Equalloudnesskäyrät

Equalloudnesskäyrät, also known as equal-loudness contours or curves, are a series of graphs that illustrate the perceived loudness of a sound at different frequencies. They represent the subjective experience of how loud a sound is to the human ear, rather than its objective physical intensity. Developed through psychoacoustic experiments, these curves show that our hearing sensitivity varies significantly with frequency. At low frequencies, a sound needs to be much louder physically to be perceived as equally loud as a sound at mid-frequencies, around 1 to 5 kilohertz, which is where human hearing is most sensitive. Conversely, at very high frequencies, the required physical intensity also increases again.

The most well-known set of equalloudness curves were developed by Fletcher and Munson in the 1930s and have since been refined by others, leading to international standards like ISO 226. Each curve on the graph corresponds to a specific level of perceived loudness, typically measured in phons. A phon is a unit of loudness level, where a sound with a loudness level of 40 phons has the same perceived loudness as a 1000 Hz tone at 40 dB sound pressure level. When comparing sounds, it's important to consider these curves because a sound that measures higher on a decibel meter might not sound subjectively louder than another sound if their frequencies differ significantly and fall on different equalloudness contours. These curves are crucial in audio engineering, acoustics, and the design of audio equipment to ensure accurate sound reproduction and to understand how humans perceive sound across different frequencies.