Updated: Jun 23, 2018
Many times when shopping for pairs of microphones, often small diaphragm condenser mics, you'll see them offered as a matched pair. What is this and is it worth extra money?
IN MY HUMBLE (or often not so humble) OPINION-----
Man am I gonna piss off manufacturers by saying this, but it's very often not necessary.
So for starters, what is a matched pair?
Microphones can be tested to see exactly how they respond to all the different frequencies that make up the sound we hear. These tests look like a graph, showing how loud each frequency was reproduced by the mic. In theory, a perfect test would be a flat line. That's where the phrase "oh that mic is very flat" comes from.
If you are recording in stereo you need two mics. Left and right. One for each ear yes? So in a perfect world those two mics should sound exactly the same. The stereo image you record will sound like you actually being there in the room. A tested and matching pair of mics have the best chance of giving you a perfect stereo image.
BUT, is it necessary?
These days modern mic manufacturers do a very good job of quality control. If you are buying two of the same mic that were made relatively close to each other in time (like say the same month or two?) you're very likely not going to be able to tell the difference between the two, so spending extra money for a matched pair is not really a great idea.
It would be best to not try and pair an older mic with a newer one. Time does things.
If everything else is perfect and you want to have the best of the best, by all means, use matched mics. If you don't spend extra money on a matched set, it's likely you won't be able to tell the difference, especially with the higher end nice mics.