Sona: Denotes a measure of perceived loudness. It was defined that a sinusoidal tone of 1 kHz and a sound level of 40 dB corresponds exactly to one sone. This fixed assignment is also the difference to the unit of measurement Phon, where it was only defined that a sound level of x dB at 1.000 Hz also corresponds to x phon. All other volumes are related to this.
