| Author |
Message |
    
Vanillagorilla
Advanced Member
Username: Vanillagorilla
Post Number: 568
Registered: 4-2005
| | Posted on Sunday, May 14, 2006 - 12:47 pm: | 
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Could someone explain the difference. Am I to understand you have to use an electret in a power mic where power is applied?
I'm looking to replace a defective element in a friends NON amplified Fannon desk mic. Problem is I don't have one small enough in my box 'o junk. I found electret online small enough but wonder if they'll work? Needs to be no larger in dia than 3/4" or so...again..for a NON amplified mic.
Thanks for any info!
Hank |
Tech833
Moderator
Username: Tech833
Post Number: 1350
Registered: 8-2002
| | Posted on Monday, May 15, 2006 - 11:17 am: |
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Hey Gorilla.
A dynamic mic element is a lot like a regular speaker, only in reverse. When sound waves strike the diaphragm, they vibrate it. The vibrations move it back and forth. Since the diaphragm is connected to a small coil in the back of it, and that coil rides within a magnetic field, as the diaphragm moves back and forth, a small electrical field is generated. The electrical field is transferred to the audio amp in the radio ( or sometimes within the base of a power mic) and amplified to a useable level.
In an electret mic element, a small DC voltage must be applied to the element. As sound waves strike the transducer, the small DC voltage is varied at the audio rate. A DC coupled amplifier in your radio or power mic isolates the DC and amplifies the DC voltage differences into a useable audio signal. Without the DC bias voltage on the element, it will not work. |
Hollowpoint445
Senior Member
Username: Hollowpoint445
Post Number: 1224
Registered: 6-2004
| | Posted on Monday, May 15, 2006 - 2:40 pm: |
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Just to clarify, what Tech833 described as an electret element is actually a condenser element.
An electret element doesn't need voltage to convert mechanical movement into an electrical signal because there is a material with a permanent electret charge attached to the diaphragm. The movement of that material in relation to the back plate varies capacitance and creates an electrical signal. The reason electret elements need voltage to work is because the output is so low and the impedance is so high. The signal needs to be amplified and the impedance lowered to a useable levels. That's accomplished by an FET which is incorporated into the element capsule itself. |
Vanillagorilla
Advanced Member
Username: Vanillagorilla
Post Number: 571
Registered: 4-2005
| | Posted on Monday, May 15, 2006 - 2:41 pm: |
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Thanks for the info 833. Valuable info at its best. 
I'll keep looking for a SMALL dyn element.
Hank CEF559 |
Kid_vicious
Senior Member
Username: Kid_vicious
Post Number: 1605
Registered: 9-2004
| | Posted on Tuesday, May 16, 2006 - 12:31 am: |
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check mouser.
the brand name is kobitone.
they might have the size you want.
incidentally, one of these is the D104 replacement you see on internet auction sites.
matt |
Vanillagorilla
Advanced Member
Username: Vanillagorilla
Post Number: 575
Registered: 4-2005
| | Posted on Friday, May 19, 2006 - 5:02 am: |
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Thanks again HP and KV. Another post worth printing out for the notebook |
