Headphones are small sound transducers that are worn on or in the ears . In the early days of radio people only listened to headphones; however in mono , i.e. That is, the audio signal was the same on both earphones . There are also headphones with just one earpiece.
The inventor of the headphones has not yet been clearly identified. Headphone-like devices have been used since the invention of telephony and radio. Alexander Graham Bell's telephone, for example, was already a headset, which, however, also served as a microphone and therefore had to be moved back and forth between mouth and ear when used. Some sources point to the American Nathaniel Baldwin as the inventor of the headphones. Baldwin (1878–1961), founder and owner of the Baldwin Radio Company in Salt Lake City, launched his headphones called "Baldy Phones" in 1910.
A special form is the bone conduction receiver , which emits vibrations to a bone in the head, which the ear then perceives.
- Ear canal headphones (intra-aural) or in-ear headphones / canalphones (literally also "in-the-ear headphones")
- The earphones are inserted into the ear canal . This variant is used, for example, for in-ear monitoring . They are available in different materials such as foam or silicone .
- In the professional field, however, in-ear monitoring is individually adapted to the ears by incorporating the listener into an otoplastic made of silicone or acrylic . This custom-made product is made by hearing aid acousticians . They are very comfortable and safe to wear, durable, easy to clean and offer the best isolation from outside noise.
- Earbud earphones
- Also called half-in-ear headphones, these are earphones that are inserted into the auricle (pinna) . Some people find this uncomfortable. But they are space-saving and suitable for on the go.
- Earbuds and intra-aural sound transducers can very easily lead to irreversible damage to the inner ear at permanently inadequate volume levels, as the high sound energy is conducted directly into the sensitive ear canal.
- Shell headphones
- These headphones are larger and are placed over the ear cups, they are produced in different versions:
On-ear headphones (supra-aural) , also “on ear”
The headphone shell covers the ear but does not surround it.
Circumaural headphones , also called "over ear"
The headphone shell completely surrounds the ear, the headphone drivers use the entire anatomy of the auricle via sound reflections.
- On-ear headphones (supra-aural) , also “on ear”
- Both types of headphones are available either as a closed or an open shell system, depending on usage behavior, habits or preferences. The headphone shell closed on the back is better suited for shielding from annoying outside noises in concentrated studio work, the headphones open on the back prevent unpleasant excessive ear warming through the air exchange.
- The head speaker is a rare special form . These are two small loudspeakers that are hung over the head and sound completely free for the ears. This enables a more natural localization (see below) . The best known model is the AKG K 1000.
- Also rare is the bone conduction earpiece , which emits vibrations to a bone in the head, which the ear then perceives.
Variants of shell headphones
The terms “open” and “closed” do not refer to whether headphones surround or rest against the ear, but to the isolation from the environment. Circumaural headphones can also be open, and those on top can also be closed.
- Open headphones
With the open design, the connection to the acoustic outside world is retained through the headphones. For this purpose, the cover of the earpieces is permeable; it is perforated or slotted and more permeable materials are used. The sound is emitted from the membrane both in the direction of the ear and outwards. This should achieve a higher level of transparency and make the sound more spatial. At the same time, there is better heat exchange, unpleasant sensations such as heat build-up or sweating are reduced. The disadvantage of this design is that the sound waves generated by the headphones and the environment can be heard alternately: interfering noises from outside penetrate the ear, conversely, the reproduced sound penetrates outside and may be perceived as annoying by the environment.
- Closed headphones
In the closed form, the ear is largely shielded from the outside, the sound only radiates towards the ear. The shielding builds up more pressure in the bass range. The construction of this design is more complicated, mainly due to reflections, and thus more expensive with the same sound quality. The advantage is the greater independence from the outside world, again with regard to the noisy environment as well as less disruptive radiation to the outside. The heat generated by the lack of air exchange can occasionally be perceived as uncomfortable when worn for a long time.
- Half-open headphones
Half-open headphones are designed to combine the respective advantages of the other two designs. They have fewer (partly extra insulated) openings to the outside than open headphones.
Sound converter technology
The construction principle comes from the early days of audio technology and was used for both loudspeakers and headphones. It is typically a membrane made of steel moves, radiates the sound directly (see figure). The current from the amplifier flows through two coils pre-magnetized with a permanent magnet, similar to an electromagnet , the magnetic poles of which are located a short distance behind the sheet steel membrane. The premagnetization is essential for sound reproduction, because without it the membrane would vibrate at twice the frequency (the iron membrane would be attracted once for the positive and then again for the negative half-wave). As a result of the premagnetization, the membrane receives a magnetic (as well as mechanical) prestress B 0 , to which the active alternating voltage is added or subtracted.
Such converters were used, for example, in early radio technology or military communications; They were also used in Morse headphones and telephone receivers . Their impedance was mostly 2 to 4 kΩ (kiloohms). They could therefore be used in tube amplifiers or in detector receivers without an output transformer .
Because of the poor reproduction quality (very high distortion factor, severely limited frequency range, etc.), electromagnetic converters are generally no longer used today.
As with a dynamic loudspeaker , the sound conversion arises from the movement of a coil fed by the sound signal in a magnetic field : A moving coil in the center of the membrane is located in the narrow air gap of a strong permanent magnet mounted on the headphone frame and becomes longitudinal when the audio frequency voltage is applied through the interaction of constant and variable magnetic fields Vibrations driven, which are transmitted to the surrounding air via the membrane.
To avoid excessive partial vibrations and for reasons of material inertia, the driver diaphragm is made of a light material with high rigidity, for example cellulose , plastic or metal.
The electrodynamic diaphragm drive is the most widespread today, it offers cost-effective production, uncomplicated operation and, given the current state of the art and the correspondingly high construction effort, also delivers the highest reproduction quality.
Isodynamic or orthodynamic or magnetostat
The structural arrangement of the elements of the sound transducer is similar to that of an electrostatic push-pull loudspeaker, in which a constantly electrically charged flat membrane moves between the perforated stators that are controlled by the high-voltage audio frequency .
In the case of isodynamic sound transducers, on the other hand, the membrane is driven by the electrodynamic effect of a regular audio frequency voltage, which is fed to a conductor path (a flat coil ) that is glued or vaporized in a spiral from the center of the membrane to the outside . When the LF voltage is applied, the evenly clamped membrane moves in a homogeneous magnetic field between the pole plates of two opposing permanent magnets or several flat magnet bars, which are perforated for pressure compensation .
An adequate efficiency of the isodynamic driver systems can only be achieved with relatively large and therefore heavy magnetic disks with a high magnetic energy density, which results in an unusually high weight and an uncomfortable wearing comfort of the headphones.
Balanced armature transducer
The balanced armature transducer design ("BA", literally: balanced armature) is primarily intended to increase the electrical efficiency by eliminating the load on the diaphragm, as is characteristic of many other types of drive. The BA principle consists of a permanent magnet and a movably mounted armature that is precisely centered in its magnetic field. In the center of the magnetic field there is no resulting force on the armature, hence the term “balanced”. When current flows through the coil of the armature, the armature magnetizes so that it is easily moved in one direction or the other. The membrane is attached to the armature with a drive and then generates sound waves.
The design is not mechanically stable and the armature would stick if attracted by the permanent magnet. A relatively stiff membrane with a high restoring force is therefore required to keep the armature in “balance”. Although this has a negative impact on efficiency, this design can produce sound better than any other from little power. This principle was introduced as "Baldwin Mica membrane wireless headphones" as early as the 1920s.
Today they are usually used in ear canal (in-ear) headphones and hearing aids because of their small size and low impedance. They are usually limited to the human hearing range (around 20 Hz to 16 kHz) and require a higher seal than other types of drivers in order to deliver their full potential. High-end models can use multiple BA drivers to better represent the sound spectrum. With the help of a passive crossover, these are combined into an overall sound image. There are also models that combine BA drivers with classic coil diaphragm drivers for the bass range.
The principle of the electrostatic drive (see also electrostatic loudspeaker ) works like a condenser microphone that is operated in reverse . The drive mechanism consists of a thin, conductive coated polyester membrane film, which is constantly charged electrically with the positive bias ( bias or EHT) of a high-voltage cascade and is clamped between two perforated metal plates - the stators . For an adequate efficiency of the membrane drive, a high drive voltage is necessary, which is made available by a special step-up transformer , which is directly connected on the primary side to the low-impedance loudspeaker outputs of a regular audio amplifier with sufficient output power.
Newer model variants work without the transformer, which is disadvantageous in terms of transmission, with specially designed headphone amplifiers, which have to be operated with very high symmetrical supply voltages of around ± 500 volts in order to generate an appropriate volume level. The high-tension audio frequency is fed to both perforated stators and moves the pre-charged membrane film over its entire surface due to the changing conditions of the electric field.
Despite the relatively simple construction of the sound transducer, the electrostatic headphones are usually more expensive than a model with an electrodynamic drive due to the higher operating costs.
Due to its extremely thin and therefore light membrane, which is often only a few micrometers thick, the frequency range of electrostatic headphones normally extends far beyond the audibility limit of approx. 20 kHz; The almost inertia-free reaction of the membrane makes the transducer extremely pulse-faithful, which benefits a high resolution of the spatial information of the signal. In addition, the isoplanar vibration behavior of the membrane offers a minimum of partial vibrations and thus contributes to the particularly natural and clear sound result of the electrostatic headphones when optimally designed.
Electrostatic headphones are usually operated with voltages from 100 V to over 1 kV and are placed on the head of the listener, but their use is still considered safe due to the extremely low currents. The best known manufacturer is the company Stax Ltd. Such systems are valued by audiophiles, but they are more complex to manufacture and accordingly higher in price.
Piezoelectric converters typically have a high level of efficiency and poor sound quality (hardly any bass reproduction, pronounced resonances). The impedance is high (depending on the frequency, several kiloohms). For example, they were used as so-called crystal earphones for detector receivers .
Signal connection (transmission technology)
- Wired headphones (passive)
- Here the signal is passed through a cable to the coils or electrodes. The headphones are passive.
- Wired headphones ( USB )
- Headphones with a USB connection contain a minimal USB sound card , integrated either in the USB plug or in the headphones themselves.
- Induction loop headphones
- The earliest wireless signal transmission to headphones consists of an induction loop running around the room , which is fed directly with the amplified NF signal . In the simplest case, the headphones also only need one coil for reception, in which an LF voltage is induced by the magnetic field of the induction loop. There were also small hearing aids with a battery, coil and amplifier for connecting an earphone.
- Infrared headphones
- The signal is (usually) analog frequency modulated or digitally coded with an LED infrared transmitter and transmitted to the headphones. A line of sight between the transmitter and receiver (headphones) is necessary. If the signal is transmitted digitally, it must first be converted into an analog signal by a D / A converter . If the signal is analog, an FM demodulator takes over the conversion.
- The headphones have an integrated IR receiver and amplifier, and a rechargeable battery is usually used as the energy source .
- Analog wireless headphones
- As with infrared headphones, the signal is transmitted wirelessly. Instead of infrared, however, radio waves are used. The transmission frequencies differ depending on the manufacturer and model, but only certain frequency ranges are permitted. Wireless headphones / transmitters are often incompatible with one another.
- With wireless headphones, the signal is usually transmitted via FM. An FM demodulator converts it into an audio signal. A rechargeable battery usually also serves as the energy source.
- Digital wireless headphones
- Here the radio signal is transmitted digitally (e.g. via Bluetooth ) rather than analog . The received signal is first converted into an analog audio signal by the headphones' built-in D / A converter - conversion as close as possible to the loudspeaker minimizes the signal and quiet noise, which is often perceived as annoying, and enables interference-free playback. The additional A / D conversion required for analog sound sources has a negative effect on the quality. These headphones usually also need a battery.
- (The advantages of digital-to-analog conversion close to the loudspeaker also apply to digitally transmitted IR headphones.)
The electrical resistance to which an alternating current is opposed is the impedance (Latin for "impedire" = to hinder, to prevent). This is the relationship between the voltage and the current on a line or component. In headphones, this component is the voice coil. The impedance is measured in ohms (Ω).
- Low-impedance headphones : The impedance of headphones is in the range of 4–100 Ω : electromagnetic and electrodynamic headphones, earphones
- Medium-resistance headphones : The impedance is in the range 100–1000 Ω: Electromagnetic and electrodynamic headphones
- High-impedance headphones : The impedance is in the range 1–4 kΩ: Electromagnetic headphones, among other things, for detector receivers (out of date). With piezoelectric headphones, the impedance is even higher depending on the frequency.
Basically, low-impedance headphones are suitable for battery-operated devices, while medium and high-impedance headphones are more intended for stationary systems.
Active noise canceling headphones
Headphones with active noise reduction based on anti- noise technology have been available for a number of years . A microphone on the outside of the headphones picks up outside noise. With the help of electronic components, the out-of-phase oscillation of those noises is generated. This signal is then mixed with the audio signal of the actual channel. The noise and the added signal are now canceled. With this technology it is possible to actively eliminate low-frequency noise in particular. This technology has long been used in the headphones of airplane pilots to reduce noise. By mainly switching off the lower-frequency interference noises, the sound level in the pilots' headphones and thus the damage to health could be reduced.
A simpler and more effective way of suppressing background noise is to use closed, circumaural headphones. With a suitable construction, higher attenuation is possible above 500 Hz than with active noise suppression. This type of shielding also works at higher levels.
Directional information for headphone playback
The sound emitted by the headphone drivers acts exclusively on the ear assigned to the respective headphone shell and not on the head and on both ears, as in natural hearing. In the case of intra-aural earphones, the complex acoustic filter effect, which is important for perception, of the anatomy of the auricle, which is differently shaped in each individual, is overridden.
As a result, the brain lacks the HRTF necessary for an appropriate sound evaluation , in particular the directional information that is indispensable for the acoustic localization of the sound sources: Instead of a natural frontal location , the design-related strict separation of the two stereo signals by the headphones creates an unnatural-looking in-head localization . There are various different approaches to reducing this ICL , ranging from a simple, slight angle of the headphone driver via the S-Logic headphone technology from Ultrasone to more complex electronic manipulations such as the subsequent mixing in of the signal components of the other stereo channel that are decisive for directional perception ( crossfeed ), Acoustic directional mixers simulated with DSP hardware or the Dolby Headphone method are sufficient.
The diffuse field equalization also contributes to a significantly more spatial impression and an improved front-back localization (outside of the head localization): The linearity of the headphones is not matched to a direct sound source, but rather to many sound sources from different angles in accordance with natural hearing Generate diffuse sound field (Recommendation ITU-R BS.708 of the International Telecommunication Union ; see glossary Hifi-Forum).
Experiments on the functionality of the directional localization of human hearing are mainly carried out using headphones. The term lateralization is used for this , in order to present differentiated test signals separately to the ears and to examine their effects on the lateral deflection ( direction of the auditory event ).
Connection and reinforcement
Since headphones are usually passive systems, they must in most cases be connected to an amplifier in order to be able to generate a signal with an acceptable volume. Stereo headphones are usually connected via an asymmetrical plug-in system with a common ground, as is the case with the regular 3-pin jack plug with a diameter of 6.3 or 3.5 millimeters (for small devices such as dictation machines, MP3 players or cell phones often also 2, 5 millimeters). When using stereo headphones with a symmetrical amplifier concept, a four-pin connector system (e.g. four-pin XLR connector) is necessary because of the separate grounding of the two stereo channels.
Earlier systems also used five-pin DIN square plugs (rotatable by 180 ° with loudspeaker switch-off ), loudspeaker plugs according to DIN 41529 (also cascadable) or simply banana plugs . Exceptions are, for example, detector receivers and old telephone systems with carbon grain microphones that do not require an amplifier.
The headphone sockets of portable music players or amplifiers are often fed by low-impedance LF amplifiers, which means that headphones with a lower input impedance can be operated with a sufficient level and good attenuation . High-impedance amplifiers such as tube amplifiers have output impedances of sometimes 100 ohms, which makes headphones with a higher impedance necessary to achieve approximately similar attenuation values. Since low-impedance headphones need less power to reach the same level, portable music players have longer battery life with them. Electrostatic headphones require a higher voltage (for example 280 or 580 volts) and must therefore be connected to their own power supply units or via a transformer to the speaker outputs of a full or power amplifier.
Market volume and spread
In 2020, seven out of ten (71 percent) German citizens aged 16 and over stated in a representative survey that they own headphones. This roughly corresponds to the previous year's figure (70 percent). Earphones with cables are particularly widespread (46 percent share of headphone ownership in Germany), followed by completely wireless true wireless models (24 percent) and earplugs that are connected to one another with a (neck) cable but connected wirelessly to the playback device become (19 percent). 18 percent own wireless shell headphones, 15 percent their wired version. In 2012, 11.1 million headphones were sold in Germany for 306 million euros.
Even if the ability of headphones to cause hearing damage has been well documented, it is still not clear to what extent these are actually involved in the spread of hearing damage among children and adolescents. The studies on this do not give a clear picture. According to various studies, headphones in connection with MP3 players or similar devices can generate very high and potentially harmful noise levels of up to 126 dB at the eardrum. Be particularly careful with volume settings above 60%.
Although the use of headphones has increased continuously since the middle of the 20th century, large health surveys in the USA between 1988–1994 and 2005/2006 found little or no increase in the prevalence of hearing loss among adolescents. Other sources of noise, such as visits to discos, are also discussed as a further cause of the slight increase in prevalence.
According to the Physikalisch-Technische Bundesanstalt, so-called artificial heads can be used to measure the stress on the ears from headphones . In the literature, the maximum noise threshold is given as a level of 85 dB over eight hours, from which irreversible hearing damage can be expected. This corresponds, for example, to 88 dB over four hours, 91 dB over two hours and so on (see also noise-related hearing loss ).
- Historical newspaper article about Nathaniel Baldwin as the inventor of the headphones. (English)
- Book Radiola: The golden Age of RCA , at Google Books (English)
- Stax, manufacturer of electrostatic headphones
- Headphone Impedance, delamar.de
- Glossary HiFi forum
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- Joachim Hofer: The television drama has become Loewe's undoing Handelsblatt from July 1, 2019, accessed on December 18, 2019.
- How many headphones are bought each year? testbericht.de, accessed on August 28, 2013.
- Hayo A. Breinbauer et al .: Output capabilities of personal music players and assessment of preferred listening levels of test subjects. Outlining recommendations for preventing music-induced hearing loss. The Laryngoscope 122.11 (2012): 2549-2556.
- Elisabeth Henderson, Marcia A. Testa, Christopher Hartnick: Prevalence of noise-induced hearing-threshold shifts and hearing loss among US youths. Pediatrics 127.1 (2011): e39 – e46.
- Jerry L. Punch, Jill L. Elfenbein, Richard R. James: Targeting hearing health messages for users of personal listening devices. American journal of audiology 20.1 (2011): 69-82.
- Report on possible hearing damage caused by excessively loud toys , ptb.de (German), accessed on February 3, 2011