The "Feel" of a Bore, Part 3
Several years ago I wrote an article called "The 'Feel' of a Bore". In that article I discussed the effects of bore size and taper on the amount of resistance a player feels. In the meantime I have reached a different insight into the matter. In the following article I will discuss my current views on the matter, which are quite different. I stress that what follows is my personal and current (2009) view on things.
Bore size is irrelevant
There are many factors that contribute to how "open" or "closed" a bore feels. The size of the bore probably only plays a minor role. Let's first discuss some physics. I am not an expert on the matter, but this is my understanding of how it works:
As the lips vibrate, a "standing wave" is created in the instrument. This wave has high pressure points (nodes) and low pressure points (anti-nodes). This wave is reflected off the open end of the instrument, the bell, back towards the player's lips. As a matter of fact, more than 90% of the energy of this wave is reflected back into the instrument. It is this that creates back pressure and allows us to maintain a vibration in the lips. Only a small percentage of the energy is "lost" out of the bell. This is the sound that comes from the instrument. The more energy that is reflected back into the instrument, the easier it is to maintain the vibration in the lips. The more energy that is "lost", the more difficult things become. The player experiences this difficulty in maintaining the vibration as resistance.
Interestingly, as we ascend the scale and play higher, the last node (high pressure point in the standing wave) sits further and further beyond the end of the bell. Consequently, more energy is lost and it becomes more difficult to maintain the vibration in the lips. This is why playing high is more difficult than playing low.
In other words, it isn't the air moving through the instrument that creates the sound. Theoretically, if you could vibrate your lips without breathing into the instrument, sound would be produced since the sound is caused by the standing wave of the vibration of the lips, not the air. In one test someone (I think it was a euphonium player, but I could be wrong) was asked to smoke a cigarette and play his instrument before exhaling thereby breathing/playing the smoke into the instrument. It took several minutes before the smoke started slowly wafting from the bell.
It follows that the internal volume of an instrument has little effect on perceived resistance of the instrument. This doesn't mean that the bore has no effect at all. It certainly does effect tuning (larger volume = lower tuning). It also effects the tone, atlhough that is more complicated than simply saying larger bore causes darker tone.
So what is relevant?
Several factors contribute to the feel of a bore, such as valve alignment or mouthpiece gap. In my own experience, the wrap, that is the shape of the instrument, and especially the main tuning slide, has a lot to do with it. The diameter of the bell seems to be involved as well.
Valve alignment. When the valves are out of alignment, which is usually in the vertical (on Conn instruments at least, rotational alignment is rarely a problem), a part of the outside of the valve intrudes on the tubing of the instrument. If you were to travel down the tube, you would run into a semi-circular ridge along one half of the tube. While the instinctive reaction is that this obstructs the airflow, that isn't the case as shown earlier (well, yes, but negligable). Air flow is not important. What happens is that a part of the standing wave that we create by vibrating our lips is reflected by the edge of the outside of the valve intruding on the inside of the tubing. This reflected energy is lost, since it isn't in the right place. As discussed above, the more energy you lose, the more difficult it will be to maintain vibration in the lips and the more resistance the player experiences.
Mouthpiece gap. As a rule of thumb, the further a mouthpiece is inserted into the mouthpiece receiver, the easier the low end of the range becomes and the more difficult the upper end of the range becomes, and vice versa. This is (in my experience/opinion) valid even for instruments that don't have a distinct "step" or "rim" in the mouthpiece receiver. Let me illustrate the effect with an example. I was playing a 1948 Conn 22B New York Symphony with a standard modern Bach-like mouthpiece gap. It played OK. I then bought a 1941 Conn 22B New York Symphony. Using the same mouthpiece, this thing was very stuffy compared to the 1948 22B. I thought it was a dog. Then a while later I read something and wrapped a piece of tape around the end of my mouthpiece. It improved the 1948 22B considerably, but the effect on the 1941 22B was astounding. Much better. I then had Kanstul make me a custom backbore with the inside shape of my old mouthpiece and the outside taper taken from an original Conn mouthpiece from that period. That improved things even further on the 1941 22B. It went from being the most difficult to play above the staff to the easiest. On the 1948 22B it didn't make much difference, perhaps increasing overal resistance just a bit, going too far the other way.
Wrap/Main tuning slide. Compared to a few years ago when I wrote the first "The feel of a bore" article, I have had the chance to play many more models of Conn cornet, trumpet and flugelhorn. From all these instruments I have reached the conclusion that, for me, the tightness of the wrap and probably especially the main tuning slide, appears to be very important. Allow me to explain.
Please take in mind that my own "standard" instrument is the late 1930's/1940's model Conn 22B New York Symphony. This is a 0.438" bore instrument. Compare that to a 20A Flugelhorn. It takes a cornet mouthpiece and after a short tube goes into a valve section at 0.422". Quite a bit smaller than the 22B. However, after the valve section you get a rather wide main tuning slide and an even wide bell curve. The bore expands significantly through the main tuning slide. For me, this instrument has too little resistance. Compare that to the 8A Victor "Slender model". The leadpipe, which is only slighly shorter than on most trumpets, gradually expands to 0.438" at the start of the main tuning slide (same as the 22B), and then expans to 0.468" through the main tuning slide. The valve section is 0.468". Looking at the bore size, this should feel much larger than the 22B. However, the main tuning slide is very narrow. To me, this instrument feels very similar to the 22B. Similarly, the Connstellation has a very wide main tuning slide (and bell curve), and to me feels much more open than the 22B in despite of it having the same bore size, 0.438".
Diameter of the bell. I haven't worked out yet in my own mind how the bell size relates to the feel of the bore, but comparing the 36B Connstellation and the 38B Connstellation in feel as well as in Conn's own literature, the diameter of the bell does appear to make a difference. The 36B and the 38B Connstellation are essentially the same instrument. The differences are in the 36B having lighter weight bracing and having a smaller diameter bell. Conn itself wrote in the 1960's catalogs that the 38B has a large bore feel while the 36B has a medium bore feel. The only plausible reason for this is the diameter of the bell, 4 5/8" versus 5 1/8". Seems reasonable if the difference in size of the bell opening allows a different amount of energy to "escape". I don't know whether the larger bell would allow more or less energy to escape and hence be more or less efficient than the smaller bell. For someone accustomed to an instrument such as the 22B with a smaller bell, the large bell 38B feels like a bottomless pit that takes a lot more energy to keep going. To someone accustomed to "large bore feel" instruments, the 36B with its smaller bell might feel rather stuffy. I don't know if the the person accustomed to the "large bore feel" is "overblowing" the smaller feel instrument that requires less energy (more efficient), or the other way around.