Electret Condensor Mic Elements

| marzo 29, 2016

Electret Condensor Mic Elements

By David – K3DAV  (3/8/2014)

Electret Condensor Mic Elements

Electret Condensor Microphone elements have been called «Little Wonder Mics».  Mainly for their small size, small price, and big quality audio.  They come in all sizes and styles.  Some have leads sticking out the bottom for easy PC board mounting, and others just have flat solder points to solder wires to the elements for homebrew projects and mountings.  But they are all very small and easy to mount in just about any kind of mic shell, and they have very surprisingly good quality sound.

For simplicity, the term «Electret Condensor Mic» will now be referred to by it’s acronym, «ECM«.

Chances are that you see and use more than 2 of these little audio wonders every day in your normal daily activities.  Here are just a few devices that use ECM mic elements. 

  • The mic in your cell phone. 
  • The mics built in to your computer or laptop or other internet access device. 
  • All Microphones designed for computers.
  • Most electronic land based and cordless telephones. 
  • Pocket digital recorders.  
  • Speaker and boom mic headsets.  
  • Bluetooth headset or earpiece. 
  • Most interactive devices that operate with voice commands like GPS and Car Stereo’s. 
  • Security devices designed to react to sounds in a secure area.
  • Mics built into digital cameras.
  • All mics designed to connect externally to digital cameras.
  • Lepel (Tie clip) mics like they use on TV by studio news anchors, talk shows, wireless mics..etc..
  • Police, Fire and emergency crew portable radios.
  • Construction site and warehouse hand held radios.
  • Commercial Airline and Military radios. 

Have you ever seen a federal agent with the FBI, CIA, or Secret Service talking into their hands?  Yes they are talking into an ECM mic to their transmitters. 

How about ham radio?  All Icom brand stock and desk mics are ECM type.  Other brands like Yaesu are starting to see the benefits of using ECM elements with their radios.  All hand held HT radios from every manufacturer, have an ECM built in usually behind a tiny little pin hole above the speaker.  Separate HT speaker/Mics also use ECM elements.  Companies like Heil Sound , MFJ and others, make and sell mics just for Icom Radios and HT’s that incorporate ECM elements. 

Never the less, it is easy to say that over 80% of communications equipment used today are equiped with ECM mic elements.

The point is that as electronic devices get smaller and smaller, big dynamic mic elements just will not fit into them.  Can we make tiny dynamic elements?  Of course we can, but they sound flat with no tone quality, and they break easily.  This is where the ECM comes in handy.

Most ECM elements are pretty small, usually less than 1 centimeter wide and deep.  And they can produce audio quality equal to many expensive dynamic studio mics.  But the best part is that these little audio wonders usually cost less than $1.

By the way, if you scrape off the black dust filter on the top, this is what the ECM looks like naked.

Electret Condensor Mic Elements

What Is Electret Material?

Before we get into how an ECM mic is constructed and how they work, it is important to understand what «Electret Material» is, and why it does what is does.

The main diaphram disc plate inside an ECM is made of Electret material.  Quartz and some forms of silicon dioxide are natural forms of electrets.  But the material used to make electret plates today, are synthetic polymers.  The term «Electret» comes from Electric and Magnet.  The electret material holds a permenent electrical charge.  As different sounds and pressures are forced against the electret, it produces magnetic properties which make it react by moving in and out much like a speaker cone does.

In order to explain this better, let’s use some diagrams.  The first diagram is a crosscut view of an ECM element showing every part inside and how they are spaced.

Electret Condensor Mic Elements

  The picture above shows the internal parts of the ECM element.  The first part inside near the top is the Electret Material placed between a metal washer above it, and a plastic spacer below it.  This is shown better in the photo below.

Electret Condensor Mic Elements

Above are the actual parts disected from an ECM element.  On the left, you see the 3 pieces that make up the diaphram.  On the right, are the 3 pieces put together as one piece which is the diaphram.  Under the Diaphram is the metal Pick-Up plate that is soldered directly onto the center leg of the FET transistor.  This center leg of the FET is called the «Gate Lead».  The Gate Lead serves as the input to the transistor which acts as an amplifier.  Inside the case, the Electret plate, and the metal Pick-Up plate are spaced only by the .0015″ plastic spacer attached to the Electret plate.

Electret Condensor Mic Elements

In Fig.1 above,  the sounds or your voice enters through the small hole on top of the mic case.
In Fig.2 above,  the sound hits the electret material plate, and causes a magnetic movement up and down, towards and away from the metal Pick-Up plate (as depicted by the little arrows).

Electret Condensor Mic Elements

As the Electret plate moves, it creates and varies the capacitance values between the Electret plate and Pick-Up plate. (As shown in Fig.3 above)  This action generates the electrical currents that carry the sound directly into the FET transistor to be amplified.  In the old days, a capacitor was called a condensor.  The Electric, magnet, capacitor effect is how the name Electret Condensor, was given this device.

Electret Condensor Mic Elements

Fig. 4 above, highlights the heart of the ECM mic element. It is a simple FET transistor. As stated earlier, the center leg is the input to the FET. The metal Pick-Up plate that is soldered directly to this lead picks up the audio from the electret plate and sends the sound through the transistor which amplifies it and outputs the high gain audio through the (Drain Lead) of the FET which sticks out the bottom of the ECM.  The third leg called the (Source Lead) of the FET is the is the ground side of the FET. This lead serves as the audio ground, and the ground side of the Phantom Power.

The FET Is An Electronic Transistor,

So How Does It Get Voltage To Operate?

The (Drain Lead) serves 2 purposes.  First it is the audio output positive (+) terminal that connects to the radio or sound system inputs.  But it is also where the positive power wire is connected.  (+) DC voltage is fed into the FET through the Drain Lead.

Now you may wonder, «how can the audio output lead also be a power input lead to power the FET at the same time?  Won’t they interfere with each other?»  The answer is so simple it is almost stupid.  But it works.  The currents created by the audio coming out of the lead is AC.  And the currents created by the voltage going into the lead to power the FET is DC.  AC audio and DC power currents, are virtually invisible to each other and can pass each other through the same wire like 2 ships passing on the water.

But how does the voltage get on the audio line?

Inside your Icom radio or other audio amplifying system, there is a little circuit that feeds a low current DC voltage directly to the audio wire that connects to the mic.  There is a capacitor on the other side of the voltage insertion circuit to prevent DC voltage from going back into the audio circuit and damaging it.  The voltage can only go in one direction towards the mic.  But the AC current from the audio can pass through the capacitor and directly into the audio circuit. 

This type of system is called «Phantom Power».  All Icom radios use this Phantom Power on their (+) audio lines to feed power to the ECM elements they use in their stock hand mics, and their better desk mics.  The Phantom Power is normally between 7.5 and 8 volts DC.  Most ECM elements will accept any voltage between 1 and 10 volts, and still operate normally.  The only difference being, higher voltage near 10VDC will make the gain in the FET go higher (meaning louder).

So what’s the big deal about ECM’s?

ECM’s have something that make the big expensive mic manufacturers a little nervous.  And that little something is high quality audio, and a very rediculous low price of under $1.  Yes it is true.  An ECM element on a ham radio can and will usually sound as well or better than most expensive dynamic studio and broadcast mics.  I can hear some of you laughing already thinking I am just whacked out and that this article is a joke.  But let me assure you that I am not joking or trying to mislead you with false claims.  It would only cost you a couple of dollars to try and prove me wrong.

Will an ECM sound better against the more expensive dynamic studio mics in a recording or broadcast studio, or into Hi-Fi equipment?  No, the expensive dynamic mic would sound better than the ECM in those cases.  But not as much better as you would think.  Those studios have  professional digital equipment with very wide frequency ranges, so the big dynamic mic would sound better. 

But will an ECM sound better than an expensive dynamic studio mic connected to a ham radio?  Well….  it is possible, and it has been done already.  Ham radios do not enjoy the wide frequency response of recording and broadcast studios.  But the frequency response and gain factors of the ECM mics are becoming a high quality, low cost alternative to great audio reports on ham radios.

ECM elements can have very wide frequency response from 10Hz up to 30,000Hz, depending on the ECM style you get.  Larger sized ECM’s have lower bass response, while smaller ECM’s tend to offer higher treble response.  But the spacing of the internal plates, and the value of the FET transistor are what determine the frequency response and sensetivity of the ECM.

They do have one minor drawback.  They tend to distort with high dB levels.  If you scream loud into the mic or there is a lot of loud noise around you, the ECM can not handle the high dB sound pressure levels, and the loudness will sound distorted.  But for the average and slightly above average voice levels in normal Two-Way radio communications,  the ECM is a very solid performer. 

Do You Want Real Proof Of the ECM Mic Quality???

If you need a better example of the high quality available from an ECM element, listen to the hosts of any talk show on TV and all of their guests.  Or listen to the network and local news anchors read the news.  Listen to the news anchors and guests on CNN or MSNBC.  Then ask yourself how good they all sound.  Every one of those talk show and news anchors are using those tiny lepel tie-clip ECM mic elements.  When ever you see someone on TV wearing a little tie-clip or lepel mic, that is an ECM mic element.  And they are the same quality as the $1 ECM elements available through any parts dealer.  NO KIDDING!!!  REALLY!!!!  I’M NOT JOKING!!!

In My Honest Opinion….

I have been using ECM elements on my Icom 746PRO and my old Icom 706MKIIG radios.  The model ECM elements I use have a frequency response from 40Hz to 18,000Hz.  On FM Simplex, I am told it has much more audio gain and sounds more natural and cleaner than my old Heil PR-30, which I loved a lot and paid $260 for. 

In Sideband mode, I notice a faster and more consistant higher power level, and I am told my audio is the cleanest and most natural sounding it has ever been.  All Reports on SSB say I have a nice warm bass, clean natural midranges, and crisp but not slurred high tones.  Loud and clean with no distortion.  You can’t ask for better reports than that.  And all from a mic element that cost me around .81 cents, $1.14 after shipping. 

Another interesting aspect of the ECM is that you can double up on them and increase the gain.  If you connect 2 ECM elements in parallel, you increase the audio gain by almost 40%.  This is becaause you are now combining the output gain factors of 2 FET transistors.  So if you need a little more mic gain than the radio can give, wiring 2 ECMs together will aid in that idea.

The cool part is that any ECM from a computer mic or a digital camera mic to a studio lepal (Tie Clip) mic, will work very well on your Icom radio.  WHAT?  You say you don’t have an Icom or a brand of radio that has Phantom Power to feed an ECM?  Well don’t get your underwear in a bunch.  There is a very simple adaptor that you can make to feed the correct voltage to feed an ECM element on your radio.

All ham radios have one pin on the mic jack that does nothing else but supply 8VDC for whatever you want to power.  Here is the simple adaptor you can make that uses that 8VDC pin to power an ECM element.  Build this adaptor in a box or small well shielded wire harness, and insert it as close to the radio mic jack as possible.  This modification can also be built into a box with an 8 Pin round female mic socket wired for Icom mics, then the output wire would be wired and connect to your own brand radio mic jack.  This would allow you to just plug in and use any ECM type mic wired for Icom’s, on your own brand of radio.  Either way, I think you would be very surprised at the quality an ECM element can offer your radio.

Check out this link to a company called «Digi-Key».  They have a vast assortment of ECM elements.  Mix and match a bunch of them to see what you like.

concerning this article, please feel free to contact me any time at  k3dav_msn.com

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