TubeNet

there is an interesting post on the otj forum about false tones and it gave me a question. why do false tones exist? i have seen several sites explain the physics of all other notes but no one goes into false tones.

NOT a scientific hypothesis from me, but more of a visualization...

Say that you take a rope or chain and hold it vertically, with the top in your hand and the bottom at a fixed point. Twirl it so that you generate standing waves, whether it's a single arc (fundamental) or the harmonics above.

Now, do it again, only leave the end free. The easiest, most stable harmonic has, in descending order, a large arc, a single node, then a free-swinging section about half as long as the upper arc.

To me, that's how a false harmonic works. The free end seems like it describes how a false tone sounds so different from its valved counterpart -- the resonance "reaches outside the bell", in a sense.

I don't need a scientific explanation to add legitimacy, though. I just play 'em.

daktx2 wrote:there is an interesting post on the otj forum about false tones and it gave me a question. why do false tones exist? i have seen several sites explain the physics of all other notes but no one goes into false tones.

I though I saw something on this on one of the physics of brass pages...

I though all brass had this. I've never picked up a (Bb) horn I couldn't play the false E/Eb on. No the truepedal Bb I've never managed to hit, but ever Bb tuba, trombone, baritone, trumpet and cornet I've played let this ring easily. Just luck?

-Thomas

Leland wrote:To me, that's how a false harmonic works. The free end seems like it describes how a false tone sounds so different from its valved counterpart -- the resonance "reaches outside the bell", in a sense.

That doesn't sound right to me. The pressure at the open bell is unconstrained and must average to zero. This provides a pulsed reflection back to the mouthpiece, and if the lips part in time with that reflection, you have a self-sustaining note; aka, resonance.

That the false tone is resonant is surely the case. That the pressure at the bell open avarages zero also seems assured. Thus, the false tone must be like a regular tone, in that it is a resonant reinforcement of the vibration of the lips in time with the vibration of the air within the horn.

The explanation that makes the most sense to me is that the parting of the lips is not in time with the main negative pulse, but rather in time with the third harmonic of the main negative pulse. The shape of the waveform includes the reflection back from the bell that provides enough of a pressure hole so that the lips can part easily, even out of frequency with the main part of the waveform. This creates a new waveform. Each single wave is reformed at the point of the lips parting, creating a tone different than the one implied by the length of the tubing.



In the waveform above (which is a low Bb--not a pedal or a false tone), you can see the main pulses, though the negative pulse is not at all obvious. When that main pulse reaches the bell, it reflects back to the mouthpiece. If the valleys in the reflected wave form are in time with the buzz, you get a sustained, resonant note. But notice the other valleys in the wave--each of these will reflect back, too. They correspond to overtones in the sound. If the next parting of the lips (in the buzz) happens on one of those valleys, it might still speak, creating a new pulse before the previous one had ended. This makes the higher frequency than the pedal.

The difference in feel is that the vibration of lips is being sustained by a secondary pressure valley rather than the primary one. Depending on the resonance of the instrument and the quality of the buzz, it can sound quite good. Above the second harmonic, there are notes in the harmonic series that are too resonant to permit a false tone. Thus, it would requires tremendous embouchure discipline to play an Eb false tone on a Bb tuba for the Eb just below the staff. The resonant F is too close, and will pull the note away from that Eb. Also, above the pedal, the sound has less of the upper overtones, and finding the secondary negative pulse is harder.

Rick "who plays false-tone low Eb's routinely on his four-valve Bb Holton" Denney

Have a look at:

http://www.phys.unsw.edu.au/~jw/brassac ... html#pedal

Note that for the C trumpet given as an example, the true funadmental is F below the pedal C (which doesn't correspond to a resonance at all!). The "false" F tone is actually twice the fundamental.

Use the fingering for a major 5th above the desired note and fire away.

In this old post from TubeNet, Dr. Young opines that the false tone is actually the real fundamental of the tuba.

0.7*f0 produces a tone that is 82.5 cents sharp of Eb 5 spaces below the bass clef staff on the BBb tuba. It would be better if the designers adjusted the shape to yield 0.667 f0 which would be a very good Eb. As I have said many times Jodi Hall proved experimentally at The C. G. Conn Research Lab that this is the real fundamental of the BBb tuba and that the pedal Bb is only a preferred tone. Brass instruments do not work as does a simple string which is used as a crutch in teaching open tone series to students who know little physical science. Years ago I had on old Wunderlich BBb tuba made more than a century ago by the instrument maker (at that time of the Chicago Symphony). It's fundamental was D five lines below the bass clef staff.

Leland wrote:NOT the resonance "reaches outside the bell", in a sense.

I like that --- thinking "outside the bell".

UncleBeer wrote:In this old post from TubeNet, Dr. Young opines that the false tone is actually the real fundamental of the tuba.

Great thread. Looking at the rest of it, I wonder if the same eff3ects might me why I have trouble with the pedal Bb and not the "false" Eb on the horns I've played. This past suggests that the bore design has a big effect on those. I need to try a very different hon and see if it changes for me.

ThomasDodd wrote:I need to try a very different horn and see if it changes for me.

I tried a VERY different horn for a summer -- my 2v King GG contrabass. As it turned out, I was the only instrument with less than three valves, so when many of our hornline exercises went down to three buttons, I bent the pitches to match (at least, as much as I could). I even did them with the spit valves opened up to knock out the horn's pitch center.

Additionally, I used false tones fairly often, which ended up being in the low C and Bb range in concert pitch terms. A GG contra's open false tone centers best at a low concert C.

So, by the time I got back to my BBb tuba, my low register came out much easier than before.

Switching to a 2-valve G contra is a little extreme for "trying out a different horn", though..

The false tone produced by a tuba seems very similar to the very lowest resonance of a loudspeaker horn, and unfortunately it's really complex to describe, but I'll try. Horn speakers are resonant to the same extent as tubas, but because the speaker driving the small end of the horn is controlled by a music signal rather than by the horn resonances, a speaker can play every note over a range of frequencies whereas a tuba is restricted to those frequencies at which the air column resonates. In a horn speaker, when a note is played near a horn resonance, there is more acoustic pressure on the speaker driver and it vibrates less to maintain more or less a constant power output. When a note falls between the resonances of the horn, the acoustic pressure is less and the speaker vibrates more. Large bass horns use this effect to their advantage to increase the output below the lowest harmonic of the horn, and it results in a wildly flapping speaker cone about half an octave below the lowest horn resonance if the resonances were to be tuned to a harmonic series (though in speakers they usually are not). The pressure waves returning from the horn are timed in such a way that they pull the speaker along rather than resist its movement.

Resonance is a good thing for tubas since they are driven by vibrating lips that interact with the air column to reinforce resonances. Lips like to vibrate when the pressure pulses returning from the resonating instrument coincide to the pressure pulses from the buzzing lips. It's kind of like hitting a squash ball over and over again againt the wall in a squash court. The racket has to swing so that it strikes the ball as it returns. In between resonances of a tuba, something else happens. The pressure pulses returning from the instrument are completely out of synch with the lips and try to stop the lip from vibrating, so the lips just naturally jump to a different harmonic that does resonate. It is extremely difficult to buzz a note on a tuba that is between two nice, resonant harmonics.

The false tone on a tuba is a special case since it is not between harmonics, but below them. The lowest harmonic on the BBb tuba is the low Bb. The pedal Bb seems to be a harmonic, but in fact is the lowest common multiple of all the harmonics above it. If you add up all the harmonics of a tuba from low Bb up, it makes a wave that repeats at a frequency that comes out to be pedal Bb even though there is no fundamental at that frequency.

It seems to me that there is a strong similarity between the wildly flapping cone of a bass horn speaker half an octave below the lowest resonance, and the false tone of a tuba half an octave below the lowest resonance. It could be that lips can vibrate weakly while being pulled along by the returning wave from the horn. If the normal operation of the lips is like hitting a squash ball as it comes toward you, playing the false tone would be like hitting the squash ball after it bounces off the back wall and is moving away from you. It's just hard to add much speed to that ball, and similarly the false tone resonance is weak.

Anyway, that's my theory.

-Eric