The scientific “unit” we call the decibel (dB)

I don’t have many pet peeves. That said, no matter how hard I try, I just can’t get over the sheer madness of the scientific “unit” we call the decibel (dB). What’s a decibel? Well, the most common answer is “uhh". The second most common answer is that it’s “a way to measure loudness”. But it isn’t! A decibel is not a unit in any conventional sense: it’s more akin to a prefix such as mega- in megabyte. It describes a change in magnitude. On the face of it, the idea makes sense. We sometimes want to say that some quantity has increased 10× or 1,000× — and in engineering, these numbers can get large. In principle, we have several types of shorthand notations; for example, instead of “300,000” we can write “3e5”. That said, I don’t know how to pronounce “3e5”, so it’s not unreasonable to come up with a name for the exponent. “An increase of five clerts” could mean that something has grown by a factor of 105. This brings us to a pseudo-unit called the bel. At first blush, it works just ... Read full article.