There is no such word as dynamicism, so I just made it up! I haven’t talked about the subject of dynamics in the past but I have a definite take on them. I think of dynamics not as different volumes, but the same dynamic moving from place to place, near and far. I imagine a forte dynamic being close and full without being harsh. If a mezzo-forte dynamic is called for, I visualize the forte being moved a suitable distance away, losing none of the intensity and life in the sound. If a piano dynamic is called for, the sound moves further away, still keeping all of the intensity of the forte. In other words the timbre of the sound doesn’t change, only the proximity. The piano and pianissimo have as much projection as the forte, only not as present.
A good way to achieve this coming and going is to change the size of the airstream. Generally speaking, when playing forte the object is to fill the entire cup of the mouthpiece with the airstream.
When playing softly the object should be to aim the airstream directly into the throat, bypassing as much of the cup as possible. Of course any air entering the mouthpiece probably goes everywhere, but lucky for us the brain is a marvelous manipulator. Just the act of thinking of aiming the airstream in a certain size and direction causes a dramatic change in the type of sound produced. When playing a forte dynamic and using the entire cup of the mouthpiece, the embouchure will open slightly, increasing the size of the airstream. This opening will cause the airstream to slow down a fraction, thereby creating a rounder, mellower sound, desirable in the louder dynamics. Conversely, when mentally bypassing the cup and aiming the airstream directly into the throat of the mouthpiece for the softer dynamics, the embouchure will automatically narrow, increasing the rate of flow. This will insure that the sound of the softer dynamics have the same intensity and focus as the louder volumes.
It must be said that when an instrument comes from the factory it tends to produce a laser-beam type sound at the louder dynamics, and a fog-horn type sound at the softer dynamics. It is our job to reverse this. In order to get the same sound at different dynamics it is necessary to do different things to compensate for the natural tendencies of the instrument. As a dynamic gets softer it is natural for the sound to lose focus. As a dynamic increases in volume, there is a natural tendency to become more concentrated. If this is not accounted for by the players actions, the desired sound at these different volumes will be the opposite of what is needed for the right sound in a phrase.
When playing the louder dynamics the airstream naturally moves at a faster rate. As the dynamic decreases it is important that the rate of air flow not slow in exactly the same rate as the dynamic. The air flow should actually increase in speed in relation to the dynamic getting softer. In other words think faster air when playing soft and slower air when playing loud. The mental image I described regarding aiming the airstream into different places of the mouthpiece will be of great help in achieving the desired type of sound for each dynamic level. If a graph was drawn of the relationship between volume and air stream, it would show that the air actually should move faster in relation to the volume in soft playing than at forte and above volumes.
Another facet of producing the right sound for every dynamic is where the embouchure is in the mouthpiece. The tendency of most players is to be set too low for most dynamics, especially the softer ones. To keep the same focus and intensity of sound in the softer dynamics it is necessary to have enough firmness in the corners to have the airstream hit high up in the mouthpiece. A good way to insure that the embouchure is set with enough firmness in soft dynamics is to set for a third higher than written, then play the written pitch. The sound will be more focused and if the length of the note is long it will be easier to hold steady.
If a wider, less focused sound is called for, especially in the lower middle register, such as the solo from the Mahler 3rd symphony, the embouchure should be set slightly lower in the mouthpiece which will cause the airstream to hit lower and the entire cup will be used in producing the sound. Unless a specifically more unfocused sound is called for, such as the Mahler 3 solo, it is always prudent to play with the clearest sound possible. Since there is a certain size slot for every note, the best sound will be produced in the upper 3rd portion of that slot. Take middle Bb for example; it is one of the easiest notes to produce on trombone, however there is a tendency to under set the embouchure because of that ease, which causes the sound to emerge lifeless and dull, especially when coming from the low register.
Some players might say they want a big sound from their equipment and prefer a rather unfocused, dark-type sound. My answer would be; get a bigger horn and mouthpiece, and play it as clear and focused as possible. Again, my concept for choosing the type of sound that generally works best is; play the biggest equipment you can physically control, and play it as small and clear as you can.