These videos have helped me to better understand how the reed vibrates and give an image to the sound that until now I could only imagine.
From the study of the videos, I believe that the most fascinating fact that emerged is the composition of the cycle of vibration of the reed. Before this experiment, I assumed that a cycle was composed of only two movements. One of closing to the closed phase and one of opening to the maximum amplitude. It is evident that the vibration is more complex. The intermediate phases between the closed phase and the maximum opening are decisive in creating the sound of the reed. Unfortunately, with the equipment available to me, a detailed analysis of the single phases of the cycle is impossible. A more precise measurement could further enrich the knowledge about the reed.
By comparing several reeds, it is possible to observe some differences, but it is difficult to establish what consequences they may have on the sound with the data currently available. The vibrational motion that I was able to observe remains similar between them. I think the differences may lie in the duration and amplitude of the movements, but with the current setup it is not possible for me to reach that kind of detail.
During the experiment I found that for the vibration of the reed to begin, I needed to create a relatively high pressure, reaching as high as 120/130 mBar. Once the vibration began, the pressure inside the box began to rise very quickly and I had to immediately decrease the inlet airflow to avoid exceeding 150 mBar and activate my safety valve. Once I decreased the pressure, I could easily achieve a relatively stable vibration around 100 mBar. Decreasing the pressure further there was a definite point where the reed changed its vibration frequency dramatically. At that junction point of just 2 or 3 mBar the reed would emit a croaking, unstable vibration. Decreasing the pressure further, the reed's pitch continued to drop, and at this level of pressure, it was very difficult to obtain stable frequencies for more than a few seconds. Reducing the pressure again, the reed stopped its vibration at a pressure of about 80 mBar, much lower than at the beginning.
These pressure measurements are indicative and are not fixed values. With each new test, even with the same reed, these pressure values vary slightly and therefore it is not possible to state them with certainty. What is clear is the general behavior of the reed. To start its vibration it is necessary to create a relatively high pressure inside the box, but to maintain it it is possible to use much less pressure. The minimum pressure point where the reed stops its vibration is almost half of the pressure needed to start it.
From these observations I deduce:
As explained previously with my setup I am only able to precisely control the airflow into the box and not directly the pressure. Noticing that with the beginning of the vibration of the reed my pressure in the box tends to rise very fast I deduce that the outflow has suddenly reduced. This is caused by the closing of the reed opening during vibration. The blades are pushed against each other by the drop in pressure generated by the airflow until the flow is completely obstructed. This is the moment of the closed phase. The greater the pressure in the box, the greater the velocity of the airflow through the reed. This high speed has direct consequences on the low pressure that is generated between the two blades of the reed and therefore on the intensity of the force that sucks the blades towards each other. This causes the reed to have smaller, faster vibrations. As a bassoonist I recognize this effect in the registers of the instrument. The high register requires a lot of muscle activity to sustain it, but it is possible to play musical phrases of several seconds without the need to breathe. In contrast, with lower pressure the reed has a lower frequency, slower vibration but a greater amount of air required. Playing the bassoon in the lower register fully reflects these sensations. Not much physical effort is required to sustain the sounds, but it is necessary to take breaths more often.
Interestingly, more air and pressure are required for the beginning of the reed vibration than for its maintenance and end. This fully confirms the difficulties for us bassoonists in the attack of a note, especially in pianissimo. In order to obtain an attack, it is therefore necessary to have a peak of energy that must immediately drop in order to continue the sound in the same sonority, color and intonation. I find very interesting the awareness of the behavior of the reed during the beginning of its vibration. The clean attack of a note is easily one of the most difficult aspects to perfect. In an orchestral player's career, this skill is critical to blending one's sound with that of the other instruments. Knowing how the reed behaves in a neutral situation, without the bassoonist's intervention, can help us understand what the instrumentalist's role should be in achieving the desired sound. Fortunately, unlike my box, the bassoonist can take advantage of the lip setting to make the task easier.
Another aspect that I find interesting to report is that I was able to get a stable vibration for only a few seconds. After that, the reed would gradually begin to increase in frequency. I hypothesize that these variations are due to the unstable nature of the reed. While a reed is not vibrating it tends to settle into the most stable position that its structure allows. When it is stressed and put into vibration this stability is lost, and it tries to find another one. The material is therefore in constant motion and continues to settle for the situation in which it finds itself. In addition, changes in humidity and temperature further influence the process. In my situation, for example, the continuous flow of dry air from the compressor quickly dried out the reed, causing it to change even faster. We bassoonists notice many of these changes in the reed as we play, but I have always felt that the main differences felt in vibration during a performance are a direct response to the countless air changes, lip tension and tongue flicks that are used while playing. However, I have noticed that the reed is unstable even in a neutral situation with a continuous and steady flow of air. As a bassoonist I understand that it is essential to always be ready to adapt to the situation. It is not possible to anticipate and predict everything before a performance. While practicing, it is important to experiment with as many situations as possible so as not to be taken by surprise when the reed inevitably vibrates in an unexpected way. It is most effective to remain dynamic, to go along with and incorporate reed changes into your instrumental technique.
The junction point of just 2 or 3 mBar that results in a pitch change in reed vibration I believe is what we bassoonists call the "crow" of the reed. When we want to test the richness of vibration of a reed we blow in a particular way inside the reed, and we can get this croaking sound. From the ease with which we produce it and its quality we can get more feelings about the characteristics of the reed.