Building a Wide Range is the Result of Air Control and Strength
Building a wide range is one of the real marks of an accomplished player. Higher notes come from your lips buzzing faster, and that happens for a few reasons: more air pressure from the diaphragm pushing air through your lips faster, the gap between your lips getting smaller, and your lips becoming firmer and stiffer.
Try this: without moving your slide or valves, slowly slur from your lowest note all the way up to your highest, and notice how much faster your focused air needs to move for each successive note.
Getting a fat sound as you climb
To keep a full, “fat” sound as the pitch rises, keep the gap between your lips as open as possible, and control pitch mainly by speeding up the focused air moving through lips you’re holding firmly in place. Don’t just press the mouthpiece harder into your lips to try to go higher — that’s a common trap that caps your potential fast.
Building range through strength
On trombone, an entire octave (or more) is available in first position alone. Build lip strength by slurring through that whole range, bottom to top and back down, in first position, then second, third, and so on through seventh — then back up through the positions. Do this every practice session; strong lip muscles are essential for both range and endurance.
Pursing your lips more tightly makes them firmer and thicker, producing a higher buzz when there’s enough air pressure behind them — much like whistling, where the gap between your lips shrinks as the pitch rises. Another trick: shrink your mouth cavity by raising your tongue, moving from a “doo” syllable toward a “dee.” The same volume of air moving through a smaller space naturally speeds up.
When you hit your limit
Eventually you’ll bump up against your physical limit in one of these areas. To keep climbing past it, combine all the techniques above rather than lean on just one. The real key, above everything, is properly focused air combined with enough lip strength to hold your embouchure steady as the air pressure builds.
Tip: push your jaw out slightly for lower notes, pull it back in for higher ones. To play louder, blow more air; to play higher, blow faster air through a smaller opening.
Try this: without your instrument, blow out an imaginary candle right in front of your lips, then try blowing it out again as if it were three metres away, pursing your lips and focusing the air through the corners. Notice how differently you blow — carry that same feeling into your playing.