The Sound of Bells

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Great Bookham, Surrey, St. Nicolas, 2

Recorded: WAH 13/2/00
Analysed: WAH 6/1/01

These two bells are the treble and tenor of a ring of four. The middle two bells, by local repute, were sold in the 1820s, suppposedly cracked by being rung with a hammer. The frame for four was thought by George Elphick to be 17th century (probably co-aeval with the newer bell) but incorporating parts of a mediaeval bellframe. The older bell has no inscription but was thought by Elphick to be by a London founder, possibly Burford, and date from around 1400. The younger is Eldridge 1675. These bells are included because they are an interesting example of how the different physical profiles used in the past give rise to different intensity profiles. Here is the sound of the 1400 bell and here the Eldridge.

Bell Founder Tuning
1 Burford ca. 1400 none since
2 Eldridge 1675 none since

Tuning of main partials

Tenor nominal: 956Hz.

Bell Hum Prime Tierce Quint Nom'l S'quint O'nom.
1 -2372 -1302 -880 -529 527 - 1233
2 -2350 -1120
-1131
-852 -465 0 672 1211

(The figures in this table are given in cents. For all partials except the nominal, the interval is given from the nominal of the bell. Intervals for the nominals are relative to that of the tenor. Pairs of values indicate a doublet. Frequencies for the quint are often not given, especially if inaudible.)

Intensity plots

Here is the spectral analysis of the 1st (1400) bell:

Great Bookham 1st

Here is the analysis of the 2nd (1675) bell:

Great Bookham 2nd

Commentary

The 1400 bell has a dramatically different intensity profile to the other bell in the tower and to a modern bell. The nominal is so small as to be very hard to spot. Even when looked at over a much shorter time period after the strike, the nominal is still much less intense than the lower partials. Remarkably, the nominal still determines the pitch of the bell. Estimating the note of the bell by comparing it with a sine wave suggests a pitch of about 650 Hz. The half nominal for this bell is 648.8 Hz, the prime 611 Hz, so that the former clearly sets the pitch.

It is interesting to note that the founder of this bell has achieved a hum only 28 cents sharp of an exact two octaves below the nominal, solely by controlling the shape of the bell - and likewise an octave nominal with a very typical value. I suspect that the accurate positioning of the hum has a large part to play in our perception of the pitch of this bell, making up for the almost inaudible nominal.

The shape of this bell looks fairly modern, though it might be a little long in the waist.

The second, larger bell has a more normal intensity profile. This bell is unfortunately spoilt a little by a loud doublet on the prime which is clearly audible when the bell is chimed.


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Last updated January 6, 2001. Site created by Bill Hibbert, Great Bookham, Surrey