UK Registered Charity Number: 1154107

Conservation by Re-use

Helping churches acquire surplus and/or redundant bells to be hung for

English-style full-circle bell-ringing.

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Sound of Bells – Doublets & Beats continued

The figure below shows how a vibrating body can generate beats, for clarity the example frequencies have been exaggerated. The first two waveforms show a doublet generated by the vibrating body and the lower waveform shows the resulting sound heard by the listener. It is believed that some medieval founders cast eccentrically shaped bells so that the frequency pairs were so far apart they would not beat2.

The effect of individual partials differs depending if the bell is used for ringing or chiming. The high-frequency partials (e.g. the Nominal) tend to be high-intensity and short-duration whereas the low-frequency partials (e.g. the Hum, Prime & Tierce) are  generally lower-intensity but long-duration. When a ring of bells are rung the ear typically hears the first 0.25 Second of an individual bell striking before the next bell sounds; this short duration is known as the Strike Note with the dominant partial being the Nominal. The Strike Note is examined in more detail in a later section.

When bells are chimed a much greater time elapses between individual bells being struck and the dominant partials tend to be the Hum, Prime & Tierce. This helps explain why some bells when struck or rung individually are tonally poor, but sound much better when rung as part of a ring of bells.

For ringing bells, the Nominal is used as the reference frequency, and the remaining four partials are tuned with reference to the Nominal (note 1). Tonal analysis of pre-Simpson tuned bells shows that bells for English style change-ringing have been tuned with respect to the Nominals, with the Prime partials relatively untuned. An analysis of  mainland European cast bells made by E. W. Van Heuven6 implies that many pre-20th Century carillon bells have been tuned with respect to the Prime, with the Nominal relatively untuned.

Superposition of two Sound-waves