In Part I, we discussed the typical symptoms of the most common form of hearing loss, sensorineural hearing loss. As you may recall, in most cases, but not all, vowels (a, e, i, o, and u) remain audible to the patient, but consonants (s, f, t, v, etc.) become inaudible. This is because those two types of sounds of speech have different pitch ranges.
Vowels are predominantly strong and low-pitched, while consonants are usually weaker and higher in pitch. Also, consonants are the sounds that give speech its clarity, while vowels give speech its rhythm, quality, tone, and inflection.
Here’s where the irony comes in… When a person suffers from sensorineural hearing loss, it typically affects the higher pitches of their hearing range more than the lower pitches. 
To the right is a diagram [click to enlarge] of a hypothetical patient’s hearing thresholds by frequency or pitch (x-axis) and intensity (y-axis). It’s also possible to plot other environmental or speech sounds on the graph and so anything above the red and blue line is theoretically inaudible to the hypothetical patient, while anything below is audible. This is why patients will often observe that they can hear nearly everyone, but yet understanding what is being said is another story altogether.
In Part III, we’ll discuss why the higher pitches of someone’s hearing are affected more than lower pitches and in Part IV, the basics of proper amplification.
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