Sax on the Web Forum banner

1 - 20 of 24 Posts

·
Registered
Joined
·
50 Posts
Discussion Starter #1
Hi guys,

I have been doing some (beginning) research on sax theory.

Some questions:

CONICITY

I am not clear about how the “degree-of-conicity” affects
the pitch of the partials. The only place I have found that it
shows up in a formula is in Scavone’s dissertation (page 17
and 18), which indicates that more conicity lowers the
“cut-off” frequency, resulting in fewer high-frequency
partials and a darker sound.

However on page 66:
“making a cylindrical bore slightly conical divergent will raise its
fundamental resonance and compress the partial frequency
ratios from odd integer multiples.”

“slightly” ???????

How much “slightly” to make the first partial= *2? Is there
a point where the conicity is so great that the first partial is <*2?

BOUNDRY LAYER EFFECTS

How much smoothing of the bore do you techs do?
cleaning (of course)
polishing?
tone hole edge smoothing?
octave-vent perturbation reduction?

OCTAVE-VENT LOCATION

Scavone and Benade indicate that the further a tone hole is from
the optimum, the sharper the tone will be. The first
octave vent is normally set to optimize F, and, therefore, D and
G# should be sharp. If my sax 2nd register D is sharp and the G#
is flat. would you lower the vent?

Much thanks,

jim
 

·
Registered
Joined
·
50 Posts
Discussion Starter #2
Sorry, I meant

"which indicates that more conicity lowers the
“cut-off” frequency, resulting in fewer high-frequency
partials"

Should be :

which indicates that more conicity RAISES the
“cut-off” frequency, resulting in MORE high-frequency
partials

That is one of the reasons that a Buecsher TT C-Melody
sounds dark (some say dull).

Right?

I'll try to do better.

jim
 

·
Registered
Joined
·
1,393 Posts
On the other hand, it's making sense to me and I'm hoping some experts respond with their ideas because I find this subject fascinating and would love to learn more...
 

·
Distinguished Technician & SOTW Columnist. RIP, Yo
Joined
·
17,204 Posts
Likewise.
 

·
Registered
Joined
·
645 Posts
Hiya!

In my attempts to intonate a clarinet I got in touch with different aspects on acoustics affecting the intonation.
You have a little about cut-off frequencis here http://www.phys.unsw.edu.au/jw/saxacoustics.html
I´d guess that Scavone however gives it a more thorough basic view.

About the clarinet http://www.clarkwfobes.com/Tuning%20article/Tuning%20the%20Clarinet%20for%20PS.htm


(Basic link where others can be lead from http://www.phys.unsw.edu.au/music/flute/ )

When overhauling an instrument I always try to remove as much of what´s on the inside and in the tone holes but wasn´t supposed to be there in the first place. No polishing (unless silver), just trying to restore it to what the manufacturer tried to achieve in the beginning.
 

·
Registered
Joined
·
50 Posts
Discussion Starter #7
Register holes too long?

Kymarto writes elsewhere:

"OK, I went back and read the Benade paper, and indeed he mentions that saxes typically use register holes that are too large and too long, and this causes intonational problems, so I am probably wrong about the pip having to be quite large to shift the intonation of the second ocatve upwards. Benade says that indeed the hole should be quite small, but it also needs to be quite short (1 mm) at the same time. Most sax pips are much longer than that. So the bottom line is that if you make the hole smaller you should also make it shorter. If you don't you risk response problems."

Are we sure Benade was talking about the total length or just the height
above the pip hole?

jim
 

·
Distinguished Member and Forum Contributor 2008
Joined
·
6,395 Posts
jimmyperks said:
Kymarto writes elsewhere:


Are we sure Benade was talking about the total length or just the height
above the pip hole?

jim

YES......:? :scratch:
 

·
Forum Contributor 2007-2012, Distinguished SOTW Te
Joined
·
3,314 Posts
I am not an acoustics expert, although I want to be. I'll take the plunge here...

BOUNDARY LAYER EFFECTS

I don't think techs have a consensus on this one. Some books/techs advocate a completely smooth bore, while others say that the brass will develop a texture based on how the boundary layer "etches" (for lack of a better word) the horn over time, and the texture of the brass/funk on the inside of the horn is what makes old horns feel "broken in".

I am not sold on either- I just try to keep the horn clean, and I chem-clean and gently scrub horns when I repad or overhaul them, but I don't try to get the inside of the horn buffed to a mirror shine. But I don't leave the funk in there, either.

OCTAVE VENT LOCATION

I suppose that if your second octave D is sharp and your G# is flat, you could lower the octave vent on the body, I suppose. I would first try messing with key heights etc. before resorting to that sort of saxual operation, and only if the intonation was not able to be corrected easily via the embouchure. I have heard on some Conn baris that moving octave vents helps intonation- I think its the transitional and chu baris (haw!) that people are referring to most commonly.

CONICITY

I think you'd have to pay Leblanc or Selmer or Buffet quite a bit of cash to get exact numbers on this one.
 

·
Registered
Joined
·
250 Posts
jimmyperks said:
CONICITY

I am not clear about how the “degree-of-conicity” affects
the pitch of the partials. The only place I have found that it
shows up in a formula is in Scavone’s dissertation (page 17
and 18), which indicates that more conicity lowers the
“cut-off” frequency, resulting in fewer high-frequency
partials and a darker sound.
These are two different things the way I understand it. The degree of conicity can raise or lower the cut-off frequency which will determine the overall character of the sound. The proportionate size of the tone holes to the bore can do the same thing. If you take either in isolation, a change in the conicity or tone hole sizes will change the cut-off frequency thus changing the point at which the higher partial components are allowed to escape through the tone holes or are reflected back in the bore. You are not actively changing the partials themselves. They are what they are in relative strengths for any given frequency (resonance of the bore to length ratio). The conicity in combination with the tone hole lattice determines the point at which more or less of those higher partials are allowed to escape the lattice or be reflected back internally...

However on page 66:
“making a cylindrical bore slightly conical divergent will raise its
fundamental resonance and compress the partial frequency
ratios from odd integer multiples.”

“slightly” ???????

How much “slightly” to make the first partial= *2? Is there
a point where the conicity is so great that the first partial is <*2?
I believe that is a reference to the function differences for a cylinder and a cone stopped at one end (clarinet vs sax) The presence of a cone changes the operating register from the odd integer multiples (Clarinet = 12th) to even integer multiples (sax = octave)

BOUNDRY LAYER EFFECTS

How much smoothing of the bore do you techs do?
cleaning (of course)
polishing?
tone hole edge smoothing?
octave-vent perturbation reduction?
Cleaning... yes
Polishing...rather difficult
Tone hole smoothing..Basically yes
Octave-vent perturbation reduction-mostly never..

Boundary layer effects are probably more prevelant for higher frequencies, Harmonics, Altissimo, etc..

OCTAVE-VENT LOCATION

Scavone and Benade indicate that the further a tone hole is from
the optimum, the sharper the tone will be.
Yes that is correct and can easily be demonstrated on a clarinet. Play a second register note and then open and close the register key but keep sounding the same register. You will hear the pitch deviation increase as you use tone holes furthest from the optimum in either direction. Because of the conicity of the Sax you need at least two whereas on clarinet you can get away with one. The cylindrical bore utilizes a register vent that can operate on a third of the total operating length. Conicity (reducing the odd intergers to even operations) makes the register vent operate to half a sounding length. Because that reduces the effective area for operation, you need at least 2 vents to cover an octave length. At least that is the minimum for simple mechanics with reasonable intonation when the effect of the register vent is considered....

Joe B
 

·
Distinguished SOTW Member
Joined
·
3,329 Posts
On register holes:

Benade is speaking about the total length of the octave register tube. Basically the pip should not be higher than 1mm above the neck wall. I am, however unclear about how the tube inserted into the neck (to avoid saliva fouling the pip) should be counted in this equation. Essentially the math is only done, in my understanding, for a side hole above the tube wall. My guess is that the length of the tubing inserted into the neck has some deleterious effect, but not as much as as the height of the pip above the neck.

OCTAVE PIP:

Read Benade's paper on this at:

http://ccrma.stanford.edu/marl/Benade/

go to "Writings">"The 70s" and look under 1973 for "Register hole design for cone woodwinds". Interesting stuff. I don't believe that placement affects the actual intonation much, but rather the efficiency of the detuning of the fundamental necessary to sound the second partial optimally. As the size of the register hole is increased, there begins to be an effect on the actual pitch of the second partial, but that is rather small at the diameters normally employed for register holes, in my understanding.

Benade points out that to be effective at all dynamics, the register hole must not only inhibit the sounding of the first peak (the fundamental), it must also detune it so that there can be no cooperation between the first and second peaks at higher dynamics. He says:

"To be effective a register hole must produce maximum noncooperation between resonance peaks if it is to displace a tone from low register to second register. It must also produce sufficient damping of the first resonance peak that its participation in an oscillation at low playing levels is disfavored. In practice, one finds that 2 or 3 % shifts in the detuned frequency of the first peak can be noticed by a player. Craftsmen are quite familiar with the problem of diagnoisng and of correcting such size of adjustments. Saxophones customarily use a fairly large-diameter vent hole of a length sufficient to produce proper detuning, but such proportioning gives inadequate damping to the detuned resonance. Vent holes of this type are known to cause all sorts of trouble, so that many saxophones practically ignore their regular keys. Furthermore, there is a great deal of difficulty with the intonation behavior of the instrument as a result of such register holes. If, however, one uses very short holes of small diameter, which optimizes both the low-level and the high-level playing requirements for the hole, once can get marked improvements in the response of the register key, and often considerably reduce the intonation difficulties as well."

BOUNDARY EFFECTS

Boundary effects only occur at ~1mm from the walls, so in a large diameter woodwind such as a sax such effects are really minimal (as compared to a recorder, for instance). Certainly it is wise to smooth any edges within a bore to reduce turbulence, but with thin walled metal instruments this is next-to-impossible while still maintaining structural integrity. You can certainly smooth tone hole edges in a clarinet (and top-end instruments such as Buffets have chamfered edges) but not in a sax or a flute.

CONICITY:

In my understanding, as the cone angle diverges from the ideal, the overtones of the note sounded deviate further and further from the harmonic series. If I am not mistaken, as the cone angle narrows the partials are spread, until at unity the first partial completely disappears and the second partial sounds at the register break. Higher cone angles compress the partials, so that the octave is sharp, the octave + a fifth is sharper still, etc. If you want the math I can probaby find the formulae that describe the function, but it is not easy math as I recall.

HTH,

Toby
 

·
Distinguished Technician & SOTW Columnist. RIP, Yo
Joined
·
17,204 Posts
I once read a technical dissertaion on acoustics of the trumpet, whiuch are possibly relevant here.

Basically, the trumpet is cylindrical tube, effectively closed at one end, like a clarinet. Hence, it ought to produce only odd harmonics, like a clarinet.

However because of some very clever acoustic jiggery-pokery in the shape of the mouthpiece cup, and the flare at the open end, these harmonics are so distorted in pitch that they are made to fit the odd-and-even pattern of a flute or violin.

So I would assume that altering the taper, ie 'flare" of a sax would also alter the frequencies of the higher overtones relative to the fundamental.
 

·
Distinguished SOTW Member
Joined
·
3,329 Posts
Have a look at Benade for a good dissertation on woodwind acoustics:

http://ccrma.stanford.edu/marl/Benade/

"Writings">"The 70s"--check under 1977 for the 83-page paper "Acoustical evolution of wind instruments"

Check the bottom of pg. 3 for the equations relating to the partial shifting in a cone as compared to a cylinder. Indeed, a cone slightly raises the fundamental frequencies as compared to a cylinder, and compresses the overtones progressively as you go up the series.

Toby
 

·
Registered
Joined
·
50 Posts
Discussion Starter #15 (Edited)
Thanks!

I really find all of your inputs informative and exciting. I am carefully
reading your comments and studying the references. I hope we can
keep it going.

Some preliminary observations:

OCTAVE-VENT

I need some definitions. Is the "pip" just that part of the vent
that sits outside the wall?
For now I am going to define the vent-length as the distance from
the bottom of the vent tube to the top which contacts the pad.

As I understand, to prevent the fundamental from sounding you
short it to the outside. This is done by placing a low resistant
hole on the bore at 1/2 the length from MP tip to the pertinent
tone hole. A “low resistant” hole is one with a short vent-length
and a large radius. However, at loud levels, this may not be
sufficient and, in addition, the frequency (phase?) needs to be
shifted by introducing a reactive component to the vent.

If I were designing a sax, I would start with a short-as-practical
vent-length and a large hole. I would, then, blow loudly and reduce
the radius of hole until the octave was stable.

Presumably, you would wind up with a radius that conforms with
the requirement for a proper ratio between resistance and reactance
that shifts the fundamental frequency 25%, as indicated by Benade.
If I understand the acoustics of a "Tube of Small Diameter" the
diameter of the tube affects the ratio of resistance to inertance,
but the length does not affect that ratio. Consequently, leave it short.

Doesn't moving the vent, only, affect the octave pitch and not
the lower register pitch which you might not want to change
by using pad height or shims. Surely, there has been some
experimentation…………………………

Is it right that the oboe uses just a hole in the bore for an octave-vent?
Hence, Benade's 1mm.
Question: Do oboe players not salavate?


More later,

jim
 

·
Distinguished SOTW Member
Joined
·
3,329 Posts
The pip is the whole shebang--whatever gets put in the hole drilled in the neck.

No, you don't want or need a large-radius vent hole. You only need to interrupt the fundamental at 1/2 the wavelength which effectively kills that vibratory mode. The hole doesn't need to be very large to do that; in fact if it is large it starts to detune not only the first but the second partial upwards, so you want to keep the hole very small. The problem is, as I read it, that if the vent tube is long AND the hole small, there is still too much cooperation between the lower partial and the second partial, so that at loud dynamics there is the tendency to break back down to the fundamental. So the idea is not to detune the note too much with a large vent hole, but rather to keep the hole small and make the length of the vent very short.

I don't think you end up shifting the phase--I guess that is locked by the effective ends of the tube. You just need to shift the frequency of the fundamental slightly in relation to the frequency of the first partial.

It appears that the ideal is to have the vent hole sitting almost flush with the surface of the neck, with the hole small enough not to detune the partials upwards.

Where did you see Benade saying shift the fundamental 25%? That is a huge amount. A couple of percent seems to be sufficient to inhibit cooperation between the two modes at loud dynamics.

I believe that after the pad clears the hole by about 30% there is no more effect, so the pad height over the hole is basically not a factor with a register hole.

If the vent is small, as it should be, it does not affect the pitch of the second mode. As you move the vent away from the ideal position (1/2 the wavelength of the fundamental) you progressively disinhibit the fundamental from sounding, especially at higher dynamics. The effect becomes more like a leak than a register vent, jumping to the second mode at loud dynamics but creating big response problems with both at softer dynamics, I believe. But it definitely does not shift the pitch of the second mode, or it shouldn't if you follow Benade's advice.

The oboe uses a metal sleeve with a small vent (inserted into a larger hole) which extends only marginally above the body. There is no tube inserted into the bore, since the holes are on the top of the tube. Occasionally the water inside the tube follows a path which fouls one register vent or the other, especially when the horn is held almost vertically. The solution is to blow the water out, then put a small patch of bore oil arond the hole with a turkey feather, which changes the path of the water.

Actually , there is no need to have a long vent inside the body on saxes, as the water is definitely going to be flowing along the bottom of the neck. It is totally stupid IMO. You need such a beast on a Boehm clarinet, which traditionally has the register vent on the bottom (also rather stupid), but definitely not on a sax. Nor would it be difficult to make the actual position of the hole 1mm above the neck.

Toby
 

·
Registered
Joined
·
50 Posts
Discussion Starter #18
pips

Hopefully, we can soon come to a consensus about the requirements
for effective octave-shift venting.

Do we agree?:

1.The octave vent hole should be positioned so as not to collect
water (on top).
2. The pip should be as short as practical.


Still being debated:

1: Best diameter of the pip hole.
2: The effect of the pip location, up and down the bore, on pitch.

The “25% frequency shift” can be found on page 1 of:

http://ccrma.stanford.edu/marl/Benade/

go to "Writings">"The 70s" and look under 1973 for "Register hole design for cone woodwinds".

Also on page 457 of his “Fundamentals of Musical Acoustics”.

He talks about the shift in frequency of the, desired, mode-2 partial (quasi-
2nd harmonic) on page 459.


I am having trouble understanding “intermode cooperation”.

jim
 

·
Distinguished Technician & SOTW Columnist. RIP, Yo
Joined
·
17,204 Posts
"BOUNDARY LAYER EFFECTS How much smoothing of the bore do you techs do?"

Smoother the better? Hmm. So why is shark-skin rough. Isn't it because the friction between the surrounding fluid and the fluid trapped in the roughness, is less than the friction between the surrounding fluid and a smoother surface? And wouldn't the same apply to a woodwind bore.

And is our aim to reduce friction here or not?

I have heard of oboe players dragging steel wool through their brand new oboe to take the polish off it.

Too many questions, and insufficient knowledge base in this writer.
 
1 - 20 of 24 Posts
Top