Final answer:
The loudness of a person's voice is primarily determined by the volume of air in the lungs which affects the amplitude of the sound pressure wave resulting in a louder or softer voice.
Step-by-step explanation:
The loudness of a person's voice depends on the volume of air in the lungs. When air flow from the lungs increases, the amplitude of the sound pressure wave becomes greater, resulting in a louder voice. The amplitude of a sound wave is what determines its loudness or volume, so a larger amplitude corresponds to a louder sound, and a smaller amplitude means a softer sound.
It's also important to note that the human ear's sensitivity to different frequencies can influence the perceived loudness. While the amplitude is the primary factor for loudness, if a frequency is in a range where the ear is more sensitive, the sound may be perceived as louder. Additionally, rates of speech and how you project your voice can impact the effectiveness of communication, regardless of the actual volume.