Topic: Electret Condenser, Back electret, Condenser, Capacitor...all the same?

[Roving Sign]

Are these the same thing...sort of the same?

What's the difference...?

[Kyle]

I think electret/back electret are the same and use a pre-polarized capsule which can be powered by a battery or phantom. Standard condensers need voltage (60v  ) to polarize the capsule. There may be other differences; I am not sure. Conderser and capacitor are the same...

 

[j.mart]

http://en.wikipedia.org/wiki/Microphone

I find this very useful

[guysonic]

Back Electret is the higher quality version of electret as the diaphragm is NOT polarized, instead a lighter much thinner  diaphragm is used with the metal back plate (behind the diaphragm) having the polarized charge element.  Constucted in this way, the high to very high frequency response of the mic is greatly improved. 

Costs more to manufacture, and most electret found in catalogs are not the back element type.

Regular electret types have their frequency response limited to about 16,000 cycles, while back electret pickups have flat response out to >23,000, and still operating with good output at beyond 40,000 cycles!

[ghellquist]

First of all, it makes no difference really to us users. A good mic is a good mic regardless of whats inside it. For all I care it could be chicken manure as long as it sounds good. There is a tradition here, but it is more about tradition than about real differences. Good microphones could conceivable be made using a lot of different techniques, evolving over time -- just witness how hip ribbon mics has become lately, earlier a more or less dead technology.

All types in the question are condensor mics, also called capacitor mics as they work on the capacitance changing in the condensor mic element. In order for them to work you need a polarizing voltage in the mic. It can be supplied from the outside (battery or phantom) or it can be permanently "burned" inside the mic.

Electret condensors has the polarizing voltage burned into a plastic membrane. This was a rather recent innovation (60-s or so). The first versions had the polarizing voltage burned into the front membrane, a technique still used at times.

Later versions moved the polarized membrane to the back, allowing the front membrane to be made thinner or even from other materials. There are some really good back electret mics around. One example is that most, if not all, of the DPA mics (former B&K) use that technology. My DPA 4003-s, generally acclaimed as among the very top omni mics, are internally back electrets with a stainless steel mic membrane.

(Extra: For the really interested only true pressure omni mics can be made with the very stiff stainless steel membrane. Cardoids require much softer membranes).

Most condensor studio mics today are made in China (if you count them) and most use externally polarized condensor capsules. This generally means that they need phantom power. Some are good, some not.

All condensor mics, regardless of type requires some kind of electronics inside them, often called a head amp. The reason is that the signal from the mic element can not travel very far before detoriating. We are probably talking a few inches as maximum here. So there is at least one transistor or tube inside the mic casing. This head amp needs some kind of power supply which could be as little as a 1,5V battery, phantom power or even a special 200V external power supply.l

So to summarize: It makes a difference to the producer what technology to use. To the user all that counts is the result.

Gunnar

[CHURCH-AUDIO]

electrets condenser mics are pre-polarized meaning the diaphragm has a static charge on it. The voltage applied to this mic has nothing to do with the diaphragm it simply powers the fet. Back electret is like guysonic said a pre-polarized back plate the charge is made to the back plate rather then the foil membrane. Capacitor is a mic whose charge is made externally. Companies like sennhieser made mics like the  MKH-4O and others these were true capacitor mics that used a high frequency power supply to supply the mic 200 volts it needed to charge it's diaphragm. Very high end but very sensitive to outside humidity due to the increased voltage. It is based on the electrostatic theory just like the headphones most real B&K and APO pacific mics work under the external polarization voltage.

All condenser mics work on the variation of capacitance made when you place a back plate as close as you can to a foil membrane using a thin Mylar washer. The vibration of the foil diaphragm causes a change in the special relationship between the back plate and the diaphragm resulting in a creation of ac current. Thus an electromechanical signal in direct relation to the movement of air molecules is created. Sound all of these mics have there place Capacitor not good for wet weather Electret condenser good for most applications does not have long term stability due to the fact that the foil loses it charge over time. Back electrets better because metal back plate is more stable then Mylar film for holding charge. Capacitor mics have great stability do to external polarization of the capsule and the wide choice of diaphram meterials like titanium and steel these materials are very strong and less likely to stretch over time and with temprature changes giveing these mics the best choice for nist sound measurements.

Chris Church

Are these the same thing...sort of the same?

What's the difference...?

[ghellquist]

Companies like sennhieser made mics like the  MKH-4O and others these were true capacitor mics that used a high frequency power supply to supply the mic 200 volts it needed to charge it's diaphragm. Very high end but very sensitive to outside humidity due to the increased voltage.

Wow, Chris.

A bit difficult to understand some of the writing in your post. Also see several (more than three) statements I cannot really agree with as true.

Want to refute the specific point I have quoted though. The MKH40 is known to be very UN-sensitive to humidity as condensors go. In fact the MKH-series seems to be a favourite among the on-location film people exactly due to that. I would also be very surprised if there is 200V-s in there, but then I am no expert on the RF technique used.  (I do use a MKH40 at times).

Gunnar

[Roving Sign]

With regard to back electrets - I've heard it said that the back plate loses its charge over time and degrades the mics perfomance...?

[ghellquist]

With regard to back electrets - I've heard it said that the back plate loses its charge over time and degrades the mics perfomance...?

This is true of course. Everything detoriates over time.

For a DPA 4006 as example, I would not expect any measurable change in 20 years, and for it to stay withing specs for something like 100 years.
You might read a bit more here:
http://www.dpamicrophones.com/Images/DM01856.pdf

Gunnar

[CHURCH-AUDIO]

Sir you are correct. I should have said the Sennheiser models 105,405,805 are true capacitor microphones - not the hkh40. Also, the Schoeps CMT series operates the same way using a radio frequency oscillator at around 8mhz. Also, I said in my statement an AC voltage is generated - thats incorrect. I should have said varying capacitance is created. Also, I made another mistake when I said that capacitor mics are very sensitive to humidity. I should have said Voltage divider capacitor mics are sensitive to humidity. I just re-read the section on condenser/ capcitor mics in my Handbook for Sound engineers second addition.

I stand corrected, I guess I should do some more reading. I am getting a bit dull on the subject of audio. I guess you lose it over time if you dont keep up with the studying. Thanks for reminding me.

Chris Church

Companies like sennhieser made mics like the  MKH-4O and others these were true capacitor mics that used a high frequency power supply to supply the mic 200 volts it needed to charge it's diaphragm. Very high end but very sensitive to outside humidity due to the increased voltage.

Wow, Chris.

A bit difficult to understand some of the writing in your post. Also see several (more than three) statements I cannot really agree with as true.

Want to refute the specific point I have quoted though. The MKH40 is known to be very UN-sensitive to humidity as condensors go. In fact the MKH-series seems to be a favourite among the on-location film people exactly due to that. I would also be very surprised if there is 200V-s in there, but then I am no expert on the RF technique used.  (I do use a MKH40 at times).

Gunnar

[RebelRebel]

http://www.powells.com/biblio/72-0240519612-0


buy this book. outstanding resource.

Church Audio, no offense man, but please consider using periods/punctuation. Your stuff is terribly hard to read.

[guysonic]

my 20y.o. old senn. mke2002's are back-electret, and are still fairly close to each other (less than 2dB diff).

With regard to back electrets - I've heard it said that the back plate loses its charge over time and degrades the mics perfomance...?

This is true of course. Everything detoriates over time.

For a DPA 4006 as example, I would not expect any measurable change in 20 years, and for it to stay withing specs for something like 100 years.
You might read a bit more here:
http://www.dpamicrophones.com/Images/DM01856.pdf

Gunnar

Pondered this issue also, but after getting mic these (modified back-electet Panasonic) sets for refurbishment service that are 10-16 years old, and finding most all measure within .25 dB to 1 dB if original documented calibration, I am not the least concerned with these particular capsules loosing charge or changing anything for at least 10-20 years of normal user service!