Newsgroups: rec.audio.tech
Subject: Re: PC MICROPHONE input impedance
References: 
"Suu Quan"  writes:

> I'm shopping for a MICROPHONE for my Compaq Presation 1800T laptop. I found
> that vendors out there either
> 
> - don't advertise the microphone impedance

That's true. Usually the exact impedance does not matther
in this case. For typical electtret microphones used with
computer sound card the impedance is typically few kilo-ohms.

> - say they'll work on any sound card

That's where they usually simply lie for marketing resons
or make claims without better knowledge. It is possible
to make a microphone which work with most soundcards because
they are quite similar, but not for all, because there
are some differences on some soundcards.

You can find some information on different microphone inputs used
in soundcards and how microphones for them are typically made at
http://www.hut.fi/Misc/Electronics/circuits/microphone_powering.html#soundcard
Be aware that those ones shown on the pages are not the all
possibilities that can exist.

> - advertise impedance from 24 ohm to 6,000 ohms.

Sometimes they tell real impedance, sometimes not.
I have not learnt to trust all the technical information
on the computer hardware especially on this field.
They are far too often misleading or wrong.

> Does the impedance matter? 

It does not matter much on the computer soundcard microphone
applications where microphone cables are not long.

> does it have to match the sound card's? 

No. Impedance matching as per se is not used in soundcad microphone
connections.

> and how  I find out about the sound card characteristics without 
> its paper documentation?

Paper documents (if the information in them is right) is the simplest
solution. Manufacturer web page is another. Or you can try their
helpdesk but that is usually waste of time.

One option of you have enough measuring equipments and technical
knowledge you can measure those characteristics yourself.
I am not going to the details of making those measurements.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/