The appearance of the sound

Giangiacomo Sala

Luthiers throughout the centuries have always tried to adapt and improve the characteristics of the instrument to the needs of the musicians of their time. I myself, as a bassoonist, am also a luthier of my own reeds and in their construction I try to help my musical needs as much as possible. It was in trying to improve the characteristics of my reeds that I felt the need to know better how they work. I wanted to understand how my manipulations on the reeds went to influence their functioning and consequently the sound generated. So, I decided to observe a reed while it vibrates and understand its movement. I want to repeat the experiment on different reeds to note any similarities and differences.

EXPERIMENT

In the experiment I did, my attention was focused on how the reed vibrates. What I was most interested in was the movement of the tip of the reed as it vibrates.

How does the vibration happen?

From a physical point of view, the vibration of the reed is triggered when an airflow of sufficient velocity and flow rate passes through the reed. This is because the air, passing through, creates an area of low pressure that sucks the two blades against each other. At this point the opening of the tip is closed and the air is no longer able to pass, and the suction effect is lost. The elastic tension of the cane pushes the two blades to reopen and return to their initial stable position. However, this causes the reopening of the passage for air to flow back into the reed and renew the cycle. These passages are happening at very high speeds. If the sound emitted by the vibration of the reed has a frequency of 442Hz this means that the reed completes its vibration cycle 442 times per second. Observing these vibrations at such high speed is a challenge.

How to observe?

In order to observe the vibration motion of a reed, the best way is to obtain a film. For this purpose, some problems arise. The optimal method would be to observe the reed being played by a bassoonist but obtaining images from inside the mouth is complicated. The limited space available and the fact that the speed of vibration of the reed is too fast prevents normal cameras from capturing its movement. Filming of this kind requires instrumentation that is too specific and difficult to find. So, I decided to simplify the conditions by creating a reed observation box. In this transparent and conveniently sized box, it is possible to set a reed in vibration with the help of a compressor and more easily obtain footage. At this point remains the problem of the speed of vibration of the reed. Although now quite common, the use of high-frequency cameras is complicated and very expensive. For this reason, under the advice of Professor Peter Pabon, I opted for the use of a strobe light for filming. With this intermittent light it is possible to produce pulses of light and obtain an effect comparable to slow motion as well with a normal video camera.

Tip

Tip