Condensor Microphone theory

[Neil Ogilvie]

Something that has been buggin me for a while....

In a standard Capacitor, there is a a non-conducting material between the positive and negative plates - in a Condensor Microphone is this the air? Or is there something other than air that allows the capacitance? (Mylar?)

I would have thought it would be only air, since its capacitance does not need to be very high, but I'm not sure.

If someone could spread light on this it would be grealty appreciated.

Cheers, Neil

 

[Track Rat]

Air is the spacer. The diaphram is coated with a conductive material (gold, aluminum, etc) and the the back plate in charged with voltage. When moving air (sound) hits the diaphram, the gap between the diaphram and the back plate will changed accordingly, thus generating the output voltage. This is a WAY dumbed down explination.

 

[Han]

Right! In a Neumann M149 the space between the membrane and the backplate is so little that a human hair will not fit there.

 

[acorec]

Something that has been buggin me for a while....

In a standard Capacitor, there is a a non-conducting material between the positive and negative plates - in a Condensor Microphone is this the air? Or is there something other than air that allows the capacitance? (Mylar?)

I would have thought it would be only air, since its capacitance does not need to be very high, but I'm not sure.

If someone could spread light on this it would be grealty appreciated.

Cheers, Neil

Any two conductors seperated by an insulator is by definition a capacitor. Air is an insulator.

 

[Jeeper]

Neumann has a PDF booklet on their site that shows a diagram and tells a little about cond. capsules. I was unable to link the file but try Neumann.com for it. To branch down to it from their home page click on info pool then general information then documents. Then its the top file listed on that menu "Book "Microphones", Bore/Peus". That book makes for quite good reading on basics.

Sorry I couldn't link for you but with their site structure I just couldn't do it.

Good Luck

 

[Slackmaster2K]

I would direct you to the thread that's stickied to the top of this forum!

 

[Neil Ogilvie]

I would direct you to the thread that's stickied to the top of this forum!

Yeah, read that, but couldn't find the direct information that I was looking for.

Cheers for the replies, I was pretty sure the air was the insulator, just had to check.

Thanks again.

 

[Jeeper]

Have a look at page 31 again, I'm the same way I miss things that are right there when I read also.

From Neumann Book:

"5. Condenser microphones

The basic construction of a condenser microphone is shown in Fig. 15: a diaphragm with a thickness of 1 ... 10 µm made of metal or metallized plastic is arranged very close to a perforated, electrically conductive oppositely-charged electrode (backplate). Impinging sound waves move the diaphragm and change its distance from the backplate and thus the capacitance
of the air-dielectric capacitor formed by the diaphragm and the backplate. Due to the close proximity of the diaphragm to the backplate (5...50 µm), the restoring force and damping of the diaphragm are primarily determined by the air cushion behind it, and can be adjusted to the required value by a suitable choice of diaphragm spacing and by holes drilled in the backplate (but not through it)."

Please don't take this as an attack I just assume you missed the answer you wanted. Maybe one day you'll get to return favor and get me straight on something, we all have a lot to learn. I know I'll need help finding an answer some day also.

Good luck.

 

[Neil Ogilvie]

Please don't take this as an attack I just assume you missed the answer you wanted. Maybe one day you'll get to return favor and get me straight on something, we all have a lot to learn. I know I'll need help finding an answer some day also.

I don't take it as an attack at all - but thankyou all the same for taking time to look up stuff like this. Its what makes this BBS such an amazing source of information and help.

Thanks to everyone who replied.

Neil