Clapper height tonal variation

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Re: Clapper height tonal variation

Postby JohnGouwens on Tue Apr 30, 2013 5:50 pm

Well, Gideon, I was sure that at some point you said to me that you could not emphasize different partials by tapping the bell at different heights, but I confess I am not finding that comment from you at the moment - and I looked in both your forum comments (I can peruse all the comments you have made together - and think everybody can do that, actually) and our Facebook exchanges, so provisionally, I must retract that comment. Anyway, we do know, as it has been made obvious, that by striking the bell too high some undesirable emphasis on some less-pleasant partials is a likely result. Of course, this test is limited - what else would show up if we could go even higher? Would the same thing happen with Taylor bells (my suspicion is that the latter would be worse), what about, say, Paccard bells? I suspect the same would happen, but maybe not to the same degree. The G&J bells have much more apparent partials (and therefore far more character) than most continental bells.
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Re: Clapper height tonal variation

Postby Gideon Bodden on Tue Apr 30, 2013 10:52 pm

Ok, this must be a case of misunderstanding then, I must have not expressed myself well. Of course clapper height matters. The principal partials of the bell (minor third, nominal, 12th, double octave etc.) all have a antinode in the sound bow of the bell, this is the simple reason why a (traditional) bell will only sound good when struck at the sound bow. When the clapper strikes at a higher spot, of course, the principal partials will sound at a considerable lower volume, while many other partials, the ones that have a node at the sound bow, will sound (wildly) predominant. No test needed to predict that, this is textbook campanology.
Much more interesting is the situation in which the sound of a bell is being disturbed by 'clashing' untuned partials, like the ones we describe as 10th, 11th I&II. A very small adjustment of the height of the strike spot might practically kill one of these partials, and thereby ending the clash. In case of 'problem bells' this might be an option worthwhile to endeavor. The largest bell of the Culver carillon is a good example, as the 10th and the first 11th are so close to each other that they fight. By raising or lowering the clapper it might very well be possible to dampen the first 11th, drawing a less agitated sound from this bell. Maybe we could work on an experiment?
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Re: Clapper height tonal variation

Postby JohnGouwens on Tue Apr 30, 2013 11:33 pm

Alas, not on that bell! That's the swinging clapper, so lots of wildly heavy hardware and no way to adjust height. I have indeed used that adjustability to reduce the effect of certain tuning flaws on bells where the clappers are adjustable. That is one of several reasons why I would like to have the all the other bells (#32-50, counting from the top) fitted with adjustable clappers. Can you think of any reason why that couldn't or shouldn't be done?
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Re: Clapper height tonal variation

Postby Gideon Bodden on Tue Apr 30, 2013 11:50 pm

JohnGouwens wrote: That is one of several reasons why I would like to have the all the other bells (#32-50, counting from the top) fitted with adjustable clappers. Can you think of any reason why that couldn't or shouldn't be done?

No, I can not think of any reason why that couldn't be done! If it should? One could argue, if it comes to being able to adjust the height of the strike spot, it wouldn't serve any purpose after the ideal height has been established, you will never have to change it after that. Then why wanting it to be adjustable? (yes, being able to turn the clapper ball around and get a fresh strike spot, but that's a different purpose). We're only talking about really problematic bells. In case of 'normal' good quality bells, it would be satisfactory to have the clapper strike at the 'normal' height, and one mm. higher or lower wouldn't matter really.
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Re: Clapper height tonal variation

Postby JohnGouwens on Wed May 01, 2013 1:08 am

Agreed there, Gideon, but I suspect it would be more expensive and complicated to arrange a clapper design that allows turning the clapper while prohibiting vertical adjustment. One of the technical issues is whether a larger clapper ball would tend to work loose, and perhaps need something other than nuts above and below to hold them in place. I'm thinking keeping the nuts but adding a setscrew one can work with a hex wrench.
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Re: Clapper height tonal variation

Postby TerryMcGee on Wed May 01, 2013 11:07 pm

I wonder if you had two nuts, one above and one below, tightened and then secured with hex set-screws, they might still come undone after a while. I imagine that as the ball hits, its face compresses and its height swells momentarily, before returning to normal. The height is constrained under pressure between two nuts, so after a while, we might find that the height shrinks a little, loosening the nuts. I wonder if it might be better to lock the top nut in place with one or two hex bolts (after getting the height right), then having a big spring washer between the lower nut and bottom of ball to allow some movement but still keep the pressure firmly on?

Alternative to the hex bolts for locking the top nut might be to have two top nuts, firmly locked together.
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Re: Clapper height tonal variation

Postby Gideon Bodden on Wed May 01, 2013 11:46 pm

JohnGouwens wrote:One of the technical issues is whether a larger clapper ball would tend to work loose, and perhaps need something other than nuts above and below to hold them in place. I'm thinking keeping the nuts but adding a setscrew one can work with a hex wrench.

Spring washers serve no purpose here. Set screws are not a good idea, they become loose as well, and they damage the thread on the stud. You need a good size stud, one nut above and one below the clapper ball and lock them with (non-permanent) loctite. In case of iron clapper balls, be prepared it might be a hell of a job to get them loose again after some time, because of rust. No such problems in case of (far superior) manganese brass clapper balls and stainless steel studs / nuts etc.
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Re: Clapper height tonal variation

Postby TerryMcGee on Thu May 02, 2013 1:07 am

What do you see as the "far superior" qualities of the manganese brass balls, Gideon? (Other than corrosion resistance.)
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Re: Clapper height tonal variation

Postby JohnGouwens on Thu May 02, 2013 1:58 am

What???? You're advocating a return to manganese brass such as Eijsbouts used in the 1970s? I cannot agree with that! It has surely been by now established that annealed cast iron clappers produce a far more agreeable sound.

You greatly exaggerate the concert about rust on iron clappers. First of all they are up inside the bells, so water incursion is minimal, and most likely would happen only with condensation in certain weather conditions. Secondly, if you've tightened the nuts above and below properly, it's sealed, and water isn't going to get in. I've had such clappers on my bells for 33 years (and several are original to 1951), and have never had more than slight external surface rust - easily brushed off, and easily prevented by painting. Also the clappers don't have to fit particularly snugly on the shaft - and you absolutely don't want them threaded or you can't turn them without changing the height and creating the very problem we are here discussing. Light-duty Loctite might well offer a good solution. I see your point about a setscrew damaging the treads, especially if inserted into the nuts themselves, since they would then be at the point where you are using the threads. A setscrew through the clapper ball itself would contact the shaft at a point that, frankly, doesn't matter. I'm not clear what advantage there might be to a spring washer. I want the clapper held fast, not jiggling loose. A locknut is the obvious answer, and I suspect it would only be needed on the lower nut, since that's the one that would tend to come loose from impact or vibration. That offers the added advantage that it sets the ideal vertical position more firmly. When you turn the clapper, you loosen the upper not only, and leave the lower nut and locknut alone. That is a solution that is beautiful in its simplicity.
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Re: Clapper height tonal variation

Postby TerryMcGee on Thu May 02, 2013 5:16 am

Mr Verdin tells us:

BALL:
The rounded part of the clapper containing the largest concentration of mass which strikes the bell at the sound bow level. Bells [sic] are usually made spherical or pear shaped. Some American chimes have bullet shaped clapper balls. Clapper balls are made of various materials, usually steel or bronze. Bronze is preferred (usually manganese bronze) for carillon bells as it produces a “warmer” tone; that is, a tone richer in the lower partials, i.e. less harsh. The bell material should be softer than the bell metal so that repeated blows over many years will wear away the clapper and not the bell.

http://www.verdin.com/info/bell-glossary.php
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