The smallest sound wave that can be detected by the human ear depends on various factors, including the individual's hearing sensitivity and the conditions under which the sound is presented. In general, the threshold of hearing is defined as the minimum sound pressure level that can be detected by the average human ear at a frequency of 1,000 hertz (Hz).
Under optimal conditions, a healthy human ear can typically detect sound waves with a pressure level of around 0 decibels (dB) SPL. This level corresponds to the faintest sound that can be heard in a quiet environment. However, it's important to note that individual variations in hearing sensitivity exist, and some people may have more sensitive hearing than others.
At extremely low sound pressure levels, close to the threshold of hearing, the perception of sound becomes less reliable, and individual differences in hearing thresholds become more pronounced. Additionally, factors such as background noise and the duration of the sound can also influence the detectability of sound waves.
It's worth noting that the human ear is generally more sensitive to sounds in the frequency range of 2,000 to 5,000 Hz, with the threshold of hearing being lowest around 3,000 to 4,000 Hz. At frequencies below 1,000 Hz or above 5,000 Hz, the threshold of hearing tends to increase.
In summary, while the smallest sound wave that can be detected by the human ear is typically around 0 dB SPL at 1,000 Hz under ideal conditions, there are individual and contextual factors that can influence this threshold.