Levels & Frequencies of Sound
Normal hearing is 20 decibels and above. The audiogram of familiar sounds shows that different sounds occur at different frequencies. For example, a dripping faucet that has a soft low frequency sound may be heard at 15 decibels while a barking dog would be around 70 decibels. Also, different types of noise are generated at different frequencies, but can have the same decibel level. For instance, the sound of a semi-truck going down the road is a low frequency that can reach very high levels of decibels. Whereas the sound of a circular saw or a power tool would be a very high pitched sound, but at an equal high decibel level.
Understanding Hearing Loss
Most people with a hearing loss don't have flat hearing profiles, but they have some frequencies that are worse than others. Most of the time we see a high frequency hearing loss. For an example of how that affects the ability to understand what somebody is saying, we need to look at what sounds occur at each individual frequency.
So for example, if we look at a simple word like "free," there are 3 different sounds in there. There is the soft "f" sound that occurs at high frequency somewhere between 4 and 6 thousand hurtz. There is an "r" sound, which a mid-frequency sound, and then there's the "ee" sound which is a much lower frequency sound.
The difficulty with somebody in a high frequency hearing loss is that distinguishing the word "free" from the word "three" involves all the same syllables except for the first sound. The "f" and a "th" are both high frequency sounds, so distinguishing between them can become difficult. Therefore, people with a high frequency hearing loss don't complain that they can't hear, but rather that they can't understand other people. This is exaggerated in a situation like a crowded restaurant, a family gathering, or a church environment where there is a lot of background noise and it becomes difficult to understand what people are saying.
How Hearing Aids Help
The reason that a hearing aid works very well is because it amplifies each frequency according to the hearing loss. So if there's only a mild hearing loss in a mid-frequency, like where the "r" is, then that will be amplified just a little bit. Whereas the high frequency where there is more hearing loss will be amplified to greater degree so that we achieve an amplification which allows for a relatively flat hearing level. If you just turn the volume up, or use a simple amplifying device, then it equally boosts every frequency. Then you'll end up hearing the low frequencies louder than what is comfortable while the high frequency sounds aren't getting a correct boost to level them out with the other sounds.
Just How Visible are Hearing Aids?
Well, here's a look at a friend of mine wearing one of the shortest hair cuts possible with one of the larger modern hearing aids.