This International Standard specifies the relations existing, for the condition of equal-loudness level, between the sound pressure levels and frequencies of pure (sinusoidal) continuous tones in the following conditions :
a) the source of sound is directly in front of the listener (frontal incidence);
b) the sound field in the absence of the listener consists of a free progressive plane wave;
c) the sound pressure level is measured in the free progressive plane wave in the absence of the listener;
d) the listening is binaural;
e) tne conditions of equal-loudness level are determined by the modal value of the judgements of an adequately large group of listeners;
f) the listeners are otologically normal persons in the age group from 18 to 30 years inclusive.
The relations are expressed by means of an equation in bilinear form, with the sound pressure level as the independent variable and the loudness level as the dependent variable, for the pre-ferred frequencies in the one-third octave series from 20 to 12 500 Hz inclusive.
NOTES
1 In accordance with convention, the reference dependent variable is taken to be the sound pressure level of a 1 000 Hz tone, i.e. the loudness level expressed in phons. However, the form of the equation remains unchanged (but with transformed coefficients) if the variables are interchanged or if a tone of another frequency in the preferred one-third octave series is taken as the reference.
2 The data in this International Standard are approximately equal to equal-loudness level relations between narrow bands of random noise, not exceeding the auditory critical bandwidth.
3 Without extrapolation of the experimental data, the upper limit of the frequency range could not be extended to the next preferred frequency in the one-third octave series. For further information regarding the range from 12 500 to 15 000 Hz, see 111.
Graphical and short tabular presentations of the relations are given in annexes A and B.
Annex C specifies the correction to be applied to obtain the equal-loudness level relations for narrow bands of random noise in a diffuse sound field and the resulting equal-loudness level function.