In the last post, I described the reed as a small musical instrument. Now I'd like to discuss how to tune that instrument, bringing out aspects in the sound for musical purposes. By this I don't mean getting the reed to play in tune (That would be a great topic for a later post!). Instead, I mean tuning as in adjusting the tone quality of the reed.
I think we'd all agree that a great bassoon tone is characterized by complexity. It has lows, highs and mid-range frequencies that all contribute to a robust sound.
We are all looking for that "Omni-Reed" that does it all -- plays high, low, loud, soft, dark, bright, etc. Indeed, a reed is a set of acoustical compromises, a little bit of everything. As I said in the last post, we really need about three different reeds when playing a three octave scale. Our lips and breath support simply manipulate one reed into different sizes and shapes.
Given that each piece of cane has unique qualities, we need to be able to adjust each reed a little bit differently to bring out those qualities of sound listed above.
So how do you tune a reed? If we go back to the Tonal Spectrum Chart, we can choose to weaken or strengthen a particular area on the reed to emphasize or de-emphasize parts of the sound.
- Leaving the rails thicker than usual will give greater support to the sides, keeping them more open when pressure is applied by the lips or air. If you read my previous post, you'll know why this brings out the lows in the sound.
- Making the second wire less round will prop open the sides of the reed.
- Making the spine less thick will make the rails thicker in comparison. This is why scraping the spine will brighten the reed, by the way.
- Leaving the spine even thicker than usual compared to the channels and rails will make the sides of the reed collapse more quickly when pressure is applied, leaving only the spine area open and vibrating.
- Making the wires more round will accomplish the same thing
- Removing cane from the rails will also do this.
This means scraping more cane out of the part of the blade just off-center from the spine, but not near the edge of the blades.
Why does weakening the channels bring out the mid-range of the sound?
Another reed analogy!
Think of the reed blade as an arch in a window or door.
If the areas of the arch in between the keystone and the ends of the arch contain greater mass, the pressure on those structural points is greater. Too much and the arch may collapse.
This is true of the reed as well. If the channel areas are thick, the reed's structural supports must support greater weight. With an arch gravity makes this greater weight felt. With the reed, it's the wires.
More thickness in the channels, therefore, tends to close the tip from the greater weight. This is why after scraping the channels the tip may open a bit. There is less weight for the spine and sides to support, so the tip has greater "lift"
When the channel area is lightened, it vibrates more freely. The difference in tone quality is noticeable, mainly through greater focus and roundness. A reed with good lows and highs can sound hollow. A perceived roundness or openness in the sound indicates the greater presence of mid-range frequencies in the reed's vibration.
Armed with this information, you can make up for weaknesses in a reed's tone, turning up the highs, turning down the lows, etc. to bring more complexity and fullness to the reed's sound.