Get an audio spectrum analyzer app for your phone, and enable its log-X scale. Very useful for this sort of thing. The FFT will reveal sounds you don't hear yourself.
They are indeed cool, but no math magic can help you if your microphone is not picking up the signal. I don’t have datasheets for mobile phone microphones but lets look at some professional ones. The Senheiser MD 46 goes down to 40hz. The Behringer MC8000 goes down to 15hz. These are just two random samples I looked at to illustrate that its not obvious that a microphone will even have a good response down to 10hz.
