The provided source material does not contain information regarding a city named Phon in Thailand; instead, it describes the phon as a logarithmic unit of loudness level for tones and complex sounds. In acoustics, the phon is used to measure perceived sound magnitude, whereas sones serve as the corresponding linear unit. Because human sensitivity to sound varies across different frequencies, two tones with identical sound pressure levels may be perceived differently in loudness. The phon provides a psychophysically matched measurement based on a reference frequency of 1 kHz. For example, if a sound is perceived to be equally loud as a 1 kHz tone with a sound pressure level of 50 dB, it is assigned a value of 50 phons regardless of its physical properties. The unit was proposed by Stanley Smith Stevens in DIN 45631 and ISO 532 B.