The ZOEN Blog has a great article up on using resonance fingerings for clarinet.
One of the most problematic aspects of clarinet playing is achieving an even, fluid timbre across the instrument’s range, through all dynamics and articulations. Barring extreme altissimo, the most unforgiving notes on the instrument are the throat tones – F, F#, G, Ab, A, and Bb. They tend to be weak, stuffy, out of tune, hard to project, and unpredictable from player to player.
I ALWAYS play my throat tone Bb with the “resonance fingering.” It’s something I think I started doing in college while using a “crappy” Buffet clarinet they had (by “crappy” I mean it played the throat tones out of tune and stuffy).