Have you ever before used a microphone in an digital device, in the studio, or in film? There’s a good chance it to be an electret condenser microphone. These microphones are usual in our day-to-day lives and are worth learning about.

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What is one electret condenser microphone? one ECM is a form of condenser microphone transducer which method its functions on electrostatic principles. Condenser mic capsules basically work as capacitors and require a charge offered quasi-permanently by electret product (a portmanteau that electric and magnet) in the capsule.

In this finish guide, we’ll further specify electret condenser microphones (ECMs), looking in ~ their architecture characteristics, how they work, your applications, and, that course, a few electret microphone examples.

Table the Contents

What Is one Electret Condenser Microphone?

An electret condenser microphone, as the surname suggests, is a kind of condenser microphone.

The main difference in between an ECM and also a “regular” condenser microphone is the technique in which the condenser capsule that the microphone is polarized (charged).

As we’ll gain into in the next section, exactly how Do Electret Condenser Microphones Work? Condenser capsules act together parallel-plate capacitors and require a resolved charge throughout their bowl to function properly.

The polarizing voltage that reasons a solved charge throughout the plates is usually supplied by external way (typically via phantom power or an external power supply v FET and tube condensers, respectively).

However, over there is another method of giving the plates v a solved charge, and that is, together you’ve probably guessed, the enhancement of electret material in the capsule design.

So electret condenser microphones utilize electret product in your diaphragms to maintain a “quasi-permanent” charge throughout their plates. This frees up sources so the the powering methods can be used more effectively to power the impedance converters, printed circuit boards and also other energetic components in ~ the microphone.

What Is Electret Material?

So what is this magical, permanently charged, electret material we’ve been discussing?

Electret product is any kind of dielectric product that has a quasi-permanent electric charge or dipole polarization. These materials generate irreversible internal and external electric fields and can properly charge other electrical components, such together capacitors.

As mentioned, the hatchet “electret” comes from electrostatic and magnet. Electrets are basically the electrostatic equivalent of a permanent magnet.

Electret materials commonly have high electric resistance and also chemical stability and will preserve their electric charge for long periods the time (in the hundreds of years).

Electrets are generally made through melting down dielectric product and enabling this material to solidify whilst in a solid electrostatic field. Polar molecules naturally align themselves in ~ this electrostatic field while the material is melted and remains in this position as the material hardens, producing a irreversible electrostatic bias.

In microphones, the electret material is typically Polytetrafluoroethylene (PTFE) plastic in film type or solute form.

A bit Of history On Electret Condensers

The very first electret condenser microphones to be crude, indeed. The an initial electret microphone was designed in 1920 (by Yoguchi the Japan), yet it wasn’t until 1961 the electret microphones might effectively be provided in market-ready products.

More special, it to be the foil electret microphone designed in 1961 by James West and also Gerhard Sessler at Bell Laboratories.

The an initial early electret microphone was created in 1938 by the Bogen agency and was well-known as the No-Voltage Velotron. Unfortunately, in ~ this time, electret technology was rudely (to speak the least), and although these mics worked, it was not lengthy that the electret product would begin to lose its charge and render the mic ineffective.

The very first successful electret condenser microphone to hit the industry was the Sony ECM-22P In 1968.

Sony ECM-22P

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Even in the early on days that commercially easily accessible electret mics, the modern technology was spotty in ~ best. In fact, in these times, the hatchet “true condenser” came about to identify the remarkable externally-polarized condenser microphones from their electret counterparts.

Electret an innovation has come a long means since then, and also today the is uncovered in numerous professional-grade studio condenser microphones and even in measure up microphones.

To discover a good deal much more about microphone history, please consider reading through my short article Mic History: Who created Each kind Of Microphone and When?

Types the Electret Microphones

There space 3 key ways in i beg your pardon electret product is added to one ECM to provide the long-term charge. This 3 electret types are:

Foil electretBack electretFront electret

What is a foil electret condenser microphone? A foil electret condenser mic employs a movie of electret product as its diaphragm rather than having a distinctive diaphragm bowl coated in electret material (like a front electret). Silver paper electrets are the most common, but the lowest-quality electret mics since electret movies perform poorly as diaphragms.

What is a ago electret condenser microphone? A back electret microphone is a condenser mic with a permanently charged capsule due come electret product being fixed to the stationary backplate. Not having actually electret material fixed ~ above the front plate (diaphragm) rises diaphragm accuracy, and the electret is an ext durable since it’s stationary.

What is a front electret condenser microphone?A prior electret condenser mic is anelectret micwith nobackplate. Rather, thecapacitoris developed by thediaphragmand the inside surface of themic capsule. An electret movie is addressed to the inside front sheathe of the mic and also the diaphragm is linked to the input of theFET.

Consumer electronics and project-grade ECMs additionally come with different output connector types. This include:


Pin-type ECMs have actually conductor pins to carry the unbalanced signal out of the mic.

Pin-type ECM

Terminal-type ECMs are a bit an ext flexible and have your terminals easily accessible to attach to assorted circuits.

Terminal-type ECM

Wire-type ECMs have actually their signals lugged out by a wire and also can be positioned more away from their intended PCBs.

Wire-type ECM

How do Electret Condenser Microphones Work?

Now that we have actually an understanding of what electret microphones space let’s take it a deeper look into how they function.

We’ll begin with a straightforward and straightforward diagram that a back electret condenser microphone capsule and also impedance converter for recommendation throughout this section:


As v all microphones, ECMs have actually diaphragms that reaction with outside sound tide (variations in sound pressure). This diaphragm activity is converted into a coinciding mic signal that is climate outputted by the microphone.

But there’s a lot much more to know than this basics!

The Electrostatic ethics Behind The ECM Transducer

First, let’s talk about the electrostatic ethics that are the communication of ECM functionality. Note that these values are the exact same for every condenser microphones.

We’ll start with the fact that the condenser microphone capsule is essentially a parallel-plate capacitor.

This capacitor is made of a movable prior plate (the capsule diaphragm/membrane) and a stationary backplate (known simply as the backplate).

This capacitor must host a consistent charge in between the diaphragm and also backplate to function properly. Through ECMs, this charge is provided by the electret product (either ~ above the diaphragm, backplate, or somewhere else in the capsule design).

Once the capsule has its fixed charge, we have the right to use the following electrical formula to understand exactly how the capsule works:

V = Q • C

V = voltage throughout the plates.Q = electric charge between the plates.C = capacitance that the parallel-plate capacitor.

The microphone’s audio signal starts as the sports in voltage throughout the capsule’s capacitor plates. Analog audio signals are, after ~ all, AC voltages through frequencies between 20 Hz – 20,000 Hz.

The AC voltage native the capacitor should be altered before it can efficiently be outputted indigenous the microphone, but the capsule transducer is the beginning of the microphone signal.

So, by looking in ~ the above formula, we see that, with a addressed charge, any adjust in capacitance will develop an inversely proportionate readjust in voltage. This method that, in bespeak to create an AC voltage mic signal, we require the capacitor’s capacitance to differ up and also down (oscillate around its setpoint).

How have the right to the capacitance be transformed within a condenser microphone capsule? Let’s take it a watch at one more capacitance formula to find out:


C = capacitance of the parallel-plate capacitor.A = area of the plates.ε0 = dielectric constant.d = distance between the plates.

In the above formula, we have actually two constants: the dielectric continuous and the area the the key (the movable diaphragm and also stationary backplate). The movable diaphragm, which reacts to sport in sound push level, enables for alters in the distance between the bowl (d in the above equation).

So by moving the diaphragm, we alter the distance in between the key of the capacitor.

According come our second equation, any adjust in distance in between the capacitor plates causes a proportionate change in the capacitance the the capacitor/capsule.

According to our an initial equation, any change in capacitance reasons an inversely proportionate readjust in voltage throughout the plates.

As we’ve discussed, one AC voltage throughout the bowl is essentially our mic signal. Via the electrostatic values mentioned above, any sound tide at the condenser mic diaphragm reason a coinciding mic signal!

The Electret Material

What really separates ECMs from continual condenser microphones is the electret material. As formerly mentioned, the electret material allows for a fixed electrical charge across the parallel-plate capacitor. This resolved charge, again, is crucial from ECM capsules to function properly.

The Impedance converting Transistor

The transducer element and the electrostatic ethics that administer it room pretty clever. However, there’s one large issue through ECM capsules (and condenser microphone capsules in general, for the matter).

This issue is the extremely high impedance in ~ the capsule output.

The condenser capsule must keep a really high impedance in order to store the save on computer charge across the plates indigenous leaking away.

Similarly, the is necessary to have an impedance converter instantly after the capsule to take the audio signal native the ECM capsule effectively. With ECMs, this impedance converter is commonly in the kind of a JFET (junction-gate field-effect transistor).

A JFET is an active electronic machine with 3 terminals. Let’s have a look at a basic diagram that a JFET complying with by a list of the terminals:

S = sourceD = drainG = gate

The capsule’s high-impedance calculation signal is sent to the door of the JFET where it create a circuit with the source-gate terminals.

The gate deserve to be thought of as a high-impedance input, capable of receiving the capsule’s calculation signal without significant degradation (which would certainly be the case if the input to be low-impedance).

For much more information on microphone impedance, examine out my write-up Microphone Impedance: What Is It and Why Is it Important?

The JFET is provided power via an external resource (typically phantom strength or DC biasing). This successfully sets up the source-drain terminals to have electrical present flow with them. This existing is reasonably low-impedance and also can be sent through the rest of the microphone and the final mic output.

The current in between the source-drain deserve to be believed of together the JFET (impedance converter) output. The “outputted” AC voltage, together we might guess, has a much reduced impedance than the “inputted signal.”

The “input signal” essentially modulates the current of the “output signal.” Therefore, a high-impedance signal going to the gate-source terminals that the JFET can effectively modulate the low-impedance signal at the source-drain. This is wherein the impedance come in.

Note the JFETs might also provide a type of pseudo-amplification in between their input and also output.

To learn more about transistors in microphones, inspect out my related article, titled carry out All Microphones have actually Transformers and also Transistors? (+ Mic Examples).

Further Circuitry and also The Microphone Output

Depending top top the specific electret condenser microphone, there could be added circuits because that the mic signal to happen through prior to being outputted from the microphone.

These circuits may encompass (but space not restricted to) the following components:

High-pass filtersPassive attenuation gadgets (PADs)AmplifiersAnalog-to-digital converters

To learn an ext about HPFs and also Pads, inspect out the adhering to My brand-new Microphone articles:What Is A Microphone High-Pass Filter and Why usage One?• Audio EQ: What Is A High-Pass Filter & how Do HPFs Work?What Is A Microphone Attenuation Pad and What Does the Do?

Powering The active Components Of one Electret Condenser Microphones

ECMs have permanently charged capsules and do not call for an outside polarizing voltage to apply a fixed charge throughout their plates.

That being said, electret condenser microphones room still energetic microphones. Your impedance converters need power (provided by external means) to duty properly, as carry out the contents mentioned in the ar above.

In studio-grade and also measurement ECMs, the wanted powering technique is phantom power, which uses +48 V DC ~ above pins 2 and also 3 (relative to pen 1) of the balanced audio cable associated to the microphone.

With lavalier and also other miniature ECMs, the desired powering an approach is regularly DC biasing. This technique entails sending +5 V DC follow me the audio conductor of an unbalanced line and is usually gave by the wireless transmitter bodypack the lav mic connects to.

In customer devices, which commonly use electret microphones, the mics are powered through the very same battery, power supply, or strength mains that power the remainder of the device.

With every that information in mind, the following simplified diagram of one ECM must make sense:


To learn an ext about powering microphones through phantom power and also other methods, inspect out my in-depth short article What Is Phantom Power and How does It work-related With Microphones?

Applications that Electret Condenser Microphones

At the start of this article, I pointed out that electret condenser microphones room one, if no the most, frequently used microphones ~ above Earth.

With that, let’s take away a look at some usual ECMs:

Measurement microphonesStudio condenser microphonesFilm microphones (shotgun mics, lavalier mics, etc.)Consumer electronics (laptops, cellphones, etc)Professional medical tools (such as hearing aids)

The applications that the above microphone types range native telephone calls to blockbuster movie audio; hit documents to help those of us with hearing impairments.

Electret Condenser Microphone Examples

To really learn around electret condenser microphones, we need to take a look at some examples:

Earthworks M50

The Earthworks M50 (link to check the price in ~ sweetwater) is great measurement microphone with an electret condenser capsule. It has actually a wide frequency solution ranging all the way from 5 Hz come 50,000 Hz (the human range of hearing, which many EMCs aim to reproduce, is just 20 Hz – 20,000 Hz).

This microphone tells us that electret microphones, with the appropriate design, have the right to be top performers and incredibly accurate transducers.

DPA 4006A

The DPA 4006A (link to examine the price top top Amazon) is a top-of-the-line microphone in general (not only compared to other electret condenser microphones).

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This pencil microphone performs practically as precisely as a measurement microphone yet is no marketed that way. Rather, the 4006A is created to it is in a go-to microphone for accurate and also detailed sound manufacturing in the studio.

To learn more about pencil microphones, check out my write-up What are Pencil Microphones and also What space They used For?

Rode NT1-A

The speak NT1-A (link to check the price ~ above Amazon) is among my an individual favourite microphones. Ns would take into consideration this microphone a “prosumer” product, gift somewhere between top-of-the-line professional and also full-out consumer-grade. I’ve personally offered this microphone on countless professional jobs in my career together an audio engineer.

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Sanken COS-11D

The Sanken COS-11D (link to examine the price on Amazon) is one industry-standard lavalier microphone for film, television and also other screened media.

This mic has actually a miniature electret condenser capsule and also works top top DC predisposition voltage.

To learn an ext about miniature lavalier microphones, inspect out the following My brand-new Microphone articles: How and Where To attach A Lavalier/Lapel Microphone best Lavalier Microphones for Interviews/News/Presentations ideal Lavalier Microphones because that Actors

Challenge electronic devices CEM-C9745JAD462P2.54R

The difficulty Electronics CEM-C9745JAD462P2.54R (link to check the price on Amazon) is among the numerous examples of inexpensive ECMs top top the industry today (it’s additionally quite a mouthful). These little pin-type project ECMs would be very similar to what we would intend to uncover in consumer-grade electronics.

iPhone (2008)

The initial iPhone utilized an ECM v an prompt ADC to record and transmit audio. Subsequent models have actually been designed through MEMS microphones.

With the climbing popularity and development of MEMS microphones, numerous consumer maker manufacturers are opting because that MEMS mics over ECMs. MEMS mics are lot smaller and becoming cheaper to build and, in part ways, outperform ECMs (particularly in customer devices favor cellphones).

To learn more about MEMS microphones, examine out my post What Is A MEMS (Micro-Electro-Mechanical Systems) Microphone?

Related Questions

What is a FET microphone? A FET microphone is a solid-state energetic microphone that uses a FET (field-effect transistor), as opposed to a vacuum tube, as its impedance converter. FET mics are generally condenser microphones however can have dynamic transducers as well.

See more: Does Eggnog Go Bad? How Long Is Eggnog Good For After Sell By Date

To learn much more about FET microphones, examine out my short articles What are FETs & What Is Their duty In Microphone Design? and What are The Differences between Tube & FET Microphones?

What is an energetic microphone? An energetic microphone is a mic that needs power to role properly. Every condenser mics are active, and some ribbon dynamics space active. Energetic components in ~ mic designs encompass impedance converters (tubes or FET), externally-polarized capsules, and also some materials within a mic’s published circuit boards.

To learn much more about energetic (and passive) microphones, check out my article Do Microphones need Power To role Properly?