Every microphone produces a unique sound. Although some artists think you can use EQ to make mics sound like each other by messing with the frequency response, this only affects one of the many things that make them unique.
How Microphones Work
The diaphragm in microphones is the flour in the cake. All mics have a diaphragm and couldn’t work without them.
The diaphragm is a thin piece of metal foil on top of an electromagnet. It’s so thin that sound causes it to vibrate, which in turn effects the electric current running through the electromagnet.
The pattern in the current can either be turned back into sound right away, by amping it up and running it through a much larger magnet near a much larger diaphragm (ie. a speaker), or it can be converted to a digital number pattern. Either way, the electrical pattern a microphone produces is completely dependent on the exact way the diaphragm moves.
Human ears have eardrums instead of metal diaphragms, and use nerves instead of magnets. This means that mics “hear” sound totally differently from how we do.
When we hear the playback of a song, we are listening not to the sound, but to a metal diaphragm’s vibrations when encountering the sound, translated into a bunch of numbers, and then reproduced by a speaker diaphragm.
At each stage of this process there is the chance for the sound to be subtly distorted. This slight distortion inherent in almost all microphones is also one of the characteristics that sets them apart. Different mics have different levels and types of distortions depending on what components they use. You can equate this to the rasp or breathiness that makes someone’s voice different than someone else’s.
The way the sound hits the diaphragm is also different with every mic. Some mics are designed like ears: they deliberately pick up ambient noise from many directions and echo it to the diaphragm, while others use slits or holes to try to cancel out the sound from the sides.
All microphones pick up some amount of “on-axis” sound, from the direction they’re designed to pick up, and “off-axis” sound, from other directions, and both are coloured by the way the sound gets delivered to the diaphragm. This colour can have a lot of effects other than frequency response, like changing the relative volume or character of the sound.
The bottom line is that microphones are all unique, and you’re likely going to get a different sound depending on which ones you use. Pro studios buy cabinets of mics to have as many flavours as possible; but you might just have to find one or two that really work for your particular sound.