Clarinet bell suppresses tonehole back-reflections at short wavelengths

Evidence

Shorter wavelengths pass by the tonehole more readily than do long wavelengths; much less sound reflects from the hole at short wavelengths. One of the jobs of the bell of a clarinet may be to reduce back-reflections of the wave energy that has made it past a tonehole, thus preventing undesirable shifts of resonance frequencies. — Eric J. Heller, Why You Hear What You Hear- An…, 1599