A microphone or microphone is a sound transducer that converts airborne sound as alternating sound pressure vibrations into corresponding electrical voltage changes as a microphone signal. This distinguishes microphones from pickups that convert solid-state vibrations. Underwater microphones are called hydrophones .
In the common design, a thin, elastically mounted membrane follows the pressure fluctuations of the sound. Through its movement, it simulates the temporal distribution of the alternating pressure. A transducer, which is mechanically or electrically coupled to the membrane, generates an audio frequency alternating voltage corresponding to the membrane movement or a corresponding pulsating direct voltage .
History of the microphone
Developments in the microphone
The development of the microphone went hand in hand with the development of the telephone . In the history, the basic transducer principles are listed, the different acoustic designs resulted in the course of the improvement of individual models.
The Italian engineer Antonio Meucci , who emigrated to the USA , developed a telephone in 1860 based on an electromagnetic transducer that he had also invented. However, he was not a successful businessman and was not granted a patent. The Scottish deaf-mute teacher Alexander Graham Bell , who is now mostly cited as the inventor of the microphone and who worked in the laboratory in which Meucci's invention was stored, applied for a technically similar patent on February 14, 1876. In 1887, the US government initiated proceedings to cancel the patent. However, this was discontinued after Meucci's death and the expiry of the patent.
In the course of the development of what he called the "telephone", Philipp Reis was the first to build a contact microphone, which he presented to the public for the first time in 1861 as part of his telephone prototype. Based on the model of an auricle, Reis recognized that instead of an eardrum, a horn covered with a membrane could also be used. At Reis, this bell jar ended in a case. He provided the membrane with a platinum contact which, when at rest, just touched another contact that was fixed in the housing. This contact and an external resistor is DC passed. If there was an alternating sound pressure on the membrane, it began to vibrate, which led to the contacts being more or less compressed depending on the movement of the sound waves . With this experimental set-up, Reis had invented the contact microphone, from whose principle the carbon microphone was later developed, which was used for recordings in the early days of broadcasting.
The realization that carbon can very easily convert the vibration of a diaphragm into electrical impulses led to the development of the carbon microphone at the end of the 19th century . In 1877, Emil Berliner developed a sound transducer in Bell Labs , USA, which used the pressure-dependent transition resistance between the membrane and a piece of carbon to generate signals. However, David Edward Hughes is regarded as the inventor of the carbon microphone , who first publicly presented a similar development based on carbon rods on May 9, 1878 at the Royal Academy in London. Hughes was also familiar with Philipp Reis' contact microphone, having experimented with an imported telephone from the German inventor in 1865 and achieved good results.
In the same year, the Englishman Henry Hunnings improved the microphone by using grains of coal instead of carbon sticks. The carbon microphone in the form in which it remained basically unchanged for the next 100 years was constructed by Anthony C. White in 1890. This “carbon grain microphone” was in use as a studio microphone until the 1940s; today it is considered the first “real” microphone and was only replaced by the condenser microphone .
Georg Neumann developed the carbon microphone further in 1923, which greatly improved the sound quality, especially at low frequencies. His breakthrough came with the development of the low frequency (NF) condenser microphone . The membrane and the counter-electrode form a capacitor that is charged to a direct voltage; the movement of the membrane changes the capacitor capacity, from which the signal is obtained. This transducer principle was qualitatively far ahead of the sound recording technology of its time and is still standard today for microphones of the highest quality.
In 1928 Georg Neumann founded a company to market his condenser microphone, Georg Neumann & Co KG in Berlin, which is still one of the leading microphone manufacturers today. The first functional production model, the Neumann CMV3 , also called the “Neumann bottle”, can be seen on many contemporary film recordings. The first microphone with electrically switchable directional characteristics is also legendary , the Neumann U47 from 1949. It is still one of the most sought-after and expensive microphones today: a functional, well-preserved U47 is sold for around 5000 euros.
From 1920 the radio came on. Stage actors and cabaret artists who now appeared on the radio found the microphone irritating. A microphone instead of speaking to an audience took some getting used to; Moreover, by the late 1920s, microphones were so sensitive that you no longer had to shout into them. The 1929 BBC Hand Book dedicates a separate chapter to the microphone with the heading "My Friend Mike" ( Mike as the English short form for microphone ):
- “I've known Mike for a long time. I first met him in 1922. He didn't have a throne then, just hung around like that. I think it is very sensitive because it is wrapped in cotton towels. I like Mike because he always speaks so well of me and is never sick and introduces me to people I would never have known without him. "
In 1962, Gerhard M. Sessler and James Edward Maceo West invented the electret microphone , a variant of the condenser microphone, which today is the most common type of microphone with a 90 percent market share. Gerhard M. Sessler and Dietmar Hohm also invented the silicon microphone at the TH Darmstadt in the 1980s .
Important manufacturers of condenser microphones: Sidney Shure Georg Neumann GmbH Berlin (part of Sennheiser since 1991), Sennheiser (specialty: HF condenser microphones), Microtech Gefell GmbH (in Gefell , formerly Neumann & Co. KG , later VEB Microphone Technology Gefell ), Schoeps , Danish Pro Audio (formerly Brüel & Kjaer ), AKG Acoustics , Brauner Microphones.
Important manufacturers of measurement microphones: Brüel & Kjaer, GRAS, Microtech Gefell GmbH, Norsonic, PCB Piezotronics.
Depending on the acoustic design of the microphone, the membrane follows the sound pressure ( pressure microphone , non-directional microphone) or the sound pressure gradient ( pressure gradient microphone , directional microphone). The converter principle is decisive for the technical quality of the microphone signal , which is characterized by the signal-to-noise ratio , impulse fidelity , harmonic distortion and frequency response .
Microphone converters can be categorized as follows:
The dynamic microphone works on the principle of electromagnetic induction . From a technical point of view, the speed of the membrane movement in the dynamic microphone leads to the signal, not the momentary deflection, which is why it is also known as a speed receiver . The main area of application of dynamic microphones is the live area . In addition to live use, the dynamic microphone is also used to mike drums (snare drum, cymbals, tom toms, etc.), occasionally also for vocal or instrument recordings.
Moving coil microphone
The moving coil microphone is a type of dynamic microphone. The term relates to the structure of the transducer: In moving coil microphones, the membrane is firmly connected to a coil ( moving coil ), as in an electrodynamic loudspeaker , which is moved by the membrane movement in a permanent magnetic field (air gap of a pot magnet). The relative movement of the coil and the magnetic field generates the signal voltage through induction. The advantages of this type of microphone are:
- relatively robust against mechanical loads
- tolerates high sound pressures (advantageous for singing and loud instruments)
- does not require a power supply
- is relatively inexpensive.
Moving coil microphones have an upwardly limited playback spectrum due to the coil mass and poor impulse behavior. They are good for close-ups because their non-linear distortion is low, even at high sound levels.
A ribbon microphone (engl. Ribbon microphone ) is a design of the dynamic microphone. With this type of microphone, the transducer principle and acoustic functionality are closely linked.
The membrane of the ribbon microphone is a zigzag folded aluminum strip two to four millimeters wide and a few centimeters long. It is only a few micrometers thick. When stimulated by incoming sound , the movement in the magnetic field induces a voltage corresponding to the speed of movement, which can be tapped at the ends of the aluminum strips.
Ribbon microphones have an almost linear frequency response in the operating range ; their extremely light membrane gives them good impulse behavior . In principle, sound can reach the membrane from both sides. The acoustic design is therefore that of a pressure gradient microphone. The directional characteristic of a figure eight follows from this. Ribbon microphones are not suitable for recording the lowest frequencies.
The condenser microphone (engl. Condenser microphone ) operates according to the principle of the physical capacitor . Since the diaphragm deflection and not the diaphragm speed leads to the signal, the condenser microphone is technically an elongation receiver .
Condenser microphones come in many different forms, as this term only describes the transducer principle. However, the term has established itself colloquially as a microphone class, as sound properties are closely linked to the principle of conversion.
With the condenser microphone, an electrically conductive membrane a few thousandths of a millimeter thick is attached to a metal plate and is electrically insulated. From a technical point of view, this arrangement corresponds to a plate capacitor , which has an electrical capacitance . Incoming sound causes the diaphragm to vibrate, which changes the distance between the two capacitor foils and thus the capacitance of the capacitor. Such devices can also be implemented as microsystems .
Low frequency technology (NF technology)
As soon as an electrical voltage is applied, a potential gradient arises between the membrane and the plate . In the case of a high-resistance supply (typically gigaohm range), the fluctuations in capacitance lead to voltage fluctuations with an essentially constant charge of the capacitor - an electrical signal. As an RC element, the capacitance of the capsule and the supply resistor form a high-pass filter that limits the lowest frequency that can be transmitted. A voltage source is required to achieve the potential gradient between the capacitor plates and to supply the microphone amplifier ( impedance converter ). Usually you use the 48-volt phantom power of the microphone preamplifier or the mixer ; see also: Symmetrical signal transmission .
High frequency technology (HF technology)
Alternatively, the capacitance of the capacitor can also be measured using HF technology. For this purpose, the impedance can be measured, in particular in a measuring bridge with phase-sensitive readout, or the capsule is used as a frequency-determining component in an oscillator. This makes the restriction to high-impedance follow-up amplification superfluous. It is also possible to generate a signal down to any low frequency (the microphone is actually a fast barometer). The capsule is optimized for other parameters than with the NF technology. B. be less voltage resistant. The circuit complexity is usually higher than with LF technology. If the supply is not clean (with remnants of the clocking of a switch generator for the phantom power), intermodulation can cause interference. Here, too, the circuit is mostly supplied via phantom power.
Condenser capsules are used both as pressure microphones and as pressure gradient microphones. Some condenser microphones have a switchable directional characteristic . This is made possible by the combination of two pressure gradient microphones (double gradient microphone).
The condenser transducer is the recording standard in recording studios today because of the high signal quality. However, it is quite sensitive (especially to moisture of any kind) and can even be damaged by very high sound pressure. Dynamic sound transducers therefore dominate in the sound and live areas.
Electret condenser microphone
The electret microphone is a special type of condenser microphone. An electret film is applied to the capacitor plate opposite the membrane , in which the electrical membrane prestress is so to speak “frozen”. Some microphone capsules contain a microphone preamplifier for the weak signal streams. Simple microphones require a low operating voltage of 1.5 volts. The current requirement of 1 mA favors the use in mobile devices and on / in computers.
Such electret microphones are not suitable for high sound pressures; the low supply voltage of the preamplifier limits the possible transmittable sound level. Modern electret microphones are also used for studio and measurement purposes.
The carbon microphone is an electroacoustic transducer principle in which the pressure fluctuations of the sound cause changes in an electrical resistance. The pressure-dependent transition resistance in the carbon granulate stored behind the membrane is used for conversion .
Carbon microphones have poor reproduction properties; the mass of the metal membrane limits and distorts the frequency response, the carbon grains cause noise, especially when moving. The non-linear relationships between pressure and contact resistance of the carbon grains result in non-reproducible, non-linear distortions.
The main advantage of the carbon microphone is its high output signal - in a DC circuit it provides a signal sufficient for remote transmission and playback with an electromagnetic earpiece. Reinforcement is not necessary.
Carbon microphones were therefore used in large numbers in telephones in the past . It is believed that the invention of the carbon microphone greatly accelerated the development of telephony. After a certain time, the granular carbon in the microphones of the telephones condensed, which led to a significant reduction in voice quality. For this reason, dynamic capsules or electret capsules with an additional circuit for amplification and signal adjustment have been used since the 1970s. These modules could replace the carbon microphones in telephones without changing the circuitry.
In professional sound engineering, the carbon microphone was replaced by the condenser microphone as early as the 1920s and 1930s . In communications technology, the electret microphone dominates the market today .
Piezo or crystal microphone
A piezoelectric microphone is a microphone design, the converter principle on the properties of piezoelectric based elements. A membrane follows the pressure fluctuations of the sound. It is mechanically coupled to a piezoelectric element. It is minimally deformed by the pressure fluctuations and outputs these as electrical voltage fluctuations. Piezoceramic lead zirconate titanate (PZT) is usually used as the piezoelectric material .
Such microphones were popular in the 1930s to 1950s. They are mechanically robust and have advantages due to their simple design. A major disadvantage of this converter technology is the high distortion factor . In principle, they are not suitable for high-quality recordings and could not prevail over the carbon microphone in telecommunications technology either . Vibration conversion using piezoelectric elements, on the other hand , is widespread in contact sound transducers ( pickups in turntables and for instruments, structure-borne sound pickups , vibration pickups ). The forces available here are usually much greater and lead to better transmission properties than is the case with airborne sound.
The acoustic design is decisive for the directional characteristic and the frequency response. In contrast to loudspeakers , the size of the diaphragm does not play a role in microphones with regard to their bass reproduction, since microphones, like human ears, only act as sensors and not, like loudspeakers, have to compress air in the low-frequency range with the smallest possible stroke. Infrasound sensors are an exception .
In microphone technology, the directional characteristic describes the sensitivity of a microphone in the form of a polar diagram, i.e. the output voltage in relation to the sound pressure, depending on the angle of sound incidence . One can differentiate between the conditions in the direct field and in the diffuse field .
The directional characteristic depends on the acoustic design of the microphone capsule and on external form elements (e.g. boundary microphone , shotgun microphone ). The strength of the directional effect is described with the degree of bundling or the bundling factor . The directional characteristic of microphones is measured in anechoic rooms in the direct field D. The microphone is rotated at a distance of 1 m from a 1 kHz sound source and the output level of the microphone signal is measured as a function of the angle of incidence.
The directional effect is characterized by characteristic patterns:
- Sphere (omnidirectional = non-directional)
- Eight (figure-of-eight characteristic = dipole, opposite polarity front and rear )
- Club (club characteristic, shotgun)
A pure pressure microphone has no directional effect, i.e. a spherical directional characteristic (omnidirectional). A pressure gradient microphone in its pure form (e.g. ribbon microphone ) provides a figure eight as directional characteristic. The directional characteristic "lobe" is obtained through the principle of the interference tube ( shotgun microphone ).
The standardized shapes between omnidirectional and figure-of-eight characteristics are “wide cardioid”, “cardioid”, “supercardioid” and “hypercardioid”.
Due to the complex conditions of the sound field, the real directional character in practice differs individually from these theoretical patterns. Strong deviations in the pattern can be observed when the wavelength of the signal frequency is in the range of the capsule diameter. Therefore, the smaller the membrane diameter, the smaller the distortion. The greatest deviations are to be expected with pressure gradient microphones , the directional character of which has been modified from a pure figure of eight to the cardioid with acoustic time-of-flight elements or a double-diaphragm design. In the case of pressure microphones, for example, the pressure accumulation effect as well as sound shadowing by the microphone body lead to a directional effect at high frequencies.
If the deviations from the theoretical directional characteristic are to be avoided even at high frequencies, the microphone may only have a fraction (less than half) of the wavelength at the highest required frequency as the dimensions of the sound transducer. This is achieved with measuring microphones with a capsule typically 12 mm down to 3 mm in diameter. Since the recording area and the recorded sound energy are the square of the diameter, this leads to less sensitive microphones with possibly poorer noise behavior. The noise is of course also dependent on the polarization voltage, the components and the circuitry of the subsequent amplifier.
Some microphones must be used with sound sources with directional sound from the side. Such microphones must also have a suitable frequency response from the side, which only a few manufacturers manage (see example diagram).
Pressure microphones (microphone with pressure characteristics, pressure receivers ) are mainly non-directional (omnidirectional). This construction is widely used in the form of electret microphones, e.g. B. in cell phones or headsets .
In contrast to a pressure gradient microphone, the microphone capsule of a pressure microphone is closed at the rear: the sound-absorbing membrane is attached in front of a cavity closed at the rear. This prevents the sound from migrating around the membrane and affecting the rear side as well. Incoming sound is always reproduced with the same polarity regardless of the direction of incidence. The pressure microphone reacts to fluctuations in air pressure in a similar way to a barometer . Such a microphone can therefore also be used at very low frequencies down to the infrasound range. In the metrology therefore usually pressure microphones are used.
The directional characteristic of a sphere is always given for pressure microphones. All microphones with directional characteristics other than those of the sphere, especially those with switchable characteristics, are realized with the design of the pressure gradient microphone.
Pressure gradient microphone
In the case of a pressure gradient microphone (microphone with pressure gradient characteristics), the microphone capsule is open on the back, in contrast to a pressure microphone - the membrane is accessible for sound from all sides. This microphone design is scientifically also known as a pressure gradient receiver or a fast receiver .
Since the sound also reaches the back of the membrane, it does not follow the absolute sound pressure, as is the case with the pressure receiver, but the pressure gradient or the speed of sound . A typical example is the ribbon microphone.
The pressure difference arises because the sound has to migrate around the membrane in order to also affect the rear. The time Δt required for this results in a “pressure difference” (a pressure gradient).
- Δp = p front - p back
For a given Δt , the faster the change in sound pressure, the higher the pressure gradient. The resulting pressure gradient Δp decreases accordingly towards lower frequencies . See: acoustic short circuit .
If a signal hits the diaphragm exactly from the side (90 °), there is no pressure difference and therefore no diaphragm movement. When sounding on the back of the membrane, the polarity of the microphone signal is reversed (voltage inverted).
The directional characteristic in the described symmetrical basic design is that of a figure eight. The design of the microphone also allows other directional characteristics that lie between omnidirectional and figure eight, such as the wide cardioid, cardioid, supercardioid and hypercardioid.
All directional characteristics apart from the sphere (pressure microphone) can also only be realized with pressure gradient microphones.
The term boundary microphone , Engl .: " boundary layer " or " pressure zone microphone ," a microphone design called display sound operation. It is a special case because the microphone body is a conceptual part of the acoustic design.
The microphone body is a plate on which a pressure microphone capsule is usually embedded flush with the membrane. Its directional characteristic thus results in a hemisphere. The converters are usually designed as a capacitor or electret. This design was developed in order to take advantage of the advantageous acoustic properties that occur on sound-reflecting surfaces without impairing the sound field itself. The microphone is placed on a large sound-reflecting surface, e.g. B. on the floor or a table. In this way, it receives the maximum sound pressure without superimposing room sound components, which leads to a balanced frequency response and an acoustically good spatial impression:
- No annoying reflections occur on reverberant surfaces , as this is where they arise.
- In rooms, their natural resonances are picked up less by this microphone; By placing the microphone on a boundary surface, there are no sound-coloring comb filter effects that occur within the room. With moving sound sources there are no differences in timbre.
- Room signals R are attenuated by 3 dB compared to direct signals D, which means that direct sound is preferred.
In a shotgun microphone , also interference microphone (engl. Shotgun microphone ) of the microphone body is formed by a pre-built interference tube added.
A shotgun microphone has a distinctive lobe characteristic, which is created by an interference tube that is open to the front and is installed in front of a pressure gradient microphone and provided with lateral slots or bores. Depending on the pipe length, this causes a significant increase in the directional effect from around 1 to 2 kHz. At lower frequencies the directivity corresponds to that of the microphone capsule (cardioid or supercardioid pattern).
Concave mirror microphone
Microphones in the focus of a parabolic mirror are used as directional microphones for bird watching, among other things . Depending on the size of the mirror, the directional effect only occurs at high frequencies (from around 1 kHz).
The alternating voltage resulting from the sound conversion, the microphone signal , is characterized by the following parameters:
The frequency response of a microphone results from its acoustic design, the microphone tuning and the transducer principle. The smaller and the lighter the membrane (and possibly the moving coil), the fewer natural resonances it has in the audible frequency band (20 Hz to 20 kHz). The less it resonates , the more undistorted it reproduces the sound. The acoustic design of the pressure gradient microphone, for example, places limits on low frequencies; In addition, the frequency response of all microphones is dependent on the acoustic angle (directional characteristic, pressure accumulation effect ) and, in the case of pressure gradient microphones, on the distance to the sound source ( close-up effect ).
Microphones convert sound pressure into alternating voltage . The field transfer factor is measured in millivolts per Pascal (mV / Pa), which increases roughly proportionally with the membrane size. For example, with electret microphones, small 1/4-inch capsules have 5 to 10 mV / Pa, 1/2-inch capsules 30 to 50 mV / Pa, and one-inch capsules up to 100 mV / Pa.
The smaller the capsule, the more susceptible it is to noise due to the low transfer factor. However, the cause of the noise is not the microphone membrane, but the electrical internal resistance of the capsule. For example, with dynamic microphones this is the resistance of the moving coil, with electret microphones it is the load resistance. The higher the internal resistance, the more noisy the microphone, but generally the higher the output voltage. Compared to moving coil microphones, electret capsules have a terminating resistance that is at least ten times higher and therefore at least √10 times (√10 ≈ 3) higher noise - but they also deliver significantly higher signal voltages.
As impedance is called the electrical output resistance of the microphone with AC voltage in the audio signal region. While dynamic microphones often have impedances around 600 Ω, capacitor capsules have a very high impedance, but since they require a working resistance, only this appears as an impedance to the outside (with electret microphones in the range between 1 and 5 kΩ). The higher the impedance of the microphone output, the more noticeable the cable capacitance of the connection line: High frequencies are attenuated by long cables.
The distortion factor indicates the percentage of non-linear signal distortions in the useful signal. With dynamic microphones, the distortion factor is low, non-linear distortion usually only occurs at very high, irrelevant sound levels . In electret and condenser microphones, the non-linear relationship between the deflection of the diaphragm and the voltage output distorts the signal non-linearly above certain levels.
Electromagnetic susceptibility, hum
The most common hum interference is caused by ground loops (also known as hum loops). In most cases, it is not the microphone itself, but the cable and the type of connection that are responsible for such interference. These can be eliminated by using differential (symmetrical) cable routing or ground cables that are routed separately for shielding. The susceptibility to interference increases with the length of the cable. A good shielding of the cable can eliminate the electrical interference, symmetrical cables are insensitive to magnetic interference anyway.
Microphone cable partially have a Mikrofonieeffekt , they are sensitive to impact sound and motion when their braid or shielding generated upon movement changing contact resistances. Microphony poverty is a quality criterion for microphone cables.
Digital microphone interface
The AES42 standard defines a digital interface for microphones that directly generate a digital audio stream. The processing chain impedance converter - microphone preamplifier - A / D converter is integrated in the microphone housing. The connection is made via an XLR plug, the power supply of the electronics via phantom power (Digital Phantom Power (DPP), 10 V, max. 250 mA). By modulating the phantom voltage, such microphones can be operated remotely, for example to set attenuation / directional characteristics.
- Symmetrical signal routing : mono signal, three wires: ground, positive signal pole "Hot", negative signal pole "Cold"
- Asymmetrical signal routing: mono signal, two wires: ground, signal
- Asymmetrical signal routing: stereo signal, three wires: ground, left signal, right signal
Symmetrical signal transmission is less susceptible to interfering signals, especially with long cable lengths.
Overview of common audio connectors: audio connector
XLR cannon plug,
3 -pin + housing ground
|NAB 6.35 mm
jack plug ,
|NAB 3.5 mm
jack plug ,
Large / small cloth plug ,
3-pin + housing ground;
|application||Analog mono microphone,
AES42 digital microphone signal ,
studio and stage
|Stereo microphone, home
|Occupancy||Pin1 = ground
Pin2 = hot
Pin3 = cold
housing = shielding
|Tip = Hot / Left
Ring = Cold / Right
Ground = Ground, shielding
|Tip = left
ring = right
ground = ground
|Pin1 = Hot
Pin2 = Cold (small ground)
Pin3 = ground (small cold)
|electric wire||three-wire, shielded||three-wire, shielded||three-wire, shielded||three-wire, shielded|
Stereo signals Line signals
digital audio ( AES / EBU )
DMX (lighting technology)
insert signals (amplification)
signals Stereo signals
Line IN / OUT
These connection standards are the most common today. Some older microphones have a DIN or Tuchel plug . Occasionally there is also the "Klein-Tuchel" - especially for compact clip-on microphones with a separate radio transmitter.
The following applies to all microphones: The “male” on the microphone plug emits the signal and the “female” on the cable coupling accepts the signal.
Simple microphones are asymmetrical and only have a coaxial cable (2 lines) as a connection line . This is also the case with electret microphones with tone wire feed - they work on the PC / sound card by using the supply voltage (usually 5 V) provided at these microphone inputs and working on the source resistance (a few kiloohms) of this voltage.
Wireless microphones are used wherever a cable connection is disadvantageous for technical, practical or optical reasons. Dynamic vocal microphones with integrated transmitters ( picture ) can be found on stages . Electret clip-on microphones or headset microphones (also known as neckband microphones or headset ) with a separate battery-operated radio transmitter ( bodypack ) are often used in television productions or in the performance of musicals .
The main disadvantages of radio transmission are a high purchase price and higher operating costs ( battery operation ).
In Europe, radio microphones usually transmit the useful signal in a frequency-modulated (FM) manner on the registration-free frequency band around 433 or above 862 MHz, the range is between 100 and 250 m. Which frequency bands can be used depends on the regulations of the respective country. In Germany there are also general assignments in the range from 790 to 862 MHz, which, however, expired in 2015 due to the digital dividend . In February 2011, the frequency range of 823 to 832 MHz, known as the duplex center gap (also known as the duplex gap or center gap ), was allocated for wireless microphone use . This assignment is limited until December 31, 2021. In April 2020, the frequencies 470 to 608 and 614 to 694 MHz were generally assigned in a channel grid of 25 kHz until December 31, 2030, which means that the fees for the approximately 18,000 individual assignments on these frequencies to date omitted. Signal dropouts due to the superposition of radio waves are avoided in professional transmission systems by using double reception technology ( antenna diversity , English true diversity ). To increase the system dynamics, a compander system consisting of a compressor on the transmitter side and an expander on the receiver side is used; this achieves a signal-to-noise ratio of up to 110 dB. Some models transmit the signals digitally (then mostly in the 2.4 GHz ISM band). The digital systems are less sensitive to RF interference: With the FSK or PSK modulation methods, the frequency or phase position of the signal can be recognized and reproduced despite RF noise.
Kate Bush is considered to be the first artist to have a headset with a wireless microphone built for use in music. For her tour Tour of life 1979 she had a compact microphone connected to a self-made construction made of wire clothes hangers , so that she did not have to use a hand microphone and had her hands free and could dance her rehearsed choreography of expressive dance on the concert stage and sing with the microphone at the same time . Later, her idea was also adopted by other artists such as Madonna or Peter Gabriel and used in performances.
Microphones can also be categorized according to the application:
- according to the size of the membrane (small membrane / large membrane, the limit is 1 inch),
- according to the directional characteristic (see acoustic design)
- according to the external design:
- Handheld microphone
- Clamp, clip-on or lavalier microphone (lavalier microphones are usually condenser microphones and require phantom power).
- Announcement microphone with push-to-talk button, stationary use with stand and " gooseneck " or as a handheld microphone e.g. B. for walkie-talkies
- as an integral part of devices such as headsets , telephones, hearing aids .
- after use:
- Speaker microphones are microphones whose characteristics and volume are specially optimized for speech. These usually have an integrated cage as pop protection and a strong directional sensitivity to the front.
A very recent development (as of 2020) are membrane-less microphones that record air vibrations using optical methods. Because of their very high bandwidth, these microphones are particularly suitable for high-frequency ultrasound recordings.
Multi-channel microphone systems
Two microphones together form a microphone system for stereo recordings , which thus capture a very specific recording area for the direction of the audio event on the full stereo loudspeaker base. There are a number of stereo miking methods based on psychoacoustic effects:
- Runtime stereophony
- Intensity stereophony
- Equivalence stereophony
- Binaural stereophony
With all methods (stereo or surround) so-called support microphones are set up in complicated recording situations in order to emphasize soft voices a little more. Their level is weakly mixed with the actual main signal.
Acoustic measurement technology uses microphones with omnidirectional characteristics and a frequency response that is as linear as possible. A special application is the localization of sound sources using microphone arrays .
Wind screen (pop screen)
A wind or pop screen protects microphones from air currents that occur when speaking or outdoors and that cause rumbling, rumbling, “popping” (especially when closing sounds like “B” or “P”) background noises. Sometimes the noises are so loud that they overdrive the following amplifier and a real pop is created. Pressure receivers are less susceptible than pressure gradient receivers. Foam or fur covers are used ( jargon : windjammer , fur , Zwelch , dead cat , dog , poodle or pompom ) and pop umbrellas in recording studios. Many microphones have a permanently installed basket made of metal and gauze to protect the membrane , which also keeps wind out to a certain extent . In the case of studio microphones, the pop screen is also used to keep moisture and condensate away from the sensitive condenser membrane when speaking and singing.
In order to decouple the rumbling or rumbling in the audio signal, caused by vibrations ( structure-borne noise ), from the microphone, studio microphones are hung on the stand in an elastic suspension, the spider . Spiders consist of a holder in which the microphone can swing freely through a rubber band stretched in a zigzag. Carbon microphones are particularly sensitive to vibrations, which is why you can often see speaker microphones outside the studio in elastic holders in old photos. Vocal microphones usually have a mounting of the microphone capsule with elastomer foams to decouple handling noises .
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- Microphone sensitivity dB re 1 V / Pa and transmission factor mV / Pa
- Historical microphones, with sound samples
- Portraits of many classic microphones, excellent photos
- Beautiful photos - vintage microphones
- All microphone directional characteristics and other parameters (PDF; 314 kB)
- Collection of modern and historical microphones
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- Thomas Görne: Microphones in theory and practice. 2nd edition 1996, p. 87.
- Gerhart Boré, Stephan Peus: Replacement circuit for a carbon microphone - December 24, 2008 - ( Memento of December 24, 2008 in the Internet Archive ) - Neumann Company
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- EBS: microphone directional characteristics and further parameters - pdf Sengpielaudio
- EBS: Difference between hypercardioid and supercardioid - pdf - Sengpiel-Audio
- the directional characteristics (PDF; 79 kB) - EBS
- Michael Dickreiter: Handbook of the recording studio technology. 6th edition. 1997, Vol. 1, pp. 146, 161.
- Thomas Görne: Microphones in theory and practice. 2nd Edition. 1996, p. 167ff.
- Thomas Görne: Microphones in theory and practice. 2nd Edition. 1996, p. 39.
- Thomas Görne: Microphones in theory and practice. 2nd Edition. 1996, p. 41ff.
- Michael Dickreiter: Handbook of the recording studio technology. 6th edition. 1997, Vol. 1, p. 164.
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- Claire Laborey (Director): Kate Bush - Powerful and eccentric. In: ARTE France Documentary - Culture and Pop > Pop Culture . 2019, accessed September 18, 2019 .
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