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.


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?


Apology to Students: Matlab from Hell

To every student who ever gave up Physics – especially those who left my own class over the years; I feel your pain. My very last class in 2007 was involved an experience just like this with Alex and his calculator trying to use the formula for geostationary satellites.

I’m not so old that I don’t remember what this feels like, in my case it was accounting.

Had a happy 2007.
The highlight was getting to see three of biggest living heroes; Steve Earle (Midlands Music Festival), Guy Clark (Johnny Keenan Banjo Festival) and John Prine (NCH), all within six months of each other.

I am only allowed to say that now because in two days I am getting married.

Have a happy 2008

Guy Clark:

John Prine

Steve Earle: