Microphone types and technologies

Microphones of all types
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Microphone types and technologies

Post by superphool » Sun Aug 25, 2019 5:17 pm

Microphones can be built using several rather different principles - and a vast number of variations around each of those principles.

The commonest types are:

Dynamic microphones - a coil moving within a magnet, acting as an electrical generator and directly producing a small voltage when sound vibrations move the diaphragm and attached coil.
The construction of these is very similar to a loudspeaker, but rather small and with a very light diaphragm and coil system.
(In fact, a normal loudspeaker will work, rather inefficiently, as a dynamic microphone).

This is a cross-section diagram of a typical dynamic microphone capsule:

The Shure SM58 is a good example of a well known dynamic microphone - these are the type with a chrome mesh ball end, seen in just about any live music performance.
An example in my collection: Image

Condenser microphones - There are two very distinct types of condenser microphone, which devious sellers often use to mislead buyers:

The original, externally polarised or "true condenser" type, was invented around 1930 and still generally considered the top standard for studio microphones.

These have an extremely thin diaphragm which has been metallised over part of its surface. This is mounted against a perforated metal backplate, with a small space between the two.

When the diaphragm is charged to a suitable voltage (typically near 50V), sound vibrations (which in turn vibrate the diaphragm and change its spacing from the backplate) change the capacitance between the two parts and this causes the bias voltage to vary in proportion to its movement.

A common size for these is about 34mm overall and with a diaphragm diameter of about 25mm, though there are different sizes.

This is a cross-section diagram of a typical condenser microphone capsule:

(The two images above are from the Shure web page explaining the two technologies, here - well worth reading if you are interested in more details: Difference between a dynamic and condenser microphone)

The other type of condenser microphone is the Electret condenser. With these, an "electret" plastic layer is used to provide the bias voltage for the condenser microphone effect. An electret is typically a material which is exposed to a high voltage while moten and allowed to solidify with an electrostatic charge trapped within it.

Electret microphone capsules are generally far smaller than true condenser types, down to just 2 or 3 mm across in some cases.
These are the type used in mobile phones and just about any application using a small microphone over the last few decades.

The ones used in handheld microphones are typically around 10mm diameter, though sizes from 6mm or smaller to 20mm+ are possible.
The smaller mass produced ones can be incredibly cheap - eg. ten or fifteen medious size capsules for a pound from some ebay sellers.

Ribbon microphones - these also work by moving an electrical conductor within a magnetic field to generate a voltage, however rather than a diaphragm and coil as with a standard dynamic microphone, the diaphragm itself is a strip of metal suspended between the poles of a magnet.

Sound vibration move the metal strip "ribbon", causing it to generate a minuscule voltage.
The ribbon is normally connected directly to a transformer, which converts the very low output to a higher level more suitable for feeding out of the mic to other equipment.

This is a diagram of such a microphone:

(From the fully detailed wikipedia article, here: https://en.wikipedia.org/wiki/Ribbon_microphone)

Crystal (or ceramic / piezoelectric) microphones - these were once commonly supplied with low cost tape recorders, but are now quite rare.
They use a piezo-electric crystal to convert movement of the microphone diaphragm into an electrical voltage.

More details of these on Wikipedia here; the page also covers various other microphone technologies, both the ones mentioned here and other more obscure types:

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