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

[Anomalocaris]

Wrong

DBs are multiplicative, in that they provide a multiplicative scale for numbers.

Adding DBs equals MULTIPLYING values.
Example: +20db = x 10, +40db = 10 x 10 = 100, +60Db = 10 x 10 x 10 = 1000, -20db = 1/10, etc

Thus the machine with +20db more noise level is TEN times louder than the other*. APPROXIMATELY the 100db machine is dominant (assuming the sound waves do not create interference, cancel each other out n stuff. Lets not go down that rabbi thole today), because the total air pressure is only x1,1 of the dominant one.

That way you can easily display wide ranges of numbers in plots, or display certain behaviours that are multiplicative, making them look "Linear" in the "multiplicative realm" of DBs.

*in terms of air pressure..... but heres the catch: With +20db the air pressure is TEN times more, but human ears work in a LOGARITHMIC scale, just like DBs and we have subjectively linear perception according to a db scale! That way we can distinguish between a sound of  a fly and a starting 747 next to us, two sound events separated by 10^12 in terms of sound pressure. We dont perceive the plane being gazillions of times louder, but only tousands of times, according to the multiplicative perception we have. We kinda perceive an event with 60+db (compared to another), which is x1000 times louder, in fact like 3x (+20db) louder.

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.