Analyzing the Sound of a Ringing Bell

Here is a question I received today (Feb. 10, 2005) from Augustana history professor, Dr. Lendol Calder.  It prompted me to locate a Website by Bill Hibberts that provides an extensive treatment of the sound and tuning of church bells.  He also provides an excellent, free program called Wavanal (for a PC) that generates the sound spectrum (does a Fourier analysis) of the sound contained in any .wav file.

I'm looking for the word that best describes the last, lingering notes one hears after a large bell has been rung.  Everyone in Music I've queried says to ask you.  Reverberation?  Resonance?  What?  [the question comes up as I write an essay where I want to use this word metaphorically to describe the fading knowledge of old maxims like "He who goes a-borrowing goes a-sorrowing."]

Lendol Calder

Although this term is not commonly used, the name of that sound is "tail" (the slow decay of a bell's partials, often over tens of seconds).  For further details about the rather complex sound of a bell, go to this Website.  On the menu on the left, click on "Glossary of terms", then scroll down to "tail".  A related term is "splash" (the sound produced immediately as the clapper hits the bell).

It is tempting to use the word reverberation to describe this lingering sound.  However, this word is used to describe a particular environment rather than the source of sound.  Reverberation time in a room is defined as how many seconds it takes for the sound pressure level to decrease by 60 decibels after the source of sound stops.  This corresponds to a drop of the sound intensity by a factor of 1 million.  In a typical classroom this time is about 0.7 seconds.  In a concert hall it ranges from 1 to 2 seconds depending of the size of the hall and its construction.

Whenever an instrument is played (or a bell is rung), in addition to describing the basic sound in terms of its harmonic content, the sound always builds up at a certain rate (attack).  The sound then gradually drops down (decays) to a lower level.  There may also be a short time when the sound stays constant (sustained).  Finally, the sound is allowed to drop to zero (release).  Basically each note that is played has an intensity envelope referred to as the ADSR envelope.  With a bell, the attack, decay and sustain are short and the release may take several seconds depending on the characteristics of the bell.

Thank you for your question.  I hope this helps.

Dave Renneke