Untuned student instruments

[Chuck(G)]

If you're wondering about the flatness of the 2nd partial (low Bb on a BBb) tuba, a lot can be explained by the bell effect, I think.

A narrow bell will tend to flatten the lower partials more than the upper (this has little to do with the size of the bell flare, but rather the taper of the bell itself). A wide bell + bottom bow taper will tend to make the lower partials sharper.

I think the stinky 3rd partial on many 6/4 blunderblusses is less of a matter of the 3rd being flat and more of the 2nd being sharp (think about it). As you go up the series, the bell effect matters less, but at the bottom it can make substantial difference.

For mid-range problems, the bell will have little or no effect on intonation.

This is my experience, at any rate.

On some very old big European tubas, the taper is so wide that the intonation is almost unusable. Simply rolling up a piece of cardboard into a more-or-less cone shape and shoving it down the bell can do wonders.

[MaryAnn]

I've seen this on 3-valve piston Eb tubas and on cheaper, front-bell Eb alto horns. The "octave" is rather securely a 9th, and basically impossible to lip into tune. Since I don't personally have this problem (the octave being a 9th) on any of my better instruments, I've always labeled it a construction design problem and not purchased said instruments. So it's not the kids' fault, this time.

MA

[Chuck(G)]

...and old gigantic Martin BBb tubas don't have this problem at all because ___________ ...

While they look big, I don't think they're as large as, say a 20J throught he bottom-bow-bell branch. They're wound a lot tighter and are more squat, so they look bigger, but start at the end of the bell and measure the diameter at intervals going toward the mouthiece. I think you'll find they're smaller.

Just a guess, Joe.

[Donn]

If you're wondering about the flatness of the 2nd partial (low Bb on a BBb) tuba, a lot can be explained by the bell effect, I think.

Well, for my Alex baritone, it isn't exactly the 2nd partial, it's only the 2nd partial Bb. And maybe A, but G and below is fine.

Anyway, more compelling evidence that it isn't the bell: I fixed it!

I really have made some attempts to clean this thing out, but this evening just on a whim, I ran magnet balls all the way through it. I could hear something fall out of the bell end afterwards, like large grit, probably nothing that could have made any difference, but at any rate, now the Bb comes up "A#" on the tuner, when before that procedure it was more like A.

Now I just need to get the valves moving a little more freely, and figure out how to deal with the absurd ergonomics.

[Chuck(G)]

Now I just need to get the valves moving a little more freely, and figure out how to deal with the absurd ergonomics.

I suspect that you might have closed up a leak somewhere.

I'm not saying that the bell's the only thing--just that it can be a contributing factor in bad low-range intonation.

Consider what the bell (actually the conical section after the valves) does acoustically over a simple striaght pipe. It raises the pitch of the lower harmonics more than the upper harmonics. A strongly flaring bell will tend to move the lowest harmonics up more than a bell that flares less strongly. If the bell effect is too strong, then the space between the 2nd and 3rd partials will be too narrow. Tuning one's instrument so that the 2nd partial is in tune results in the 3rd partial sounding flat.

See, for example:

http://www.phys.unsw.edu.au/jw/brassaco ... html#bells

Right now, I've got a big old Bohemian horn in the shop for work. I'm guessing that the 20" bell may not be original (I'm not sure, but the way it's attached makes me wonder). The notes toward the top of the staff are almost unplayably flat. I suspect that a smaller bell might correct that.

I'm doing a lot of guessing here, but the horn's going to be pulled apart for overhaul anyway, so I'll have a chance to check my theory out.

[Donn]

Consider what the bell (actually the conical section after the valves) does acoustically over a simple striaght pipe. It raises the pitch of the lower harmonics more than the upper harmonics. A strongly flaring bell will tend to move the lowest harmonics up more than a bell that flares less strongly. If the bell effect is too strong, then the space between the 2nd and 3rd partials will be too narrow. Tuning one's instrument so that the 2nd partial is in tune results in the 3rd partial sounding flat.

See, for example:

http://www.phys.unsw.edu.au/jw/brassaco ... html#bells

Not that I pretend to know anything special about this (remember - I am NOT a professional!), but I believe that web page is terribly confusing. Where he says

So one can think of introducing a conical or flared section of the pipe as raising the frequencies of the standing waves, and raising the frequencies of the low pitched resonances most of all.

... as best as I can make out from the preceding material, he's really saying that where cylindrical bores give you the "stopped pipe" odd partials, a conical bore gives you the full series. Clarinet vs. saxophone - it doubles the frequency of the lowest partial, etc.

I know it's hard to believe that he could have expressed himself so poorly in that case, but that's what I got out of the page he cites as background.

So I look forward to hearing about your upcoming empirical tests, because I put a lot more stock in that, than this.

[Anterux]

I have a bass trumpet that has the 2nd so low that is almost impossible to tune by lipping it up.

I also had an oval bariton that has the exact same problem. I sold it. Both are chinese made.

I'm talking about the 2nd partial. Not the foundamental.

I was hoping someone has an explanation for this, if not a cure... But reading the posts before, I thing it's kind of obscure yet...

Please note that the bass trumpet and the oval euphonium although both in Bb, they are completely different in terms of bell shape and size, conical shape, tube diameter, etc.

I would like to understand more of this...

Kind Regards.

[Dean E]

. . . but at any rate, now the Bb comes up "A#" on the tuner, when before that procedure it was more like A. . . . .

I have one of the cheap Korg tuners, and I assume that it is not measuring the fundamental low notes, but rather overtones. I'm tempted to buy a strobe with a real microphone to pick up and analyze the actual note--not the overtones.

[Allen]

Consider what the bell (actually the conical section after the valves) does acoustically over a simple striaght pipe. It raises the pitch of the lower harmonics more than the upper harmonics. A strongly flaring bell will tend to move the lowest harmonics up more than a bell that flares less strongly. If the bell effect is too strong, then the space between the 2nd and 3rd partials will be too narrow. Tuning one's instrument so that the 2nd partial is in tune results in the 3rd partial sounding flat.

See, for example:

http://www.phys.unsw.edu.au/jw/brassaco ... html#bells

Not that I pretend to know anything special about this (remember - I am NOT a professional!), but I believe that web page is terribly confusing. Where he says

So one can think of introducing a conical or flared section of the pipe as raising the frequencies of the standing waves, and raising the frequencies of the low pitched resonances most of all.

... as best as I can make out from the preceding material, he's really saying that where cylindrical bores give you the "stopped pipe" odd partials, a conical bore gives you the full series. Clarinet vs. saxophone - it doubles the frequency of the lowest partial, etc.

... ...

For those of us with science or engineering backgrounds often have trouble explaining things to those with different backgrounds. None the less, I'll try, with a somewhat different approach.

Brass instruments all have varying tapers, including sections with cylindrical, conical, and more complex tapers (especially the bell section). None of the simple shapes gives a musically useful series of resonances. A physicist will frequently analyze a complex object in terms of simpler objects or shapes, and that's what the referenced web page does. This approach can seem confusing to people who are not used to this approach.

A tuba can be analyzed in terms of a cylinder that is closed at one end, but with extensive modifications to shape: the mouthpiece with its cup and venturi, the leadpipe, the cylindrical section through the valves, the expanding bore, the bell stack. The analysis problem of the entire tuba seems large and impossible. However, dividing up the problem into smaller pieces makes it seem more possible.

To me, the miracle is that the open notes of a tuba are anywhere close to the harmonic series. Anything a craftsman does to affect one partial has an affect on others.

Cheers,
Allen

[Allen]

. . . but at any rate, now the Bb comes up "A#" on the tuner, when before that procedure it was more like A. . . . .

I have one of the cheap Korg tuners, and I assume that it is not measuring the fundamental low notes, but rather overtones. I'm tempted to buy a strobe with a real microphone to pick up and analyze the actual note--not the overtones.

Actually, electronic tuners measure the repetition rate of the incoming sound. [Technically, they measure the period, then mathematically convert that to frequency.] At a given pitch, this repetition rate would be the same for a sound with or without any fundamental. A strobe tuner would not give you any more or better information about the note's pitch.

A strobe tuner can give you information about the overtones of the note you are blowing: whether the overtones are lined up with the harmonic series. Some people think that this is useful information. I don't have an opinion on whether that's better than just using your ear.

Cheers,
Allen

[Rick Denney]

[Technically, they measure the period, then mathematically convert that to frequency.]

Really? I would have thought they use a series of flip-flops to divide the frequency into the range of a quartz-controlled oscillator, then digitally count pulses in each reference interval, and then average a series of those short reference intervals into a longer sampling period to filter out noise. But I'm just guessing. It takes a fraction of a second for my tuners to respond to a note, and that makes me thing there is a sampling period.

I love strobe tuners, not so much because of the information they give about the harmonics, but rather because they can help explain what I hear when a note satisfies a Korg but not my ear. Our sound can have overtones that change the pitch perception. But a strobe tuner provides no guidance--only measurement. When the sound is right, it doesn't matter what the strobe says.

Rick "a veteran of pulse-counting systems, but not at sound frequencies" Denney

[Chuck(G)]

Really? I would have thought they use a series of flip-flops to divide the frequency into the range of a quartz-controlled oscillator, then digitally count pulses in each reference interval, and then average a series of those short reference intervals into a longer sampling period to filter out noise. But I'm just guessing. It takes a fraction of a second for my tuners to respond to a note, and that makes me thing there is a sampling period.

There are many ways to measure frequency. In audio frequencies, the simplest way is to use a zero-crossing-detector to (and maybe a low-pass filter) to get at the fundamental. After that, you can do things a number of ways. You can have the measured signal trigger a high-frequency counter (driven by a reference) which gets you a quantity that's directly proportional to the frequency being measured. Or you can have the measured frequency count while a low frequency reference is used as the trigger, which gets you a quantity that's proportional to the reciprocal of the frequency.

There are analog methods also. For example, you can simply have the measured (and level-normalized) signal charge a capacitor during a certain interval and simply measure the voltage across the cap at the end of each interval.

For very close measurement, one can use the error voltage developed by a phase-locked loop as an indicator of the difference of the measured frequency and a reference. One might even use this method as a strobocon.

I've got an old Seiko that works as a semi-Strobocon by scanning a row of LEDs using a reference frequency (which depends on the note you're trying to measure). The audio signal is fed (after filtering) right to an amplifier that drives the LEDs. When you see a stationary pattern on the LEDs, you're in sync with the reference. Yes, you can also see harmonics very easily.

I don't see what the magic is in the old mechanical strobocon tuners. The same thing can be done electronically at much lower cost and with higher accuracy--and in a smaller, lighter, package.

[Allen]

Thanks to Chuck(G) for his fine expansion on the topic.

I have sent a PM to Rick, so the majority of TubeNetters don't have to be subjected to discussions and descriptions of the innards of tuners. If anyone else is interested in the methods and electronics involved in making tuners, PM me.

Cheers,
Allen

[Rick Denney]

I don't see what the magic is in the old mechanical strobocon tuners. The same thing can be done electronically at much lower cost and with higher accuracy--and in a smaller, lighter, package.

And cheaper. Maybe the lack of one on the market demonstrates that it isn't that helpful. But I'd like to have one.

What Allen was too nice to say in public in order to refute me is that a sampling method requires a long sample, because tuba frequencies are too low. Being off by even one pulse would make a bigger difference than a 1-cent tuning change for tolerable (a second or less) sampling periods. The approach he described is to turn it around and count fast clock pulses between audio frequency pulses. Easy to do digitally and as accurate as the precision of a clock--he mentioned a 1 MHz clock in his message to me.

Rick "who brought a pocket knife to a gunfight" Denney

[Chuck(G)]

The approach he described is to turn it around and count fast clock pulses between audio frequency pulses. Easy to do digitally and as accurate as the precision of a clock--he mentioned a 1 MHz clock in his message to me.

My HP low-frequency meter (measures out to about 5 digits into the sub-Hz range) uses a 10 MHz clock--and it's 1970's vintage. Nowadays you could easily use a 100MHz clock--or faster.