On the one hand the aim of this artificial „woodwind player“ is a reproducible sound generation as close as possible to the real playing situation, but without the influence of a human player. On the other hand it provides the opportunity for a comparison of different reeds or different embouchure positions, both in conjunction with quantifying their contribution to the timbre. Due to the transparent assembly, recording of motion pictures of the reed oscillation is possible. Using the computer as a closed loop control ensures a reproducible excitation.
During the excitation process, the player controls the following embouchure operating values:
Normally the player is used to altering these parameters automatically without thinking about it. For quantifying the above mentioned embouchure parameters it is vital to be able to change one operating value while holding the two others constant. This is an impracticable task for human players.
RIAM can be split into three sections:
Unlike the human oral cavity, the artificial mouth of RIAM is built using transparent plastic. In comparison to the human cavity the new synthetic cavity still has a larger volume and a different surface. Inside the artificial cavity are synthetic lips on an adjustable mounting. Stepper motors allow a controlled movement in the X and Y axes). The required amount of air can be supplied by any kind of air pressure source with an output pressure of up to 10 bar. An electronic fine-tuning valve provides accurate air pressure inside the artificial mouth. A large electromagnet (solenoid) simulates the maxillary muscles.
To provide reproducible operating parameters the following sensors are used:
All gauges have an electronic output.
To ensure noise-free signals the measurement values are digitized as near as possible to the mechanical excitation system. These readings are captured by a LabView DAQ interface.
The user-interface is written using National Instruments "LabView". Beside providing controlelements the software controles the airpressure and lip-contact pressure in a closed loop.
After RIAM sets up communication with the PC and calibrates its positioning system, the user is asked to insert the instrument. To prevent damage to the instrument while mounting and to provide a sealed seat, a soft silicon ring clamps the clarinet barrel firmly to RIAM. A threaded cap prevents slippage in the clamping ring and a supporting arm keeps the instrument stationary and fixes it over the whole length. Because of the different sizes and shapes of the reed instrument types, RIAM initializes the embouchure position each time an instrument is inserted. During this initialisation the embouchure system samples the accurate position of the mouthpiece using a laser. This self-adjustment provides reproducible positioning of the artificial lips on the instrument. After initialization, the user can define the operating values. In many cases the alteration of the operating values is required. Now these adjustments can be simply done during the experiment by moving the graphical scroll bars.
After the successful stabilization of the initial transients, the optimal values of lip contact pressure, lip position and air pressure can be read directly from the PC screen and stored. The stored values can be used for analysation or as a preset for a next time excitation.
Detail top view
RIAM was used to investigate the differences of the embouchure operation values of three different types of reeds. For all measurements the same mouthpiece, a Wurlitzer W4 (Viennese type) was used.
The reed types:
The FIBRACELL reed was shortened 2.5 mm to fit onto the Viennese mouthpiece. Different embouchure positions were tested by producing tones from e3 to e4. The procedure starts by adjusting the x- position so that the lip contact gauge is parallel to the reed. This adjustment ensures a correct measurement. The y- position is then defined and an air pressure of 50 mbar (for RICO 35 mbar) is applied. Then the lip contact pressure is increased until the reed oscillation produces a correct sound. Figure 1 displays the correct lip contact pressure for different y- positions to excite a stable sound.
Figure 1: lip contact pressure vs. the lip position (measured from the tip of the mouthpiece)
The largest force is needed exciting the dry LEUTHNER reed. After the reed is soaked in water for a few minutes, the required lip contact pressures can be reduced significantly. Because of the dry air stream through the mouthpiece the tip of the reed dehumidifies very quickly. This effect causes a change of the spring constant of the reed and consequently a change of the reed resonance frequency. For musicians, this case occurs after a long playing pause. With a "dry" reed it is more difficult to play the instrument, which is especially subject to “noise”. In general the lip contact pressure increases with the distance between the lip and the tip of the mouthpiece.
Figure 2: regions of potential sound generation for the tested reeds
To study the interaction between lip contact pressure and air pressure a practical embouchure position on the basis of Figure 1 was selected. On the one hand the positions were chosen to be in the middle of the useable embouchure region, and on the other hand to provide enough range for variation of the lip contact pressure. The selected lip positions are 13 mm for the RICO reed, 12 mm for the FIBRACELL and the wet LEUTHNER and 11 mm for the dry LEUTHNER reed.
After adjusting the lip position on the reed, the lip force was increased in steps of 0.1 N. For each force value the possible air pressure was varied until the oscillation stops. Figure 2 displays the extracted results. It should be noted that at low lip contact pressures the reed opening is so large (especially for the FIBRACELL and the dry LEUTHNER reed) that the air pressure valve cannot provide the required amount of air.
For all tested reeds the determined regions look similar. When the lip contact force is increased the air pressure must decrease for a stable sound generation. Maximum and minimum values of the air pressure converge when the lip contact pressure is increased.
The presented artificial mouth for reed instruments allows a highly reproducible excitation of clarinets. Studies showed interesting differences between the embouchure parameters of different reeds.