How do mics work

The condenser diaphragm acts as the front plate in a parallel-plate capacitor capacitors used to be called condensers. The parallel-plate capacitor requires a fixed charge for the condenser mic to function properly.

This is often provided permanently by electret material electret condensers or externally via DC power phantom power, DC bias, etc. As varying sound pressure moves the diaphragm back and forth, the distance between the parallel plates changes.

This causes a coinciding fluctuation in capacitance. In a fixed charge capacitor, changing the capacitance causes an inversely proportionate change in voltage across the capacitor. Therefore, as the diaphragm moves back and forth about equilibrium, an AC voltage is created across the plates. After passing through some more circuitry, this electrical signal is outputted as the mic audio signal!

Other than the popular dynamic and condenser microphones, there are other types of microphone transducers. Some types worth mentioning include:. How do liquid microphone transducers work?

Liquid mics work as a cup filled with conductive liquid water and sulphuric acid. A diaphragm reacts to sound waves, causing an attached needle to vibrate accordingly in the conductive liquid.

How do carbon microphone transducers work? Carbon mics work as capsules with carbon granules pressed between two metal plates diaphragm and backplate. A voltage across the plates causes a current through the granules. As the diaphragm moves, it alters the pressure and resistance of the granules, creating a low-quality electrical mic signal.

Like the condenser microphone, the two electrical leads of the carbon mic are taken from each of the plates. The crystals yield high-impedance mic signals that coincide with the sound waves around them.

How do MEMS microphone transducers work? MEMS mics have integrated preamps and analog-to-digital converters and output digital audio. What is a laser microphone transducer? Laser mics work with laser beams to detect sound vibrations in objects and surfaces.

The laser beam is directed at a surface and reflects off the surface, returning to a receiver that converts the beam interferometrically into an audio signal. In the vast majority of microphones, the diaphragm is an obvious part of the design.

The microphone diaphragm moves according to the varying sound pressure around it. The diaphragm, directly or indirectly, causes an electrical signal that coincides with its movement. The diaphragm is held by and works within the housing of the microphone. Without a proper capsule design, the microphone diaphragm would be ineffective, and the mic would not convert energy. Two common moving-coil dynamic microphone cartridges are pictured below. Plus Top 3 Most Popular Capsules. Each of these capsules has found its way into numerous high-quality microphones throughout the years notably the AKG C 12 and the Neumann U Their designs have been replicated year after year since their inceptions and , respectively.

Although not necessarily part of the transducer element of a microphone, these following components are often necessary for a microphone to function properly as a transducer. What is a transformer? A transformer is a passive electrical device that links two circuits without connecting them physically. It does so via electromagnetic induction, a magnetic core and conductive windings connected in each circuit.

A basic transformer comprises a primary winding of conductive wire, a secondary winding of conductive wire, and a magnetic core. Each winding is part of its own circuit. Both windings wrap around the magnetic core but do not touch one another.

The AC signal from the microphone transducer and other components between the transducer and transformer runs through the primary winding of the transformer. In an ideal, lossless situation, the ratio of windings yields the following results given as secondary winding to primary winding :.

In other words, having more turns on the secondary winding will increase the voltage, decrease the current, and increase the impedance in the secondary circuit. This is known as a step-up transformer. Conversely, having fewer turns in the secondary winding will decrease the voltage, increase the current, and decrease the impedance in the secondary circuit. This is known as a step-down transformer. Some microphones are designed with step-up transformers, some with step-down transformers, and some with no transformers at all.

The AC signals generated from moving-coil cartridges and ribbon elements are typically very weak. They have low voltage and low impedance. Step-up transformers effectively boost the AC voltage to a healthier mic level signal without increasing the signal impedance to unusable levels. Vacuum tubes and some FET microphone designs output relatively high-impedance signals too high for effective signal transfer to professional preamps. Step-down transformers bring the output impedance down to a usable level.

What is a microphone impedance converter? A microphone impedance converter generally refers to a solid-state transistor-based circuit that converts the high-impedance signal of condenser capsule output to a higher-voltage, lower-impedance signal for the mic to output.

Note that vacuum tubes are also impedance converters. These active devices have three terminals:. Basically, the signal at the gate can be thought of as an input, while the output can be thought of as the signal between and out of the source and drain. In this way, the transistor is similar to the transformer.

This is a thin piece of material such as paper, plastic or aluminium which vibrates when it is struck by sound waves. In a typical hand-held mic like the one below, the diaphragm is located in the head of the microphone. When the diaphragm vibrates, it causes other components in the microphone to vibrate. These vibrations are converted into an electrical current which becomes the audio signal.

Note: At the other end of the audio chain, the loudspeaker is also a transducer - it converts the electrical energy back into acoustical energy. Missetting that switch can cause hilarious results. Bidirectional mics also exhibit this phenomenon. It is posible to exaggerate the directionality of cardioid type microphones, if you don't mind exaggerating some of the problems. The Hypercardioid pattern is very popular, as it gives a better overall rejection and flatter frequency response at the cost of a small back pickup lobe.

This is often seen as a good compromise between the cardioid and bidirectional patterns. A "shotgun" mic carries these techniques to extremes by mounting the diaphragm in the middle of a pipe. The shotgun is extremely sensitive along the main axis, but posseses pronounced extra lobes which vary drastically with frequency.

In fact, the frequency response of this mic is so bad it is usually electronically restricted to the voice range, where it is used to record dialogue for film and video. You don't need a special microphone to record in stereo, you just need two see below. A so called stereo microphone is really two microphones in the same case. There are two kinds: extremely expensive professional models with precision matched capsules, adjustable capsule angles, and remote switching of pickup patterns; and very cheap units often with the capsules oriented at deg.

Use of a single microphone is pretty straightforward. Having chosen one with appropriate sensitivity and pattern, and the best distortion, frequency response, and noise characteristics you can afford , you simply mount it where the sounds are.

The practical range of distance between the instrument and the microphone is determined by the point where the sound overloads the microphone or console at the near end, and the point where ambient noise becomes objectionable at the far end. Between those extremes it is largely a matter of taste and experimentation. If you place the microphone close to the instrument, and listen to the results, you will find the location of the mic affects the way the instrument sounds on the recording.

The timbre may be odd, or some notes may be louder than others. That is because the various components of an instrument's sound often come from different parts of the instrument body the highest note of a piano is nearly five feet from the lowest , and we are used to hearing an evenly blended tone. A close in microphone will respond to some locations on the instrument more than others because the difference in distance from each to the mic is proportionally large. A good rule of thumb is that the blend zone starts at a distance of about twice the length of the instrument.

If you are recording several instruments, the distance between the players must be treated the same way. If you place the microphone far away from the instrument, it will sound as if it is far away from the instrument. We judge sonic distance by the ratio of the strength of the direct sound from the instrument which is always heard first to the strength of the reverberation from the walls of the room.

When we are physically present at a concert, we use many cues beside the sounds to keep our attention focused on the performance, and we are able to ignore any distractions there may be.

When we listen to a recording, we don't have those visual clues to what is happening, and find anything extraneous that is very audible annoying. For this reason, the best seat in the house is not a good place to record a concert. On the other hand, we do need some reverberation to appreciate certain features of the music.

That is why some types of music sound best in a stone church Close microphone placement prevents this. Some engineers prefer to use close miking techniques to keep noise down and add artificial reverberation to the recording, others solve the problem by mounting the mic very high, away from audience noise but where adequate reverberation can be found. Stereo sound is an illusion of spaciousness produced by playing a recording back through two speakers.

The success of this illusion is referred to as the image. A good image is one in which each instrument is a natural size, has a distinct location within the sound space, and does not move around. The main factors that establish the image are the relative strength of an instrument's sound in each speaker, and the timing of arrival of the sounds at the listener's ear.

In a studio recording, the stereo image is produced artificially. Each instrument has its own microphone, and the various signals are balanced in the console as the producer desires. In a concert recording, where the point is to document reality, and where individual microphones would be awkward at best, it is most common to use two mics, one for each speaker. The simplest approach is to assume that the speakers will be eight to ten feet apart, and place two microphones eight to ten feet apart to match.

Either omnis or cardioids will work. When played back, the results will be satisfactory with most speaker arrangements. I often laugh when I attend concerts and watch people using this setup fuss endlessly with the precise placement of the mics. This technique is so forgiving that none of their efforts will make any practical difference.

The big disavantage of this technique is that the mics must be rather far back from the ensemble- at least as far as the distance from the leftmost performer to the rightmost. Otherwise, those instruments closest to the microphones will be too prominent. There is usually not enough room between stage and audience to achieve this with a large ensemble, unless you can suspend the mics or have two very tall stands.

There is another disadvantage to the spaced technique that appears if the two channels are ever mixed together into a monophonic signal. Or broadcast over the radio, for similar reasons. Because there is a large distance between the mics, it is quite possible that sound from a particular instrument would reach each mic at slightly different times. Sound takes 1 millisecond to travel a foot. This effect creates phase differences between the two channels, which results in severe frequency response problems when the signals are combined.

You seldom actually lose notes from this interference, but the result is an uneven, almost shimmery sound. The various coincident techniques avoid this problem by mounting both mics in almost the same spot. This is most often done with two cardioid microphones, one pointing slightly left, one slightly right. The microphones are often pointing toward each other, as this places the diaphragms within a couple of inches of each other, totally eliminating phase problems.

No matter how they are mounted, the microphone that points to the left provides the left channel. The stereo effect comes from the fact that the instruments on the right side are on-axis for the right channel microphone and somewhat off-axis and therefore reduced in level for the other one.

The angle between the microphones is critical, depending on the actual pickup pattern of the microphone. If the mics are too parallel, there will be little stereo effect.

If the angle is too wide, instruments in the middle of the stage will sound weak, producing a hole in the middle of the image. There are some very fine German cardioid microphones in which the diaphragm is mounted so that the pickup is from the side, even though the case is shaped just like many popular end addressed models.

The front of the mic in question is marked by the trademark medallion. Every microphone has a property known as directionality. This describes the microphone's sensitivity to sound from various directions. Some microphones pick up sound equally from all directions; others pick up sound only from one direction or a particular combination of directions. The types of directionality are divided into three main categories:.

Picks up sound predominantly from one direction. This includes cardioid and supercardioid microphones. Uses: Capturing ambient sound; Situations where sound is coming from many directions; Situations where the mic position must remain fixed while the sound source is moving. Notes: Although omnidirectional mics are very useful in the right situation, picking up sound from every direction is not always desired.

Omni sound is very general and unfocused - if you are trying to capture sound from a particular subject or area it is likely to be cluttered by other sources. Cardioid means "heart-shaped", which is the type of pick-up pattern these mics have. Sound is picked up mostly from the front, to a lesser extent the sides, and minimally from the rear.

Uses: Emphasizing sound from the direction the mic is pointed while leaving some latitude for mic movement and ambient noise. Controlling feedback. Notes: The cardioid is a very versatile microphone, ideal for general use. Handheld mics are usually cardioids. Cardioid mics have a proximity effect. This is the cardioid or "heart-shaped" pattern that picks up less from the sides at the expense of some sensitivity to the rear. Uses: When more directionality than the cardioid is desired.

Can be more effective against feedback. Uses: Figure-of-eight microphones have uses in various stereo and ambient techniques. They also work well when capturing two people facing each other like across a table. The very-low side sensitivity can be helpful in controlling feedback and leakage.