As you have already gathered in previous parts of this manual, your sense of hearing depends on a complex and delicate set of organs. They can tolerate loudness for an amount of time without causing discomfort, irritability and permanent physical damage to your eears.
The Center for Disease Control (CDC) prescribes a recommended permissible exposure time for different levels of loudness. For every three decibel increase of a sound, the exposure time for most people is halved, as shown below.
To get a better idea, the next chart shows the approximate loudness of various sounds as reference points for the decibel levels shown above.
While these all seem informative and clear enough for most people to understand, a good way to appreciate this is to associate it with your daily life. If you are on Android, go to Google Play Store and install Sound Meter (regular or Pro version). It measures the decibel level of your immediate surrounding. We can’t fully account for the app’s accuracy because not all Android phones are made equal. If your phone has a cover, try making a reading without to check if there’s any effect. If there is, chances are, the reading when coverless is more accurate. In any case, the readings out to be a fair enough reference.
I took the reading above while driving in my old car, with the stereo on at modest volumes. The app read at 69dB at the time the screen was captured. It is far from a complete story, though. Luckily, the app can generate a graph of the decibel levels across time, like so:
The app read my drive from the house to the supermarket, across a short drive with varying levels of traffic. According to the app, it was around 62-65 decibels with the engine running at low RPMs which jumps up to around 72-73 decibels when revving or running at relatively higher speeds. I turned the app off right after parking, with the car idle and at full stop (that short jump at the end from around 55dB happened when I picked the phone up to close the app). These levels were somewhat surprising to me, as they were higher than I expected. Perhaps if I was driving fast on the expressway, I would expect being exposed to 72-75dB, but not while driving at 40-50 kilometers per hour in moderate traffic. It was an eye opener as far as it seems that I have slightly overestimated my level of awareness for my immediate environment.
As an activity in the course, try using the app while you go about your daily routine. Take readings whenever you can — while in your room, or inside a car, while in a bar watching some band playing or working in an manufacturing plant — anything and anywhere. Make yourself aware of the loudness of the sounds you subject yourself to everyday. Then head to the MMS 172 course site’s discussion forum to write about your readings and your thoughts about them.
CDC. (2011). Noise and hearing loss prevention facts and statistics: charts and graphs. Retrieved from http://www.cdc.gov/niosh/topics/noise/chart-lookatnoise.html.
DangerousDecibels. (n.d.). Decibel exposure time guidelines: how loud is too loud? Retrieved from http://dangerousdecibels.org/education/information-center/decibel-exposure-time-guidelines/.
Tremaine, H. (1969). Audio Cyclopedia. Howard W. Sams and Co., Inc., Indiana, IN, USA.