A resonance unsupported by cooperating upper harmonics produces a wobbly, unstable note

Evidence

Playability and timbre will be seriously degraded with badly tuned harmonics. This may be explored by attempting to play the “unused” lowest resonance, below the pedal tone, left behind by the realignment and shifting of the higher resonances by the mouthpiece and bell design. This resonance is unsupported by the cooperation that develops when upper harmonics of the resonance frequency are also resonances. The note can be played with some difficulty, but the tone is wobbly, with no sense of the lock-in support of harmonics. — Eric J. Heller, Why You Hear What You Hear- An…, 1558