Is there a musical note with a frequency of 7.8 hertz?

Answer 1

Given that the A above middle C has a frequency of 440 hertz, the lowest note on a regular piano has a frequency, rounded to two decimal places, of 27.50 hertz. Taking this an octave further down gives a frequency of 13.75, too low for a human ear to hear.

Descending ten semitones, to two Bs below the bottom end of a piano, gives a frequency approximately equal to 13.75/(2^(1/12)10) = 7.72 Hertz, the closest genuine note to a 7.8 hertz frequency.