[Bell Historians] Stretch tuning

[Bickerton, Roderic K (SELEX) (UK)]

Bill Hibbert's most interesting response, to me poses the question: 
Why have thick trebles with all the tuning problems associated with a
variable casting scale?
 
Is it a matter of acoustic power?
Possibly but:
The days when the absolute maximum sound and carry from a peal of bells
was required are long passed, and a huge amount can be done with louver
design and bell chamber internal design to increase output, should it
ever be needed.
 
Is it sound balance?
Possibly but:
The sound output from a bell is governed by the amount of energy the
clapper imparts.
It is not that difficult to turn that down on larger bells, although I
appreciate it is more complex than simply fitting a smaller clapper,
because the dynamic of the way the energy is imparted must generate the
correct intensity from each partial.
 
Is it ringing dynamics
Possibly but:
Combinations of "hang out",  counter weight, wheel size and clapper
dynamics can enormously vary the dynamics, to give a small bell big bell
dynamics.
One only has to look at the improvement in mini rings to see that
demonstrated.
 
What other considerations are there? 
Tradition?, Credibility, or something I have completely overlooked?
 
.

________________________________

From: bellhistorians at yahoogroups.com
[mailto:bellhistorians at yahoogroups.com] On Behalf Of Bill Hibbert
Sent: 06 December 2007 09:43
To: bellhistorians at yahoogroups.com
Subject: [Bell Historians] Stretch tuning


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Responses to various posts and questions:

> CSZ's question on the history of stretch tuning:
Stretch tuning (of e.g. 20 cents per octave or more) was the common 
practice for higher numbers in the 18th and 19th centuries. Taylors 
in particular used a huge amount of stretch in peals such as St 
Pauls Cathedral and the old Worcester 12. Whitechapel (as RO's 
posting of some while back showed) were tuning strike notes, not 
nominals, until the 1920s which guarantees stretch if the trebles 
are thicker than the tenors. Stretch tuning stopped with the 
introduction of true-harmonic tuning, but as Andrew Higson says, 
Taylors re-introduced it from the early 1950s until the 1970s. I am 
aware of one stretched peal from Whitechapel from this period 
(Cornhill 1958) but perhaps there are others I haven't come across.

> Rod's comparison of bell stretch with piano stretch:
In pianos, stretch tuning arises because the upper partials and in 
particular the 2nd harmonic are slightly sharp due to the stiffness 
of the piano string as it crosses the bridges. As a result, if the 
octaves in a piano are tuned for zero beats, they will be slightly 
stretched. The amount of stretch depends on the quality of the 
piano's construction; high quality grand pianos need less stretch 
than cheap uprights. As Rod says, a few cents in the octave is the 
typical amount.

Stretch in bells arises for a completely different reason; 
compressed upper partials (which occur in thick, heavy bells) 
flatten the strike note. The effect is large: 25 or 30 cents is not 
uncommon. Therefore, in a peal with thick trebles and thinner 
tenors, if the trebles are not stretched some people will say the 
trebles are flat, or dull sounding. I wrote an RW article on this a 
while ago, I don't have the reference with me. My PhD research has 
now proved the effect beyond reasonable doubt and provides a way to 
calculate the effect, though you'll have to wait until it's 
published to read the details. Investigation of half-a-dozen 
stretched 19th and 20th century twelves gives satisfactory 
correlation between theory and practice.

Stretch tuning is not at all to everyone's taste. In fact, there are 
two modes of pitch perception experienced by different listeners, 
and sometimes the same listener under different circumstances. Most 
listeners hearing bells rungs close together in changes experience a 
holistic effect (the strike note, shifted by the upper partials). 
Other listeners, especially bell tuners, hear the individual 
partials, particularly if one or two bells only are being rung.

> Richard Offen and St George's Perth:
Richard's comment that the trebles are thin is an important clue. If 
this is so, the strike notes will not be flattened to the same 
degree as for thick trebles. It sounds as if stretch has been 
applied in a formulaic way to these bells when it was not needed. 
Tuning figures (especially the octave nominals) would settle the 
matter. Plus, Richard used to be a bell tuner ...

> CSZ quoting from Frederick Meyer, on carillon stretch:
This was an interesting account, which I had not heard before. In 
carillons, of course, the little bells are not thickened up as they 
would be for change ringing, and so the pitch shifts are much less. 
Another experiment written up in the thesis investigates which 
partials determine pitch in bells. In little bells (e.g. the top end 
of carillons), the prime and/or hum take over from the nominal.

Cheers,

Bill H



 


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