What is a Condenser Microphone?

The microphone is essentially a transducer that can convert sound waves into electric energy, and can be used in a variety of settings where audio is needed, such as for recording audio, delivering lectures and presentations, and broadcasting on television or radio.

There are various kinds of microphones available on the market. Each of them uses different methods in converting sound energy into electric energy. For instance, dynamic microphones convert sound energy into an electric signal by electromagnetic induction. Sometimes you don’t want to hold the microphone and walk independently. For these cases, wireless microphones like lavalier mics can easily be attached to your dress’s collar. USB microphones can be connected to the USB port of your computer and record audio easily. Every microphone requires a preamplifier to strengthen the signal so that it is audible.

In this article, we discuss specifically condenser microphones. What is a condenser microphone? At its core, it converts the acoustic energy into electric waves via the process of electrostatics. Let us go into more detail now.

The Condenser Microphone

The condenser microphone is a transducer that converts sound into audio by the electrostatic principle. In this microphone, you will notice a diaphragm just like all other microphones. This diaphragm acts as one of the plates of the capacitor. It responds to the change in pressure of the sound waves. You will also find another plate that serves as the other plate of the capacitor. Another thing you will notice is the impedance converter circuit for charging the electric power properly.

People usually use condenser mics to record audio in studios. These microphones respond to a wide frequency range in comparison to dynamic or other microphones. But their input sensitivity is a bit lower, i.e. they pick up input signals fast. So, to avoid this, you should use these microphones in a quiet place like a studio.

Benefits of Condenser Microphones

• Condenser microphones are small in size. It is so because they don’t have any moving coil or magnet within them.
• It has very high sensitivity. So, it can record the sounds of the instruments.
• It responds to a wider frequency range because the diaphragm moves at a fast rate.
• Light in weight.

Limitations of Condenser Microphones

• The condenser microphone requires external power to operate.
• They are expensive in comparison to other microphones.
• It can handle a certain amount of input signal.
• External temperature and humidity affect condenser microphones.
• If you invest in cheap condenser microphones, then it can generate noise.

Working Principle of Condenser Microphones

Condenser microphones are just like other microphones, i.e. they also convert sound waves into an electric signal. They do so by electrostatic principle.

These condenser microphones are parallel plate capacitors. A capacitor is an electric component whose main aim is to store electric energy. They are in the form of two metallic plates separated by a dielectric medium. The dielectric can be air, glass, paper, or an oxide layer.

The diaphragm is the principal component of microphones. It is a thin membrane that connects to the capsule of the microphone, mainly around the perimeter. The diaphragm consists of extremely lightweight material. The condenser diaphragms mainly consist of gold-sputtered mylar, but the diaphragm consists of thin metal foil if you use old condenser mics.

When the mechanical wave energy, i.e., acoustic energy, vibrates, the diaphragm or the front plate of the capacitor also moves. The other plate, known as the backplate, is static. The backplate mainly consists of brass. How can the moving plate in the condenser microphone or parallel capacitor convert the sound energy into electric energy?

The first principle of electrostatics says that the voltage between the two parallel plate capacitors is the product of the charge between the plates and the capacitance.

In equation form,

V = Q ×C

Where V = voltage in between two plates

Q = Electric charge in between two plates

C = capacitance of a capacitor(the ability of the parallel plate capacitor is storing charge.

The SI unit of Capacitance is Farad(F). One Farad of Capacitance means electricity of one coulomb changes the electric potential between the parallel plates by one volt. As the plates are very close to each other, the opposite charges in them attract each other. So the capacitor stores more charge for a given voltage.

We need to charge the capacitor to function correctly. In actuality, the condenser microphone holds a fixed amount of charge. That is why these mics need an external power source to work, and the capsule of the microphone maintains high impedance to prevent the drainage of the charge.

Now let’s discuss our second electrostatic principle. The second electrostatic principle says that capacitance is always equal to the dielectric constant multiplied with the quotient of area and diameter of the plate 

Here C = capacitance

          ∈₀   = dielectric constant

           A = Area of the plate

           D = Diameter of the plate

Now, if I combine both the equations by assuming the dielectric constant and the area of the plate constant, then we have the following relationship:

This indicates that the voltage of a parallel plate capacitor depends mainly on the distance between the plates.

We know that the sound waves have the power to vibrate the diaphragm or the upper plate of the capacitor. Now when the diaphragm vibrates, there is a change in distance between the plates. It causes voltage in between the plates. This AC voltage is known as an electric signal. So this proves that the condenser microphone is a transducer.

But there is a problem with the condenser microphone. The signal generated by the condenser microphone has a high impedance which means the condenser mics have low current but have high voltage. So the signal needs to pass through an impedance converter so that the microphone can use this signal.

What Is a Condenser Microphone Capsule?

You can refer to the entire component of the transducer as the capsule of a condenser microphone. It has a housing that holds both the back and front plate of the capacitor. The electric leads emerge from both the plates, and effectively it carries the signal produced by the condenser microphone to the impedance converter.

Polar Patterns of Condenser Microphones

Polar pattern is an essential specification of a condenser microphone. The polar pattern of a condenser microphone depicts the response of your mic towards each direction. It will tell you which direction the microphone will accept or reject sound. You can avoid unwanted sounds that may interfere while recording by selecting a microphone’s correct polar pattern. The polar pattern differs from situation to situation.

To understand the polar pattern of a condenser microphone, imagine a 360-degree field that surrounds your mic while performing on stage. The front of your mic is zero degrees, where almost all microphones have high sensitivity, i.e., they accept almost all the sound waves.

The 360-degree field consists of smaller circles, and each circle has 5 decibels to decrease insensitivity.

The most popular polar pattern seen in most condenser microphones is a cardioid pattern. The word cardioid comes from a Greek word meaning heart. We have an in-depth article explaining What is a Cardioid microphone, which may be interesting to read. So, this polar pattern condenser mic picks up sound from a heart-shaped area. If you imagine in three dimensions, then the polar region will be like an apple.

This polar pattern makes the condenser mic unidirectional, i.e. they pick up sound only from one side of the microphone. In other words,they are best sensitive at zero degrees and least sensitive at 180 degrees.

Aside from cardioid, there are various other polar patterns:

#1. Super-Cardioid Condenser Microphone

People usually misunderstand super-cardioid condenser microphones as cardioid condenser microphones. But the super-cardioid microphone is entirely different. These microphones have a directional polar pattern, i.e., they are pretty sensitive on their axis and null at 127 degrees and 233 degrees. People use these microphones for shooting films.

The super-cardioid polar pattern is more direct in comparison to the cardioid polar pattern. Super-cardioid mics are mainly found in shotgun mics or on the top of the camera.

These polar patterns pick up sound from behind the microphone. So if you are using a super-cardioid polar pattern microphone on your camera, you will need to keep the operating noise as low as possible. Our write up titled What is a Supercardioid microphone may be of interest.

#2. Omnidirectional Condenser Microphone

The omnidirectional condenser microphone picks up sound from all directions, i.e. a full 360 degrees. They are suitable for recording acoustic instruments or in the orchestra.

One limitation of this microphone is that they do not have any null point. So the omnidirectional condenser microphone cannot reject unwanted sound. They are least sensitive to the noise of wind in comparison to other polar pattern condenser microphones.

Another thing you should keep in mind is that when the microphone’s body becomes larger, it becomes difficult for the sound waves to reach the body of the microphone. It affects the ideality or capability of picking up sound with an omnidirectional condenser microphone.

#3. Bidirectional Condenser Microphone

We call the bidirectional condenser microphone the figure-8 microphone, because it picks up sound from both front and back sides and rejects the sound from both sides. In this microphone, the diaphragm of both sides is exposed equally to the pressure of sound.

Impedance Converter

The impedance converter is the internal preamplifier of the condenser microphone. It helps in boosting the voltage of the signal produced by the capsule of the microphone.

The microphone should have a very high impedance to hold a constant charge between two parallel plate capacitors. The high impedance prevents the drainage of the charge when there is a poor signal.

Another thing I want to say is that when the microphone has a high impedance, the signal finds it challenging to travel in the signal wire and almost degrades before it reaches the desired device. So you need an impedance converter immediately after the capsule of the condenser microphone. It helps strengthen the signal, and finally, there will be a minimum signal loss between the microphone capsule and the integrated circuit.

These impedance converts play a vital role in condenser microphones. We measure the impedance in ohms. There are two main types of impedance converters. They are as follows.

#1. Vacuum Tube Impedance Converter 

You can call this vacuum tube condenser microphone an electron tube. It is an electronic device that controls the current flow between the electrodes, mainly when voltage applies to these electrodes.

This process takes place in a vacuum. It will be critical if little oxygen is present inside the tube. Remember that your device may burn if little oxygen is present in the tube during the transmission of the signal.

The vacuum tubes of the condenser microphone require three electrodes, i.e., anode, cathode, and control grid. That is why you can call them triodes. The outer covering of the vacuum tube converter consists of either glass or ceramic. The flow of electrons in the tube produces an electric current inside the tube.

The vacuum tube impedance converter has mainly four components:

• Heater
• Anode
• Cathode
• Grid

The condenser microphone requires an external power source to heat the heater inside the vacuum tube.

When the heater heats in a good manner, the cathode starts emitting electrons. These electrons will repel each other but will attract towards the anode. So the electric current will start flowing from cathode to anode.

But the current will have a low impedance in comparison to the output of the capsule of a condenser microphone. This current is constant until the signal passes over the grid of the vacuum tube.

Now comes the importance of triode. In a triode, there is an introduction of a third electrode called grid which is present between the cathode and anode. The grid consists of a cylindrical screen or a helix of fine wire, but it never touches the cathode. The wire can resist very high temperatures, and they do not emit electrons by themselves. It serves as the input of the vacuum tube and acts as a gate for electrons. 

The grid controls the flow of electrons from the cathode to the anode. If there is a greater amount of negative voltage on the grid, then most of the electrons coming from the cathode will repel, and very few can enter the anode. If there is a greater positive voltage on the grid, more electrons will attract the anode. So the change in voltage in the grid affects the current flow. The vacuum tube amplifies the signal and creates an impedance that the circuit of the condenser microphone can easily handle.

Remember that you can get better amplification if you place the grid closer to the cathode than the anode.

#2. Field-Effect Transistors

The transistor is a semiconductor component that is present inside the condenser microphone for amplification. Semiconductors are materials that have conductivity in between the conductors and nonconductors. But by adding some amount of impurities to the pure semiconductor, you can increase the conductivity of silicon. You can call this process doping. When the pentavalent metal adds to the silicon, i.e., the element with five valence electrons in the valence band, they are called n-type semiconductors. If the trivalent metal, i.e., three electrons on the valence band, are added to the pure silicon, they are called p-type semiconductors.

The p-type semiconductor has more holes, and the n-type semiconductor has more electrons.

There are various types of transistors, including bipolar junction transistors and field-effect transistors. The bipolar junction transistor uses both holes and electrons to carry charge. It is a current controlled device. But it generates more noise, and radiation affects it.

Nowadays, condenser microphones are coming with field-effect transistors as impedance converters. They are accurate, small in size, and less expensive in comparison to vacuum tube impedance converters. They even require less power for amplification. They take the high impedance signal from the condenser microphone capsule and convert it into a low impedance signal.

The field-effect transistor is a three-terminal device, consisting of a source, gate, and drain. It is a voltage-controlled device. The current flows on the path of the semiconductor called the channel. At both the ends of the channel, you will find two electrodes called drain and source. The gate acts as a control electrode. The voltage application in between the gate and source varies the current flow from source to drain. In this way, the field-effect transistor amplifies the weak signal from the microphone capsule.

The are two main types of field-effect transistor:

#1. Junction Field Effect Transistor

In a junction field-effect transistor, an N-type bar or P-type bar consists of silicon, and its side contains PN junctions.

They are of two types, one in the N channel and the other in the P channel. In the N channel, you will find the channel consists of N-type material with the two sides containing P-type material. You will find three terminals, i.e., source, drain, and gate, here. A depletion region forms in between the two P channels when you connect them. Remember that the depletion region is free from charge carriers. The drain current depends on the potential difference between the gate and the source.

When you connect the drain and the source terminal to a battery, the current will flow from the source towards the drain, and the electronic flow will flow from the drain towards the source.

But after increasing voltage to a certain extent, the width of the N channel reduces. So there is obstruction of current. You can control the flow of electrons via the gate terminal. The potential difference between the gate and the source controls the depletion region or the output current.

#2. Metal Oxide Semiconductor FET

MOSFET is also a field-effect transistor with four terminals: source, gate, drain, and body terminal. They also amplify the weak signal produced by the capsule of the condenser microphone.

Power Requirements of Condenser Microphones

The condenser microphones require external power to polarize the capsule or run their PCB. The mic also needs power for the impedance converter, preamplifier within the microphone, and the circuit. 

Now, how do these microphones get power? Well, there are various options to supply power to the microphone:

#1. Phantom Power

Phantom power is one of the best external power sources for condenser microphones compared to other power sources.

It is a process of supplying direct current to the condenser microphone to run its circuit. Sometimes the battery that is present inside the microphone delivers phantom power. But in most cases, the mixer provides the direct power source, and it carries over to the microphone by the cables. The standard value of phantom power is within 11 to 52 volts, but the studio microphone usually has 48 Volts. You will find a button on the preamplifier, i.e., of 48 volts. You just need to switch on and off according to your needs.

In some cheap condenser microphones, you will not find a button of phantom power. You need to add phantom power externally and between the mic and the preamplifier to function correctly.

Now, why do we call this power source phantom power?

In the early 1900s, people used condenser microphones. Those mics require a power source to operate. That power source was very close to the mic, and it was very large and heavy. So, these mics were not very comfortable to use. Then research went into improving condenser mics. After some development, an external board was implemented, which supplied the external power to the microphone, and it worked properly but was invisible. So, people started calling this power supply phantom power.

You can apply this power source to other microphones like dynamic microphones. But many microphones, except condenser microphones, do not require external power. However, do read the instructions from the manual before supplying an additional power source to any kind of mic.

#2. External Power Supply Units

These power units connect the plug of the wall and the microphone to supply the power required by the microphone.

If your condenser microphone uses a vacuum tube as an impedance converter, I suggest using the external power supply units for your mic.

#3. T Power

Earlier, people used T power to supply power to the microphone. They provide the 12-volt DC to the microphone by audio cables. However, it is not that safe. So, the phantom power replaced it.

#4. DC Biasing

Biasing refers to the supply of DC voltage externally to set a fixed current and voltage. The microphone used a junction field-effect transistor as an impedance converter and used DC biasing as an external power source. A low direct current voltage ranges within 1.5 to 9.5 volts transmits along with the microphone by the audio cables.

#5. Plug-In Power

Plug-in power is the low current of five Volt DC voltage that supplies to the condenser mic as an external power source.

#6.USB power

USB power is mainly five volt DC voltage, which supplies power to the field-effect transistor impedance converter in the mic and the analog to digital converter.

#7. Battery

A battery can supply the power source externally to the condenser microphone.

What Are The Various Types Of Condenser Microphones?

There are different types of condenser mics. Let me describe all the types of mics in detail.

#1. Electret Condenser

Electret condensers do not require any external bias. Electret is a dielectric material usually present on the plate of the parallel plate capacitor. This material has high resistance and is chemically stable. Electret material in condenser microphones will not decay for more than a hundred years.

The electret condenser is obtained when you melt a dielectric material like plastic or even wax, which contains polar molecules, and then solidify them again in an electrostatic field, which permanently creates an electrostatic bias.

The modern electret condenser uses Teflon material as an electret material. They have a built-in negative charge. In an electret condenser, you will find a diaphragm like all other condenser microphones. Here also, you will find a backplate, but on the backplate, you will find a film of Teflon material with negatively charged particles. That’s why the diaphragm will have positively charged particles. Both positive and negative charge particles will create a voltage in between the plates.  

Now we know voltage is the ratio of built-in charge between two capacitor plates and the capacitance.

V = Q ×C

The second electrostatic principle says that capacitance equals the dielectric constant multiplied by the plate’s area and diameter quotient.

Now when the sound waves strike the diaphragm, then the diaphragm displaces. When the diameter in between the plates decreases, the capacitance will increase. Now the voltage is inversely proportional to the voltage. So, when the capacitance rises, the voltage drops.  

Similarly, when the diameter of the plates increases, the capacitance will decrease. So the voltage will increase. So the voltage difference generates an electric signal from the electret condenser microphone.

Characteristics of Electret Condenser Microphones

• Sensitive to high temperature and humidity.
• Excellent frequency response.
• No need for any external bias.

Applications of Electret Condenser Microphone Microphone

• Radio microphone at sports meets.
• Tie clip microphone for lectures.

#2. Externally Polarized True Condenser

A true condenser needs an external power source to polarize the capsule. The power source is mainly phantom power of 48 volts. But the requirement of power is steady here. In contrast, in an electret condenser, we don’t need to supply any external force to the capacitor plates of the condenser microphone, which is the main drawback of a true condenser.

But still, reputed companies manufacture true condensers, and their popularity is not less than electret condensers in the market.

#3.Tube Condenser

The tube condenser uses a vacuum tube as an impedance converter. These condensers are not that precise compared to tube condensers, but they produce excellent sound quality.

#4. FET Condenser Microphone

The FET condenser microphone is also known as a solid-state condenser microphone. These condenser microphones use a field-effect transistor as an impedance converter.

Transistor technology is quite popular in most condenser mics, making these mics inexpensive to manufacture. It requires a small amount of power for charge polarisation compared to a tube condenser.

The microphone capsule converts the acoustic energy or sound waves into electric energy. But the signal has impedance, and the level is very low. The FET transistor in this microphone can effectively convert poor signals into proper signals when it is out from the microphone.

The field transistor is mainly of two types, i.e., MOSFET and JFET. The MOSFET is quite common in digital microphones, whereas your FET condenser microphone uses JFET (junction field-effect transistor) in the microphone.

#5. Audio Frequency Condenser and Radio Frequency Condenser Microphones

The working principle of audio and radio frequency condenser microphones is the same, i.e., both the microphones contain capsules that have a front plate and backplate. As the distance between the front and backplate changes, the charge changes and converts the audio signal into a mic signal.

However, both differ by the impedance converter. The audio frequency microphones have a circuit of high impedance. When the air contains more water vapor, the charge inside the microphone capsule tries to escape into the air rather than the circuit. It creates a popping sound and decreases the signal level from the output of the microphone. The dust particle also accumulates in the microphone’s diaphragm because of high biasing voltage, which finally reduces the efficiency of an audio frequency condenser microphone.

Another microphone called the radio frequency microphone works much better in humid environments than the audio frequency microphone. Radio frequency microphones have a circuit of low impedance. In this condenser, the change in capacitance of the parallel plate capacitor changes the circuit’s resonant frequency.

#6. Small Diaphragm and Large Diaphragm Condenser Microphone

We can divide the condenser microphone by the size of the diaphragm in two ways, i.e., small and large-diaphragm condenser microphone.

By the rule of thumb, the large-diaphragm condenser microphone is one inch or more than one inch in diameter. The small diaphragm is one inch or less than one inch in diameter. But the reality is different because you may find large-diaphragm microphones whose diaphragm size is less than one inch, so it can become confusing.

Let’s talk more about small and large diaphragm condenser microphones in detail.

The large-diaphragm condenser microphone emerged first in the market in 1930. The large diaphragm captures more sound energy and generates a high voltage signal. Their size is quite large in comparison to a small condenser microphone. The main aim of these microphones is to produce a louder sound, giving the feeling of recorded sound.

They use any polar pattern, but their pattern is not that consistent compared to small-diaphragm condenser microphones. These microphones are used by singers and those giving a presentation in front of the public. Apart from vocals, people use them for recording instruments. You can find these large-diaphragm condenser microphones at all sorts of price levels on the market.

Small diaphragm condenser microphones are pencil-shaped and emerged in the market in the year 1950. They have an excellent signal-to-noise ratio. Their frequency response is beyond the hearing of human beings.

Their polar pattern is very consistent, and these microphones use any polar pattern. The main aim of these microphones is to produce a neutral and uncolored sound, and you will always like to capture the sound produced by these microphones originally. It never adds any flavor to the sound. So, you can use these microphones for any purpose. Again you can find these microphones at a range of prices in the market; we’ve written an in-depth article on how much microphones cost.

So, while choosing any of these microphones, you cannot say a particular microphone is good or bad. Both are pretty good as recording instruments. You would need to choose according to your purpose or need for recording.

Let me distinguish these two microphones in the table below.

#7. Miniature Diaphragm Condenser Microphone

The wireless systems use a miniature diaphragm condenser microphone. It connects to the wireless transmitters, and those transmitters send signals without the cables. They also provide suitable DC voltage to the impedance converter so that they can work properly and you can get a good quality sound.

Miniature diaphragm condenser microphones are popular in lavalier or lapel microphones.

Applications of Condenser Microphones

You can use the condenser microphone everywhere, but these are used more often for recording sound in studios.

Here are some of the common applications of condenser microphones:

• Shotgun microphones which are for recording videos or film
• Wireless lavalier microphones
• Consumer device
• Instrument mic
• Vocal mics in the studio
• Voice over mic

How Do Condenser Microphones Differ From Dynamic Microphones?

Condenser microphones are far different from dynamic mics. Let me list out all the differences in detail. Read our article on the differences between condenser and ribbon microphones.

• The condenser microphone uses the electrostatic principle in converting the audio signal into a mic signal. Still, the dynamic mic uses the electromagnetic induction principle in converting the sound into a mic signal.
• The condenser microphone is highly sensitive, but dynamic mics have low sensitivity.
• The condenser microphone requires an external power source to operate, but dynamic mics don’t need any external power to operate.
• The size of the condenser microphone is small as they don’t have a moving coil or permanent magnet. The size of the dynamic mic is a bit large because dynamic microphones contain a coil and magnet inside the microphone.
• The transient response of the condenser microphone is fast, but the transient response of the dynamic mic is slower.
• The condenser microphone produces self-noise, but dynamic mics do not produce any self-noise.
• The maximum sound pressure level is within the limit for condenser microphones, but the sound pressure level is beyond the limit for dynamic microphones, which is difficult to measure.
• The frequency response for condenser microphones is flat or extended, but for dynamic microphones, it is colored.
• Read more with our guide to What is a Dynamic microphone?.

How Do Side Address Microphones Differ From Front Address Microphones?

The driving feature of the large-diaphragm condenser microphone’s design is that they pick sound from one side or both sides of the microphone but not from the end sides. So, people call them side-address microphones.

Small diaphragm condenser microphones are pencil-shaped and capture sound from the end but not from the sides. Thus, they are known as end-address microphones.

Both side-address microphones and end address microphones play an essential role in recording sound. The location of your microphone’s focal point will help you visualize the polar pattern so that you can use it properly at an audio source.

Frequently Asked Questions

Parting Words

Condenser mics use capacitor plates inside the microphone capsule, and the change in capacitance helps convert the sound energy into an electric signal. But they need an external power source to make that electric signal audible to everyone. People mainly use these microphones for studio applications as they produce good quality sound. For more reading, our very thorough guide to Ribbon microphones may also be useful.

I hope this article has helped you in understanding the condenser microphone and its workings. Keep some of the information here in mind if you intend to buy a condenser microphone in the near future.

Please do share your suggestions for this article in the comments below.

More recommended reading:

• What Is a Hypercardioid Microphone?
• What Is an Omnidirectional Microphone?
• Complete List Of Microphone Types