by Neil Bauman, Ph.D.
One lady wrote: “I thought that people with normal hearing had 0 dB (decibel) hearing loss. Was I mistaken?”
Yes and no. How’s that for an answer?
Zero dB is the theoretical “normal.” In truth, some people have better hearing than this and others worse–mostly worse. Audiologists classify anything between -10 dB (10 dB above the 0 dB line) and 25 dB as “normal.” (Notice that your audiogram goes to -10 dB, not just to 0 dB.)
Within this “normal” range, hearing still varies enormously. For example a person hearing “normally” at -10 dB hears 1,000 times better than a person hearing “normally” at 20 dB, yet all this variation is considered “normal.”
In actual fact, few people hear at the theoretical 0 dB because they have damaged their ears from loud sounds, from ear infections, from taking ototoxic drugs to fight ear infections and other illnesses, from having tubes put in their ears–and a number of other causes.
Another misconception is that at 0 dB, there is no sound–that it is totally quiet. One person asked, “Is there such a thing as 0 dB? There can’t be, can there? Wouldn’t that be silence?”
Surprise! Zero dB isn’t the absence of sound like you might think, but is the result of the ratio (expressed in logs) between a measured level of sound (that you hear) and a published standard. (That standard happens to be 10 to the minus 12 watts per square meter in case you are interested. This standard is set at the volume of the faintest sound the average person with “perfect” hearing can just barely hear.)
If you really want to know how it works, if the faintest sound you can hear is the same as the above sound standard, then the ratio between them is 1:1 and since the log of 1 is 0, you are hearing at a level of 0 dB. (See how simple it is–grin!)