Equal loudness contours, hearing curves, phons, sones and audiometry. This site allows you to measure equal loudness contours--the frequency response of your own ears. The flash script allows you to play sound files with a range of frequencies and sound levels with the click of a mouse. The total size of all files is approximately 400 k. Because both the chart and the instructions refer to these units, you may wish to go first to What is a decibel?
Warning 1. Do not start with a panel in the top third of the chart: you risk making a very loud noise and even perhaps hurting your ears.
Warning 2. Results using this test cannot be regarded as clinical data. Although the sound files have been carefully prepared, the actual sound level and spectral purity depend on the frequency response of your sound card and headphones. They may, however, be helpful for comparison, such as left vs right ear, or for changes in hearing over time, assuming that you use the same hardware. Note, however, that daily fluctuations in hearing are common. If you are worried about your hearing, consult an audiologist.
For best results you will need reasonably good quality headphones that enclose your ears completely and seal out external noises. Ordinary loudspeakers, and especially the small ones that come with computers, have such poor response, particularly at low frequency and are so much affected by interference effects and resonances that results obtained with them are useless. They may also be damaged by low frequencies.