ABSTRACT
Experiments have been carried out with large numbers of people who have been asked to listen to a steadily quietening tone and then indicate when they can no longer hear the tone. Any convenient sound pressure will do but to make all the numbers positive the zero is chosen to be the smallest detectable pressure-in other words near the lowest part of the curve. To take a very obvious example, a person who has a slight hearing impairment would think that the sound from the television set is too quiet while another person might think it was too loud. The frequency is then changed and the person is asked to make an adjustment so that the loudness is the same. The point is that the frequency range one hears depends on the level of the sound at the ears.
