs reduce the noise in the auditory canal, this protective mechanism is less likely to trigger, and full sensitivity of the ear is maintained. With normal sensitivity, a listener has excellent hearing while listening to helmet speakers through the earplugs. This technique allows excellent hearing of speech, music and most external sounds at sustainable levels without hearing damage.
Listening to music through headphones while exercising can be dangerous. Blood may be diverted from the ears to the limbs leaving the inner ear more vulnerable to damage from loud sound.[10] A Finnish study[11] recommended that exercisers should set their headphone volumes to half of their normal loudness and only use them for a half hour.
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