Natural sources of Pink Noise for Microphone Calibration

[1100xxben]

You really cannot "calibrate" a microphone in this manner. Even if you had a perfect pink noise source, as soon as you put it into an environment that is non-anechoic, you will have altered the response with reflections that will cause it to no longer be a flat source. Calibrating a microphone requires a very controlled environment.

[dboe]

I wanted to check the frequency response of a microphone and cannot of course use a speaker as they are an unknown value.

I have heard that an air compressor can be used to generate full spectrum pink noise. Any credence to this? How about other good sources for pink noise?

Or is there a better DIY way to check how flat a mic is?