Bell profiles

[Bill Hibbert]

In response to messages from DJB, Carl and CD:

This is all a little bit old ground, I think we've covered quite a 
lot of it before. However, here's my two pennyworth:

Regarding the Whitechapel move to true harmonic, Alan Hughes told me 
a while ago that during the twenties there was a lot of experimenting 
in profiles going on, and that for commercial reasons the trials 
tended to be shipped to customers, so the record of the experiments 
still exists in bronze for those interested enough to investigate.

As regards Taylors, I think the transition, though there was a major 
leap forwards in 1896, actually covered many decades. I wrote an RW 
article on this a while ago, there is an extended version at 
http://www.hibberts.co.uk/history1.htm. Since writing this account I 
have taken many more recordings of bells but have not yet updated the 
history to fill in more of the gaps. In brief:
* Grimthorpe probably got Taylors casting bells that in principle 
could be tuned to have an octave hum, though obviously prior to the 
mid 1890's they didn't actually attempt such tuning.
* in 1896-ish Taylors made two major innovations: they got a profile 
that allowed sharper primes, especially in smaller bells; and they 
found out how to tune hum, prime and nominal in octaves
* sometime between 1908 and 1913 they found out how to tune quints as 
well. Whether this involved a change of profile I don't know
* sometime in the 20s or 30s they changed the profile of their bells 
to give an equal tempered rather than a just tierce. Whether this was 
the profile change in 1924 referred to by DJB I don't know, I'd have 
to look at peals of suitable dates. The change required to alter the 
tierce would most likely involve changing the shape of the external 
bulge at the soundbow.

In this connection (Dave, I hope you don't mind me responding to your 
private email in public) the retuning of York St. Olave in 1916 is of 
interest. You said that these bells had been tuned externally in the 
region of the soundbow, this would most likely affect the tuning of 
the tierce relative to the nominal. Consulting Taylor's records of 
course would give a definitive answer to why this was done.

The most remarkable thing for me about this business of different 
profiles is the ability of the founders to produce bells of rather 
different profiles and relative weights which are still harmonically 
tunable. For anyone interested in the effect of various profiles on 
tuning, André Lehr's papers give a good explanation: there is one at 
http://www.hibberts.co.uk/lehr.htm which includes graphs of where to 
take the metal off to affect differemt partials. Of these graphs, 
Lehr says "With the help of these graphs the bell founder will easily 
tune an untuned bell" which I think is a very optimistic comment 
indeed! - though I know that Ben Kipling has incorporated these or 
similar curves into a program predicting where to take the metal off 
to achieve particular tuning results.

Bill H