The QC factor was determined in the mid-1990s by audio installers at spring break in Daytona Beach.
They conducted informal tests inside a Honda Accord boom-car. Their goal was to determine if a frequency existed that would send a woman inside a bass vehicle into spontaneous orgasm.
After testing more than 50 female volunteers, the magic frequency was found to be precisely 33 Hz.
Sorry for the lack of info here, its a bit rough, but there isnt too much info on the web about this, I shall keep searching on it.