The alto flute is built specifically for its low register and rich tone colour. Its bore is ideally an optimum size to enable the low notes to have maximum sonority. The flute, in comparison, has a compromised bore size to ensure an even sound across the three registers. The relatively large bore of the alto flute means that there are fewer high harmonics in the sound, so the tone quality is less piercing in the high register than the concert flute.
The expectation with the alto flute is often that it is a quiet instrument, which does not project well. Although this may be the case, when considered in comparison with an instrument such as a trumpet, composers are often surprised by the instrument's dynamic range and potential for relatively loud, projected sounds, especially in the middle register. It should be noted that playing loud on the alto flute requires an alteration of C flute technique, and time must be taken by the player to develop the required control of the air stream.
The following examples demonstrate the dynamic curve of the alto flute, dependent on non-linearities of the instrument and the ear. Chromatic scales in each octave are played p and then f. Although the maximum dynamic of the instrument increases as the pitch ascends, the tone becomes more airy in the upper register at louder dynamic levels.
Dynamic curve of the alto flute: p
Dynamic curve of the alto flute: f
The alto flute uses more air than any other wind instrument (except for lower members of the flute family), which has obvious limitations in terms of sustaining a fortissimo dynamic. This must also be taken into consideration when scoring with other instruments. For example, a fortissimo on the piano would easily drown out an alto flute at the same written dynamic. The pitch range of the instrument also creates balancing problems within an ensemble. Conversely, the alto flute is capable of very quiet, controlled dynamics. This should be carefully notated to ensure that the player doesn't over compensate to ensure the sound projects.
Dynamic range on the alto flute is controlled predominantly by tone colour rather than actual dynamic. This means that a note played at the upper limits of its dynamic may be made to project more by intensifying the tone colour. The same is true of quiet dynamics – altering the tone colour will increase or decrease the apparent projection of the note.
Dynamic range of the alto flute