 The Clarinet BBoard
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Author: Marty
Date: 2000-02-03 19:27
What is a polycylindrical bore, and how does it differ from a non polycylindrical bore. Is this the standard and if so why? What are the advantages and disadvantages of the polycylindrical bore.
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Author: paul
Date: 2000-02-03 20:37
This is a well beaten-down subject. Where can we begin this discussion?
A rough description of the polycylindrical bore is that it's a series of stepped tapers, like taking a large coffee can and putting a large soup can into it, then a smaller soup can, then finally a small tomato paste can into that. Get two sets of these cans. Now, cut the tops and bottoms of all of the cans out and lash them together with duct tape end-to-end. Go from very large to very small, connecting the very small ones together and gradually going back up to the largest one. Or, go from the very smallest to the largest and connect the two largest cans together. See the series of cylinders? Now, set your eyesight on the inside of the cans instead of the outside. There you have it. This is a rough idea of the polycylindrical bore. Except it's cut into a piece of wood and both the "soup cans" and the tapers "between soup cans" are a lot smoother than the can and duct tape example. Some horns bores are hand made, but most of the well known brands of clarinet bores are done with computer numerically controlled (CNC) lathes in very modern factories today.
As I recall, there are lots of references to the advantages of the poly bore, its history, etc. I'll give you a hint. This invention made the Buffet R-13 the marque of professional classical music performance in the modern day clarinet.
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Author: Don Berger
Date: 2000-02-03 21:49
Paul - Your coffee-soup can analogy is great, BUT the dimensions are a bit large. The bore variations from cylindrical are small, between about 14.5 mm to some 14.8, and may have several forms, also some makers use the "reversed-cone" bores. The most recent study [to my knowledge] is that by Lee Gibson, "Clarinet Acoustics" available from Amazon etc for some $15. To my mind the integration of bore-size and "character", tone-hole size and placement and pad "height" and other venting is greatly complicated, there are some patents [Carre in particular] which give info, but the real details seem to be "trade secrets". I like the subject but find it VERY complex! Don
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Author: Kurt
Date: 2000-02-04 02:31
Ok, very nice. Now, is this common for woodwinds or something specific to clarinets?
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Author: Eoin
Date: 2000-02-04 09:51
Clarinets have a basically cylindrical bore. Most other woodwinds, including oboes, bassoons, saxophones, have a conical bore, so "polycylindrical" would certainly not apply to them. Flutes appear to have a cylindrical bore, so they may use something similar.
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Author: paul
Date: 2000-02-04 13:49
Conical bore: Take a piece of notebook paper and roll it up. Make sure the top of the paper is rolled up tighter than the bottom and tape or glue the ends so they stay that way, so as you look at your finished work as it stands on a table top, you see a cone like an ice cream cone. If you stood the cone of paper on a table and walked a few feet away, it would look somewhat like a triangle. Saxophones are built on this premise. Compare and contrast the sax to the clarinet in playing/tone behavior in your own research project.
Cylindrical bore: Take another piece of notebook paper, but this time make sure the top and the bottom are glued together to make what would look like a paper towel tube, with a straight up and down look to it. The clarinet and the flute do appear to be built this way. But, why is the clarinet so different from the flute even though they are built on the same bore design concept? A good research project starts here.
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Author: Todd twholle
Date: 2000-02-04 22:22
This is an interesting and apparantly very complex topic. Which end of this polycylindrical bore is the larger one, the upper or the lower? I obviously have no real idea about the construction differences of different kinds of clarinets, even though I have been swabbing three different ones out for a few years. I guess they are basically purely cylindrical bore instruments because I found only about .005" difference in bore diameter when I measured one. I took a look at a couple of Recorders( yes, the deadly "Blockflutes") that I have, and see that they have an appearantly conical bore where the fipple is at the larger end. These instruments overblow an octave, ( as does the flute;which by the way also has a conical bore)and have a very characteristic tone. I wonder if this "reversed bore" situation also applies to the polycylindrical bore of some clarinet upper joints. It seems like if so, that it would do something to change the tone as well as possibly adding a little blowing resistance to the clarinet.
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Author: Mario
Date: 2000-02-08 13:26
This very interesting thread has dealt, so far, with what is a polyclindrical bore, and how they are built. But the interesting question is why do we need them in the first place. Quite a few things have been written on this topic. Last year in Osteend, Steven Fox gave an excellent seminar on what this is all about.
Take a perfect cylindre. Attach a clarinet mouthpiece to it, and see what happens. Even with advanced mechanisms, the sound will be un-even (color-wise and response-wise), and will be grossly out-of-tune. In addition to a number of other techniques (such as the placement and shape of tone-holes), the polycylindrical bore is used to solve these problems as much as possible. Even today, a chosen bore configuration will be an exercize in compromises. Different manufacturers will choose different combinations to get the results they want. On my Rossi for instance, the chalumeau forked eb is sharp, but the clarion fork Bb is perfectly in tune, while on the R13, forked Eb is just a tad sharp while forked Bb is a tad flat. This is a choice made by the designer. Rossi favors a clarion perfectly in tune and prefer to introduce tuning problems in the chalumneau, hence his choice of solutions, etc. Other designers will disagree and create a different instrument.
In order to understand how a polycylindrical bore works, you ust picture the sound wave of a note inside the bore. This sound wave has crests and troughs (it is a set of waves). Enlarge the bore where a crest is, and you lower the pitch, the pressure, and the color. Shrink the bore and you get the reverse. Where troughs are present, acting on the bore results in the opposite effect. We have to remember that each notes is made out of many frequencies with they own little phases. So, at a given time, there are numerous little crests and little troughs all over the place in the clarinet. Minute adjustments in bore sice might work for one not, not for the other, might make a given note brigther or darker, might increase its pressure, etc.
Add to that the dimension and exact placement of tone holes (the larger the hole, the lower the pitch, the lesser the pressure, the duller the color, etc.), the height of pads (the higher the pad, the higher the pitch, the lesser the pressure, etc.), and you can get an idea of the complexity of selecting the right combinations of solutions in the design of a clarinet. These are all trade secrets. Same holds for mouthpiece design b.t.w. which has similar parameters to play with.
There is no mathematical model at the moment that can deal with the higher order issues required to model the clarinet. The models that we have can capture what happens in pure cylindre. Nothing can predict the result of a particular set of choices. So, clarinet making remains an art with little science to help the designer. It is empiricism at its best.
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Author: Dee
Date: 2000-02-08 18:16
Very well said, Mario. I think it will also help players to understand why they must be responsible for playing in tune rather than relying on the instrument to be in tune.
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