From: Birger Petterson (BirgerPetterson_at_worldnet.att.net)
Date: Sun May 14 2000 - 15:05:52 EDT
This question pops up quite often. So I'll post this info.
Microphone connections for electret type of microphones used on IBM PC
compatible computers for voice recognition.
The majority of the above microphones terminate with a 1/8 inch stereo
phono plug. It is also known as a 3.5 mm stereo phono plug.
The tip accepts a bias voltage, which is a positive DC voltage.
This voltage can range from 3 to 9 volts DC.
The middle connector is generally not connected to anything.
The third connector is generally the ground or shield connection.
Some soundcards on desktops provide a positive D.C. voltage on the third
connector. Andrea furnishes a black connector, which reverses the
connection of the tip and the third connector.
The Shure 505 microphone requires a positive D.C. voltage on the middle
connector.
To get around this problem you can use a headphone adapter which you can
obtain from Radio Shack number 274-368 a.
If your desktop sound card has an amplifier that is too powerful, then
you can use the gray plug that Andrea furnishes. This cuts down on the
microphone input.
On a IBM ThinkPads which have a stereo microphone input, but which does
not provide a positive DC voltage to the tip of the microphone plug, has
a outer ring which looks silver in color. This outer ring is supplied
with a positive 5.0 DC voltage through a 2.7 k ohm resistor.
You can use a ThinkPad adapter converter available from Andrea which
will provide bias voltage for your microphone.
Andrea also furnishes a bias battery box which furnishes DC voltage for
your microphone.
There are some desktop soundcards which supplies a positive DC voltage
to the tip of the electret microphone which is not adequate. The use of
a bias battery box in this situation will help the microphone to work
properly.
The mini phono plug is even smaller than the
1/8 inch or 3.5 mm phono plug that I have been discussing.
If you are using a Jabra ear microphone with your cellular phone, then
you will know what the mini phono plug is.
There are other types of microphones which are used for voice
recognition which I have not discussed.
If you wish to know more about microphones from a layman's point of
view, you can read an article that I wrote for
http://www.speechcontrol.com
Adapters, Battery bias boxes, microphones etc can be obtained at the
above.
Please note that microphone makers sometimes change their features and
specifications without notice.
Also; Dynamic microphones do not require bias voltage.
Some Condenser microphone have a battery included for its power
requirements.
The ThinkPad Manual does state– well you look for it.
Birger
I do not sell anything.
This archive was generated by hypermail 2.1.3 : Thu Jan 23 2003 - 09:56:05 EST