It is important to realise that, although hearing aid technology is very good these days it cannot restore your hearing to its original condition, it is an aid to your hearing which should provide you with significant benefits in a variety of listening situations.
Why do I still have trouble hearing with my hearing aid on?
Even if the hearing aid is appropriately chosen and well fitted you still may not hear as clearly as you would like, particularly in very noisy situations. The reason for this relates to the type of impairment most people suffer after significant damage to the hearing organ.
Soft sound is too soft, but loud sounds are too loud (reduced dynamic range)
Hearing impaired people have trouble hearing softer parts of speech, often describe missing the beginnings and ends of words, or even unknowingly ignoring people when they are not looking at them. Somewhat ironically the ears ability to limit loud sounds is often also impaired leading to an abnormal growth in the loudness of sounds, sometimes to the extent that the hearing impaired individual may judge loud sounds to be more disturbing than a normal listener.
Speech is made less clear, fuzzier (frequency discrimination).
For most, hearing loss entails a loss of clarity of speech as well as a loss of loudness. You can imagine this by imagining a piano keyboard with some of the keys completely stripped off (or perhaps by listening to a piano being played with fists rather than individual fingers). Two similar pitched speech sounds may now sound almost identical leading to the need to guess which sound was heard.
Speech is harder to follow at speed (temporal resolution)
The ears ability to understand speech sounds which closely follow one another over time can be compromised. This means that fast speech can be very difficult to follow.
Speech is hard to understand when in background noise
Because of; a lack of audibility (reduced dynamic range), the distorted nature of the speech sounds (frequency discrimination), and difficulty trying to hear speech snippets in gaps in a background noise (temporal resolution), it is harder to hear the speech clearly when in noisy situations.