The smallest sound wave that can be detected by the human ear depends on various factors, including the frequency of the sound wave and the individual's hearing capabilities. In general, the human audible range falls between approximately 20 Hz and 20,000 Hz (20 kHz).
The threshold of hearing refers to the minimum sound pressure level required for a sound to be barely perceptible to the average human ear. At a frequency of 1,000 Hz (1 kHz), which is commonly used as a reference, the threshold of hearing is typically around 0 decibels (dB) sound pressure level. As the frequency deviates from 1 kHz, the threshold of hearing may increase slightly.
At extremely low frequencies below the audible range, humans may not perceive the sound as a traditional auditory sensation but might feel or sense it as vibrations. These very low-frequency sounds are often referred to as infrasound.
It's important to note that individual hearing capabilities can vary, and factors such as age, exposure to loud noises, and hearing impairments can affect a person's ability to detect and perceive different sound frequencies.