The perception of loudness in human hearing is not solely determined by the frequency of a sound, but also by the characteristics of our auditory system. Our ears are more sensitive to sounds in the mid-range frequencies, typically around 1,000 to 4,000 Hz. This sensitivity is due to the anatomy and physiology of the human auditory system.
At very low frequencies (up to 50 Hz), our ears have reduced sensitivity, and we perceive these sounds as quieter compared to mid-range frequencies. This reduced sensitivity is partially because the human ear is less efficient at detecting and transmitting low-frequency sounds. Additionally, at extremely low frequencies, the physical properties of sound waves (such as their wavelength) can make it difficult for the ear to efficiently process and transmit the sound to the brain.
Similarly, at very high frequencies (15,000+ Hz), our ears also have reduced sensitivity. This decreased sensitivity is partly due to the mechanics of the inner ear and the limitations of the hair cells responsible for detecting high-frequency sounds. These hair cells can be less responsive or even absent at the extreme high end of the audible frequency range.
Furthermore, environmental factors such as background noise can also affect our perception of loudness. In everyday situations, mid-range frequencies tend to dominate the ambient noise spectrum, so we are more attuned to sounds in that range.
It's worth noting that the perception of loudness is also subjective and can vary from person to person. Different individuals may have different thresholds and sensitivities to specific frequency ranges.