Your ear canal is a closed tube (open to the atmosphere on one end, closed by the eardrum on the other). The length is about 3 cm, which means f1 = (344/(4*.03m)) ~ 3000 Hz. This is the lowest frequency where your ear itself "resonates", and that"s why the Fletcher-Munson curve is a minimum at about this frequency - you are most sensitive to waves of this frequency, because your ear canal actually resonates with the sound, what"s the NEXT harmonic that"s allowed?