Like I tell people in the Lean Hardware Workshop, where software professionals are learning hardware skills, decibels are so fundamental to analog and RF hardware. You just have to understand them.

Today I want to tell you about a stupid decibel error I made, and also show you a decades-old trick that hardly anyone knows to mentally computing decibels FAST.

Awhile back I posted a neat article from New Atlas about a mechanical doohickey that boasts "200x the bass" from your smartphone speaker.

But I made a huge error. I said:

This tiny device "boosts sound pressure levels up to 200 times". That's 23dB. Yeah, I believe that, but it'll only boost sound in exactly 1 direction or else this guy invented some CRAZY physics. #ConservationOfEnergy

Can you spot the error?

It took not long for the Internet to correct me. A smart commenter wrote:

"200X SPL" -> log(200)*20 = 46dB SPL.

My error isn't a mathematical one. It's a physics one.

Sound pressure (SPL) is a measure of amplitude. I computed it (incorrectly) considing it a measure of power. That difference changes the answer exponentially.) See, I'm an electrical guy. I do RF, antennas, amplifiers. Everything in my world is power. ¯_(ツ)_/¯

According to this chart by Shure, my error could mean the difference between the loudness of a typical restaurant and a jet taking off!
earphone_spec_3

Want to learn how to mentally compute decibels like a friggin' supercomputer?
Here's a trick an old man taught me.

Thanks for reading!