Speech horns need meter-wide bells to avoid coloring male voices

Evidence

An ideal speaking trumpet or horn guides the sound out without reflection. Reflections at the large end—the mouth—cause resonances that enhance certain frequencies but color the sound, making speech less intelligible. Reflections are significant for wavelengths longer than the diameter of the mouth. A typical male speaking voice is around 80 to 100 Hz (plus many harmonics of that frequency), so the horn end should be 4 meters wide so as not to color the voice with one or more undesirable resonances. — Eric J. Heller, Why You Hear What You Hear- An…, 549

Categorization

• CANDY: Fun specific fact: the ideal speaking-trumpet bell for a male voice would be four meters wide — a great trivial fact for a cocktail party.
• XREF: Connects to end-reflection physics and why real acoustic horns deviate from the ideal exponential form.