A key controlling a very small hole in the tube wall of a woodwind instrument which, when opened, assists the player to sound the second and higher registers. In a reed-energized instrument under satisfactory playing conditions there exists a state of vibrational cooperation between the reed and the resonating air column. The air flow through the vibrating reed contains a set of harmonically related frequency components, and normally several of these are close in frequency to the natural vibration modes of the air column. When the performer plays in the first register, the reed vibration frequency is near that of the first air column mode. Opening a speaker key inhibits this regime of cooperation by changing the frequency of the first mode and reducing its strength; it is then more favourable for the reed to vibrate at a frequency close to that of the second mode. In the oboe and saxophone two, sometimes three, ‘speakers’ are provided, each used with a particular group of tone holes; since the second mode frequency of these conical-bore instruments is twice the first mode frequency, the second register notes are an otave above those obtained in the first register with the same fingering. The ‘half-hole’ mechanism of the oboe may also be regarded as a ‘speaker’. In the clarinet a single register key is usually found sufficient; in this case, the second mode of the cylindrical air column has a frequency three times that of the first and the fingering repeats at the interval of a 12th.
See also Overblowing.
PHILIP BATE/MURRAY CAMPBELL