Earphone response was measured on a KEMAR® manikin that has the same acoustic properties as the average head and ear. 25-band accuracy scores are calculated by summing the difference between the earphone response and the target response in each 1/3 -octave band from 50 Hz to 12.5 kHz.
In the 1970s, Consumers Union used an "Accuracy Score" to rate loudspeakers. Consumer Reports reported that it was possible to predict listeners' loudspeaker ratings within 8% from a calculation based on one-third-octave frequency response measurements converted to loudness in sones. The average error in loudness from a perfect system, subtracted from 100%, gives the accuracy score. Etymotic Research extended this 21-band calculation to a 25-band calculation and routinely uses the 25-band accuracy score in all earphone designs.
Other in-the-ear earphone manufacturers do not report accuracy scores, but Etymotic Research continues to test competitive products. The accuracy scores of Etymotic earphones are higher than all competitive earphones we've tested, except electrostatic headphones that cost thousands of dollars.