Mouthpiece Buzzing Confusion

Nicholas Drozdoff

Mr. D's Music

Shedding Some Light On A Slightly Misunderstood Topic

Aside: This article is possibly a little controversial. Good. I hope to get a few people a little worked up. I'll probably be one of the ones getting worked up! However, it is important understand what is going on. Please, if you don't understand the discussion below, use my email links to contact me. Also, if you find egregious mistakes, don't let me get away with them! I welcome the intellectual give and take. The italics below represents reader induced corrections.

Possible Misconceptions About Mouthpiece Buzzing and Other Stuff!

I have been intrigued by a statement of physics made by many good trumpeters/teachers. I have heard two fine players who teach trumpet make the following claim: when you play a note on trumpet and try to sustain the tone while removing the mouthpiece from the horn, the note should stop because of the removal of the feedback from the horn. In fact, one of these teachers even claims that one shouldn't actually be able to properly sustain a tone on a mouthpiece when it isn't in the horn!

This is not quite complete. What we have here is an incomplete understanding of physics. While it is possible for some trumpeters to find that their buzz stops when the trumpet is removed from the mouthpiece, it is just as possible to find trumpeters who can sustain a buzz while playing and removing the horn and then even the mouthpiece, buzzing only the lips! It turns out that there are rather complex models for understanding how a trumpet and trumpeter works.

What in fact happens is this: as the mouthpiece is removed from the horn while you are still playing the note, the feedback is indeed removed, thereby removing the support of resonance. What this physically means is that now you have no "slots" or notes that will pop out discretely. You can play a continuum of pitches for a rather wide range. It is also harder to play due to the fact that, without resonance, it is "all you" or your lips making the tone. The horn is no longer helping. The mouthpiece, by itself, acts as a tiny "megaphone" of sorts. There is no reason whatsoever that you shouldn't be able to sustain a tone while doing this. You will need to concentrate in order to maintain the tone as this resonant support disappears.

It might feel a little funny for some players to feel the feedback suddenly disappear. OK, it might feel more than just a little funny and they may unconciously stop the lips from vibrating by opening the aperature between the lips too much in the process. This will stop the note, but it is the player allowing the note to stop as a result of the resonance being removed. Again, you will need to concentrate on maintaining a focus of the aperature and the muscles will work harder, but this is not impossible to do.

Here is a quote from a reader who wanted to shed some light on all of this. "Think for a moment of the analogy of pushing a swing - it takes very little effort, exerted at the right time, to keep the swing oscillating with a fairly high amplitude. This is because the mass and the rope length combine to form a resonant system, which helps us out. Now imagine manually trying to lift the person and the swing up and down at the same rate. Even if you don't try to lift them as high (buzz softer than you play the trumpet) it is still much more work." (name withheld pending permission) The analogy that I might use would be a mass on a spring bobbing up and down. We don't have to use much effort to keep it bobbing up and down at the resonant frequency as long as the spring is there. We do, however, need to exert more effort to keep the mass bobbing up and down manually at the same frequency. However, it is not impossible to do, just tougher.

In physical analysis of the spectrum of resonance produced by trumpets a device is used to energize the horn electromechanically. The device is called a salpignometer. They were used by the likes of Arthur Benade and William Cardwell, both expert acousticians and physicists on brasswinds. In the best device the horn is energized by a transducer that places a membrane over the mouthpiece sealing it (closed end resonance). The membrane is exposed to a chamber that is driven by a small speaker. The sound pressure level is controlled by a small feedback loop and voltage controlled amplifer. If the mouthpiece is removed from the horn while this device is playing it, it doesn't suddenly stop producing a tone. It simply stops resonating. The tone continues, but it is only a "mouthpiece" tone. Now as, explained, the device is designed to do this. You're lips are not. The feedback control loop maintains the tone as you remove the mouthpiece from the horn. In the case of your lips, your ears and the physical feel provide the feedback control loop which will enable you, with a little concentration, to maintain the tone. You make the necessary adjustments to do so. The device simply tells the amplifier to the speaker to turn up or down, as the case may be.

Now in an article written in the International Trumpet Guild Journal , Volume 25, Number 4 for June of 2001, Thomas Moore (associate professor of physics at Rollins College in Winter Park, Florida) points out that it is very possible for a trumpeter to play a note on a trumpet, and, while still holding the note, remove the trumpet while leaving the mouthpiece on the face and the note will stop. He further demonstrates that the inverse occurs as well; that is, a player can place the mouthpiece to his lips, start a blow wihtout any buzz whatsoever and then put the horn on the mouthpiece while blowing and a note determined by the length of the horn, the lip mass and lip tension will suddenly appear. So what is the problem? Are there two ways of playing? Do trumpets work in more than one way?

I think the answer to the question is yes, trumpets and trumpeters function on multiple levels. Professor Moore's article points out that, while the lips may not be vibrating, per se, there is some very subtle noise emerging from the mouthpiece while the player is blowing it. Now, resonant systems are specifically designed to generate large reactions to very tiny inputs. Therefore it is not hard to conclude that some of this noise contained enough frequency content of the right note to generate sufficient feedback to the lips to cause them to vibrate at a particular note even though there was no apparent vibration of the lips while the player was buzzing the mouthpiece.

However, this does not mean that the acoustic driver concept is wrong either. Thinking of the lips as a driver designed to provide vibrational input to a trumpet of any desired frequency, much like a speaker driver is another valid way of thinking of how the lips are working. The big mistake is to make the conclusion that while playing a trumpet, the lips aren't really vibrating. I have heard reputable trumpet teachers actually make this statement and then do the above mentioned demo (removing the horn from the mouthpiece while playing it and listening to the note drop out) to prove that the lips don't really vibrate while playing the trumpet. That simply is not true! What is the case is that it is possible to blow a mouthpiece in such a way as to have no intial vibration. However the addition of the horn which then begins to resonate (due to feedback) on a note included in the noise of the air escaping between the lips CAUSES the lips to vibrate.

Another Statement That Needs Clarification:

Another mistaken statement made by some trumpeters is that there is a pressure node at the mouthpiece while they are playing. This is impossible!

The problem is, many people don't understand what nodes and an antinodes are. It would help to clear that up.

A pressure node is a region in which the air pressure is constant. It is the same as the ambient pressure in the room. A pressure antinode is a region in which the pressure is not constant but in fact is wildly changing from below ambient pressure to above ambient pressure. It is doing so at the frequency of the pitch being produced.

Now let's consider what the lips are actually doing when playing a trumpet. When one produces a note they start by putting the lips up to the mouthpiece. The lips are initially closed and the horn is sealed at one end (closed end resonance). The player then increases the air pressure in the mouth behind the lips. He/she does so with the muscles around the ribs and the abdominals (it was pointed out by a reader that the diaphragm only functions on inhalation, NOT expiration, hence this correction). Depending on the muscular tension holding the lips together, the pressure reaches a point at which the lips burst open, releasing a burst of air, a high pressure pulse, into the trumpet. Again, due to the muscular tension in the lips, they slam shut because pressure drops suddenly in the mouth. The lips are now held closed again, the pressure builds up and the process repeats again.

Now, it should't be a big jump to realize that a pressure antinode is present at the mouthpiece. The air pressure is varying wildly from a high pressure produced when the lips burst open to a low pressure caused by Newton's laws when the lips are closed.

A pressure node is always present in the vicinity of the bell. I say in the vicinity because different notes reflect from different points in the horn, but that is the subject of another essay.

In Conclusion

I have a great deal of respect for the musicians who have occasion to make such mistakes. What bothers me is that they occasionally inadvertantly influence students erroneously. If they are indeed true academics and intellectuals, they should be willing to accept correction and modify their positions. They should be glad to actually know that they can make statements based on correct information giving credence to their academic positions. In short, there is nothing to be lost by getting it right. Brused ego notwithstanding, that must, of necessity, include me. By heeding the well thought out comments on the part of readers and peers I hope that I have been enabled to improve this page and not be allowed to inadvertantly participate in erroneous influence myself.

Nick Drozdoff

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