Dynamic microphone
A dynamic microphone is a microphone that converts sound pressure pulses into equivalent electrical voltage pulses according to the principle of electromagnetic induction . It is also called an electromagnetic microphone.
Working principle
All dynamic converters use the principle of induction to convert a rapid diaphragm movement Δv in m / s into a voltage change Δ U in volts. The moving coil microphone, a design that is reminiscent of a loudspeaker , is common today . Another type of dynamic converter is the ribbon microphone .
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 called a speed receiver . The main area of application of dynamic microphones is the live area. Condenser microphones are mostly used in the studio .
In contrast to condenser microphones, dynamic transducers generate their own signal voltage, so that they do not have to rely on external voltage sources and consequently do not need phantom power . The resulting voltage pulse is only sent via the microphone cable to connected devices for further processing without using the cable for power supply.
Physics of the dynamic microphone
Electroacoustic conversion principle of the dynamic microphone:
- (proportional)
Induction law for a dynamic microphone:
- Δ U = generated signal voltage as voltage fluctuation
- Δ v = change in the mechanical speed as the mechanical deflection speed of the conductor (membrane with voice coil)
- B = magnetic flux density which is proportional to magnetic field strength H is
- l = length of the electrical conductor as moving coil wire or ribbon
The formula shows that the conductor length l (coil wire or ribbon) has a decisive influence on the internal resistance (output impedance) of the microphone in practice. If the conductor length is very short, as with a ribbon microphone , the voltage generated and the internal resistance decrease accordingly. If the coil consists of a large number of turns - the purpose of a moving coil microphone is to ensure a high voltage - then the internal resistance is quite high. Even in the case of an inferior microphone that has only a weak magnetic flux density B , the generated voltage drops. Strong magnets, on the other hand, have the advantage of high signal voltage.
Designs
Moving coil microphone
The moving coil microphone (also moving coil microphone) is an electroacoustic transducer that works according to the electrodynamic principle of the dynamic microphone. Both the design of the pressure gradient microphone and that of the pressure microphone are common.
The term moving coil microphone refers to the technical arrangement of the components of the transducer: In the moving coil microphone, the membrane is firmly connected to a magnetic coil which “dips” into a static permanent magnetic field due to the membrane movement. See also: moving coil . The relative movement of the coil and magnetic field generates the signal voltage by induction. This is proportional to the speed of the membrane.
Moving coil microphones do not require any subsequent impedance matching or balancing ; both can be achieved by dimensioning and wiring the coil alone.
Basic disadvantages: The sound wave has to move the mass of the membrane with the coil and perform electrical work. Moving coil microphones therefore have a low sensitivity and show a sluggishness in the transient response , which means that the finest details are not recorded, which can, however, be desirable: They deliver an “earthy”, powerful sound, high-quality models are therefore also used for studio recordings. Moving coil microphones do not have as high a transmission spectrum as condenser microphones and are unsuitable for long-distance recordings due to their low sensitivity. The relatively high mass of the membrane system also makes it sensitive to structure-borne noise , such as handling noises; In order to reduce such interference, the entire technical unit (the microphone capsule) in high-quality moving coil microphones is mounted in the microphone housing so that it can vibrate.
The advantages of this type of microphone are that they are usually quite robust against mechanical loads and can withstand high sound pressures . They also do not need a power supply, which can be an advantage in mobile operation. The simple design allows inexpensive production and makes this type of microphone almost indestructible.
Ribbon microphone
A ribbon microphone (engl. Ribbon microphone ) is an electro-acoustic transducer, which, like all dynamic microphones operates on the principle of induction. The transducer principle and acoustic design are closely linked in the ribbon microphone.
The membrane of the ribbon microphone is a zigzag folded aluminum strip 2–4 mm wide and a few centimeters long. The strip is only a few micrometers thick. Depending on the design, one or two such strips are clamped between the two poles of a permanent magnet in such a way that they vibrate slightly to and fro when excited by incoming sound. The movement in the magnetic field induces a voltage proportional to the speed of movement, which is tapped at the ends of the aluminum strips.
A transformer must be connected downstream in order to increase the very low induced voltage by a factor of about 30. This also increases the impedance of the microphone from around 0.2 ohms to the output impedance of 200 ohms that is common in studio technology .
Ribbon microphones have an almost linear frequency response in the operating range ; the very low mass of the membrane gives them good impulse behavior . In principle, sound can reach the membrane from both sides. Their acoustic construction is therefore that of a pressure gradient microphone . The directional characteristic of a figure eight follows from this. They are not suitable for recording the lowest frequencies.
Ribbon microphones are sensitive to wind, vibrations and fast movements. The proximity effect is quite clear because of the pressure gradient at low frequencies. This booming effect in the vicinity of the sound source can be reduced by using a high-pass filter.
Ribbon microphones achieve very low diaphragm masses and could therefore, with restrictions, be viewed as high-speed sound receivers. Microphone developers contradict this assumption and prefer to use the word pressure gradient microphone or pressure gradient receiver.
literature
- Thomas Görne: Microphones in theory and practice. 8th edition. Elektor-Verlag, Aachen 2007, ISBN 978-3-89576-189-8 .
- Norbert Pawera: Microphone Practice . 4th edition. Franzis Verlag, Munich 1993, ISBN 3-932275-54-3 .
- Fritz Kühne: mono, stereo and transistor microphones. 7th edition. Franzis Verlag, Munich 1966.
- Michael Dickreiter , Volker Dittel, Wolfgang Hoeg, Martin Wöhr (eds.): Manual of the recording studio technology . 2 volumes. 8th, revised and expanded edition. Verlag Walter de Gruyter, Berlin / Boston 2014, ISBN 978-3-11-028978-7 or e-book ISBN 978-3-11-031650-6 .
Individual evidence
- ^ Michael Dickreiter: Handbook of the recording studio technology . 6th edition. 1997, volume 1, p. 189 ff
- ↑ Microphone Test 2016. In: mikrofon-tests.org. Retrieved November 2, 2016 .
- ^ Michael Dickreiter: Handbook of the recording studio technology . 6th edition. 1997, volume 1, p. 192 ff.