What unit is used for measuring loudness?

The correct answer, phon, is a unit that measures perceived loudness and is specifically designed to reflect the way humans perceive sound intensity. Loudness is a subjective measure that varies depending on frequency, and the phon scale accounts for this by equating everything to a reference level of 1 kHz. Therefore, if a sound is perceived as equally loud to a reference tone of 1 kHz at a certain level, it is measured in phons.

In contrast, decibels are a logarithmic unit used to quantify sound intensity but do not directly correlate to perceived loudness across different frequencies. Sound pressure level is typically measured in decibels and represents the pressure level of sound, which can vary significantly across frequencies without indicating how loud that sound is perceived. Hertz measures the frequency of a sound wave, indicating how many cycles occur in one second, but does not provide information on loudness. Understanding these differences is crucial in the context of measuring and managing hearing-related issues, especially when fitting and dispensing hearing aids.