In a woodwind the register hole produces a transition from low to second playing register in two ways. At low dynamic levels the hole must increase the damping of the first mode sufficiently that oscillation cannot be sustained.
Oscillation then takes place on the basis of the second resonance peak.
At high dynamic levels this effect of the hole is insufficient intermode cooperation can still sustain the low register oscillation, so that the first mode frequency must be suitably shifted relative to that of the second mode to make their cooperation impossible. Optimum hole reactance raises the first mode frequency 25 per cent. Oboes and English Horns traditionally have vent hole proportions in agreement with this design. Small modifications invariably give trouble. Most saxophones are dramatically improved by reworking the vent holes to the present specification.