by Neil Bauman, Ph.D.
It’s no secret that you need to protect your ears from louder sounds if you want to preserve your hearing over your lifetime. However, for the average person, the decibel (dB) scale makes in difficult to understand the actual impact of increasingly loud sounds on their ears.
For example, a sound of 100 dB is not 20 units louder than a sound of 80 dB, nor is it 20 TIMES louder. In actual fact, it is 100 times as loud, but this is not obvious unless you understand the logarithmic nature of the decibel scale.
Thus, a new way of understanding sound will make it easier to put these numbers into perspective. This new unit of sound measurement is the Pasques (Pascals-squared-seconds). Using this scale, you can immediately see the relative difference between sound levels.
Using the above example, a sound of 80 dB for one second yields a sound exposure of 0.04 Pasques. A sound of 90 dB for one second yields a sound exposure of 0.4 Pasques while a sound exposure of 100 dB for one second yields a sound exposure of 4.0 Pasques. You can readily see that 4.0 Pasques is 100 times the exposure as 0.04 Pasques.
If you were exposed to a sound of 110 dB for one second, the result in Pasques would be 10 times greater or 40.0 Pasques and for 120 dB the result would be 400 Pasques.
Thus a sound of 120 dB (400 Pasques) is obviously 10,000 times as intense than a sound at 80 dB (0.04 Pasques).
Where this really comes home to you is looking at your lifetime exposure to sound. It is considered safe to exposure your ears to continuous sounds of 80 dB. Thus if you are on a job 8 hours a day for 40 years, you should not have noise induced hearing loss—even though you are exposing your ears to a lifetime sound exposure on the job of 2000 hours per year.
Now if you were in a really noisy environment (certain mills, construction sites, recreational events [ball games, NASCAR racing, shooting] or musical events [night-clubs, concerts]) you might be exposing your ears to sounds of 115 dB.
The question is, “What is the maximum safe time (number of hours per year) you can expose your ears to without damage?” (Remember if the sound was at 80 dB you could expose your ears to it for 2000 hours without damage. That would be equivalent to a yearly sound dose of 288,000 Pasques.)
You’re not going to believe it, but the maximum safe time for exposing your ears to sounds at 115 dB is just 38 minutes per year! (This would also be equivalent to 288,000 Pasques.)
How many people go to events that have loud sounds that exceed 115 dB and last in total for half an hour or more? If you’ve ever done that, you’ve just exceeded your noise quota for a whole year. Not a good idea. The above example dramatically shows why you need to take ear protectors and use them as the sound levels rise—if you value your hearing.
(1) Drott & Bruce. 2011. A Different Look at Noise Exposure, Hearing Loss, and Time Limits. The Hearing Review. Vol. 18, No. 5, May 2011. pp. 34-36.