Basic Acoustics – Some Rules of Thumb

After over 15 years of working with customers and training salespeople in acoustics and vibration, a few simple rules of thumb come up over and over. Here are one of my favorites and a great graphic that gives a visual representation of decibels. The graphic below is from HEAROS, maker of the “Sleep Pretty in Pink” earplug. Looks like lime green earplugs are out of style now…

Happy Thanksgiving!

  • 20 dB = one order of magnitude – 20 Log10 (10)
  • 10 dB = half an order of magnitude – 20 Log (3.16)
  • 6 dB = doubling of pressure – 20 Log10 (2)
  • 94 dB = 1 Pa

For example : A Jet Engine at 100 ft might put out 150 dB. To calculate the level in Pascals directly would require a calculator (632 Pa). Since 94 dB equals 1 Pascal, a shortcut uses the fact that this would be two orders of magnitude (134 dB, 100 Pa) times half an order of magnitude (144 dB, 316 Pa) times a doubling of pressure (150 dB, 632 Pa). So without a calculator, it can be determined that a 50 mV / Pa microphone would generate 31.6 volts at 150 dB, above the maximum level for most DAQ systems.

Decibel Levels

decibel-levels-ear-plugs

Moving Day and Basic Acoustics

After several months of posting every other day, you might have noticed there have been no posts for the past couple weeks. This is because we moved to Phoenix and moving seems to fall somewhere between death and debt in a scale of the most stressful life events. The good news is that there is a backlog of interesting topics to write about. Even the process of moving itself has resulted in some interesting new ideas. For example, a mover with almost no teeth, one leg longer than the other, and no obvious muscles had just finished moving a very heavy box when I noticed the “tool” he was using to open it. It consisted of two nails held side by side with a piece of packing tape that he could put on the end of his finger.

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I asked him about his tool and he explained that he used to use a knife until he lost several. This tool was free, safer than a knife, and much faster. He went on to show me how he cut packing tape with one fluid motion that involved sticking the tape to itself and pulling. He used to use a tape gun until he cut his leg badly one day with the cutting teeth.

These are the kind of tips you can get from experts. The next series will be the Basic Acoustics series which will attempt to summarize a wide body of information on the topic that I have gathered over more than 18 years working with experts in the sound and vibration test and measurement industry. Until we get settled in our new home, there may not be a post every other day, but quality will hopefully make up for quantity.