Why does 33 DB reduction + 22 DB reduction = 38 DB reduction not 55 DB reduction. I wear plugs and muffs and it really muffles everything. if it was only reducing 38 DB I probably couldn't even stand to be at an inside range.
Why does 33 DB reduction + 22 DB reduction = 38 DB reduction not 55 DB reduction. I wear plugs and muffs and it really muffles everything. if it was only reducing 38 DB I probably couldn't even stand to be at an inside range.
Because the dB scale is a logarithmic scale and the sum is not linear like in other scales.
https://www.noisemeters.com/apps/db-calculator.asp
And in the example used 33dB + 22dB = 33.3dB not 38dB.
Yet that isn't the real answer to the question either. the reduction is actually a ratio of the sound pressure wave before to after the restriction of the wave. The second resistance the wave encounters will have a greater effect on the wave, because the wave has already been reduced.
Those are each calculated as ratios of a measured pressure to the lowest that can be heard.
The dynamic range of human hearing and sound intensity spans from 10-12 W/m2 to 10 - 100 W/m2. The highest sound intensity possible to hear is 10,000,000,000,000 times as loud as the quietest!
This span makes absolute values for sound intensity impractical in normal use. A more convenient way to express sound intensity is the relative logarithmic decibel scale with reference to the lowest human hearable sound - 10-12 W/m2 (0 dB).
Note! In US the reference 10-13 watts/m2 is commonly used.
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Acoustics and sound are very complicated subjects. It's very difficult to easily explained all that stuff. I'm using very basic information gathered from a bunch of different sources to roughly value the differences between db levels and and roughly what to be thinking about when you're trying to offset higher-end gun fire db levels. I think a lot of people are way under protected in many situations when they're wearing what they think is adequate hearing protection.