While it is true that sound is propagated through pressure waves, the perception of loudness is not solely determined by the energy carried by those waves. The concept of loudness is closely related to the human auditory system and how it responds to different frequencies.
When we talk about the energy of a sound wave, we typically refer to its intensity, which is the amount of energy per unit of area. In the case of sound, intensity is commonly measured in decibels (dB). The relationship between frequency and energy is not a direct one; it depends on various factors.
One factor is the sensitivity of our ears at different frequencies. Our auditory system is more sensitive to mid-range frequencies, typically between 1,000 and 4,000 Hz. This means that for sounds in this range, our ears require less energy to perceive them as equally loud compared to sounds at lower or higher frequencies.
Another important factor is the way our ears physically receive and transmit sound. The human ear has certain resonant properties that affect its efficiency in detecting different frequencies. At low frequencies, the physical dimensions of the ear and the resonant properties of the ear canal can limit the amount of energy transferred to the sensitive parts of the inner ear. Similarly, at very high frequencies, the mechanics of the inner ear, including the behavior of the tiny hair cells responsible for detecting sound, can limit the amount of energy that can be effectively transmitted.
In summary, the perception of loudness is influenced by both the energy of the sound waves and the sensitivity of our auditory system to different frequencies. Due to the limitations and characteristics of our ears, low-frequency sounds may require more energy to be perceived as equally loud as mid-range frequencies.