So, after the 8th octave down, we need 49 more octaves. The calculator app on my iPhone says that 2 to the power of 40 is 562,949,953,421,312. So, 57 octaves below middle C would be one cycle per 562 trillion something seconds. One cycles per 9,382,499,233,688.533 minutes. 9 trillion something minutes. That's 6,515,624,460.894815 days. Six Billion something days. That's 17,838,807.55891804 years.57 octaves below middle c is a silly way for the author to phrase it.
Middle C is 256hz (in the US)
Each octave down represents 1/2 the frequency.
1 (this is 8 octaves…1 cycle per second)