How Do Microphones Work? (The Ultimate Illustrated Guide)

It's not often that we think about how microphones work. Microphones are part of our day-to-day lives and are somewhat taken for granted, so I'm glad you asked about how they function!

How do microphones work? Microphones work as transducers, converting sound waves (mechanical wave energy) into audio signals (electrical energy). The microphone diaphragm vibrates as it's subjected to sound waves and creates a coinciding audio signal via electromagnetic or electrostatic principles that will be outputted.

In this helpful illustrated guide, we'll take a deeper look into the inner workings of microphones and describe how all of the common microphone types work to convert sound into audio!

Related article: How Do Headphones Work? (Illustrated Guide For All HP Types)

---

Table Of Contents

• What Is A Transducer?
• The Microphone As A Transducer
• Microphone Transducer Types
• The Diaphragm And Capsule: Key Components Of Microphone Transducers
• Other Important Microphone Components For Proper Energy Conversion
• The Conversion Of Energy (From The Sound Wave To The Mic Output Signal)
• Related Questions

---

What Is A Transducer?

What is a transducer? A transducer is a device that converts one form of energy into a different form of energy.

Microphones work as transducers, converting mechanical wave energy into electrical energy. More simply put, microphones convert sound waves into audio signals.

---

The Microphone As A Transducer

A microphone's diaphragm reacts to the sound waves it is subjected to. As the diaphragm moves according to the varying sound pressure levels, the microphone produces a coinciding mic signal.

Before we get deep into the mechanics of how a microphone converts energy, let's further define the energies in question.

Mechanical Wave Energy (Sound Waves)

What is mechanical wave energy? Mechanical wave energy is the energy carried by a mechanical wave (an oscillation of matter within a medium). Mechanical waves (and, therefore, mechanical wave energy) can only be transferred in media which possess elasticity and inertia (gas, liquid, solid).

What is a sound wave? A sound wave is a type of mechanical wave defined by the pattern of disturbance of particles within an elastic medium [gas (often air), liquid (often water), or solids]. The oscillations of the particle disturbances caused by sound waves are defined within the range of 20 Hz and 20,000 Hz.

The strength of a sound wave is generally measured in sound pressure level (dB SPL) or Pascals (Pa).

Audible sound waves happen in the frequency range of 20 Hz – 20,000 Hz. Inaudible infrasound happens below 20 Hz, while inaudible ultrasound happens above 20,000 Hz.

When I say “inaudible,” I specifically mean inaudible to humans.

Electrical Energy (Audio Signals)

What is electrical energy? “Electrical energy” is defined as electric potential energy. It is supplied by electric current and electric potential (voltage) and is delivered through electrical circuitry. In modern times, electrical energy is harvested and is nearly always converted to some other type of energy (heat, motion, light, etc.).

What is an audio signal? An audio signal is an electrical signal that represents sound in the form of electrical energy. Analog audio signals are measured as AC voltages in millivolts (RMS) or decibels relative to voltage (dBV or dBu).

Microphone Transducers

So microphones convert mechanical energy to electrical energy.

How they do so varies from microphone type to type. We will discuss how each [common] type of microphone works in this article.

---

Microphone Transducer Types

There are many types of microphones out there with plenty of factors to differentiate them. However, when it comes to the transducer type, there are two main kinds of microphones:

• Dynamic microphone transducers
• Condenser microphone transducers

The Dynamic Microphone Transducer Type

When we use the term “dynamic microphone,” we're typically referring to a moving-coil dynamic mic.

However, the dynamic transducer type includes both moving-coil and ribbon microphones.

What is the dynamic microphone transducer type? Dynamic microphones convert sound waves into audio signals via electromagnetic induction. Both moving-coil and ribbon mics have conductive diaphragms that vibrate within permanent magnetic fields. As the diaphragm moves according to varying sound pressure, a mic signal is induced.

In the above diagram, the sound waves hit the diaphragm of the Shure SM57 moving-coil dynamic microphone. The SM57 converts the movement of its diaphragm into electrical energy that is eventually outputted as its mic signal.

The diaphragm moves according to the pressure applied by the sound waves (mechanical energy). The diaphragm is attached to a conductive coil, and they move together as a unit (hence the name moving-coil dynamic mic).

Note that the diaphragm itself is not electrically conductive.

There are magnets inside the cartridge (capsule) of the mic that provide a permanent magnetic field. The coil fits in a cylindrical groove within the magnets so that it doesn't touch the magnets but is strongly affected by the magnetic field.

Magnetic induction states that as the conductive coil moves within a permanent magnetic field, it experiences a change in magnetic flux. A changing magnetic flux in the conductive coil induces a voltage across it.

As the diaphragm moves back and forth about equilibrium with the sound waves, so does the conductive coil. This induces a positive change in voltage one way and a negative change in voltage the other way. This yields an AC electrical signal across the coil.

This AC signal is then often passed through a step-up transformer within the microphone and outputted as the mic audio signal.

In the above diagram, the sound waves hit the diaphragm of the AEA R84 ribbon dynamic microphone. The R84 converts the movement of its diaphragm into electrical energy that is eventually outputted as its mic signal.

The AEA R84 is one of My New Microphone's Top 12 Best Passive Ribbon Microphones On The Market.

The ribbon-like diaphragm (hence the name ribbon dynamic mic) moves according to the pressure applied by the sound waves (mechanical energy).

Ribbon diaphragms are made of conductive material (often corrugated aluminum) and sit inside a magnetic baffle that provides a permanent magnetic field.

Magnetic induction states that as the conductive ribbon diaphragm moves within a permanent magnetic field, it experiences a change in magnetic flux. A changing magnetic flux in the ribbon diaphragm induces a voltage across it.

As the diaphragm moves back and forth about equilibrium with the sound waves, an AC voltage is induced across it.

This AC signal is then often passed through a step-up transformer within the microphone and outputted as the mic audio signal.

For more information on moving-coil and ribbon microphones, check out the following My New Microphone articles:
• The Complete Guide To Moving-Coil Dynamic Microphones
• The Complete Guide To Ribbon Microphones (With Mic Examples)

The Condenser Microphone Transducer Type

What is the condenser microphone transducer type? Condenser microphones convert sound waves into audio signals with a moving diaphragm that acts as one plate in a fixed-charge parallel-plate capacitor. As the diaphragm moves, the distance between plates varies, changing the capacitance and creating an inversely proportionate mic signal.

In the above diagram, the sound waves hit the diaphragm of the Neumann KM 184 condenser microphone. The KM 184 converts the movement of its diaphragm into electrical energy that is eventually outputted as its mic signal.

The condenser diaphragm acts as the front plate in a parallel-plate capacitor (capacitors used to be called condensers).

Note that some people refer to condenser mics as capacitor mics.

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.

This AC voltage is taken from the capacitor and ran through an impedance converter/amplifier (transistor or vacuum tube). After passing through some more circuitry, this electrical signal is outputted as the mic audio signal!

For more information on the different types of microphone transducers, check out my article Microphone Types: The 2 Primary Transducer Types + 5 Subtypes.

---

Other Types Of Microphone Transducers

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

• Liquid microphone transducer
• Carbon microphone transducer
• Piezoelectric/contact microphone transducer
• MEMS microphone transducer
• Laser microphone transducer

How Do Liquid Microphone Transducers Work?

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. This causes coinciding variations in the circuit’s resistance, which causes an “audio signal.”

How Do Carbon Microphone Transducers Work?

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.

How Do Piezoelectric/Contact Microphone Transducers Work?

How do piezoelectric/contact mics microphone transducers work? Piezoelectric/contact mics work with piezoelectric materials (known as crystals) that produce AC voltage (mic signals) when subjected to varying pressure. The crystals yield high-impedance mic signals that coincide with the sound waves around them.

How Do MEMS Microphone Transducers Work?

How do MEMS microphone transducers work? MEMS (MicroElectrical-Mechanical System) mics work with a diaphragm and fixed backplate over a cavity in a base wafer. The entire “capsule” of a MEMS mic is etched into a silicon wafer by MEMS processing. MEMS mics have integrated preamps and analog-to-digital converters and output digital audio.

For more information on MEMS mics, check out my article What Is A MEMS (Micro-Electro-Mechanical Systems) Microphone?

How Do Laser Microphone Transducers Work?

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.

---

The Diaphragm And Capsule: Key Components Of Microphone Transducers

The key component in microphone transducers is the diaphragm.

In the vast majority of microphones, the diaphragm is an obvious part of the design. But even the above laser microphone receiver/sensor is considered a diaphragm.

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.

Diaphragms come in a variety of materials, shapes, weights, tensions, and sizes.

For more information on microphone diaphragms, check out my article What Is A Microphone Diaphragm?

The diaphragm is held by and works within the housing of the microphone. Depending on the microphone transducer type, the diaphragm works within the following “housing.”

• Cartridge or “capsule” (moving-coil dynamic mics)
• Ribbon elements or “baffles” (ribbon dynamic mics)
• Capsules (condenser mics)

Without a proper capsule design, the microphone diaphragm would be ineffective, and the mic would not convert energy. Let's talk about microphone diaphragms and their housings in a bit more detail.

Moving-Coil Dynamic Microphone Cartridge And Diaphragm

The transducer unit of the moving-coil dynamic microphone is often referred to as the cartridge or the “capsule” of the microphone.

Two common moving-coil dynamic microphone cartridges are pictured below. The Shure R176 is the cartridge found in the Shure Beta 58A, and the SM58 cartridge is found in the popular Shure SM58.

The moving-coil cartridge consists of 5 key components:

1. Diaphragm
2. Conductive “moving” coil
3. Magnets and pole pieces
4. Housing
5. Electrical leads

For more information on moving-coil dynamic mics, check out my article Moving-Coil Dynamic Microphones: The In-Depth Guide.

Ribbon Dynamic Microphone Element And Diaphragm

The transducer unit of the moving-coil dynamic microphone is often referred to as the element or the “baffle” of the microphone.

Below is a picture of the baffle/ribbon element of the flagship Royer R-121 ribbon microphone:

The ribbon element/baffle consists of 4 key components:

1. Diaphragm
2. Magnets and pole pieces
3. Housing
4. Electrical leads

For more information on dynamic ribbon mics, check out my article Dynamic Ribbon Microphones: The In-Depth Guide.

Condenser Microphone Capsule And Diaphragm

The transducer unit of the condenser microphone is referred to as the capsule.

For more information on microphone capsules, check out my article What Is A Microphone Capsule? (Plus Top 3 Most Popular Capsules).

Pictured below are the famous AKG CK12 and Neumann K67 dual-diaphragm condenser microphone 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 67). Their designs have been replicated year after year since their inceptions (1951 and 1960, respectively).

The condenser capsule consists of 4 key components:

1. Diaphragm (front plate)
2. Backplate
3. Housing
4. Electrical leads

---

Other Important Microphone Components For Proper Energy Conversion

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.

• Transformer
• Impedance Converter / Amplifier (Transistor and PCB)
• Vacuum Tube
• Power Supply
• Analog-To-Digital Converter
• Output Connection

Note that not all microphones have all the above components.

Transformer

Many microphones are built with transformer-coupled outputs.

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. Mic transformers increase/decrease AC voltage, block DC voltage and adjust impedance.

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. This effectively “links” the two circuits together without physically connecting them.

The AC signal from the microphone transducer (and other components between the transducer and transformer) runs through the primary winding of the transformer.

This AC mic signal in the primary winding induces a changing magnetic field and magnetic flux within the transformer's magnetic core.

This changing magnetic flux then induces a relative AC voltage across the secondary winding, which is part of the microphone's output connection circuit.

In an ideal, lossless situation, the ratio of windings yields the following results (given as secondary winding to primary winding):

• Voltage ratio: turns ratio of secondary to primary
• Current ratio: turns ratio of primary to secondary
• Impedance ratio: square of the turns ratio of secondary to primary

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.

Step-Up Transformers

When step-up transformers are used, they're typically designed in dynamic microphones.

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.

Step-Down Transformers

When step-down transformers are used, they're typically designed into active microphones after the tube or FET-based impedance converter/amplifier.

In this case, the transformer is used to drop the impedance of the mic signal before the output.

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.

The tubes and transistor circuits are designed to provide enough “amplification” to the signal so that a strong voltage is still attainable after the step-down transformer.

Impedance Converter/Amplifier (Transistor And PCB)

Many microphones are built with active impedance converters/amplifiers. These active devices are generally made with a printed circuit board (PCB) based on a field-effect transistor (FET) or junction-gate field-effect transistor (JFET).

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.

The basic microphone impedance converter/amplifier is built around a FET. Let's discuss briefly how a FET works:

FETs and JFETs are semi-conductive electronic devices that use an electric field to control the flow of current. These active devices have three terminals:

• Source (S): the terminal where the charge carriers (electrons or “holes”) enter the channel (transistor).
• Drain (D): the terminal where the charge carriers (electrons or “holes”) leave the channel (transistor).
• Gate (G): the terminal that modulates the channel conductivity.

Before explaining what this actually means for a microphone, let's take a look at a diagram of a FET:

In an active microphone, the mic capsule's signal (AC voltage) is applied to the transistor's gate to control the current and voltage between the source and drain.

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 overly simplified way of looking at things, the input of the FET/JFET controls the output without the two circuits being physically connected. In this way, the transistor is similar to the transformer.

The input impedance at the gate is extremely high and capable of receiving the very-high impedance signal of the typical condenser microphone capsule. In FET condenser mics, the transistor is often designed as close to the capsule's leads as possible so that the signal is not degraded through the wires between the two devices.

With active ribbon microphones, there is typically a step-up transformer between the ribbon element and the transistor. The step-up transformer boosts the weak voltage from the ribbon while also increasing the impedance.

The output impedance of the FET/JFET is much lower and allows the output audio signal to travel through the rest of the mic circuitry and the mic cables to the preamp or other next-in-line device.

In this way, the transistor acts as an impedance converter.

Similarly, the transistor can act as an “amplifier.” It uses the AC voltage at the gate to control a larger AC voltage between the source and drain.

For an in-depth read on microphone transformers and transducers, check out my article Do All Microphones Have Transformers And Transistors? (+ Mic Examples).

Vacuum Tube

Before transistors, there were vacuum tubes (also known as “valves”).

The vacuum tube (in tube microphones) essentially does the same job as the solid-state FET and JFET transistors. It acts to convert impedance and provide amplification to the AC signals from microphone capsules.

The most basic “amplifying” vacuum tube is a triode (meaning it has the cathode, anode, and grid).

Let's look at the parts of a simple indirectly heated triode vacuum tube:

• Heater (H): the heater is powered externally and heats the cathode
• Cathode (K): when heated, the negative cathode emits electrons that flow toward the positive anode
• Anode/plate (A): the positive plate collects electrons that flow from the heated cathode
• Grid (G): varies the electron flow between the heated cathode and the anode (plate)

Note that in the early “directly heated” tubes, the heater and cathode are consolidated into a single piece called a filament.

We apply external power to the heater (typically from an external power supply).

The heater heats the cathode, which emits electrons. These electrons flow inside the vacuum tube (the vacuum makes for very little resistance) to the positively charged anode (plate).

The capsule's output signal controls the grid. A tube mic capsule's AC signal effectively modulates the grid of the vacuum tube and varies the flow of electrons from the cathode to the anode.

So the anode (plate) “collects” an electrical current that coincides with the AC signal from the capsule.

The flow of electrons inside the tube is generally stronger than the capsule signal. If we think of the vacuum tube as an input/output device, we'd see that the output (from the anode) is a stronger AC signal than the input (at the grid).

Note that this “amplification” is actually just modulation, much like the aforementioned FET/JFETs.

The vacuum tube also acts as an impedance converter. The output signal (from the anode) has a lower impedance than the input signal (at the grid).

It's also worth noting that the vacuum tube outputs an unbalanced signal with an impedance that is still fairly high. For these reasons, tube mics will often have step-down transformers (or even transistor-based PCBs) between the tube and the output.

For more information on tubes and their role in microphone technology, check out my article What Is A Tube Microphone And How Do Tube Mics Work?

Power Supply

Some microphones (particularly tube microphones) require dedicated external power supplies to function correctly.

Active microphones of all types require some sort of power to function properly. This could be phantom power, DC bias voltage, USB power, or other types of power. In other words, the power supply does not always need to be a dedicated standalone unit.

For more information on powering microphones, check out the following My New Microphone articles:
• Do Microphones Need Power To Function Properly?
• How Are Microphones Powered? (7 Mic Powering Methods)

Analog-To-Digital Converter

In digital microphones like USB mics, there are analog-to-digital converters (ADCs).

These ADCs are required within the microphone design for the microphone to output digital audio.

The microphone as a transducer is analog. It converts mechanical wave energy into electrical energy (analog audio signals).

Like any other digital audio interface, an ADC converts the electrical signal from the microphone into the 1s and 0s of digital audio.

For more information on digital microphones, check out the following My New Microphone articles:
• Are Microphones Analog Or Digital Devices? (Mic Output Designs)
• How Do USB Microphones Work And How To Use Them

Output Connection

Finally, a microphone wouldn't be complete without an output connection. After energy conversion, adjusting the signal impedance, amplification, and balancing, the mic signal must be sent out of the mic and into a device that can effectively use its signal (preamp, mixer, interface, etc.).

There are many types of mic output connections. Common output connections include:

• XLR
• TAF5
• USB
• TRS
• TRRS

Related article: What Do Microphones Plug Into? (Full List Of Mic Connections)

---

The Conversion Of Energy (From The Sound Wave To The Mic Output Signal)

We've discussed the basics of how microphones work and the components that allow them to work properly. Now let's look at the different types of microphone transducers and which components they use to convert energy.

With each microphone type, we'll start at the sound wave and end at the microphone output.

The microphone types we'll discuss here are:

• Moving-Coil Dynamic
• Ribbon Dynamic (Active And Passive)
• Condenser (Electret, FET, And Tube)
• USB (Condenser And Dynamic)

Conversion Of Energy In A Moving-Coil Dynamic Microphone

• Sound wave
• Moving diaphragm and conductive coil
• Conversion of mechanical wave energy into electrical energy via electromagnetic induction
• Mic signal increases in level as it passes through a step-up transformer
• Mic signal is outputted through the mic output connection

Sound Wave

As always, the mechanical energy starts as a sound wave.

Moving-Coil Diaphragm/Cartridge (Transducer)

The sound wave vibrates the diaphragm in the moving-coil cartridge. There is a conductive coil attached to the diaphragm that oscillates along with it.

This conductive coil moves within a cylindrical cutaway inside a permanent magnet. As the coil moves within the magnetic field, it experiences a fluctuating magnetic flux.

Through electromagnetic induction, an electromagnetic force (voltage) is created across the coil. Since the coil moves back and forth with the diaphragm, an AC voltage is created.

A lead wire is taken from each end of the coil to move this AC mic signal down the energy line.

Step-Up Transformer

Sometimes there is a step-up transformer at the output of a moving-coil microphone.

The step-up transformer is there primarily to increase the AC voltage or strength of the mic signal.

A step-up transformer is all useful to bring the impedance of the signal up to professional microphone levels. Oftentimes the impedance of the moving-coil cartridge's signal is too low.

Additionally, the transformer protects the microphone from DC voltages like phantom power. However, this DC voltage wouldn't necessarily cause damage to the robust dynamic microphone cartridge/diaphragm.

Output Connection

Finally, the microphone must have an output. Oftentimes moving-coil dynamic mics will have a 3-pin XLR output. However, there are many other possibilities, depending on the purpose of the microphone.

Conversion Of Energy In A Ribbon Dynamic Microphone

• Sound wave
• Moving conductive diaphragm
• Conversion of mechanical wave energy into electrical energy via electromagnetic induction
• Mic signal is amplified by an active preamp (active ribbon) or increases in level as it passes through a step-up transformer (passive ribbon)
• Mic signal is outputted through the mic output connection

Ribbon Dynamic Microphone With Transformer-Coupled Output

Sound Wave

As always, the mechanical energy starts as a sound wave.

Ribbon Diaphragm/Element

The sound waves apply varying pressure on the thin, corrugated ribbon-like diaphragm of the ribbon mic.

The dynamic ribbon diaphragm oscillates back and forth within a magnetic baffle structure. Unlike its moving-coil counterpart, the ribbon diaphragm itself is conductive.

As the conductive ribbon moves back and forth, it experiences a changing magnetic flux in the permanent magnetic field. Electromagnetic induction induces a voltage across the ribbon.

Lead wires are taken from each end of the conductive ribbon and are sent to create a circuit with the primary winding of the step-up transformer.

Step-Up Transformer

Ribbon diaphragms naturally output weak mic signals (AC voltages). Therefore, a step-up transformer is needed to boost the voltage to usable levels.

Fortunately, the raw ribbon signal impedance is also low, so stepping up the signal does not push the impedance to unusable levels.

Output Connection

The signal is carried through the mic's output from the step-up transformer's output (secondary winding).

Generally speaking, ribbon mics have XLR outputs, though any output connector is possible.

Active Ribbon Dynamic Microphone With Transformerless FET Output Circuit

Some ribbon mics are active with solid-state circuitry. Active ribbon mics will output stronger signals than their passive counterparts (described above).

Let's take a closer look at how a typical active FET ribbon microphone would convert energy:

Sound Wave

As always, the mechanical energy starts as a sound wave.

Ribbon Diaphragm/Element

The ribbon diaphragm/element acts as a transducer in the same way we've described it above.

Step-Up Transformer

The step-up transformer of an active ribbon microphone will typically do most of the heavy lifting in terms of “amplifying” the signal.

These step-up transformers have higher secondary winding to primary winding ratios than their passive counterparts.

A high ratio means the step-up transformer will boost the voltage significantly at the expense of increasing the impedance even more (often too high).

Impedance Converter / Amplifier & DC Power Supply

The active impedance converter/amplifier is typically a transistor-based printed circuit board.

The signal from the step-up transformer has a very high impedance. Impedance converter circuitry effectively drops this impedance down to usable levels without degrading the signal or overly affecting signal strength.

More often than not, the power required by the active circuit is provided by phantom power (from the mic preamp or a standalone phantom power source).

Output Connection

As always, we need a standardized output connection for the mic to output its signal.

Active Tube Ribbon Dynamic Microphone With Transformer-Coupled Outputs

Sound Wave

As always, the mechanical energy starts as a sound wave.

Ribbon Diaphragm/Element

The ribbon diaphragm/element acts as a transducer in the same way we've described it above.

Step-Up Transformer

Like with the FET active ribbon mic mentioned above, the tube ribbon microphone relies heavily on its step-up transformer to boost the weak signal from its ribbon element.

Vacuum Tube & DC Power Supply

The vacuum tube essentially acts as another “amplification” step while also fulfilling the role of impedance conversion.

The step-up transformer's output is sent to the grid of the vacuum tube and modulates the stronger, lower-impedance output signal.

Vacuum tubes typically require their own separate power supply unit to function properly.

Note that the output of the vacuum tube is unbalanced.

Step-Down Transformer

This seems counter-intuitive, but a step-down transformer at the tube ribbon microphone output is generally required to “touch up” the signal. It acts to balance the signal and adjust the impedance.

Output Connection

From the step-down transformer, the signal is outputted from the mic via the output connection.

With tube microphones (including tube ribbon mics), the output connection often connects to the power supply unit. For this reason, high pin counts are common output connectors for tube mics.

Conversion Of Energy In A Condenser Microphone

• Sound wave
• The moving diaphragm in a fixed-charge parallel-plate capacitor
• Conversion of mechanical wave energy into electrical energy. The electrical signal is inversely proportionate to the distance between the parallel plates
• Mic signal is immediately amplified, and its impedance is converted (via transistor or tube)
• Mic signal is outputted through the mic output connection

Electret Condenser Microphone With Transformerless FET Output Circuit

Sound Wave

As always, the mechanical energy starts as a sound wave.

Electret Condenser Diaphragm/Capsule

The sound waves apply varying pressure to the diaphragm.

The electret material of an electret condenser capsule gives it a permanent charge. Therefore, the parallel-plate capacitor does not require external biasing to function properly.

As the diaphragm moves, it changes the capacitance of the parallel-plate capsule.

Since the charge is constant, any change in capacitance causes an inversely proportionate charge in voltage.

So as the diaphragm oscillates, the capsule outputs an AC voltage.

This AC voltage has an incredibly high impedance, so an impedance converter is required immediately after the capsule. Sending this high-impedance signal through any significant length of cable will greatly degrade its quality.

Transistor Impedance Converter / Amplifier & DC Power Supply

The impedance converter/amplifier of an electret microphone is the active component and requires external powering.

This is most often provided by some DC bias power, though phantom power is a common method of powering electret studio microphones.

Transistors (FETs and JFETs) are the centrepieces of the active impedance converters. They take in the high-impedance signal from the electret capsule and use it to modulate a stronger, lower-impedance signal at their outputs.

Output Connection

Because electret microphones are so wildly popular, there are many different output connections.

Electret microphones are found in the professional studio mic market and in lavaliers, hearing aids, cell phones, laptops, and many consumer electronics.

For more information on electret condenser microphones, check out my article The Complete Guide To Electret Condenser Microphones.

True Condenser Microphone With Transformerless FET Output Circuit

Sound Wave

As always, the mechanical energy starts as a sound wave.

Condenser Diaphragm/Capsule & DC Power Supply

The parallel-plate capacitor capsule of the “true” condenser works with the same principles as all other condenser capsules. The difference between true condenser capsules versus electret capsules is that the true condenser capsules are externally polarized.

True condensers are typically studio-grade, and so they usually are designed to run on phantom power. However, some may be powered by other means.

Transistor Impedance Converter / Amplifier & DC Power Supply

Like the active electret condenser mic, the true condenser has a printed circuit board centred around an impedance converting transistor (FET/JFET).

The path to the impedance converter needs to happen as close as possible to the capsule so that the signal does not have a chance to degrade as it travels in the wires.

The high-impedance input (gate) of the FET accepts the signal from the mic capsule. This signal then modulates a stronger, lower-impedance signal that the mic will eventually output.

Powering the active circuitry of a true condenser is achieved through the same means as polarizing its capsule.

Output Connection

True condensers mostly find themselves in the studio, so XLR output connectors are common (they are a standard for use with phantom power). However, all sorts of output connections are possible with true condenser microphones.

True Condenser Microphone With Transformer-Coupled Output

Sound Wave

As always, the mechanical energy starts as a sound wave.

Condenser Diaphragm/Capsule & DC Power Supply

The true condenser diaphragm capsule is polarized externally. It works on the same principles as any other condenser capsule.

This external polarizing voltage is often supplied by phantom power, though there are other methods.

Transistor Impedance Converter / Amplifier & DC Power Supply

The active circuitry is based around a FET/JFET and acts as an impedance converter and amplifier of the high-impedance signal from the capsule.

Step-Down Transformer

In many early FET microphones, step-down transformers were used to balance and further adjust the impedance of the output signal.

The Neumann KM 84 is featured in the following My New Microphone articles:
• 50 Best Microphones Of All Time (With Alternate Versions & Clones)
• Top 12 Best Vintage Microphones (And Their Best Clones)

Output Connection

A true condenser mic can have any output connection. However, because of their popularity in studio applications, their output connectors are often XLR-type.

Tube Condenser Microphone With Transformer-Coupled Output

Sound Wave

As always, the mechanical energy starts as a sound wave.

Condenser Diaphragm/Capsule & DC Power Supply

The externally polarized tube condenser capsule works on the same principles as any other parallel-plate condenser capsule.

It uses a fixed charge and a movable diaphragm plate. As the diaphragm moves, the distance between the plates changes, causing a corresponding change in capacitance. This change in capacitance causes an inversely proportional variation in voltage across the plates.

The AC voltage across the plates is effectively our mic signal.

The external polarization of the tube condenser capsule is typically provided by the same power supply that heats the vacuum tube.

Vacuum Tube Impedance Converter / Amplifier & DC Power Supply

The vacuum tube is commonly considered the predecessor of the transistor. In microphones, they essentially provide the same function.

The external power supply heats the tube, which causes a flow of electrons between its cathode and anode.

The high-impedance output signal from the capsule controls the grid of the vacuum tube. A vacuum tube's grid effectively alters the flow of electrons from the cathode to the anode.

Therefore, the high-impedance signal from the capsule modulates a stronger, lower-impedance signal that is outputted from the tube.

The tube effectively “amplifies” the signal while outputting a usable lower-impedance signal.

External power supplies are most often required to heat the tube.

Step-Down Transformer

A step-down transformer is often part of a tube microphone's design. These transformers further improve the impedance of the signal while also balancing the unbalanced signal from the tube.

Output Connection

Because the tube microphone requires external power, its output connection often has many pins and connects to a dedicated power supply unit.

For more information on tube condenser microphones, check out my Complete In-Depth Guide To Tube Condenser Microphones.

True Condenser Microphone With Transformerless FET Output Circuit

Sound Wave

As always, the mechanical energy starts as a sound wave.

Condenser Diaphragm/Capsule & DC Power Supply

The tube condenser microphone capsule is externally polarized via the mic's power supply unit.

Other than that, it works on the same principles as any other condenser capsule.

Vacuum Tube Impedance Converter / Amplifier & DC Power Supply

The vacuum tube works the same as the tube in a transformer-coupled tube mic.

Active PCB Impedance Converter / Amplifier

Rather than an output transformer, these tube microphones use active circuitry to balance the tube's output signal. These circuitries also adjust the impedance of the signal.

Note that the majority of the impedance conversion and signal “boosting” is provided by the tube. This allows tube mics with PCBs to largely retain their “tube sound.”

Output Connection

Because the tube microphone requires external power, its output connection often has many pins and connects to a dedicated power supply unit.

Conversion Of Energy In A USB Microphone

• Sound wave
• Moving diaphragm
• Conversion of mechanical wave energy into electrical energy via electromagnetic induction or electrostatic principles (dynamic or condenser).
• An electrical analog mic signal is converted into a digital audio signal via an internal analog-to-digital converter
• The digital mic signal is outputted through the mic output connection

Simplified USB Microphone

Sound Wave

As always, the mechanical energy starts as a sound wave.

Transducer

Although USB microphones most often have electret condenser capsules, they could work with any microphone transducer.

The transducers would work on the same principles as any other transducer of the same type.

Analog-To-Digital Converter

USB mics (and other digital microphones) have internal ADCs. This is what allows them to be USB microphones.

The ADC takes the analog AC voltage from the mic transducer and converts it to digital audio.

The bit-depth and sample rate of the converter are noted in the specs sheet of the microphone.

Output Connection

As suggested by the name, USB microphones have USB outputs. These outputs have [at least] 4 pins:

• Pin 1 provides +5 V DC. This is used to power the ADC and an impedance converter that may be used in the mic capsule
• Pin 2 carries Data –
• Pin 3 carries Data +
• Pin 4 acts as ground

For more information on USB microphones, check out my article How Do USB Microphones Work And How To Use Them.

---

Related Questions

How do wireless microphones work? Wireless microphones work to convert sound into audio the same way as wired microphones. The wireless transmitter makes the mic wireless, which takes the outputted mic signal, embeds it into a single-frequency radio signal, and sends it wirelessly to a compatible receiver.

For more information on wireless microphones, check out my article How Do Wireless Microphones Work?

Does a microphone need electricity? Although all microphones output AC electrical signals (mic signals), not all mics require electricity to function. Passive mics (like moving-coil dynamics) do not require any external power to work properly. Conversely, active mics (like condensers) do need electricity to function.

For more information on active and passive microphones as well as how to power microphones, check out my article Do Microphones Need Power To Function Properly?

For more information on microphones and electricity, check out my article Are Microphones AC Or DC Devices?