The link above leads you to a on-line hearing test. This is no doubt the best free hearing test I have encountered, and if you are curious about how good your hearing is, this test is for you!
Remember to read the guidelines before each step. Calibration is very important towards accuracy of the test.
Here is my result (using ER-4p):
In general, I have very good hearing. However, I have a relatively significant hearing loss at range between 125 Hz and 750 Hz, and this “happens” to be the range of human speech! This means I cannot hear speaking as easily as I do for music. The causes of this loss could be my extended period of using earphones for listening to podcasts, which consists most of speaking. My right ear doesn’t do nearly as well as my left in high frequencies. The highs starts to roll off significantly after 12 kHz. However, this could be due to ER-4p as I have found no such loss with my other headphones.
Protect your hearing at all costs!