Most microphones can not reliably measure down to 7 Hz. I have a pretty good Earthworks mic and it is only good down to 9 Hz. Most of these USB calibration mics like the Umik, Behringer, and omnimic, can not get anywhere near that low. And then there is the question of at what point does 7 Hz become discernible? TLS Guy would say it is not audible at all. According to the research that says it is, you need almost 110 dB just to be begin to sense it in a controlled laboratory environment:
So the question is, how do you know what you are hearing is 7 Hz? Even most bass enthusiasts have no way to tell. How do you know you are not hearing harmonics, whether it be from the subwoofer itself or stuff around the house that sympathetically resonates at some harmonic?
Anytime anyone talks about 7 Hz or any frequencies that low, nothing should be taken seriously unless the measurement techniques and an understanding of not only audiology but also acoustics can be substantiated. It is debatable whether such frequencies can be heard in the normal sense of the word. However we sense these extremely low frequencies, the subtlety and indistinct nature of this sensation will naturally lend itself to conjecture and mysticism that already plague so much home audio.
