what is the quietest sound that can be heard
The threshold of hearing is generally reported as the RMS sound pressure of 20 micropascals, corresponding to a sound intensity of 0.98 pW / m at 1 atmosphere and 25 ° C. It is approximately the quietest sound a young human with undamaged hearing can detect at 1,000 Hz. The threshold of hearing is frequency-dependent and it has been shown that the ear's sensitivity is best at frequencies between 2 kHz and 5 kHz, where the threshold reaches as low as − 9 dB SPL.