Headphones
From Wikipedia, the free encyclopedia
For other uses, see Headphones (disambiguation).
Headphones (or head-phones in the early days of telephony and radio) are a pair of small listening devices that are designed to be worn on or around the head over a user's ears. They are electroacoustic transducers, which convert an electrical signal to a correspondingsound in the user's ear. Headphones are designed to allow a single user to listen to an audio source privately, in contrast to aloudspeaker, which emits sound into the open air, for anyone nearby to hear. Headphones are also known as earspeakers, earphones[1]or, colloquially, cans.[2] Circumaural and supra-aural headphones use a band over the top of the head to hold the speakers in place. The other type, known as earbuds or earphones[1] consist of individual units that plug into the user's ear canal. In the context oftelecommunication, a headset is a combination of headphone and microphone. Headphones either connect directly to a signal source such as an audio amplifier, radio, CD player, portable media player, mobile phone, video game consoles, electronic musical instrument, or use wireless technology such as bluetooth or FM radio. Early headphones were first used by radio pioneers (crystal sets) and also by radio telephone and telegraph operators allowing a better audio reception without disturbing others around. Initially the audio quality was mediocre and a step forward was the invention of high fidelity headphones.[3]
Headphones are made in a range of different audio reproduction quality capabilities. Headsets designed for telephone use typically cannot reproduce sound with the high fidelity of expensive units designed for music listening by audiophiles. Headphones that use cables typically have either a 1/4 inch (6.35mm) or 1/8 inch (3.5mm) phone jack for plugging the headphones into the audio source. As of 2015, most headphones are amplified by a headphone amplifier, either an integrated amplifier (e.g., in an iPod) or a standalone unit. In the 2010s, headphones are used by people in everyday life to listen to audio material such as recorded music, podcasts, or radio shows. Headphones are also used by people in various professional contexts, such as audio engineers mixing sound for live concerts or sound recordings and DJs, who use headphones to cue up the next song they will play without the audience hearing, aircraft pilots and call center employees. The latter two types of employees use headphones with an integrated micropath.
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[hide]History[edit]
Headphones originated from the earpiece, and were the only way to listen to electrical audio signals before amplifiers were developed. The first truly successful set was developed in 1910 by Nathaniel Baldwin, who made them by hand in his kitchen and sold them to theUnited States Navy.[4][5]
Some very sensitive headphones, such as those manufactured by Brandes around 1919, were commonly used for early radio work. These early headphones used moving iron drivers, with either single ended or balanced armatures. The requirement for high sensitivity meant that no damping was used, thus the sound quality was crude. These early models lacked padding, and often produced excessive clamping forces on the wearer's head. Their impedance varied; headphones used in telegraph and telephone work had an impedance of 75 ohms. Those used with early wireless radio had to be more sensitive and were made with more turns of finer wire. Impedance of 1000 to 2000 ohms was common, which suited both crystal sets and triode receivers.
In early powered radios, the headphone was part of the vacuum tube's plate circuit and carried dangerous voltages. It was normally connected directly to the positive high voltage battery terminal, and the other battery terminal was securely grounded. The use of bare electrical connections meant that users could be shocked if they touched the bare headphone connections while adjusting an uncomfortable headset.
In 1943, John C. Koss, an audiophile and jazz musician from Milwaukee, produced the first stereo headphones. Previously, headphones were used only by telephone and radio operators, and individuals in similar industries.
The 3.5 mm radio and phone connector, which is the most commonly used in portable application today, has been used at least since the Sony EFM-117J radio which was released in 1964.[6][7] It became very popular with its application on the Walkman in 1979.
Applications[edit]
Headphones may be used with stationary CD and DVD players, home theater, personal computers, or portable devices (e.g., digital audio player/mp3 player, mobile phone).Cordless headphones are not connected to their source by a cable. Instead, they receive a radio or infrared signal encoded using a radio or infrared transmission link, such asFM, Bluetooth or Wi-Fi. These are powered receiver systems, of which the headphone is only a component. Cordless headphones are used with events such as a Silent disco orSilent Gig.
In the professional audio sector, headphones are used in live situations by disc jockeys with a DJ mixer, and sound engineers for monitoring signal sources. In radio studios, DJs use a pair of headphones when talking to the microphone while the speakers are turned off to eliminate acoustic feedback while monitoring their own voice. In studio recordings, musicians and singers use headphones to play or sing along to a backing track or band. In military applications, audio signals of many varieties are monitored using headphones.
Wired headphones are attached to an audio source by a cable. The most common connectors are 6.35 mm (¼″) and 3.5 mm phone connectors. The larger 6.35 mm connector is more common on fixed location home or professional equipment. The 3.5 mm connector remains the most widely-used connector for portable application today. Adapters are available for converting between 6.35 mm and 3.5 mm devices.
Electrical characteristics[edit]
Electrical characteristics of dynamic loudspeakers may be readily applied to headphones, because most headphones are small dynamic loudspeakers.
Impedance[edit]
Headphones are available with low or high impedance (typically measured at 1 kHz). Low-impedance headphones are in the range 16 to 32 ohms and high-impedance headphones are about 100-600 ohms. As the impedance of a pair of headphones increases, more voltage (at a given current) is required to drive it, and the loudness of the headphones for a given voltage decreases. In recent years, impedance of newer headphones has generally decreased to accommodate lower voltages available on battery powered CMOS-based portable electronics. This has resulted in headphones that can be more efficiently driven by battery powered electronics. Consequently, newer amplifiers are based on designs with relatively low output impedance.
The impedance of headphones is of concern because of the output limitations of amplifiers. A modern pair of headphones is driven by an amplifier, with lower impedance headphones presenting a larger load. Amplifiers are not ideal; they also have some output impedance that limits the amount of power they can provide. In order to ensure an even frequency response, adequate damping factor, and undistorted sound, an amplifier should have an output impedance less than 1/8 that of the headphones it is driving (and ideally, as low as possible). If output impedance is large compared to the impedance of the headphones, significantly higher distortion will be present.[8] Therefore, lower impedance headphones will tend to be louder and more efficient, but will also demand a more capable amplifier. Higher impedance headphones will be more tolerant of amplifier limitations, but will produce less volume for a given output level.
Historically, many headphones had relatively high impedance, often over 500 ohms in order to operate well with high impedance tube amplifiers. In contrast, modern transistor amplifiers can have very low output impedance, enabling lower impedance headphones. Unfortunately, this means that older audio amplifiers or stereos often produce poor quality output on some modern, low impedance headphones. In this case, an external headphone amplifier may be beneficial.
Sensitivity[edit]
Sensitivity is a measure of how effectively an earpiece converts an incoming electrical signal into an audible sound. It thus indicates how loud the headphones will be for a given electrical drive level. It can be measured in decibels of sound pressure level per milliwatt (dB (SPL)/mW) or decibels of sound pressure level per volt (dB (SPL) / V).[9]Unfortunately, both definitions are widely used, often interchangeably. As the output voltage (but not power) of a headphone amplifier is essentially constant for most common headphones, dB/mW is often more useful if converted into dB/V using Ohm's Law:
Alternatively, online calculators can be used.[10] Once the sensitivity per volt is known, the maximum volume for a pair of headphones can be easily calculated from the maximum amplifier output voltage. For example, for a headphone with a sensitivity of 100 dB (SPL)/V, an amplifier with an output of 1 root-mean-square (RMS) voltage will produce a maximum volume of 100 dB.
Pairing high sensitivity headphones with power amplifiers can produce dangerously high volumes and damage headphones. The maximum sound pressure level is a matter of preference, with some sources recommending no higher than 110 to 120 dB. In contrast, the American Occupational Safety and Health Administration recommends an average SPL of no more than 85 dB(A) to avoid long-term hearing loss, while the European Union standard EN 50332-1:2013 recommends that volumes above 85 dB(A) include a warning, with an absolute maximum volume (defined using 40–4000 Hz noise) of no more than 100 dB to avoid accidental hearing damage.[11] Using this standard, headphones with sensitivities of 90, 100 and 110 dB (SPL)/V should be driven by an amplifier capable of no more than 3.162, 1.0 and 0.3162 RMS volts at maximum volume setting, respectively to reduce the risk of hearing damage.
The sensitivity of headphones is usually between about 80 and 125 dB/mW and usually measured at 1 kHz.[12]
Types[edit]
Headphone size can affect the balance between fidelity and portability. Generally, headphone form factors can be divided into four separate categories: circumaural (over-ear),supra-aural (on-ear), earbud and in-ear.[13]
Circumaural[edit]
Circumaural headphones (sometimes called full size headphones) have circular or ellipsoid earpads that encompass the ears. Because these headphones completely surround the ear, circumaural headphones can be designed to fully seal against the head to attenuate external noise. Because of their size, circumaural headphones can be heavy and there are some sets that weigh over 500 grams (1 lb). Ergonomic headband and earpad design is required to reduce discomfort resulting from weight. These are commonly used by drummers in recording.
Supra-aural[edit]
Supra-aural headphones have pads that press against the ears, rather than around them. They were commonly bundled with personal stereos during the 1980s. This type of headphone generally tends to be smaller and lighter than circumaural headphones, resulting in less attenuation of outside noise. Supra-aural headphones can also lead to discomfort due to the pressure on the ear as compared to circumaural headphones that sit around the ear. Comfort may vary due to the earcup material.
Open or closed back[edit]
Both circumaural and supra-aural headphones can be further differentiated by the type of earcups:
Open-back headphones have the back of the earcups open. This leaks more sound out of the headphone and also lets more ambient sounds into the headphone, but gives a more natural or speaker-like sound and more spacious "soundstage"[further explanation needed] - the perception of distance from the source.
Closed-back (or sealed) styles have the back of the earcups closed. They usually block some of the ambient noise, but have a smaller soundstage, giving the wearer a perception that the sound is coming from within their head. Closed-back headphones tend to be able to produce stronger low frequencies than open-back headphones.
Semi-open headphones, have a design that can be considered as a compromise between open-back headphones and closed-back headphones. This may imply that the result combines all the positive properties of both designs. Some[who?] believe the term "semi-open" is purely there for marketing purposes. There is no exact definition for the term semi-open headphone. Where the open-back approach has hardly any measure to block sound at the outer side of the diaphragm and the closed-back approach really has a closed chamber at the outer side of the diaphragm, a semi-open headphone can have a chamber to partially block sound while letting some sound through via openings or vents.
Ear-fitting headphones[edit]
Earphones[edit]
Earphones (popularly called "earbuds" in recent years) are very small headphones that are fitted directly in the outer ear, facing but not inserted in the ear canal. Earphones are portable and convenient, but many people consider them to be uncomfortable and prone to falling out.[14] They provide hardly any acoustic isolation and leave room for ambient noise to seep in; users may turn up the volume dangerously high to compensate, at the risk of causing hearing loss.[14][15] On the other hand, they let the user be better aware of their surroundings. Since the early days of the transistor radio, earphones have commonly been bundled with personal music devices. They are sold at times with foam pads for comfort.
In-ear headphones[edit]
Main article: In-ear monitor
In-ear headphones, also known as in-ear monitors (IEMs) or canalphones,[16] are small headphones with similar portability to earbuds that are inserted in the ear canal itself. IEMs are higher-quality in-ear headphones and are used by audio engineers and musicians as well as audiophiles.
Because in-ear headphones engage the ear canal, they can be less prone to falling out, and they block out much environmental noise. Lack of sound from the environment can be a problem when sound is a necessary cue for safety or other reasons, as when walking, driving, or riding near or in vehicular traffic.
Generic or custom-fitting ear canal plugs are made from silicone rubber, elastomer, or foam. Custom in-ear headphones use castings of the ear canal to create custom-molded plugs that provide added comfort and noise isolation.[14]
Headset[edit]
Main article: Headset (audio)
A headset is a headphone combined with a microphone. Headsets provide the equivalent functionality of a telephone handset with hands-free operation. Among applications for headsets, besides telephone use, are aviation, theatre or television studio intercom systems, and console or PC gaming. Headsets are made with either a single-earpiece (mono) or a double-earpiece (mono to both ears or stereo). The microphone arm of headsets is either an external microphone type where the microphone is held in front of the user's mouth, or a voicetube type where the microphone is housed in the earpiece and speech reaches it by means of a hollow tube.
Telephone headsets[edit]
Telephone headsets connect to a fixed-line telephone system. A telephone headset functions by replacing the handset of a telephone. Headsets for standard corded telephones are fitted with a standard 4P4C commonly called an RJ-9 connector. Headsets are also available with 2.5 mm jack sockets for many DECT phones and other applications. Cordless bluetooth headsets are available, and often used with mobile telephones. Headsets are widely used for telephone-intensive jobs, in particular by call centre workers. They are also used by anyone wishing to hold telephone conversations with both hands free.
For older models of telephones, the headset microphone impedance is different from that of the original handset, requiring a telephone amplifier for the telephone headset. A telephone amplifier provides basic pin-alignment similar to a telephone headset adaptor, but it also offers sound amplification for the microphone as well as the loudspeakers. Most models of telephone amplifiers offer volume control for loudspeaker as well as microphone, mute function and switching between headset and handset. Telephone amplifiers are powered by batteries or AC adaptors.
Ambient noise reduction[edit]
Unwanted sound from the environment can be reduced by excluding sound from the ear by passive noise isolation, or, often in conjunction with isolation, by active noise cancellation.
Passive noise isolation is essentially using the body of the earphone, either over or in the ear, as a passive earplug that simply blocks out sound. The headphone types that provide most attenuation are in-ear canal headphones and closed-back headphones, both circumaural and supra aural. Open-back and earbud headphones provide some passive noise isolation, but much less than the others. Typical closed-back headphones block 8 to 12 dB, and in-ears anywhere from 10 to 15 dB. Some models have been specifically designed for drummers, with the aim to be able to monitor the recorded sound while shutting out the sound coming directly from the drums at the same time as much as possible. Such headphones claim to reduce ambient noise by around 25 dB.
Active noise-cancelling headphones use a microphone, amplifier, and speaker to pick up, amplify, and play ambient noise in phase-reversed form; this to some extent cancels out unwanted noise from the environment without affecting the desired sound source, which is not picked up and reversed by the microphone. They require a power source, usually a battery, to drive their circuitry. Active noise cancelling headphones can attenuate ambient noise by 20 dB or more, but the active circuitry is mainly effective on constant sounds and at lower frequencies, rather than sharp sounds and voices. Some noise cancelling headphones are designed mainly to reduce low-frequency engine and travel noise in aircraft, trains, and automobiles, and are less effective in environments with other types of noise.
Transducer technology[edit]
Various types of transducer are used to convert electrical signals to sound in headphones.
Moving-coil[edit]
The moving coil driver, more commonly referred to as a "dynamic" driver is the most common type used in headphones. The operating principle consists of a stationary magnetic element affixed to the frame of the headphone which sets up a static magnetic field. The magnetic element in headphones is typically composed of ferrite or neodymium. The diaphragm, typically fabricated from lightweight, high stiffness to mass ratio cellulose, polymer, carbon material, or the like, is attached to a coil of wire (voice coil) which is immersed in the static magnetic field of the stationary magnet. The diaphragm is actuated by the attached voice coil, when the varying current of an audio signal is passed through the coil. The alternating magnetic field produced by the current through the coil reacts against the static magnetic field in turn, causing the coil and attached diaphragm to move the air, thus producing sound. Modern moving-coil headphone drivers are derived from microphone capsule technology.
Electrostatic[edit]
Electrostatic drivers consist of a thin, electrically charged diaphragm, typically a coated PET film membrane, suspended between two perforated metal plates (electrodes). The electrical sound signal is applied to the electrodes creating an electrical field; depending on the polarity of this field, the diaphragm is drawn towards one of the plates. Air is forced through the perforations; combined with a continuously changing electrical signal driving the membrane, a sound wave is generated. Electrostatic headphones are usually more expensive than moving-coil ones, and are comparatively uncommon. In addition, a special amplifier is required to amplify the signal to deflect the membrane, which often requires electrical potentials in the range of 100 to 1000 volts.
Due to the extremely thin and light diaphragm membrane, often only a few micrometers thick, and the complete absence of moving metalwork, the frequency response of electrostatic headphones usually extends well above the audible limit of approximately 20 kHz. The high frequency response means that the low midband distortion level is maintained to the top of the audible frequency band, which is generally not the case with moving coil drivers. Also, the frequency response peakiness regularly seen in the high frequency region with moving coil drivers is absent. Well-designed electrostatic headphones can produce significantly better sound quality than other types.[citation needed]
Electrostatic headphones require a voltage source generating 100 V to over 1 kV, and are on the user's head. They do not need to deliver significant electric current, which limits the electrical hazard to the wearer in case of fault.
Electret[edit]
An electret driver functions along the same electromechanical means as an electrostatic driver. However the electret driver has a permanent charge built into it, where electrostatics have the charge applied to the driver by an external generator. Electret and electrostatic headphones are relatively uncommon. Original electrets were also typically cheaper and lower in technical capability and fidelity than electrostatics. Patent applications from 2009-2013 have been approved that show by using different materials,i.e a "Fluorinated cyclic olefin electret film", Frequency response chart readings can reach 50Khz at 100db.When these new improved electrets are combined with a traditional dome headphone driver, Headphones can be produced that are recognised by the Japan Audio Society as worthy of joining the Hi Res Audio program.US patents 8,559,660 B2. 7,732,547 B2.7,879,446 B2.7,498,699 B2 .
Orthodynamic[edit]
Orthodynamic (also known as Planar Magnetic) headphones use similar technology to electrostatic headphones, with some fundamental differences. They operate similarly toPlanar Magnetic Loudspeakers.
An orthodynamic driver consists of a relatively large membrane which contains an embedded wire pattern. This membrane is suspended between two sets of permanent, oppositely aligned, magnets. When current is passed through the wires which are embedded in the membrane, the magnetic field produced by the current reacts with the field caused by the permanent magnets and induces movement in the membrane, producing sound.
Balanced armature[edit]
A balanced armature is a sound transducer design primarily intended to increase the electrical efficiency of the element by eliminating the stress on the diaphragm characteristic of many other magnetic transducer systems. As shown schematically in the first diagram, it consists of a moving magnetic armature that is pivoted so it can move in the field of the permanent magnet. When precisely centered in the magnetic field there is no net force on the armature, hence the term 'balanced.' As illustrated in the second diagram, when there is electric current through the coil, it magnetizes the armature one way or the other, causing it to rotate slightly one way or the other about the pivot thus moving the diaphragm to make sound.
The design is not mechanically stable; a slight imbalance makes the armature stick to one pole of the magnet. A fairly stiff restoring force is required to hold the armature in the 'balance' position. Although this reduces its efficiency, this design can still produce more sound from less power than any other[clarification needed]. Popularized in the 1920s as Baldwin Mica Diaphragm radio headphones, balanced armature transducers were refined during World War II for use in military sound powered telephones. Some of these achieved astonishing electro-acoustic conversion efficiencies, in the range of 20% to 40%, for narrow bandwidth voice signals.
Today they are typically used only in in-ear headphones and hearing aids, where their diminutive size is a major advantage. They generally are limited at the extremes of the hearing spectrum (e.g. below 20 Hz and above 16 kHz) and require a better seal than other types of drivers to deliver their full potential. Higher-end models may employ multiple armature drivers, dividing the frequency ranges between them using a passive crossover network. A few combine an armature driver with a small moving-coil driver for increased bass output.
The earliest loudspeakers for radio receivers used balanced armature drivers for their cones.
Thermoacoustic technology[edit]
The thermoacoustic effect generates sound from the audio frequency Joule heating of the conductor, an effect which is not magnetic and does not vibrate the speaker. In 2013 a carbon nanotube thin-yarn earphone based on the thermoacoustic mechanism was demonstrated by a research group in Tsinghua University.[17] The as-produced CNT thin yarn earphone has a working element called CNT thin yarn thermoacoustic chip. Such a chip is composed of a layer of CNT thin yarn array supported by the silicon wafer, and periodic grooves with certain depth are made on the wafer by micro-fabrication methods to suppress the heat leakage from the CNT yarn to the substrate.[citation needed]
Other transducer technologies[edit]
Transducer technologies employed much less commonly for headphones include the Heil Air Motion Transformer (AMT); Piezoelectric film; Ribbon planar magnetic; Magnetostriction and Plasma-ionisation. The first Heil AMT headphone was marketed by ESS Laboratories and was essentially an ESS AMT tweeter from one of the company's speakers being driven at full range. Since the turn of the century, only Precide of Switzerland have manufactured an AMT headphone. Piezoelectric film headphones were first developed by Pioneer, their two models both used a flat sheet of film which limited the maximum volume of air that could be moved. Currently TakeT produce a piezoelectric film headphone which is shaped not unlike an AMT transducer but which like the driver Precide uses for their headphones, has a variation in the size of transducer folds over the diaphragm. It additionally incorporates a two way design by its inclusion of a dedicated tweeter/supertweeter panel. The folded shape of a diaphragm allows a transducer with a larger surface area to fit within smaller space constraints. This increases the total volume of air that can be moved on each excursion of the transducer given that radiating area.
Magnetostriction headphones, sometimes sold under the label of "Bonephones", are headphones that work via the transmission of vibrations against the side of head, transmitting the sound via bone conduction. This is particularly helpful in situations where the ears must be left unobstructed or when used by those who are deaf for reasons which do not affect the nervous apparatus of hearing. Magnetostriction headphones though, have greater limitations to their fidelity than conventional headphones which work via the normal workings of the ear. Additionally, there was also one attempt to market a plasma-ionisation headphone in the early 1990s by a French company called Plasmasonics. It is believed that there are no functioning examples left.
Benefits and limitations[edit]
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 3 dB. 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.[18]
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 or their gun fire).
Although modern headphones have been particularly widely sold and used for listening to stereo recordings since the release of theWalkman, 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 and phase 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. Hardpanned sounds will also only be heard only in one ear rather than from one side.
Binaural recordings use a different microphone technique to encode direction directly as phase, with very little amplitude difference below 2 kHz, often using a dummy head, and can produce a surprisingly lifelike spatial impression through headphones. Commercial recordings almost always use stereo recording, rather than binaural, because 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.
Headsets can have ergonomic benefits over traditional telephone handsets. They allow call center agents to maintain better posture without needing to hand-hold a handset or tilt their head sideways to cradle it.[19]
Dangers and volume solutions[edit]
See also: Automatic volume limiter
Using headphones at a sufficiently high volume level may cause temporary or permanent hearing impairment or deafness. The headphone volume often has to compete with thebackground 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;[20][21] however, one hearing expert found that "fewer than 5% of users select volume levels and listen frequently enough to risk hearing loss."[22] 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[23] a limit on all music players sold in the country:[23] 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).[24] 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,[25] 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 (theacoustic reflex).[26]
Some studies have found somewhat increased risks for temporary hearing damage from listening to music during strenuous exercise, compared to when listening at rest.[27] A Finnish study[28] 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.[29]
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]
Earplug
From Wikipedia, the free encyclopedia
See also: Plug (jewellery)
An earplug is a device that is meant to be inserted in the ear canal to protect the user's ears from loud noises or the intrusion of water, foreign bodies, dust or excessive wind.
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[hide]Protection from water[edit]
Some earplugs are primarily designed to keep water out of the ear canal, especially during swimming and water sports. This type of earplug may be made of wax or moldablesilicone which is custom-fitted to the ear canal by the wearer.
Exostosis, or Surfer's ear, is a condition which affects people who spend large amounts of time in water in cold climates. In addition, wind may increase the prevalence of the amount of exostosis seen in one ear versus the other dependent on the direction it originates from and the orientation of the individual to the wind.[1] Custom-fitted surfer's earplugs help reduce the amount of cold water and wind that is allowed to enter the external ear canal and, thus, help slow the progression of exostosis.
A 2003 study published in Clinical Otolaryngology found that a cotton ball saturated with petroleum jelly was more effective at keeping water out of the ear, was easier to use, and was more comfortable than wax plugs, foam plugs, EarGuard, or Aquafit.[2]
Jacques-Yves Cousteau[3] warned that earplugs are harmful to divers, especially scuba divers. Scuba divers breathe compressed air or other gas mixtures at a pressure matching the water pressure. This pressure is also inside the ear, but not between the eardrum and the earplug, so the pressure behind the eardrum will often burst the eardrum. Skin divers have less pressure inside the ears, but they also have only atmospheric pressure in the outer ear canal. The PADI (Professional Association of Diving Instructors) advises in the "Open Water Diver Manual" that only vented earplugs designed for diving should be used in diving.
Hearing protection[edit]
There are mainly four types of earplugs for hearing protection:
- Foam earplugs, mainly made from either polyvinyl chloride (PVC) or polyurethane (PU) (memory foam), which are compressed (rolled) and put into the ear canal, where they expand to plug it
- Silicone earplugs, which are rolled into a ball and carefully molded to fit over the external portion of the ear canal
- Flanged earplugs, including most types of musicians' or 'Hi-Fi' earplugs.
- Custom molded earplugs, made from a mold of the wearer's ear and designed to precisely fit all ear canal shapes. Custom molded is further divided into laboratory-made and "formed in place"
NIOSH Mining Safety and Health Research recommends using the roll, pull, and hold method when using memory foam earplugs.[4] The process involves the user rolling the earplug into a thin rod, pulling back on the ear, and holding the earplug deep in the canal with the finger.[4] To get a complete seal, the user must wait about 20 seconds for the earplug to expand inside the canal.[4]
Furthermore, they may be either disposable or non-disposable, with foam and hand rolled silicone ones generally being disposable or for use a relatively limited number of times. Custom molded are non-disposable and made from either acrylic, vinyl, or silicone materials. Custom molded come as either vented (for communication) or non-vented (for high noise). A variation of the traditional foam earplug is the no-roll foam earplug that uses a built-in central stem to push the foam plugs into the ears. These earplugs achieve a seal due to their tapered shape, rather than expansion after being rolled.
Earplugs and other hearing protection devices can be tested to ensure that they fit properly and are successfully limiting sound exposure with a number of different systems, most of which use large noise-cancelling headphones that fit over the ear and transmit the test sounds. These include the NIOSH HPD Well-Fit, as well as the Howard Leight VeriPro and 3MEARFit. [5]
Earplugs are especially useful to people exposed to excessively noisy devices or environments (80 dB or more).
| Level of noise in dB(A) | Maximum daily exposure time |
|---|---|
| 85 | 8 Hours |
| 91 | 2 Hours |
| 97 | 30 Minutes |
| 103 | 7 Minutes |
History[edit]
The first recorded mention of the use of earplugs is in the Greek tale Odyssey, wherein Odysseus's crew is warned about the Sirens that sing from an island they will sail past.Circe, their hostess, tells them of the Sirens' bewitching song that makes men drive their boats ashore and perish. She advised Odysseus to fashion earplugs for his men from beeswax so they would not be lured to their deaths by the sirens song.
In 1907, the German company Ohropax, which would produce mainly wax earplugs, was started by German inventor Max Negwer.
Ray and Cecilia Benner invented the first mouldable pure silicone ear plugs in 1962. The earplugs were valued by swimmers, as well as those trying to avoid harmful noise, for their waterproof qualities. Ray Benner, who was a Classical musician, bought McKeon Products in 1962. At that time the company's sole product was Mack's Earplugs (named after the original owner), which was a mouldable clay earplug. The Benners quickly redesigned the product to a silicone version which would become known as Mack's Pillow Soft Earplugs.[citation needed]
Present-day earplug material was discovered in 1967, at National Research Corporation (NRC) in the USA by Ross Gardner Jr. and his team. As part of a project on sealing joints, they developed a resin with energy absorption properties. They came to call this material "E-A-R" (Energy Absorption Resin). In 1972 the material was refined into commercial memory foam earplugs, made from either polyvinyl chloride or polyurethane[citation needed].
'Basic' type plugs[edit]
This kind of earplug protection is often worn by industrial workers who work within hearing distance of loud machinery for long periods, and is used by the British Ministry of Defense (MoD) for soldiers to use when firing weapons. Earplugs are rated for their ability to reduce noise. In the United States, the U.S.Environmental Protection Agency mandates that hearing protection is rated and labeled. To be rated hearing protection is tested under ANSI S3.19-1974 to provide a range of attenuation values at each frequency that can then be used to calculate a Noise Reduction Rating (NRR). Under this standard a panel of ten subjects are tested three times each in a laboratory to determine the attenuation over a range of 9 frequencies.[6] In the European Union, hearing protectors are required to be tested according to the International Organization for Standardization (ISO) acoustical testing standard, ISO 4869 Part 1 [7] and the Single Number Rating (SNR) or High/Middle/Low (HML) ratings are calculated according to ISO 4869 Part 2.[8] In Brazil, hearing protectors are tested according to the American National Standards Institute ANSI S12.6-1997 and are rated using the Noise Reduction Rating Subject Fit NRR(SF).[9] Australia and New Zealand have different standards for protector ratings yielding a quantity SLC80 (Sound Level Class for the 80th percentile). Canada implements a class system for rating the performance of protectors. Gauger and Berger have reviewed the merits of several different rating methods and developed a rating system that is the basis of a new American National Standard, ANSI S12.68-2007 [10][11]
The various methods have slightly different interpretations, however, each method has an effective percentile associated with the rating for which that percent of the users should be able to achieve the rated attenuation. For instance the NRR is determined by the mean attenuation minus two standard deviations, thus it translates to a 98% statistic. That is at least 98 percent of users should be able to achieve that level of attenuation. The SNR and HML are a mean minus one standard deviation statistic. Therefore, approximately 86% of the users should be able to achieve that level of protection. Similarly, the NRR(SF) is a mean minus one standard deviation and represents an 86% of users should achieve that level of protection. The difference between the ratings lies in how the protectors are tested. NRR is tested with an experimenter-fit protocol. SNR/HML are tested with an experienced subject-fit protocol. NRR(SF) is tested with a naive subject-fit protocol. According to Murphy et al. (2004), these three protocols will yield different amounts of attenuation with the NRR being the greatest and NRR(SF) being the least.[12]
The experimenter-fit NRR should be adjusted per the guidelines of the National Institute for Occupational Safety and Health as the required NRR ratings differ greatly from lab tests to field tests.
The NRR(SF) used in Brazil, Australia, and New Zealand does not require derating as it resembles the manner in which the typical user will wear hearing protection.
Most disposable earplugs are elastic ones made of memory foam, that is typically rolled into a tightly compressed cylinder (without creases) by the user's fingers and then inserted in the ear canal. Once released, the earplug expands until it seals the canal, blocking the sound vibrations that could reach the eardrum. Other disposable plugs simply push into the ear canal without being rolled first. Sometimes earplugs are connected with a cord to keep them together when not in use. Other common material bases for disposable earplugs are viscous wax or silicone. Custom moulded earplugs fall into two categories: Laboratory made and Formed in Place. Laboratory made requires a carefully professionally taken impression be made of the ear canal and outer ear that is sent to a laboratory to be checked and made into a hearing protector. Formed in place uses the same style of process to make an impression of the ear canal and outer ear and then turns that impression into the protector. Both types of custom moulded earplugs are non-disposable with the laboratory made typically lasting for 3 – 5 years and the formed in place lasting for 1 – 2 years.
Other devices that provide hearing protection include electronic devices worn around and/or in the ear, designed to cancel out the loud noise of a gunshot, while possibly amplifying quieter sounds to normal levels. While rich in features, these electronic devices carry a price over one hundred times that of their foam counterparts.
Since they reduce the sound volume, earplugs are often used to help prevent hearing loss and tinnitus (ringing of the ears), amongst other ailments.
Noise Reduction Ratings (NRR)[edit]
Hearing protectors sold in the U.S. are required by the U.S. Environmental Protection Agency (EPA) to have a noise reduction rating (NRR),[14] which is an estimate of the reduction of noise at the ear when protectors are worn properly. However, due to the discrepancy between how protectors are fit in the testing laboratory and how users wear protectors in the real world, the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have developed derating formulas to reduce the effective NRR.
While the NRR and the SNR (Single Number Rating) are designed to be used with C-weighted noise, which means that the lower frequencies are not de-emphasized, other ratings (NRR(SF) and NRSA) are determined for use with A-weighted noise levels, which have lower frequencies de-emphasized. The National Institute for Occupational Safety and Health recommended and the U.S. EPA mandated [14] that 7-dB compensation between C and A weighting be applied when the NRR is used with A-weighted noise levels.
OSHA has defined in their training manual for inspectors that the adequacy of hearing protection for use in a hazardous noise environment should be derated to account for how workers typically wear protection relative to how manufacturers test the protector's attenuation in the laboratory.[15] For all types of hearing protection, OSHA’s derating factor is 50%. If used with C-weighted noise, the derated NRR will become NRR/2.[15] If used with A-weighted noise, OSHA applies the 7-dB adjustment for C-A weighting first then derates the remainder.[15] For example, a protector with 33-dB attenuation would have this derating:
- Derated NRR = (33 – 7)/2
NIOSH has proposed a different method for derating based upon the type of protector.[13] For earmuffs, the NRR should be derated by 25%, for slow-recovery foam earplugs the derating is 50% for all other protection, the derating is 70%. NIOSH applies the C-A spectral compensation differently than OSHA. Where OSHA subtracts the 7-dB factor first and derates the result, NIOSH derates the NRR first and then compensates for the C-A difference. For example, to find the derated NRR for an earmuff by using the NIOSH derating system, the following equation would be used:
- Derated NRR = (Original NRR x (1-.25)) – 7
Painful discomfort occurs at approximately 120 to 125 dB(A),[16] with some references claiming 133 dB(A) for the threshold of pain.[17] Active ear muffs are available with electronic noise cancellation that can reduce direct path ear canal noise by approximately 17–33 dB, depending on the low, medium, or high frequency at which attenuation is measured.[18] Passive earplugs vary in their measured attenuation, ranging from 20 dB to 30 dB, depending on whether they are properly used,[19] and if low pass mechanical filters are also being used. Using both ear muffs (whether passive or active) and earplugs simultaneously results in maximum protection, but the efficacy of such combined protection relative to preventing permanent ear damage is inconclusive, with evidence indicating that a combined noise reduction ratio (NRR) of only 36 dB (C-weighted) is the maximum possible using ear muffs and earplugs simultaneously, equating to only a 36 - 7 = 29 dB(A) protection.[17] Some high-end, passive, custom-molded earplugs also have a mechanical filter inserted into the center of the earmolded plug, with a small opening facing to the outside; this design permits being able to hear range commands at a gun range, while still having full rating impulse noise protection. Such custom molded earplugs with low pass filter and mechanical valve typically have a +85 dB(A) mechanical clamp, in addition to having a lowpass filter response, thereby providing typically 30-31 dB attenuation to loud impulse noises, with only a 21 dB reduction under low noise conditions across the human voice audible frequency range (300–4000 Hz) (thereby providing low attenuation between shots being fired), to permit hearing range commands. Similar functions are also available in standardized earplugs that are not custom molded.[20]
Expected updates[edit]
In 2007, the American National Standards Institute published a new standard for noise reduction ratings for hearing protectors, ANSI S12.68-2007. Using the real ear attenuation at threshold data collected by a laboratory test prescribed in ANSI S12.6-2008, the noise reduction statistic for A-weighted noise (NRSA) is computed using a set of 100 noises listed in the standard.[11] The noise reduction rating, rather than be computed for a single noise spectrum the NRSA incorporates variability of both subject and spectral effects.[11]ANSI S12.68 also defines a method to estimate the performance of a protector in an atypical noise environment. Building upon work from the U.S. Air Force and the ISO 4869-2 standard,[8] the protector's attenuation as a function of the difference in C and A-weighted noise level is used to predict typical performance in that noise environment. The derating may be quite severe (10 to 15 decibels) for protectors that have significant differences between low and high frequency attenuation. For "flat" attenuation protectors, the effect of C-A is less. This new system eliminates the need for calculators, relies on graphs and databases of empirical data, and is believed to be a more accurate system for determining NRRs.[11]
Musicians' or 'Hi-Fi' earplugs[edit]
Musicians who perform music styles noted for their loud nature, especially rock music, often wear earplugs to prevent their own performances from damaging their hearing. Musicians' earplugs are designed to attenuate sounds evenly across the audio band and thus minimise their effect on the user's perception of bass and treble levels. These are commonly used by musicians and technicians, both in the studio and in concert, to avoid overexposure to high volume levels. Alternately, musicians may use in-ear monitors, which are essentially headphones that also serve as earplugs.
They generally achieve this by incorporating a tiny diaphragm to reduce low frequencies, together with absorbent or damping material for high frequencies. This means they can be quite costly, being intended for constant re-use unlike simple earplugs which are disposable. These earplugs usually give an attenuation of only about 20 dB and are not intended for protection from very high noise levels (beyond 105 dB).
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Some musicians' earplugs are custom-made for the individual listener. An audiologist administers a hearing test and makes molds of the ear. A company then makes a custom ear-piece into which different attenuator capsules can be inserted. These different capsules will provide different levels of attenuation, usually 9, 15, and 25 dB. These types of earplugs will provide the flattest attenuation and the truest isolation from outside noise, as they fit firmly into the individual's ears. They also provide much better protection from very high noise levels. This type of plug is quite popular amongst audio engineers who can safely listen to loud mixes for extended periods of time.
In other activities, hobby motorcyclists and skiers may also choose to use decibel reduction earplugs, to compensate for the ongoing noise of the wind against their head or helmet.
Electronic earplugs[edit]
The noise reduction of passive earplugs varies with frequency but is independent of value (soft noises are reduced as much as loud noises). As a result, while loud noises are softened, protecting hearing, it is difficult to hear soft noises. Active electronic earplugs exist, where loud noises are reduced more than soft noises, and soft sounds may even be amplified, providing dynamic range compression. This is done by having a standard passive earplug, together with a microphone/speaker pair (microphone on outside, speaker on inside; formally a pair of transducers), so sound can be transmitted without being attenuated by the earplug. This protects hearing, but allows one to hear normally when sounds are in safe ranges – for example, have a normal conversation when there are no noises, but be protected from sudden loud noises, or hear soft passages in music but be protected from sudden sounds like cymbal crashes.
Flight ear protection[edit]
Earplugs are available which help to protect ears from the pain caused by airplane cabin pressure changes. Some products contain a porous ceramic insert which reportedly aids equalization of air pressure between the middle and outer ear thereby preventing pain during landings and take-offs. Some airlines distribute regular foam earplugs as part of their amenity kits for passengers to aid their comfort during landings and takeoffs as well as to reduce exposure to the aircraft's noise during the flight. These can help passengers get to sleep during the flight if desired.
Sleep[edit]
Earplugs for sleeping are made to be as comfortable as possible while blocking external sounds that may prevent or disrupt sleep. Specialized earplugs for such noises as a partner's snoring may have sound-dampening enhancements that enable the user to still hear other noises, such as an alarm clock, these are specially designed so that they do not hurt the ear even when the wearer is sleeping sideways.[21]
To determine the comfort of earplugs used for sleeping, it is important to try them on while actually lying down. The pressure on the ear between the head and pillow may cause significant discomfort. Furthermore, just tilting the head back or to the side causes significant anatomical changes in the ear canal, mostly a reduction of the ear canal diameter, which may reduce comfort if the earplug is too large.[22][23]
Health risks[edit]
Earplugs are generally safe, but some precautions may be needed against a number of possible health risks, with additional ones appearing with long term use:
- Pushing in earplugs into the external ear canal may cause the air pressure to rise in it, in effect pushing against the eardrum and causing pain. This may be caused by pressure on the ear while lying down on the side, and is also the case when completely expanded foam earplugs are pushed further into the ear. To bypass the latter risk, such earplugs are instead removed, compressed and inserted to the desired depth. Vice versa, when pulled out, the resultant negative pressure pulls the eardrum. Therefore, some earplugs are better carefully screwed or jiggled out rather than yanked out. Yawning does not help to equalize this air pressure difference, since it equalizes the pressures between the middle ear and the environment, while this overpressure rather is located in the outer ear, between the eardrum and the earplug.
- If pushed too far into the ear canal, they may push earwax and debris into the canal and possibly against the ear drum.[24] As a precaution, earplugs should not be pushed further into the ear canal than they may be grabbed and rotated.[25] Earwax impacted by earplugs can be removed by irrigation or other remedies, as described here.
- There is a possibility of allergic reactions, but this is likely rare, as earplugs generally are made of immunologically inert materials.
Long-term use[edit]
Custom shaped plugs are recommended for long-term use, since they are more comfortable and gentle to the skin and won't go too far into the ear canal.
Nevertheless, prolonged or frequently repeated use of earplugs has the following health risks, in addition to the short term health risks:
- They may cause earwax to build up and plug the outer ear, since it blocks the normal flow of earwax outwards.[26] This can result in tinnitus, hearing loss, discharge, pain or infection.[26] Excess earwax should be carefully removed from the ear, and earplugs should be cleaned regularly with water and mild soap. However, foam type earplugs are usually designed to be disposable, and will expand and lose their memory property upon drying after washing with water and soap. From then on, they will expand very quickly after being compressed, making proper insertion into the ear canal quite problematic. They also lose a large proportion of sound attenuating capability after such washing and drying.
- They may cause irritation of the temporomandibular joint, which is located very close to the ear canal, causing pain. Individually fitted non-elastic earplugs may be less likely to cause this irritation compared with foam ones that expand inside the ear canal.
- Earplugs are also a possible cause of ear inflammation (otitis externa), although the short term use of earplugs when swimming and shampooing hair may actually help prevent it. Still, many pathogenic bacteria grow well on warm, moist, foam-type plugs (polyvinylchloride (PVC) or polyurethane). However, there need also be a loss of integrity of the skin for infection to occur. Hard and poorly fitting earplugs can scratch the skin of the ear canal and set off an episode. When earplugs are used during an acute episode, disposable plugs are recommended, or used plugs must be cleaned and dried properly to avoid contaminating the healing ear canal with infected discharge.
Custom molds[edit]
Noise and decibel reduction earplugs can be molded to fit an individual's ear canal. This is associated with a higher cost, but can help to reduce the discomfort typically experienced after longer use, or if the level of protection or performance is inadequate.
Pressure and flight earplug molds are less common, as they are typically not used as long as other earplugs, and are therefore less in demand.
For best results they are molded in the ear while in the position that they will be used. For instance, if they are to be used for sleeping then they should be molded in the ear while lying down, as different positioning of the jaws causes significant changes to the form of the ear canal, mostly a reduction of the diameter, risking the sleep earplug to be made too large otherwise. These changes can be felt by feeling with a finger just at the entrance to the ear canal while moving the jaws sideways, up and down or anterior and posterior.
Most moulded earplugs are made from silicone but other materials may be used, including thermoplastics.[27]