Measuring Hearing Loss

Measuring hearing loss is frequently confusing and, oftentimes, people get decibels and the concept of a percentage mixed up. Decibel is an open-ended scale of loudness that begins with zero, which is defined as the faintest sound that can be heard by a human ear. From there, regular conversation is usually around 60 decibels, most power tools fall somewhere between 100 and 120 decibels, and a gunshot might measure at 150 decibels or more. For every 10 dB (decibels) the volume increases, the perceived loudness doubles and there is a tenfold increase in sound intensity.

If someone, for example, had hearing loss that made it impossible for him or her to hear sound fainter than 30 dB, you could say this person has a 30-decibel loss. Likewise, if they have a 50-decibel loss, they cannot hear sound that is less than 50 decibels. As you might guess, the greater the decibel loss, the less a person can hear. If someone has 40-decibel loss, this person probably will not be able to hear you whisper and may have some difficulty with even regular volume speaking.

Although 0 dB is the lowest volume a human ear can hear, it should not be confused with the lowest volume a human ear usually hears. According to most classifications, even people who cannot hear below 15 or 20 dB are considered to have “normal” hearing. In addition, since there is no highest number of decibels, you cannot simply come up with a percentage for hearing loss. The decibel scale is logarithmic, meaning that an increase of 10 dB is a 10-fold increase and not simply a set percentage. For example, 50 dB is 3000 times louder than 30 dB, not a 66 % increase as one might assume.

The implications of this in measuring hearing loss are that you cannot say that someone with 20 dB of hearing loss has a 20% hearing loss. On the other hand, you can use percentages to describe ones ability to discriminate between sounds. If you have had or will ever have your hearing tested, the audiologist will ask you to put on headphones. The will then play a recording of a list of words and then ask you to say them back. The audiologist then compares what you think you heard to what was actually spoken. The ratio of correct words to the number of words spoken can be seen as the percentage of your discrimination. This can be an important measurement, but it is not a way of gauging hearing loss.

Therefore, the most accurate way of quantifying hearing loss is to say someone has a certain decibel of hearing loss, which can be equated to general guidelines describing the loss. For example, a 20-40 dB hearing loss might be considered as “mild” hearing loss by an audiologist. Above this level, but below 60 or 70 decibels might be considered as “moderate” hearing loss. Levels above this can be considered “serious” or “severe” hearing loss, with 90 to 100 dB or more of hearing loss being “profound” or “extreme” hearing loss. Again, these are just guidelines, but they help in explaining the level of hearing loss in a much more helpful way than inaccurate and meaningless percentages.

Another way of putting hearing loss in perspective is to consider what the effects of this kind of loss are on an individual as well as what they might do to remedy the situation. Those who can hear sounds at around 20 dB or less have what could be considered “normal” hearing. Mild hearing loss usually means that, although the loss is not very extensive, one might have trouble following a conversation or distinguishing other sounds when in a loud environment. Moderate hearing loss is more severe than this, but usually less than 70 dB of hearing loss. Those with this level of loss will have trouble listening to a conversation without a hearing aid of some sort. More severe hearing loss means that an individual is very dependent on a hearing aid or implant in order to hear. Extreme hearing loss is what most would consider borderline deaf, at best. Those with this type of loss depend on sign language, written text, captioned media, and lip reading. Some may benefit from an implant.