Comparison between internal and external clappers

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Re: Comparison between internal and external clappers

Postby TerryMcGee on Sun Mar 10, 2013 9:41 pm

Gideon Bodden wrote:I'm sorry, but I find this a little bit silly. Comparing an obviously heavy clapper, with probably rust and dirt on the surface and made of a probably soft metal, with an external striker that is probably A LOT lighter than the clapper and which strikes at a worn and hardened strike spot.. The difference in sound on the recording is interesting, but has hardly anything to do with internal or external striking of the bell. This can be misleading.


I don't think it's the comparison that's silly, but the reality. This 75 year old Taylors carillon, set in a beautiful tower in a beautiful park in a beautiful city is clearly capable of beautiful sound, but you should hear it now, under bongotron control. Well, you have heard it, if only one bell. I could post more, he added menacingly!

And as I said to Frances above, there are other complications in explaining the sounds of the clappers, like weight (possibly), position, etc. Approach the recording as a simple statement of fact. When you play this particular bell with the internal and external clappers, as found, this is what you get.

By the way, I find both sounds on the recording substandard. The sound with the oversized (?) clapper is dull and empty, and lacks articulation, the 12th and double octave are way too much muffled. The sound with the external striker is better, in the way that there is a good clearness and you hear what this bell has to offer, there is a great movement in the sound, and especially when listened to from a distance, this is a more musical type of sound. The downside is that this sound may be a little too thin and doesn't leave room for much dynamics.


I'd agree that both sounds are less than ideal. This carillon has no transmission system - the internal clappers of the trebles hang forlornly, unloved by anybody other than gravity. The clappers of the lower bells sit rusting in the corner. So, all I could do was to manually flick the clapper at the bell. I did the same with the electric clapper. So, regard the volume level as piano and the low harmonic development would make sense. Also it's likely to be rusty at the strike spot. I have no reason to believe it's oversized. I took a few clapper dimensions, the C two semitones down has a similar pearshaped clapper about 75mm diameter and 105mm high, if that helps. It's 400mm mouth, 330mm up to the shoulder.

I think with a transmission system and clavier, and a little cleaning up or playing in, we would find that bell would respond well to player dynamics. The electric system can only sound worse if played at full strike. Possibly not much worse, there isn't much room for disimprovement!

The recording was made using a cardioid studio condenser microphone (at about 3metres) , USB sound interface and laptop. You are hearing the .mp3 version, but I don't think that matters.

Terry
Last edited by TerryMcGee on Sun Mar 10, 2013 10:03 pm, edited 2 times in total.
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Re: Comparison between internal and external clappers

Postby TerryMcGee on Sun Mar 10, 2013 10:00 pm

Since there is interest, I should give you one more image of the comparison. These are the waveform envelopes of the two strikes, firstly the external, then the old internal clapper. The timescale is given at the top of the chart in seconds.

Image

You can see that the external clapper energy decays exponentially and quickly, while the internal clapper energy decays more slowly and linearly. The beating in the tail is accentuated by the better bass response of the internal clapper, but is too slow to be annoying. The staccato effect of the shorter bursts of energy possibly explains partly why the bongatron tunes sound so objectionable in this installation.

Terry
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Re: Comparison between internal and external clappers

Postby Gideon Bodden on Sun Mar 10, 2013 10:30 pm

TerryMcGee wrote: I don't think it's the comparison that's silly, but the reality. This 75 year old Taylors carillon, set in a beautiful tower in a beautiful park in a beautiful city is clearly capable of beautiful sound, but you should hear it now, under bongotron control.


The comparison by itself is not silly of course. Not providing a minimum of significant information about the different circumstances, is. Already it made John draw the false conclusion that the difference in sound should have anything to do with internally or externally striking. If you would take one striking device, strike the bell both from the outside and the inside with that same device with the same force etc. than maybe you would be able to come to some conclusions. No doubt the conclusion would then be, that there is not difference in sound.

TerryMcGee wrote: You can see that the external clapper energy decays exponentially and quickly, while the internal clapper energy decays more slowly and linearly.

Also this conclusion is not correct. Striking the bell with external striker / clapper by itself does not influence the way the bell sound decays. But as in this case the clapper causes the hum to sound with a lot more energy than the external striker does, your clapper waveform represents mainly the behavior of the hum note, as it is dominant. It decays more slowly by nature. The external striker does not influence the decay behavior of the hum note, it makes the higher partials more dominant, and they already have a 'staccato' character by nature. The staccato effect comes from the bell, not from the clapper, and your conclusion is wrong.
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Re: Comparison between internal and external clappers

Postby JohnGouwens on Sun Mar 10, 2013 11:14 pm

This would warrant a scientifically-controlled test - ensuring that the force was equal between the two types of clapper. A few other variables can make it harder to tell. There is, however, no avoiding the fact that an external clapper is going to sit on the bell longer.
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Re: Comparison between internal and external clappers

Postby TerryMcGee on Mon Mar 11, 2013 4:35 am

Gideon Bodden wrote:The comparison by itself is not silly of course. Not providing a minimum of significant information about the different circumstances, is. Already it made John draw the false conclusion that the difference in sound should have anything to do with internally or externally striking. If you would take one striking device, strike the bell both from the outside and the inside with that same device with the same force etc. than maybe you would be able to come to some conclusions. No doubt the conclusion would then be, that there is not difference in sound.


There used to be no doubt that objects fall at a speed according to their weight, until someone got around to testing it. I have no reason to believe there would not be a difference in tone or volume between the identical clapper striking from the inside or outside. But, until tested, it remains unproven. It begs the question though, why did we settle on internal clappers in the first place? And stick with them? There is usually some logic behind traditions.

You can see that the external clapper energy decays exponentially and quickly, while the internal clapper energy decays more slowly and linearly.

Also this conclusion is not correct. Striking the bell with external striker / clapper by itself does not influence the way the bell sound decays. But as in this case the clapper causes the hum to sound with a lot more energy than the external striker does, your clapper waveform represents mainly the behavior of the hum note, as it is dominant. It decays more slowly by nature. The external striker does not influence the decay behavior of the hum note, it makes the higher partials more dominant, and they already have a 'staccato' character by nature. The staccato effect comes from the bell, not from the clapper, and your conclusion is wrong.


Hmmm, I think you need to do a decay analysis before you jump to unfounded conclusions. The Tierce is more dominant than the Hum in the first 0.53 seconds for the internal clapper, and 0.7 seconds for the external clapper. Even after that, they fade pretty much together, in the case of the both clappers. By that time of course, most of the fun is over.

The difference in overall energy decay times is due to the startling amount of energy in the higher partials released by the external clapper, which of course dissipates quickly. Just after impact, the Nominal is twice as high as it had been in the Internal case, the Nominal Octave which wasn't noticeable in the Internal clapper case is equally high, the Tierce is lower but still very significant and the Superquint is also significant.

So, I stand by my observation. The external clapper is releasing its energy in a short, high frequency burst, while the internal clapper releases its over a longer period. Which is what the waveform envelopes show.

And it supports my earlier observation that clappers are to bells what bows are to fiddles. They exercise amazing control. We ignore that at our peril. Helping people appreciate that is my reason for airing this comparison.

Terry
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Re: Comparison between internal and external clappers

Postby JohnGouwens on Mon Mar 11, 2013 4:49 am

Thank you, Terry, for bringing more careful analysis to the behavior of the partials. I'm right there with you about external hammers. There are some extreme cases of carillons with bells up in the fifth octave (or higher) in which it became necessary to strike them either from the outside or from underneath with a clapper that comes up to strike the sound bow on the inside. It's not so easy, though, to separate the inside/outside clapper/hammer behavior from other issues, such as disparity in weight.
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Re: Comparison between internal and external clappers

Postby TerryMcGee on Mon Mar 11, 2013 4:51 am

JohnGouwens wrote: There is, however, no avoiding the fact that an external clapper is going to sit on the bell longer.


I suspect I'm with Gideon on this one. (Seems only fair!)

Perhaps you are imagining that gravity is assisting the external clapper to rest longer on the bell? The external clappers have pretty powerful return springs which more than offset the weight of the clapper (or it would droop in the rest position). So I think that renders the playing field more level.

But the second reason I'd advance is that longer time in contact with the bell would yield a rounder tone, not a brighter one. This is a clear finding from our paper: "Bell clapper impact dynamics and the voicing of a carillon" http://www.phys.unsw.edu.au/music/people/publications/Fletcheretal2002.pdf where we measured the contact time electronically with very flattened clappers and then the same clappers revoiced.

It would be interesting to add that measurement technique to any comparison of inside and outside clappers on the same bell, to see if it reveals why any differences in tone or power occur. Ditto changing the weights of clappers to determine why the optimum weight produces the best sound.

Terry
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Re: Comparison between internal and external clappers

Postby JohnGouwens on Mon Mar 11, 2013 5:17 am

Fascinating study! Thank you for sharing it! I don't have the advanced physics and math training to make out all of the study, but it is intriguing. Were the tests made with the clappers hanging free or connected to the transmission? I ask that because the transmission accounts for holding the clapper to the bell a whole lot. Gideon has been developing very low-mass transmission systems to reduce that to a bare minimum.

I have found, especially on English instruments (along the lines of Canberra) that worn, flat clappers tend to make the bells particularly clunky in effect. Whatever it is that is happening, I do know what the effect is on the tone. Now the "before" and "after" are both with the transmission connected. Maybe this was in your report (some of which I frankly couldn't follow), but did you obtain similar results? That is, after voicing, did you find the trebles longer-ringing? Was the transmission connected throughout your tests? For sure, the "drag" introduced by the transmission is a problem no matter how nicely shaped the clappers are.

I appreciate your giving this matter the study it deserves.
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Re: Comparison between internal and external clappers

Postby JohnGouwens on Mon Mar 11, 2013 6:01 am

This is timely, actually, since in my Campanology textbook, I'm including a description of the issues involved, and the need to re-voice clappers. So, I'd appreciate some help on just how it is that the longer contact with the bell can make the bell sound more resonant. It's a given that it happens (at least in my experience it has been very consistent), but I'm not sure how it happens in light of your findings. (This means I need to understand what is happening better. I'm not challenging what you found, and quite appreciate being more enlightened about it)
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Re: Comparison between internal and external clappers

Postby TerryMcGee on Mon Mar 11, 2013 10:09 am

The clappers were definitely connected to the transmission. We probably used the flick approach applied to the horizontal crank to ring the bells, so the transmission bars would be in the circuit, but not the down wires (which you will remember are flexible in Canberra's case). Whichever approach we used, it would have been used in both the before and after case. We recorded a number of strikes to ensure that we got some good clear ones.

Now that we've shown we can measure contact time, and see dramatically different contact times and spectra from the same clapper and bell with the only difference being voicing, we are in a good position to examine the effects of other issues, such as transmission inertia, player technique and so on.

I don't remember us considering the effects on the ringing length, but as you've seen in the Bathurst case, there appear to be issues there between the inside and outside clappers, so I wouldn't be surprised to see similar results on flattened clappers. We can do decay analysis showing the decay profile of each of the partials.

Incidentally, most of this (with the exception of contact time measurements) can be done using just the sound. Indeed, you can do it on your own computer using free software, or send me pairs of notes for comment.

On the topic of finding an easily understood explanation of how the contact time thing works, let's all work on coming up with a statement we can all have faith in (you too, Gideon!). I'll be back with a first try, hopefully tomorrow....

Terry
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