A-range

The human ear is generally said to be able to hear only from 20 Hz to 20 kHz. In addition, low and very high frequencies are not perceived as noisy, so it is necessary to modify the simple sound pressure level measurement according to the frequency to make the degree of noisiness closer to human hearing. The A-range is the result of this modification.
The graph on the right shows a comparison between the actual measurement in the A-range and the sound pressure level measurement itself (C-range).