Most of us are familiar with the term decibels. We know that it is a measure of sound, and that a larger decibel value means a larger sound. But the details of how they are calculated, or how different values compare to one another are not as widely known.
The first thing to note about sound levels is that they are not measured on a linear scale. Rather, they are measured on a logarithmic scale. This means that decibel values are not as intuitive as maybe we would like. A sound of 20dB is actually 10 times more powerful than a sound of 10dB, and 30dB would be 100 times more powerful than 10dB. If the scale was linear, 20dB and 30dB would be 2 and 3 times more powerful than 10dB (like with mass, for example, 20kg is twice as much mass as 10kg).
You can see why this is the case with the formula for calculating sound levels, which is as follows:
Section III: Chapter 5 Appendix B5
It is important to note that the sound pressure levels calculated with this formula are unweighted. When we want to know how loud something will sound to us, we need to take into account how the human ear perceives different frequencies. The basic effect of this is that low and very high frequencies are given less weight than on the standard decibel scale, but the exact weighting can be seen in the chart to the left. This weighted measurement is denoted as dBA or sometimes dB(A) as opposed to the standard dB for sound pressure levels. Some common sounds and their dBA level can be seen on the chart below:
Due to this logarithmic scale, adding two sounds together can also be quite counter-intuitive as well. Our Model 1100 Super Air Nozzle will produce a sound level of 74 dBA, but two side by side will produce a sound of 78dBA. The specifics of this calculation are explained in this blog here, but OHSA provides a quick and easy way to calculate, as shown in the table below:
| Difference Between Two Levels to Be Added | Amount to Add to Higher Level to Find the Sum |
| 0-1 dB | 3 dB |
| 2-4 dB | 2 dB |
| 5-9 dB | 1 dB |
| 10 dB | 0 dB |
Now that you know how to calculate sound levels, it is important to understand the dangers inherent in prolonged exposure to high levels of noise. OSHA Standard 29 CFR-1910.95 (a) shows the Maximum Allowable Noise Exposure:
If you would like to find out if you need to address the sound level in your facility, you first need to take a baseline reading of your various processes and devices that are causing the noise. EXAIR’s Sound Level Meter, Model 9104, can help you out. It is an easy-to-use instrument that provides a digital readout of the sound level (so you don’t have to mess with logarithms!) They come with a NIST traceable calibration certificate and will allow you to determine what processes and areas are causing the most trouble.
If you would like to discuss sound levels in your facility, or any of your other compressed air needs, give us a call!
Al Wooffitt
Application Engineer
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Photo of Ear auricle Listen by geralt. Pixabay License