The key to good tone is to have a lot of harmonics related to the pitch you are playing. Harmonics are components of your sound. They are what make a flute sound different from a clarinet. When we recognize someone's voice on the phone, in part we are responding to his or her unique harmonic pattern. Each instrument has it's own unique harmonic pattern.
On the clarinet any note in the chalumeau register produces 2 distinctly audible harmonics. One a 12th higher and one 5th higher than that.
So, low E makes a B (with the register key and G# above that.)
Higher harmonics tend to be quieter (and flatter).
Harmonics enable us to better understand the pitch we are playing. If you read this number sequence it's easy to understand what the next number in the sequence will be, 9,7,5,3, it's 1 of course. Your ear does the same thing with the harmonics of the clarinet.
It is easier to tune if your sound is harmonically rich, as you will better understand the note you are playing.
When we play in tune with others in an ensemble we also generate resultant and combination tones that are created by the harmonics of the different notes interacting with each other. You should hear 3 distinct notes for most pairs of notes played. Using these generated notes to tune is one the most important skills to have in order to be in tune in an ensemble.
It's possible on the clarinet to play so the harmonics are actually louder than the fundamental. This will tend to make your tone too bright. Players with rough tones often produce out of proportion harmonics or harmonics that are not related to the note they are playing, this is usually because the reed is vibrating too wildly and more lip is required to control it.
This little exercise will help emphasize the harmonics that are key to good clarinet tone.
1.Play low e forte taper the sound down until you hear a b in the sound. You can pay the B first so you know what note to listen for.
2. Adjust your embouchure and air pressure so that the B is strong
3. Do the same but now listen for a g# above the B
4. Listen for the complete chord.
5. Now play (whatever) keeping the sound rich, when it starts to wear off go back and remind yourself by repeating steps 1-3.
Play intervals above a sustained tone adjust the pitch up and down until you hear a resultant tone.