Ding Dong Measurement on High

It’s beginning to SOUND a lot like… Bells are amongst some of the earliest known musical instruments, using mechanical resonance to produce a powerful harmonious sound. The art of bell founding has been present in Europe since the 4th or 5th century. In 17th century Britain, the rise of ‘change ringing’, where mathematical patterns are rung on a set of bells, propelled bell manufacturing to industrial scales.

Figure 1 “Nominal” Mode. Hi Res version available from media contact.

When a bell is struck, the impact causes a number of different vibrations or modes. The frequency and intensity of these modes is predominantly affected by the profile of the bell. For every bell manufacturer, the profile they use is unique and gives the characteristic timbre associated with them. John Taylor & Co. can trace their bell founding origins back to the 14th century and have operated at their current location in Loughborough since 1839. The quality in the design and manufacture of their bells is renowned throughout the world, perfecting their methodologies over centuries of experimentation and iterative improvement. Their bells are traditionally cast from a bronze alloy in a size appropriate for the desired pitch, and finely tuned using a lathe and calibrated tuning forks. John Taylor bells are recognised as having a colourful and rich timbre whilst retaining a pure tone. In English style change ringing, a bell is normally manufactured as part of a set, or peal, containing up to 16 bells, tuned to a diatonic major scale. Consequently, the relative pitch of the bell to the peal is more noticeable than the absolute pitch of the bell.

Figure 2 “Quint” Mode. Hi Res version available from media contact.

Christmas arrived early for Taylor & Co. ASDEC, in partnership with John Taylor & Co., have measured the structural dynamics of two bells in unprecedented levels of detail. Whilst the subject of bell mode shapes has been extensively theorised and researched in the past, most notably in the paper ‘Normal Modes of the Modern English Church Bell’ by Perrin, Charnley and DePont. With the arrival of ASDEC’s fully robotised 3D laser vibrometry system a measurement of this scale can be completed quickly and efficiently allowing these modes shapes to be visualised from real-world, experimental data.  
Martin Cockrill, Technical Specialist at ASDEC said: “Traditional techniques at best can only provide a coarse glimpse into the murky world of structural dynamics. By utilising ASDEC’s advanced robotised laser system we were able to reveal the beauty of the bells vibration in amazing detail. A thorough, accurate measurement of any structure empowers designers to correlate their virtual models and rapidly move forward with concepts and designs that are grounded in fact.”
Each bell was scanned with approximately 4000 measurement locations, giving resolution that would be unimaginable with traditional instrumentation.
Mike Semken, Director, John Taylor and Co. Bell Foundry: “I am very impressed with the finished images and results and I am very pleased to see that they match my own FEA work very closely.”
In bell tuning language the initial note that is heard as bell is struck is the “Prime”, and the note that persists on afterwards is the “Hum” but the most relevant harmonics are described in ratio terms of the “Nominal”. Table 1 shows the partials of a “true-harmonic” tuned bell and the figures show their true shape. The shapes that the bell makes at these frequencies remain the same no matter what note the “Nominal” is tuned to. By knowing these mode shapes the manufacturer can work the areas of greatest influence for each note. If you want to see how these mode shapes animate then watch the link below on a genuine John Taylor & Co bell.

Partial

Theoretical Interval

(cents)

Hum -2400
Prime (strike note)

-1200

Tierce, minor third

-900

Quint

-500

Nominal

0

Octave Nominal

1200

[/custom_table] Table 1 Partials for a True Harmonic Tuned Bell

Figure 3 “Hum” mode. Hi Res version available from media contact.

Figure 4 “Prime” Mode. Hi Res version available from media contact.

Figure 5 “Octave Nominal” mode. Hi Res version available from media contact.

Check out the full image gallery of Structural Dynamics of Taylor & Co. bells here.

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