Behringer microphones use those little Panasonic "puck" condenser cartridges. They're very inexpensive, but they have very flat response curves. It's pretty amazing really, that these cheapo mics work so well.You can get a microphone that's calibrated and they'll send you a file with the actual response curve for you to input into your measurement system. That way, it will compensate for any ripples in amplitude and phase response. But those pucks are so flat you can use them uncalibrated and get within a decibel.