Final answer:
The threshold of hearing is the lowest intensity at which a sound becomes audible, and it is usually around 0 dB or 10^-12 W/m². Sound intensity and loudness are not the same; loudness is also affected by frequency, where humans are most sensitive to frequencies between 2000 to 5000 Hz.
Step-by-step explanation:
The intensity at which a sound becomes audible for a given individual is known as the individual's threshold of hearing. The ear is sensitive to low-intensity sounds, with the lowest audible intensity or threshold being about 10-12 W/m² or 0 dB. Sound intensity, which is not the same as loudness, is the physical quantity used to measure how much sound energy passes through an area over time.
At a given frequency, humans can discern differences of about 1 dB, and a change of 3 dB is easily noticed. The perception of intensity is called loudness, which is influenced not only by intensity but also by frequency. The human ear is most sensitive to frequencies between 2000 to 5000 Hz, perceiving sounds in this range as louder than those at lower or higher frequencies, even if the intensity is the same.
Loudness is affected by both the intensity and frequency of a sound. The reference intensity (I0) of 10-12 W/m² corresponds to the threshold of hearing at 1000 Hz. However, sound intensity and loudness are also influenced by the timbre of the sound, which is shaped by the instrument's characteristics and can be perceived differently despite having the same intensity and frequency.