Why do high-frequency sounds often seem louder than low-frequency sounds with the same amplitude?

The perception that high-frequency sounds are louder than low-frequency sounds of the same amplitude is due to the nonlinear frequency response of the human ear.21

While amplitude is the primary physical determinant of loudness, the human auditory system does not perceive all frequencies with equal sensitivity. Our ears are naturally more sensitive to certain frequency ranges than others, a phenomenon illustrated by Fletcher-Munson curves. Because of this biological variation, a sound at a high frequency will often register as louder to a listener than a sound at a low frequency, even if both possess the same physical pressure amplitude.21

To account for this subjective perception in noise pollution monitoring, electronic sound-level meters utilize frequency filters—such as the A-weighted filter—to adjust measurements so they more accurately reflect how the human ear actually perceives the loudness of various sounds.1