Conceptual Speech Distribution Chart
At normal conversational speech levels, the speech sounds are distributed unequally as the distance between the speaker and listener increases. The low tone sounds from the vocal cords (voiced), vowels for example, travel at great distances, while the high tones of the teeth, tongue, and lip sounds (unvoiced), like the /s/ for example, don’t travel far. In fact, as distance increases, word clarity decreases because the unvoiced consonants lose power significantly after 6 feet. By 12 feet, some sounds can no longer be heard and at 24 feet all sounds that would help speech understanding are muted. The “critical distance” is a calculation of the best speech reception distance between speakers in a room (35’x40’x10’). This is why communicating at a distance can be challenging, especially with doorways, hallways, and objects between the speaker and listener.
Interference from Facing or Looking Away