Microphonics

Microphonic (formerly microphonic ) is the property of electronic components, mechanical excitation ( airborne noise, structure-borne noise ) to respond to the change of their electrical parameters.

In the strict sense is understood in audio engineering, the term is an undesirable effect, operate at the non microphones unintentionally as transducer and thus cause interference. Also, one speaks of " Mikrofonieeffekt " or the "ringing " when a conversion of sound takes place on non- acoustic transducers. The English term for this is " ringing". The microphonic effect is quite commonly observed in electron tubes; Here mechanical vibrations of the housed in the vacuum system lead to clearly audible bell-like interference lengths in the output signal. The same is true for the system record - stylus. Other components such as capacitors, inductors or transformers have this effect even though to a much lesser extent. Changes in capacitance caused by stepping on cables are also counted for microphonics. Microphonic heard how the harmonic distortion, the distortion or noise and pops and crackle to the noise produced or the faults that occur.

Mechanisms of action

Electron tubes

In electron tubes, the control grid in the electron-rich space-charge region is near the cathode. By moving the grating relative to the cathode change there, the field conditions and directly affect the electron current to the anode. This leads directly to a low-frequency signal output at low frequency amplifiers. Therefore mikrofoniearme tubes with particularly rigid control grid are also provided for the pre-amplification of low-frequency signals. For example, the AC701, a triode used as an impedance transformer in condenser microphones, specified as microphonics.

In principle, all other electrodes are responsible for microphonics, the effect is, however, the control grid most, especially if it is a tube with high gain.

The vibration also when held capacitance change control grid / cathode plays a role, particularly in oscillators in FM receivers and transmitters.

Capacitors

When capacitors occur depending on the type of publication in two effects: the case of air capacitors ( variable capacitors, air trimmer) the capacitance changes due to changes in distance. This can lead, for example in an oscillator to a frequency modulation. If it is to the oscillator of an FM receiver or transmitter, the microphonic is directly heard as low-frequency signal. For ceramic capacitors with ferroelectric dielectric microphonic occurs by the piezoelectric effect. Changing mechanical stresses lead to an alternating voltage across the capacitor. Therefore, to avoid such capacitors as coupling capacitor in NF preamps.

Inductors, especially air coils, which are used in FM receiver and transmitter oscillators result in vibration- induced shape change to a frequency modulation. They are often, therefore, mechanically damped by wax or a piece of foam.

Inductors and transformers with core may cause interference voltages in vibration, depending on the material, due to the reverse effect of magnetostriction.

Cable

Microphone cable show microphonic in the form of crackling and noise when moving. This is due to the loose contact in the individual wires of the shielding with each other or to the metal surface.

Remedy

Apart from the use mikrofoniearmer components can remedy by damping of the relevant components or the entire unit. This is achieved with soft suspension, spring or rubber compounds or feet.

Incorrect use of the word microphonic

Partly be designated by the term microphonic inaccurately microphone types, microphone converter principles or microphone arrays. The proper names for this are microphone technique or miking. A recording with multiple microphones is a Polymikrofonierung. In contrast, the microphonic interferes with microphone recordings and must be avoided.