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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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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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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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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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Discussion Starter · #28 ·
kymarto said:
Interesting experiment, John. I am no expert, but let me put in a couple of cents worth of speculation.

First, it is a shame that we don't have numbers on your graphs for the x axis, which is clearly frequency. I don't know what the first smaller peak is (could be an artifact of some kind), but I am assuming that the largest peak (in the lefthand graph) at around 0.25 is the fundamental. The second large peak at around 0.4 would be the octave, and that peak just above 0.5 might be the 12th.
I agree. This is one of the weakness of my spectrum analysis software I need to address.
kymarto said:
If that is the case it looks like the warble is indeed the octave--you lose the fundamental and the first partial becomes predominant, with a significant increase in the second partial and increases in some of the higher partials.
I agree that the "visual" speaks to this effect, but what you actually hear is not an octave jump, but the pitch dropping approximately a half step.
kymarto said:
What is important to note is that there is no pitch shift of the peaks: the second graph shows the same peak positioning as the first.
Great observation!
kymarto said:
I suggest you try using the same mpc and play the octave with the octave key and compare that with graph 2. I think you will find that they are quite similar, and any differences might give you some clues as to why the octave warble is not stable and drops back to the fundamental.
Great idea! Your other observations have generated a lot of ideas to try as well.
kymarto said:
I will be interested in seeing accurate before/after graphs using the acousticoil. If it actually does reduce motorboating we should carefully check the graphs for differences in both pitch and amplitude in peaks to see if we can find anything that might help explain the effect of the coil.
I'm working on that right now. Thanks for you expert help with this.

John
 

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Discussion Starter · #38 ·
Hi Jim. Thanks for keeping this thread alive. I'm hoping we can generate more interest in acoustics is this forum. I have read the pages you made reference and I am having difficulty understanding the point you want to make with regard to mode locking and its effect on inharmonicity.

I'm afraid that I have to disagree with you that there is no inharmonicity present in woodwind instruments. Benade refers to "misaligned resonances" which I believe is the same principle and makes this statement on p. 446 of FMA.

Anything that works against the maintenance of oscillation (such as the reduction of the heights of air-column resonance peaks by frictional or radiation damping, or the misalignment of these resonances so that they fail to set up strongly cooperative oscillatory regimes) requires the player to operate the reed on the more steeply falling portion of its flow control curve. In order to produce this increased steepness, the musician is required to exert more effort in his playing, so as to provide a combination of increased blowing pressure and greater embouchure tension. This explains why instruments having either heavily damped or grossly misaligned resonances are usually described as "hard blowing," and why the player is likely to find them physically tiring to play.

It is a common observation that a really fine instrument with accurately aligned resonances can be played comfortably with a reed that is considerably stiffer than can be used on a less well aligned instrument, even if the heights of the various resonance peaks are the same in both cases.
John
 

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Discussion Starter · #43 ·
Thanks for that link. As always Fletcher is a difficult read for me. I think the essential idea is stated in his introduction.
Such mode locking is favored by nearly harmonic normal mode frequencies, by large mode amplitudes, and by large nonlineartry in the driving force.
This suggests to me as was pointed out by Benade that mode locking does occur but the process is more efficient in instruments whose bore dimensions produce harmonics close to their natural frequencies.

My understanding at this point is that the measuring of an instrument's "acoustic impedance" bypasses the non linear mode locking of the reed blown apparatus and shows the acoustic "footprint" of the instrument itself.

John
 

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Discussion Starter · #45 ·
Gordon (NZ) said:
"The non-linear reed "
To help me overcome a stumbling block, could you explain exactly what you mean by that?
The UNSW Saxophone Acoustics site at the heading "The Reed Controls the Airflow" has a good explanation of the non-linearity of the reed's function in the tone production.

John
 

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Discussion Starter · #53 ·
If the sax does this on low B and Bb but not on low C and it did not do so before the overhaul with the same mouthpiece, I would have the G# key checked---specifically the adjusting arm from the F# key that closes the G# when the bottom hand keys are pressed.

A leak light in a pitch black dark room should tell the story. If this is not it, write back and we will suggest plan Deux.

John
 

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Discussion Starter · #56 ·
think its for sure the neck cork.. when i apply teflon tape and paper its seems to be fine.. is a tapered neck better to go with?
The cork should be cylindrical from front to back the same as the interior of the shank of the mouthpiece. This means that on the tapered neck, the cork must be sanded more at the back than at the front. I am surprised that the person who overhauled your Mark VI couldn't properly fit your neck cork to your mouthpiece. This doesn't make sense.

John
 

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Discussion Starter · #62 ·
To answer your question for most mouthpieces 1/16" cork sanded lightly is the correct diameter. On some necks 3/32" is required if the mouthpiece also has a large diameter shank. Every set-up is slightly different.

How close to the end of the neck is your mouthpiece? It may be that it does not cover enough of the cork for a solid fit regardless of the tightness of the cork.

One more thing to check is with the neck tightening screw just barely snug, can you wobble the neck in the receiver? If you can there is a possibility that the neck tenon is not air tight and needs to be refit. Be aware that when you play and put downward pressure on the top of the mouthpiece with your top teeth you can change the angle of the mouthpiece or neck or both and cause one or the other to leak where they didn't when you first started to play.


John
 

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Discussion Starter · #65 ·
Try taking your mouthpiece and neck off the sax and playing on the neck only. If the note is higher than E concert, that could be part of the problem. The tenor seems to work the best with that input pitch. In my experience the sax should be played with an open relaxed throat on all tones, but it is especially critical in the low register.

Another thing to check is the opening of the low C key. If it is too closed, it can make the low D unstable. If you have an adjustable bumper, back it out to open the key and try the D again. A leak in the low C# may also be contributing to the problem. Play low D and then press the low C# key. If it improves it may be a leak in the low C# key or a venting problem with the D. Check the low C# with a leak light if you have one.

One last thought. Make sure the back of the tongue is down as if singing "AHH" when playing the low notes. It should not be necessary to relax the embouchure to play any of the low notes clearly if all the other elements are in order.

John
 
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