A Short Tutorial on Sound Level and Loudness for Voice (Article)
With regard to fundamental frequency, sound level (SL) increases about 6 dB/octave, all else being equal. This is the primary reason why females often outsing males on the opera stage if they sing an octave higher. With regard to lung pressure, SL increases about 6-9 dB/with every doubling of lung pressure. The major phenomenon here is increase in peak glottal airflow. The frequency spectrum affects loudness perception if the sound is more than a simple tone. (posted 2:34 PM, August 27, 2014)