The saxophone’s lowest notes can be notoriously unresponsive. This is partly due to the instrument’s acoustics, particularly its fairly extreme conical bore. (For technical details, see for example Acoustics of Musical Instruments by Chaigne and Kergomard, section 22.214.171.124.) The oboe and bassoon, whose bores are conical but not to such an extreme, have this problem to a lesser extent, and the tips that follow apply to those instruments as well.
For the best chance at successful low notes you need:
- A well-adjusted, high-quality instrument. Even a small leak anywhere on the saxophone makes the lowest notes more difficult. And the best-designed and most meticulously-made instruments help to minimize the difficulties of the low range.
- A good mouthpiece and reed combination. This may involve tradeoffs: a mouthpiece/reed combination that really improves the low register may, for example, make the highest notes more difficult. Since mouthpieces and reeds vary in so many ways it’s hard to make reliable generalizations, but often I find that a wider tip opening with a softer reed tend to favor the low register more (and the high register less).
- Good, stable fundamentals of saxophone technique. Breath support, voicing, articulation, and embouchure (let’s include jaw position in embouchure here) should be properly set, and shouldn’t change for the low register. If you find that you need to increase breath support, lower your voicing, change your embouchure or tonguing, or open your jaw to make the low notes succeed, then you should probably already be doing those things, in every register. Don’t make the low notes even harder by creating a moving target.
To expand on that last point a little, if you find that your low notes need a little extra help, then a small alteration to your voicing is the right way to provide it. But know the tradeoffs: lowering your voicing as you approach the low register affects pitch and tone, besides creating instability in your tone production technique. Manage these concerns by aiming for the smallest possible change.
Practice smart. No shortcuts!