What do you know today that you didn't know yesterday?

[Deesse23]

According to my sound meter, my shop vac/dust extractor runs at 80dB, my table saw at 105dB. When I run both together, I get a reading of 105dB.

Am I looking at this wrong?

Boru

dB is a logarithmic scale,  105dB sound is 316 times more energetic than 80dB sound.   Adding 80.000 dB sound on top of 105.000dB sound yields 105.014dB sound, which rounds back down to 105db.   logarithmically the power in 80db sound is just too puny next to that in 105dB sound to register significantly on top of 105 dB.

I wish we could have avoided this rabbit hole, but here we go..

There are actually TWO db scales. 20 x log and 10x log

10x log is used for comparing energies, 20x log for units that are the sqrt of energies (or db-wise 1/2).
For sound this is the energy of the sound as opposed to the pressure, because the energy is equal to pressure squared (x2 in dbs) thus you just use x10 instead of x20.
I was assuming his device measures air pressure, not sound energy.