Headphones

Headphones are small loudspeakers that are worn on or in the ears. In the early days of radio was heard only through headphones; However, in mono, that is, it was the same signal on both earphones. There are also headphones that have only one earpiece.

The inventor of the headphone has not been clearly established to date. Since the invention of the telephone and the radio headphone -like devices were used. So it was at about the telephone by Alexander Graham Bell already on a headset, but the same also served as a microphone and had to be moved alternately in use between the mouth and ear back and forth. Some sources suggest, however, the Americans Nathaniel Baldwin as the inventor of the headphone. Baldwin (1878-1961), founder and owner of Baldwin Radio Company in Salt Lake City, 1910, his " Baldy Phones " headphones listed on the market.

Known manufacturers of headphones include AKG, Audio -Technica, Beats Electronics, Beyerdynamic, Bose Corporation, Klipsch, KOSS, Philips, Pioneer, Revox, Sennheiser, Shure, and Sony.

Designs

• Earphones

• Ear canal headphones ( intra -aural ) or in- ear headphones / canalphones ( literally as " in-ear headphones " )

• Earbud earphones

• Over Ear Headphones

• A rare special form is the head speaker. These are two small speakers that are hung over his head and completely free sound for the ears. Thus, a more natural location ( see below) is possible. The best-known model is the AKG K 1000th

Variants of mussel headphones

• Open headphones

In the open type to connect to the outside world through the acoustic headphone is maintained throughout. To this end, the cover of the earpieces is permeable, ie perforated or provided with slots, and there are more permeable materials. The sound emitted from the diaphragm in both the ear and the direction to the outside. This is intended to create greater transparency be achieved, the sound is spatial. At the same time a better heat exchange takes place, unpleasant sensations such as heat accumulation or sweating are reduced. A disadvantage of this type that the sound waves produced from the headset and the environment are mutually audible noise from the outside reach the ears, conversely penetrates the reproduced sound outward and optionally perceived by the environment as disturbing.

The terms " open" and " closed " refer not to whether a headphone encloses the ear or resting, but on the insulation to the environment. Also, a circumaural headphones can be open, a resting also closed.

• Closed-back headphones

In the closed form, the ear is largely shielded from the outside, the sound plays only the direction of the ear. In the bass range is established by the shield more pressure. The construction is, in this type V.A. due to complex reflections and thus more expensive for the same sound quality. Another advantage is the better independence from the outside world, again with respect to noisy environments or by less harmful radiation to the outside. The resulting lack of air exchange heat generation is mainly during extended wear occasionally uncomfortable.

• Semi-open Headphones

Semi-open KH have to unite less, some extra- insulated openings to the outside as open and try the respective advantages of the other two designs.

Transducer technology

With headphones, there are, as with other speakers also different systems of sound conversion.

Electromagnetic

The design principle dates from the early days of audio technology, was used for both loudspeakers and headphones. It is typically an iron diaphragm moves, which radiates sound directly ( see picture). The current from the amplifier passes through two pre-magnetized permanent magnets with a coil similar to an electric magnet, the magnetic poles are located at a small distance behind the steel membrane.

Such transducers have been used for example in military communications; in Morse headphones and telephone receivers, they found also use.

Because of the extremely poor sound quality (very high harmonic distortion, severe frequency range, etc.) electromagnetic transformers are not manufactured anymore.

Electrodynamic

As a dynamic speaker, the sound conversion resulting from the motion of a fed from the audio signal coil in a magnetic field: a plunger coil in the center of the diaphragm is located in the narrow air gap of a head-mounted receiver frame, strong permanent magnets, and will at an applied audio frequency by the interaction of the constant and variable magnetic field longitudinal oscillations driven, which are transferred to the surrounding air.

To avoid excessive partial oscillation and for the sake of material inertia, the driver diaphragm is made ​​of lightweight material with high rigidity, eg, cellulose, plastic, metal.

The electrodynamic diaphragm actuator is today the most widespread, it offers cost-effective production, easy operation as well as the current state of the art and a correspondingly high construction costs highest playback quality.

Isodynamisch or ortho dynamic or magnetostat

The structural arrangement of the elements of the transducer is similar to that of a push-pull electrostatic speaker in which moves a constant electrified flat membrane between the driven with the high-tension audiofrequency perforated stators.

Isodynamic the transducer, however, the drive of the diaphragm is performed by the electrodynamic action of a regular audio frequency to a ( a surface coil) supplied from the center of the membrane outwards helically bonded or vapor-deposited conductor track. The uniformly clamped membrane thereby moves with applied LF voltage in a homogeneous magnetic field between the pole plates perforated because of the pressure balance of two opposing permanent magnets or several surface arranged magnetic rods.

A reasonable efficiency of isodynamic driver systems can be achieved, resulting in an unusually high weight and an unfavorable comfort of the headphones result only with relatively large and thus heavy magnet discs with high magnetic energy density.

Balanced Armature transducer

The Balanced Armature transducer design ( "BA", literally balanced armature ) to increase primarily the electrical efficiency by eliminating the stress on the diaphragm, as is characteristic of many other types of drives. The BA principle consists of a permanent magnet and a precisely centered in the magnetic field, movable mounted armature. In the center of the magnetic field there is no net force on the armature, hence "balanced" the term. Now, when current flows through the coil of the armature, the armature is magnetized so that it is easily moved in the one or other direction. The membrane is fastened to a drive in the anchor and then generates sound waves.

The design is not mechanically stable and the armature would be attracted to the permanent magnet, stick. Therefore, a rather stiff membrane with high restoring force is required to hold the armature in the 'balance '. Although the negative impact on the efficiency, this design can be better than any other produce sound from less power. Already in the 1920s, this principle was introduced as " Baldwin Mica Diaphragm radio headphones ".

Today they are typically used in ear-canal headphones ( in-ear earbuds ) and hearing aids due to their diminutive size and low impedance. They are usually on the hearing range of humans is limited ( about 20 Hz to 16 kHz) and require a seal more than other types of drivers to deliver their full potential. High -end models can use multiple BA drivers to represent the range of sounds better. Using a passive crossover these are combined to form an overall sound. There are also models that combine BA driver with classic coil diaphragm drivers for the bass range.

Electrostatic

The principle of the electrostatic actuator ( refer to the case of electrostatic speakers) operates as a reverse operated condenser microphone. The drive mechanism consists of a thin, conductive coated polyester membrane film which is electrically charged with the positive constant bias voltage ( bias or EHT) a high-voltage cascade and perforated between two metal plates, the stator is clamped. For a reasonable efficiency of the diaphragm drive a high drive voltage is required, which makes a special step-up transformer available, the primary side is connected directly to the low-impedance speaker outputs of a regular audio amplifier with sufficient output power.

Newer models work without the transfer technically unfavorable transformer together with specially designed headphone amplifiers that need to be operated to generate a reasonable volume level with very high symmetrical supply voltages of ± 500 volts. The highly strained tone frequency is fed to two perforated stators and moved the entire surface by the changing conditions of the electric field, the pre-loaded membrane film.

Despite the relatively simple structure of the acoustic transducer of electrostatic headphones is due to the higher operating expenses are usually higher in price than a model with electrodynamic drive.

Due to its extremely thin and so light diaphragm, which is often only a few micrometers thick, the frequency response of electrostatic headphones usually extends well beyond the audibility of about 20 kHz addition: the almost inertia-free response of the membrane makes the transducer extremely good signal fidelity that high of a resolution of the spatial information of the signal benefit. In addition, the isoplanar vibration behavior of the membrane provides a minimum of partial oscillation and thus helps with optimal design for extremely natural and clear sound result of electrostatic headphones.

Electrostatic headphones are indeed usually operated with voltages of 100 V to over 1kV, and are in this case on the listener's head, due to the extremely low currents their use is still considered safe. The most famous manufacturers is Stax Ltd.. , A Japanese company. Such systems are appreciated by audiophiles, but they are expensive to produce and therefore higher in price.

Piezoelectric

Piezoelectric transducers typically have a high efficiency and low sound quality ( no bass response, pronounced resonances). The impedance is high ( frequency-dependent, several kilohms ), they found, for example, use as a so-called crystal earphones for crystal sets.

Signal Connector

• Wired Headphones

• Headphones for induction loops

• Infrared headphones

• Analog Wireless Headphones

• Digital Wireless Headphones

Impedance

• Low impedance headphones: The impedance of the headphone is in the range 4-100 Ω: Electromagnetic and electrodynamic headphones, earphones
• Mittelohmige 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 kOhm: Electromagnetic headphones among other detector receiver (deprecated). In piezoelectric headphones, the impedance varies depending on the frequency even higher.

Headphones with active noise cancellation

See also noise- reducing headphones.

For some years there are headphones with active noise reduction based on the anti-noise technology. A microphone on the outside of the headset receives the external noise. An electronic mixing, add the reversed polarity oscillations. The signal is then mixed with the audio signal. The background noise and the admixed signal cancel out now. With this technique it is possible, especially to eliminate low-frequency noise active. This technique has been used for a long time in the headphones of aircraft pilots and Noise Reduction. By turning off the main tieffrequenteren noise could reduce the noise in the headphones of the pilots and thus the health burden.

A simpler and more effective noise suppression is the use of closed circumaural headphones. With suitable design higher attenuation than with active noise reduction are possible, especially above 500 Hz. This type of shielding also works at higher levels.

Directional information in headphone reproduction

The output from the headphone drivers sound acts directly only on the respective ear cup associated ear and not on the head and on both ears, as in natural hearing. In the intra- aural earphones also responsible for carrying important, complicated acoustic filter effect of the differently shaped in each individual ear anatomy is overridden.

Thus lacking the brain necessary for a reasonable sound evaluation HRTF, particularly indispensable for the acoustic localization of sound sources direction information: Instead of a natural front localization is caused by the maximum design strict separation of the two stereo signals through the headphones an unnatural in-head localization. To minimize this ICL there are various different approaches, ranging from a simple slight angling of the headphone driver from the headphone technology S-Logic manufacturer Ultrasone to more complex electronic manipulations such as the subsequent admixing the crucial for the perception of direction signal portions of the other stereo channel (Cross Feed ) and DSP hardware simulated acoustic direction mixer or the Dolby Headphone process rich.

The diffuse-field equalization contributes to a much more spacious feel and an improved front-back localization (except head localization ) at: The linearity of the headphones is not tuned to a direct sound source, but according to the natural listening to many sound sources from a variety of angles that a diffuse sound field generate (Recommendation ITU -R BS.708 the International Telecommunication Union; see glossary hifi forum).

In artificial head stereophonic ( binaural reproduction of sound recordings that were made on a dummy head ) Headphone playback is imperative.

Experiments on the functioning of the direction localization of the human ear are mostly done via headphones. There is the expression lateralization to separately to present differentiated test signals to the ears and to examine their effects on the lateral deflection ( Hörereignisrichtung ).

Connection and reinforcement

Since headphones are usually passive systems, they must be connected in most cases to an amplifier to produce a signal at an acceptable volume. The connection of stereo headphones is done usually on an unbalanced connector system with common ground as regular 3 -pole jack plug with a diameter of 6.3 or 3.5 mm ( for small devices such as voice recorders, MP3 players or mobile phones often also 2, 5 millimeters). During the operation of stereo headphones with a balanced amplifier concept is necessary because of the separate mass of the two stereo channels a four-pole connector system ( eg, 4 -pin XLR connector).

In previous systems also five pin DIN connector type ( rotated by 180 ° with speaker cut-off), speaker connectors according to DIN 41529 ( cascadable ) or simply banana plugs were used. Exceptions are, for example, detector receiver and old telephone systems with carbon grains microphones that work without amplifier.

Some headphones has its own volume control is installed, either integrated into the sufficiently large auricle or in the connecting cable.

The headphone jacks portable music players or amplifiers are often fed by low-frequency amplifier that can produce only low levels. For high standards (especially in the studio ), there are therefore special headphone amplifier that achieve particularly in high-quality and high-impedance headphones sound quality is better and higher volume. Headphones with high impedance are often found in high-end range. Electrostatic headphones require a higher voltage (eg, 280 or 580 volts) and therefore must be connected to separate power supplies or by transformer to the speaker outputs of a full or amplifier.

Others

• In 2012, 11.1 million headphones could be sold in Germany, which achieved 306 million euro revenue.

Risk of headphones

The headphone reproduction carries with unreasonably high listening levels due to lack of social control, a gradual damage of the highly sensitive inner ear and thus the risk of increasingly developing hearing loss. The problem is mainly that the risk is greatly underestimated by most users.

With headphones, and especially for the auditory canal airtight fitting earbuds, the sound transducer is located very close to the tympanic membrane, sound pressure levels up to 120 dB ( A) can be effective here. Sound with this intensity can already after short contact hearing damage ( see SPL ). If the ear for long periods with 85 dB ( A) sonicated, leading to irreversible damage to the hearing ( see noise induced hearing loss ).

To measure the load on the ears through headphones loud Physical- Technical Federal Institute called artificial heads can be used.