Disassemble of large diaphragm condenser capsule

Thread Starter

Willen

Joined Nov 13, 2015
328
Hi,
Do anyone tried unscrewing all the screws of true condenser capsule and fit again perfectly?

Recently someone gave me a condenser capsule. Around thin metal film diaphragm (I guess it detects sound) I am seeing some tiny grains of dust being zam from inside. So they are pushing the diaphragm and making sone tiny spots (tiny hills). So the diaphragm is not free now to move. I think it's careless manufacturing defect. And I think it affects frequency responce badly. So can I unscrew all the screws and remove the diaphragm, and clean the dust and fit the delicate film diaphragm like before?

I am talking about a capsule like this: https://www.ebay.com/itm/34mm-Large...288650644?epid=1840008675&hash=item1a60879f94 (Sorry the OperaMini of my cellphone is not uploading picture directly here.)
 

bertus

Joined Apr 5, 2008
22,097
Hello,

Looking at the specifications, the diaphragm is only 0.4 micron thick.
I hope for you that the foil is mounted on a support ring.
You will likely tear the foil when working on it.
A human hair is between 10 and 250 micron.

Bertus
 

atferrari

Joined Jan 6, 2004
4,666
Given it works poorly, you have little to loose. Go ahead and break the film in the name of self education. Enjoy the journey. And show pictures.

Happy new year, Willen.
 

Thread Starter

Willen

Joined Nov 13, 2015
328
Given it works poorly, you have little to loose. Go ahead and break the film in the name of self education. Enjoy the journey. And show pictures.

Happy new year, Willen.
Hi,
I would do but problem is this is only a single piece I got as a gift form a guy from abroad. This is the first time I am touching a large diaphragm condenser capsule. If I damaged it, maybe I will never get a chance to experiment with "True Condenser Capsule".
 

Thread Starter

Willen

Joined Nov 13, 2015
328
Added: I eventually dissembled the capsule and re-assembled successfully. I am writing an article about the whole mic project. I will post it soon in the completed project section.
 

Thread Starter

Willen

Joined Nov 13, 2015
328
Hi atferrari,
Ok sure. Now I am in home and have poor cellphone data. Probably tomorrow I will post complete article with pictures of every steps from my school's internet.
 

ian field

Joined Oct 27, 2012
6,536
Hi,
I would do but problem is this is only a single piece I got as a gift form a guy from abroad. This is the first time I am touching a large diaphragm condenser capsule. If I damaged it, maybe I will never get a chance to experiment with "True Condenser Capsule".
Condenser mic capsules seem to be the most numerous type - but I've never seen bigger than 10mm.

The common commercial ones are just a disc of piezo electric material between layers of very thin foil. There's usually a special JFET with very low gate voltage for cut off. yours could be a professional type used in the music industry. they usually use 48V "phantom supply" - I don't know anything about those.
 

Audioguru

Joined Dec 20, 2007
11,248
Condenser mic capsules seem to be the most numerous type - but I've never seen bigger than 10mm.

The common commercial ones are just a disc of piezo electric material between layers of very thin foil. There's usually a special JFET with very low gate voltage for cut off. yours could be a professional type used in the music industry. they usually use 48V "phantom supply" - I don't know anything about those.
You are talking about a modern, inexpensive and common electret mic that has 48VDC permanently stored in its electret material and has a Jfet impedance converter at the output. The Jfet is powered by an external few volts at 0.5mA.
There is no piezo. The very thin metal film diaphragm vibrates from sounds and forms a capacitance voltage divider with the stored 48VDC.

An older "condenser mic" needs to have an external 48VDC supplied by a "phantom" circuit and does not have a Jfet but since its impedance is extremely high it usually has a preamp circuit in it.

These mics do not have "layers" of foil, there is only one diaphragm.
 

MisterBill2

Joined Jan 23, 2018
13,185
If the thing had those little carbon grains then it was a carbon microphone prior to being destroyed by opening, and losing them. It was a high quality device quite when it was first made a very many years ago, and then it was a valuable antique. I have one that is probably very similar, it may be that yours was a double button carbon microphone, with a similar setup on each side. The later capacitor microphones were usually smaller diameter and had a tube amplifier as part of the assembly. They generally have much lower noise and very good frequency response. They are often still excellent microphones and may be adapted to use FETs in place of the tube. So taking it apart is a very expensive thing because it destroys the ability to make it work.
 

Thread Starter

Willen

Joined Nov 13, 2015
328
If the thing had those little carbon grains then it was a carbon microphone prior to being destroyed by opening, and losing them. It was a high quality device quite when it was first made a very many years ago, and then it was a valuable antique. I have one that is probably very similar, it may be that yours was a double button carbon microphone, with a similar setup on each side. The later capacitor microphones were usually smaller diameter and had a tube amplifier as part of the assembly. They generally have much lower noise and very good frequency response. They are often still excellent microphones and may be adapted to use FETs in place of the tube. So taking it apart is a very expensive thing because it destroys the ability to make it work.
The grains were not pure grains. These were pieces of brass, created while drilling holes in backplate. Your carbon microphone with carbon grains sounds interesting!
 

Audioguru

Joined Dec 20, 2007
11,248
Original telephones used carbon mics that sounded awful. When the carbon bits got stuck to one side the sound level became low but hitting the mic on a table shook up the carbon bits and fixed it.
 

MisterBill2

Joined Jan 23, 2018
13,185
Just as
Original telephones used carbon mics that sounded awful. When the carbon bits got stuck to one side the sound level became low but hitting the mic on a table shook up the carbon bits and fixed it.
in many products, there is a large spread of quality levels, and while telephone carbon microphones were mass produced in huge quantities, the double-button carbon microphones were far more costly and produced for far more demanding applications. The two rings supporting the edges of the diaphragm are machined from steel and then nickel plated.The two button supports are heavy cast steel as well, with the two button supports that hold the carbon granules are nicely machined brass. And the whole thing had a support ring and an 8-spring suspension. There is no comparison between the two types. The telephone mics were produced for best voice signals, not for HiFi music use. Likewise all of those military carbon microphones left over from WW2. Never intended for anything except good articulation and clear speech.
 

Audioguru

Joined Dec 20, 2007
11,248
Speech contains important high frequencies of consonants up to 14kHz. The horrible high frequency rolloff of the carbon mics and tin can transducer earpieces in the 1920's and 1930's restricted old telephones to the highest audio frequency of only 2.7kHz or 3kHz.
Restricted high frequencies drastically reduce articulation and the clarity of speech. Try hearing "sailing" and "failing" over a 3kHz restricted telephone. They sound the same. Many other completely different words also sound the same.
 

MisterBill2

Joined Jan 23, 2018
13,185
Check out the audio frequency range of most 2-way radio systems. There is a compromise in frequency response to keep the bandwidth narrower, and so some of them very intentionally restrict the high end to about 2800 hertz. But with serious processing it is understandable, although nasty to listen to. So the whole thing comes down to a set of compromises. Narrow bandwidth or fewer channels available.
 
Top