 shifting the pitch because the cooperation of the higher partials would still support the weakened fundamental mode.
- Ideally, there would be a separate register hole for each fingering. Since this is not practical, comprimises in tuning must be made. A misplaced register hole will cause the second resonance frequency to sound sharp, in proportion to the distance from its ideal location.
- Reeds Driven Closed:
The single-reed as a mechanical oscillator blown closed.
- The reed functions as a pressure-controlled valve that admits a puff of air whenever the pressure is high in the mouthpiece.
- Positive pressure pulses reflected back from the far end of the horn tend to force the reed open ... positive feedback.
- The resonance frequency of the reed is typically between 2 - 3 kHz so that the reed always vibrates in its ``stiffness dominated'' region.
- The player can control the damping of the system via his/her lips.
- The player can indirectly control the mass of the system via the placement of his/her lips on the reed.
- Oscillations are favored when the air column has one or more resonances that correspond to the harmonics of the fundamental pitch.
- ``Air Reeds'':
- The air jet mechanism functions as a flow-controlled valve that admits a puff of air whenever the air flow at the embouchure hole is inward directed.
- The flow-controlled air stream collaborates with an air column to oscillate at frequencies corresponding to air column impedance minima.
- The player can control three parameters of the air jet - blowing pressure, length of the jet, and area of the lip opening - to affect register changes and other timbral effects.
- Most efficient excitation of the fundamental frequency takes place when the time for the air jet to travel across the embouchure hole is about half the period of oscillation.
- To sound the second register, the player increases the blowing pressure (to speed up the air jet) and/or moves the lips forward to decrease the jet length. At the same time, the lip opening may be decreased to maintain loudness and tuning.
- Toneholes change the effective length of an air column.
- The larger the hole, the more the effective length is changed.
- The effective length of a bore with open tone holes is found to vary with frequency. The air column ``acts'' longer at high frequencies than at low frequencies.
- A tonehole lattice acts as a filter which transmits high-frequency sound components but reflects low-frequency components.
- The cutoff frequency of the tonehole lattice is an important factor in determining the timbre of the instrument.