Day: November 16, 2010

The origin of the decibel scale

A standard leaving cert physics exam question is “why do we have the decibel scale”?
The standard answer is that the range of sound intensities is so large that a second, much more compact scale is required to make the numbers more manageable, and for sound this scale is based on multiples of ten and is called the decibel scale (and what it measures is called sound intensity levels).

The old syllabus included a detailed analysis of this scale so that the numbers actually meant something. For the new syllabus (2002 onwards) it must have been decided that the maths was too difficult so this part was scrapped, except for one very odd ‘fact’; the student must know that a doubling of the sound intensity results in an increase of sound intensity level of  3 dB. Now needing to know that piece of useless trivia is ridiculous and is probably only there as a sop to some university professor who was horrified that the detailed analysis was dropped:

At least that’s my best guess, which doesn’t seem too dissimilar to what the author of a recent book on Physics and Music  entitled How Music Works thinks about the decibel in general.

I think the decibel was invented in a bar, late one night, by a committee of drunken electrical engineers who wanted to take revenge on the world for their total lack of dancing partners.

Ouch!

How Music Works: The Science and Psychology of Beautiful Sounds, from Beethoven to the Beatles and Beyond
by John Powell

Now what’s the betting that students will remember this explanation and forget all about the technical one?