What does the intensity of a sound wave relate to in practical terms?

The intensity of a sound wave is fundamentally linked to the perceived loudness of that sound. In practical terms, intensity refers to the power carried by the wave per unit area, which is commonly associated with how "loud" or "quiet" a sound is experienced by the human ear. As the intensity of a sound wave increases, the perceived loudness also increases, making sounds louder.

For example, a sound wave with higher intensity has more energy, which translates to greater movement of the air particles and a stronger signal to our auditory system. Consequently, the relationship between intensity and perceived loudness is significant in various applications, including medical sonography, where understanding sound intensities can aid in evaluating how ultrasound images translate into audible signals for the technician or clinician.

The other options touch upon different aspects of sound waves but do not relate to how we perceive sound in terms of loudness. Frequency range pertains to the pitch of the sound, echo duration deals with how long it takes for sound to reflect back, and wave speed involves the velocity at which sound travels through a medium, none of which directly correlate to the subjective experience of loudness.