I heard that over use, the ear drums become less effective, but my hearing is bad. To reduce further damage, should I turn down the treble or bass?
There are a number of issues wrapped up in this question. The first, which deteriorates faster treble or bass, is that Presbycusis, age related hearing loss, is a high frequency (i.e., treble) phenomenon. While hearing loss can occur due to damage of the tympanic membrane (i.e., ear drum), this is a conductive hearing loss that can be generally be well treated with hearing aids. Presbycusis and noise induced hearing loss are generally sensorinerual in nature.
Given how the inner ear works, noise induced hearing loss generally occurs at the frequency of the noise. As the sound waves travel through the cochlea they undergo frequency dispersion. This means that a low frequency sound (bass) only "travels" the whole length of the cochlea all the way to the apex while high frequency sounds are transmitted only to the base. This means that low frequency sounds are slightly more "dangerous" to the inner ear than high frequency sounds.
The final piece to realize is that not all frequencies have the same importance. For speech the articulation index, and the more recent speech intelligibility index, give more weight to frequencies in the 1-3 kHz range.
In summary, you should turn everything down and not just one particular region. If you can only turn down one region, you should attempt to preserve your hearing in the 1-3 kHz range so that you will be able to understand speech.