A nanophon is a very sensitive unit and would never be used in practice—unlike the company! The following is a brief explanation of the unit.
A phon is a measure of loudness level using a logarithmic scale.
The reference level for 0 phon is the loudness of a 1000 Hz tone at 0 dB SPL. This is 20 micropascal of sound pressure.
The scale is logarithmic with 10 phon corresponding to a ratio of 10:1 in intensity of the 1000 Hz tone. This is equivalent to a ratio of root(10):1 in pressure.
A nanophon, or nphon, difference is a very small ratio of intensity:
alog(0.000 000 001/10) = 1.000000000230
Or an even smaller ratio of pressure:
alog(0.000 000 001/20) = 1.000000000115
A loudness level of one nphon is the loudness of a 1000 Hz tone at just slightly more (2.3 fPa) than 20 micropascals.
This name was chosen for the company as it reflects a combination of precision and sound. The fact that the unit is not used for practical engineering is also an advantage as it avoids confusion.