How Microphone works ?

Sound creates waves of pressure in the air. A microphone usually has a diaphragm that can be moved by said pressure waves.

There are several different ways to make this into an electrical signal. One sort, called a dynamic microphone, is basically a speaker in reverse. A speaker has a cone (diaphragm) that's attached to a moving coil of wire, surrounded by a magnet. As an electrical signal is run through this coil, it creates a magnetic field that's repelled or attracted by the permanent magnet... so the speaker moves, creating sound pressure waves.

Like generator vs. motor, if you reverse this process, the diaphragm moves a coil of wire in a magnetic field, creating an electrical current. That's the dynamic microphone. One advantage of this sort is that it can generate a decently strong signal, another is that it's pretty rugged. You actually can use a speaker as a microphone.. but one of poor quality... mics and speakers are optimized for their intended use, even though the principles are the same.

Another kind of mic is the condenser mic... a "condenser" is just an old-timey term for capacitor, one of the fundamental passive components in electronics. If you set up two conductive plates with an insulator in-between them, you have yourself a capacitor. The value of capacitance varies with the size of the plates, distance between them, value of the insulator, etc. A condenser mic is made by making the aforementioned diaphragm one-half of a capacitor and placing an electrical charge on it. As sound pressure waves move the diaphragm in and out, the capacitance changes, and that can be used to make sound. One big advantage of the condenser mic is that its diaphragm is not loaded down with a coil, so it can move more freely, for more accurate translation of sound into electrical information. Disadvantages include fragility, weak signal (extra electronics are needed to boost it) and the need to power the mic with a voltage to set across the capacitor, and of course, the internal amplifier.

A variation of this is the electret mic. This is a condenser mic that uses a stored charge.. some materials can store an electrical charge, much in the same way that a magnet stores a magnetic polarization. These still need power for an amplifier, but don't need to charge the capacitor plate.

There are others, less common. Old telephones (see any 1940-1969 or so film) used a carbon mic. This was a made of grains of carbon between two plates, one being the diaphragm. A charge is placed across the plates, and as the diaphragm moves, the carbon compresses or expands, and the electrical resistance between the plates changes.

Another mic type is a mico electro-mechanical mic (MEMS). This is a mic basically etched in silicon, on a chip.. sound waves move the pressure sensitive area, causing electrical changes.

Yet another is called a piezoelectic mic. Certain crystals exhibit what's known as the piezoelectric effect.. a pressure on the crystal causes a small voltage to be generated. I have a guitar (Line 6 Variax) that uses such mics as a pickup, one for each string. One advantage of these is that there's not necessarily a diaphragm need... so in the example of the guitar, each mic/pickup is contact with the actual string (hidden in the bridge of the guitar).

And that's not the whole list... but in each case, you're doing sometime to convert sound into an electrical change. That's inherently analog... the electricity is an "analog" of the sound being sampled. Each of these could deliver a digital input by being routed to an analog to digital converter of some sort, then a computer.

How A Microphone Works

A microphone is any piece of equipment which translates sound waves into matching electrical waves. This will NOT be digital, it must follow the same pattern as the original. The normal method is to have a rigidly supported but slightly flexible metal, plastic or even cardboard plate called a diaphragm. This will vibrate with sound. It then passes this vibration to the electrical component behind it and that is what generates the sound. Early microphones used a container of carbon granules and a voltage across this. The carbon resistance changes with compression and de-compression and this changes the current through the carbon in step with the waves received. Modern versions normally use electro-magnetic coils and a magnet attached to the plate, this acts as a tiny generator, or a slice of crystal with the capability of generating electricity when vibrating.

Microphones are transducers, devices that change information from one form to another. They detect sound information as air pressure patterns, which they interpret and “translate” into electric current patterns. The accuracy of this transformation provides a better or worse sound. Magneto dynamic microphones have a thin metallic surface (like a diaphragm) and a coiled metal wire attached to it. When the coil is in motion, due to the magnetic field surrounding the coil, current flow is facilitated. The amount of current is determined by the frequency and speed of the motion of the diaphragm, caused by the incoming air patterns. These groups of microphones are known as velocity sensitive devices. Here are some of the most important characteristics involved in making the microphone work:

There are a number of different types of microphone. The simplest to understand is a diaphragm microphone. The diaphragm moves up and down as the air pressure (sound) hits it. The end of the diaphragm is attached to a magnet that moves inside a coil of wire. This movement generates electricity. The frequency of the electric current is related to the sound coming in to the microphone.

Double-click the Volume Control icon in the system tray, near the clock. Select Options \ Properties from the menu, and select Recording. Ensure that the microphone is selected as the recording source. Open Sound Recorder (Start \ Programs \ Accessories \ Entertainment,) and click the red circle to begin recording. If you're still not happening, find another computer and/or a different mic, and mix things up a bit. Maybe find someone that can look-over-your-shoulder to make sure you're not missing something, is also a good idea...

Microphones work almost exactly the inverse of speakers. While a speaker vibrates to send a frequency to your ear the sound of your voice vibrates the microphone. In fact some of my friends have used speakers as microphones, doesn't work so well but it still works it's just that speakers aren't going to be as sensitive as mics are since they weren't designed to be used for input.

Microphones are a type of transducer - a device which converts energy from one form to another. Microphones convert acoustical energy (sound waves) into electrical energy (the audio signal).

Different types of microphone have different ways of converting energy but they all share one thing in common: The diaphragm. 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.

Location of Microphone Diaphragm

Microphone Diaphragm

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.

Types of Microphone

There are a number of different types of microphone in common use. The differences can be divided into two areas:

(1) The type of conversion technology they use

This refers to the technical method the mic uses to convert sound into electricity. The most common technologies are dynamic, condenser, ribbon and crystal. Each has advantages and disadvantages, and each is generally more suited to certain types of application. The following pages will provide details.

(2) The type of application they are designed for

Some mics are designed for general use and can be used effectively in many different situations. Others are very specialised and are only really useful for their intended purpose. Characteristics to look for include directional properties, frequency response and impedance (more on these later).

Mic Level & Line Level

The electrical current generated by a microphone is very small. Referred to as mic level, this signal is typically measured in millivolts. Before it can be used for anything serious the signal needs to be amplified, usually to line level (typically 0.5 -2V). Being a stronger and more robust signal, line level is the standard signal strength used by audio processing equipment and common domestic equipment such as CD players, tape machines, VCRs, etc.

This amplification is achieved in one or more of the following ways:

* Some microphones have tiny built-in amplifiers which boost the signal to a high mic level or line level.

* The mic can be fed through a small boosting amplifier, often called a line amp.

* Sound mixers have small amplifiers in each channel. Attenuators can accommodate mics of varying levels and adjust them all to an even line level.

* The audio signal is fed to a power amplifier - a specialised amp which boosts the signal enough to be fed to loudspeakers.

You have all the answers you need concerning the physics of a microphone. I thought I would post for fun, "Did you know you can use your headphones as microphone?" Just plug 'em in, and start talking.

There are almost no microphones that work in the digital realm directly - disregard those answers.

Microphones are analog - they convert variations in air pressure (sound) to variations in electrical energy. As mentioned, this makes a mic a transducer. The microphone may make the conversion through electro-magnetic energy, through capacitance, or through piezoelectric effects.

The electrical energy is then amplified to the level that it can be used for recording, or to drive speakers for sound reinforcement. At this point, the signal is entirely analog.

The signal can then be converted with a analog-digital converter for use in computer recording - only then does it become digital.