Monitor levels: Interpreting the Fletcher-Munson Curve
Fletcher and Munson did research into the response of the human ear to a wide range of frequencies over a wide range of listening volumes. They came up with a set of graphs based on feedback from people who were asked to report when two different frequencies were perceived to be at the same volume. They found that the ear does not hear all frequencies equally well at different listening levels. The graphs show that the ear is less sensitive to bass and high frequencies at lower listening levels and is always most sensitive to frequencies between 1kHz and 6kHz (vocal frequencies).
What this means for audio professionals is that consistent results can be achieved (particularly when adjusting EQ) by monitoring at a consistent listening levels and at a level where your judgement is least affected by the ear’s frequency response. 83dB is considered to be the ideal listening volume.
This is quite convenient since you can listen for fairly long periods without damaging your ears. You can check your listening levels using a standard SPL meter. Once you have found a level close to 83dB, make a note of your monitor level settings on your sound card or monitor control and always use the same settings for every session. Making good EQ judgements will be more reliable than ever.