Reed shaping and voicing is a very specialised subject. However, with some care and appreciation of the processes which might cause damage it may well be possible to achieve satisfactory results.
Reed re-shaping might be necessary for two reasons:
- The tip of the reed needs to be raised above the level of the body to enable it to ‘start’ when air is released onto it
- The shape of the reed has an effect on its tonal qualities
Before a reed will start to vibrate when a key is operated and air pressure released onto it the reed tip needs to be above the level of the top surface of the reed body. If the gap is too small the reed will ‘choke’ (not play) and if the gap is too large it will either not play at all or the response/attack will be slow.
To adjust the gap it appears that slight bending of the reed is unavoidable. Metallurgists would point out that bending metal past its elastic limit weakens it but this is unavoidable since a small amount of permanent deformation is required to achieve the change in shape. (The elastic limit of a material is the extreme limit of stress it can absorb and still fully recover without deformation).
Some success has been achieved by supporting the reed near its tip in the direction it is required to be set while gently stroking the reed from bottom to top.
A good and consistent reed attack/response is desirable.
It is noted that reed manufacturers ‘voice’ the reeds in the final stages of production. The reeds are shaped (and the tip raised) the apparent aim being a reed which has good tonal qualities and is similar to its neighbours.
A plucked or struck string on a piano or guitar vibrates at a fundamental frequency and contained within that are higher frequencies (harmonics) the size and disposition of which gives the string a distinctive and unique tone. Reeds are no different in that they act in a way which produces harmonics. The reed in action appears to oscillate in a way that (simply put) resembles a fishing rod and is quite flexible with some ‘whipping’ action taking place. By shaping the reed in a curve up and away from the block an imbalance is created. It has a bias in one direction of its travel and it appears that periods of extra high velocity of the reed (especially near the tip) will occur as it tries to oscillate in an even cycle. The production of higher velocities result in harmonic generation. It follows that it takes a well-developed, trained ear to hear the harmonics (tone qualities) of a reed as well as having special knowledge of any corrective action required.
To see, (as well as hear) reed harmonics a spectrum analyser is useful.
A sample scan from an analyser is shown. Although the sampling rate of the device is fairly low and its range limited (about 5,500Hz while the human ear audio range is about 20Hz to 20,000Hz) it is sufficient to show the disposition and size of harmonics up to about the 18th at middle C (Note C8) which is a surprising 4700Hz!!
In conclusion it is felt that while reed performance can be altered by shaping to maximise performance and matching, the amount of influence that can be brought to bear is limited by the initial design, construction and reed material quality.