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Discussion Starter #1
I recently sent this question to Joe Wolfe at the Physics Department at UNSW

Dear Dr. Wolfe,

"I have an couple of interesting saxophone related questions. Why does "rifling" or putting threads in the first 3 cm of a saxophone's neck improve the response of the lowest notes? There are some manufacturers who are currently doing this on all their professional line of saxophones. Also what causes the "burble" or "motor boating" of the low C or B on some saxes that is cured in some cases by dropping a cork or plastic end plug into the bell of the instrument? Thanks.

His response:

Gday John

Inharmonic relations among the first several resonances of the sax impedance curve can make the lowest resonance very hard to play. Small modifications of the bore can tune this, but in ways that are not easy to predict.

Best
Joe

My interpretation of his response is:

1. He did not have time to go into a lengthy detailed explanation and

2. Like all great teachers, rather than give a complete answer, he merely pointed the student (me) in the right direction.

Any information or ideas on "inharmonic relations" or "inharmonicity" anyone?

John
 

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You can have a Rail soldered in there, more like a Very smooth Baffle soldered in there. I don't know any body who does this, but really, it will cost a LOT of money. It, from what I hear, really helps the intonation on these horns, and makes the lower register, ever so slightly out of tune, but play well for the musician.
 

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Inharmonicity, at lest for pianos, refers to the way in which harmonics are out of tune with the fundamental. On a piano they are sharp, caused by the stiffness of the sting next to the bridges. As I understand it, the degree can be modified (for the bass (wound) strings, by adjusting the diameter of the core, and where the windings stop short of the bridges.

Take a concert c string. Its 2nd overtone, G, is slightly sharp, so if the actual corresponding G string of this frequency is not tuned a little sharp to reduce the conspicuousness of the beat frequencies - that G string with the overtone of the C string - then the sound is unpleasant to listen to. So the result of all this accommodation is that pianos are tuned with "stretched" octaves - why do we bother to tune to them? :) - and can never be in tune with an instrument such as an organ which does not have stretched octaves.

Presumably on a not-so-well-designed sax, there is an overtone that is out of tune with the fundamental, and this sets up a conflict situation, fighting cancelling?) the fundamental. Perhaps this can be caused by the location of the sudden change in diameter from mouthpiece to neck, or by the sharp bend in the tube at the bow, where really odd phenomena must occur when the cross-sectional area suddenly almost doubles before actually rounding the bend.

Both these areas seem to be vital spots that cause burbles.
 

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interesting this acousticoil thing, but I do not see it applied to saxophone on the site, at least I didn't notice any testimonials of saxophone players, the closest we get to them is clarinets, bassoons and flutes.

this, and the analogy with rifled bits in the upper part of the saxophones (I've seen Selmer necks rifled), suggest that many different interference patterns of the air flow yeld positive results for the sound.

Incidentally has anyone ever thoght of a entirely rifled saxophones bore?
 

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OOOOpppppps! alright but I still don't see any testimonials! Soundclips with before and after are always welcome.
 

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milandro,

Sorry man, didn't intend for it to read 'mean.'

I don't know nuttin' about any of this, starting from the
first post, I just knew I'd seen this coil thingy when I was
doing some trumpet research.
 

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No prob, rabbit! I remember to have seen this some time ago to, but frankly I like gizmos but I always like to hear their impact on real sound rather than seeing a graphic alone, but thanks really! I didn't see the 2nd section. :)
 

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Discussion Starter #10 (Edited)
Having more money than good sense, I have ordered an Acousticoil to try in my tenor sax. I will post the results in this thread after I have tried it.

I am assuming that the coil works in a similar manner to the "threading" of the inside of the neck done on the Cannonball saxes and those designed by H.W.M.N.B.N. I asked Tevis Laukat, the co-owner of Cannonball if he used a formula or a measurement to know exactly where to put the rifling in the neck and he said that he just does it by trial and error, play testing the sax until it has the sound and response he is after. He also indicated that after doing several hundred, he has a pretty good feel for knowing where to put the marks to get the desired effect. All he would say about the acoustic effects of threading the opening of the neck is that "it makes the sound more interesting". He does not thread the necks to make the low notes respond better or to prevent the "burble" as H.W.M.N.B.N. claims on his saxes.

John
 

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Yes, please keep us posted!
I'd be happy to discover that a simple gizmo
actually makes an interesting difference.

Then I can sound lame in a new way.
 

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Low Note Burble

"Also what causes the "burble" or "motor boating" of the low C or B on some saxes that is cured in some cases by dropping a cork or plastic end plug into the bell of the instrument?"

I had this problem on my alto, but my tech fixed it. He said that he strengthened some of the springs on the side keys, explaining that he tho't the vibration of the low tones was popping a side key slightly open.

Keith
 

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Discussion Starter #14
kymarto said:
Here is the next compass point in the right direction:

http://www.phys.unsw.edu.au/jw/z.html

Toby
Thanks for reminding me of that section of the UNSW acoustics site. That does add some pieces to the puzzle. Benade in the notes to his class "The Evolution of Wind Instruments" makes the following statements: http://ccrma.stanford.edu/marl/Benade/documents/Benade-Physics323-1977.pdf

"We have repeatedly faced the fact that the bottom notes of a conical woodwind are blurty, coarse, and hard to control. The reason given was that peak 2 [1st harmonic] gets to be taller than peak 1 [fundamental] for a nearly complete cone. What can we do to reduce the height of peak 2 without lousing up peak 1 (and without spoiling too much of the behavior of the rest of the notes on the instrument)?

(a) Ordinary sax pads are porous (or the horn gets harsh).
(b) Sealing the pores of the leather pads for the L-H fingers (C5# through B4 flat) reduces the damping of mode 1 and so raises the height of peak 1. *
(c) This sealing does not do much to the damping of mode 2 since flow losses here come mostly from the tonehole edges, etc., etc."


*[This is a bit confusing as to which pads he means to treat. The illustration on the preceding page has the C, B, and Bb toneholes labeled.]

Based on Benade's comments, my interpretation of the "burble" or motor boating on a low C or B is that the 1st harmonic is slightly stronger than the fundamental and the the sax not knowing which one to sound quickly oscillates back and forth between the two. I plan to study this effect by recording the next sax I find with this problem and playing it back at a greatly reduced speed. When I get my spectrum analysis software working I can compare compare the harmonics to see if indeed the 2nd peak is stronger than the first.

It would also be an interesting experiment to treat just the few upper stack pads to make them perfectly airtight to see if that actually improves the response of the lowest notes. J.L. Smith recommends a product called "Chem Guard" that is a plastic coating that he sprays on sax pads to make them airtight and water proof that should work perfectly for this experiment.

John
 

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Just put bits of rubber glove or dental dam under he pads?
 

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John,

I guess that you are correct in surmising that motorboating has something to do with a tall second peak and an oscillation between the first regime (fundamental) and second (octave). I think your slowed-down recording will bear this out. But to say that motorboating happens because the sax doesn't "know" which mode to sound is less than satisfying as an explanation. Since saxes don't have minds we can't really call on their not being able to make them up as a cause for anything ;-)

Oscillations happen because of an instability in one state which leads to another state, which has a instability leading back to the original state, etc., as long as conditions last.

I think that there are some clues on pgs 8 and 9 of the Benade paper you cite. One of them has to do with reed nonlinearity and the other has to do with peak frequencies (as well as peak amplitudes, obviously). I am no expert here, but let's suppose that as you increase playing volume reed nonlinearity adds some extra juice to the second harmonic (see Benade), and because of a weak fundamental 1st peak, actually causes the sax to jump to a second-regime oscillation--up to the octave. However at the octave the extra punch from the reed nonlinearity is lost, causing it to revert to first-regime oscillation, and the cycle starts again.

Another possibility that I was considering is that if, because of the bore shape, the peaks are displaced in frequency, perhaps mode-locking in the second-order oscillation regime is lost as soon as the horn jumps to the octave, and so it drops back down to the fundamental. This is wildly speculative, but I'm sure that the causes could be found with the right brain and the right equipment.

One clue for me has to do with a similar problem with shakuhachi in the lowest notes, usually the "ro", the lowest. The shak has a reverse conical bore that widens out again at the end. At about 7/8 of its length it has contracted about 25% from the original diameter, and then opens up again at the end to about 85% of that original. If minimum diameter is incorrect, or if the flare is incorrect, or if the point of maximum contraction is incorrect, it can lead to very unstable low notes which can easily be caused to motorboat if you change the embouchure as if to overblow the octave (in other words add some energy to the second partial). This is somewhat analogous to the case mentioned above.

Consider this: a toroidial bend in the bore causes it to act as if it were wider and shorter. Perhaps this effective "widening" of the bore at the bow screws up either the amplitude or position of the peaks (or both). Contracting the bore by addition of a cork or some wax fixes the problem...

Just some thoughts, not to be taken too seriously...

Toby
 

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Discussion Starter #17
Toby said:
But to say that motorboating happens because the sax doesn't "know" which mode to sound is less than satisfying as an explanation. Since saxes don't have minds we can't really call on their not being able to make them up as a cause for anything ;-)
Actually I have owned several saxophones that seem to have a mind of their own especially on certain note combinations. If Benade can talk about woodwind bores "eating" the energy of the sound wave, resonances "talking" to one another, and sound waves "seeing" a larger tube as they go around a bend in the tubing, I think I am in good company when I say the sax doesn't "know" which note to play. :)
Toby said:
Consider this: a toroidial bend in the bore causes it to act as if it were wider and shorter. Perhaps this effective "widening" of the bore at the bow screws up either the amplitude or position of the peaks (or both). Contracting the bore by addition of a cork or some wax fixes the problem...
This is an interesting theory. However it wouldn't explain why some straight sopranos (without a bend or a change in the body taper) will "motorboat" the low B and C if the mouthpiece is not pushed in far enough. Hmm....

John
 

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jbtsax said:
Actually I have owned several saxophones that seem to have a mind of their own especially on certain note combinations. If Benade can talk about woodwind bores "eating" the energy of the sound wave, resonances "talking" to one another, and sound waves "seeing" a larger tube as they go around a bend in the tubing, I think I am in good company when I say the sax doesn't "know" which note to play. :)

This is an interesting theory. However it wouldn't explain why some straight sopranos (without a bend or a change in the body taper) will "motorboat" the low B and C if the mouthpiece is not pushed in far enough. Hmm....

John
Whatever. The point is that for an oscillation to occur you need two unstable states: state A jumps to state B, and once there state B jumps back down to state A. There must be a change in something when you get to state B--a loss of the energy that forced the change from A to B. I think it has to due with misaligned partials due to bore geometry (which could also explain your straight sax problem). BTW was the cork seal good after you pulled out the mpc?

Toby
 

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John_P said:
If you add two sine waves that have the same frequency, but different phases and amplitudes, you'll get a sine wave at the same frequency, but with some other phase and amplitude....

John
... from thread "Eft".

I presume that means that if an overtone is slightly out of tune with the fundamental, then it produces a slow 'beat frequency' that presents itself as a pulsating volume change.

Seeing "inharmonicity" refers to this very out-of-tuneness, perhaps this clarifies the statement made by Dr Wolfe in post #1.

What I wonder about my argument there, is that the does not seem much variation between saxes in the frequency of that pulsing we call burble. Surely they would not all have the same acoustic design weakness.
 

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I'm curious to see a spectral analysis of the ouput of a horn while it's "motorboating". My tenor used to do that sometimes on the low D, especially if using an old reed. I don't think that resultant sound is caused by rapid transition between octaves. It certainly doesn't sound that way to my ears. I tried to duplicate the sound by rapidly trilling all sorts of note combinations, but never came up with anything that was really close. That suggests to me that motorboating is non-linear (or inharmonic). I'm not sure of the mechanism that would cause inharmonic series to develop. They aren't stable, and so are probably hard to study.
I've never had a horn that warbles on low B or C. It's always D for me.
Perhaps there are a couple of different phenomena here that are labeled with the same word.
 
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