Playing with an incredible tone is a continuing pursuit for many flutists. Here a few tips to help you achieve that ringing, glorious sound.
Posture
How you stand effects your performance in many ways, one of which being your tone.
Open chest-keep your lungs open so the air flows in and out easily
“Loose” knees-never lock your knees while playing but keep a slight bounce
Open throat-think of having two giant marshmallows in your mouth
Air pressure in abdomen but relaxed face and neck
Embouchure
Practice with different size airstreams (thin or thick) in different octaves to achieve the best sound
Pick a few notes in each register, move flute back and forth, up and down, to find the best tone or ‘sweet spot’
Airstream
Continuous air stream
“Spinning” air
High registers need more airspeed
Intonation
Play exercises with a tuner or drone and transition to just using your ear
For loud dynamics use top lip to aim airstream down
For soft dynamics use bottom lip to aim airstream up
Resonance
Imagine an opera singer. They sing with wide open mouths to try and create space. The more open space you have in your mouth and throat, the more resonance you will achieve.
Yawning will help you raise your soft palate which allows more vertical space in your mouth
Try mimicking what happens right before you sneeze. This will open up your sinuses which then act as small resonance chambers.
Dropping your jaw and tongue will also create the space you need to find a clear, bell like tone.
Tips for a strong, steady tone
Try standing on one leg or having a friend lightly push on your shoulder as you play
Practice holding a piece of paper against the wall using only your airstream
“Sizzle” take a deep breath and let the air out slowly while making a hissing sound. Ssssss….Keep stomach firm and go as long as possible.
As you focus on one aspect at a time and practice daily, you will be able to hear the difference in your playing (and if your don't your teacher sure will!).