IS0 INTERNATIONAL STANDARD 226 First edition 1987-05-01 INTERNATIONAL ORGANIZATION FOR STANDARDIZATION ORGANISATION INTERNATIONALE DE NORMALISATION MEXflYHAPOAHAfl OPrAHM3A~Mfl l-l0 CTAH~APTM3A~MM Acoustics - Normal equal-loudness level contours Acoustigue - Lignes isosoniques normales iTeh STANDARD PREVIEW (standards.iteh.ai) ISO 226:1987 https://standards.iteh.ai/catalog/standards/sist/7919f81c-7cad-4a4f-824c- db3cd562450e/iso-226-1987 Reference number IS0 226 : 1987 (E) Foreword IS0 (the International Organization for Standardization) is a worldwide federation of national standards bodies (IS0 member bodies). The work of preparing International Standards is normally carried out through IS0 technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, govern- mental and non-governmental, in liaison with ISO, also take part in the work. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 % approval by the member bodies voting. International Standard IS0 226 wasiT preparedeh S byT TechnicalAND CommitteeARD ISO/TCPR E43,V IEW A cous tics. (standards.iteh.ai) It cancels and replaces IS0 Recommendation R 226 : 1961 and IS0 454 : 1975, of which it constitutes a technical revision. ISO 226:1987 https://standards.iteh.ai/catalog/standards/sist/7919f81c-7cad-4a4f-824c- Users should note that all International Standards undergodb3cd5 6revision2450e/ isfromo-22 6time-19 8to7 time and that any reference made herein to any other International Standard implies its latest edition, unless otherwise stated. 0 International Organization for Standardization, 1987 Printed in Switzerland INTERNATIONAL STANDARD IS0 226: 1987 (El Acoustics - Normal equal-loudness level contours 0 Introduction 1 Scope and field of application Curves defining relations between frequencies of pure tones or ’ This International Standard specifies the relations existing, for narrow bands of noise and their sound pressure levels for the the condition of equal-loudness level, between the sound condition of constant loudness level (equal-loudness level con- pressure levels and frequencies of pure (sinusoidal) continuous tours) express a fundamental property of the human auditory tones in the following conditions : system, and are of basic importance in the field of psycho- logical acoustics. a) the source of sound is directly in front of the listener (frontal incidence); In common with other subjectiveiT ephenomena,h ST AloudnessND Are-R D PREVIEW lations vary in detail from person to person but, for a group of b) the sound field in the absence of the listener consists of persons within a restricted age band and free from hearing im- . (standards.iteha free.a iprogressive) plane wave; pairments, a value for the central tendency can be determined to characterize the group. This International Standard gives curves applicable to otologkally normal persons in theISO age 226 :1987 c) the sound pressure level is measured in the free pro- group from 18 to 30 years. https://standards.iteh.ai/catalog/standards/sist/791gressive9f81c-7 cplanead-4 awave4f-82 4inc -the absence of the listener; db3cd562450e/iso-226-1987 The data specified in this International Standard primarily relate d) the listening is binaural; to continuous pure tones heard under conditions of binaural listening in free progressive plane waves with the subject e) the conditions of equal-loudness level are determined directly facing the source of sound (frontal incidence), and with by the modal value of the judgements of an adequately large the sound pressure level measured in the free progressive wave group of listeners; at the centre position of the listener’s head but with the listener absent. For other conditions of listening or other configurations f) the listeners are otologically normal persons in the age of sound field, different relations exist between loudness level group from 18 to 30 years inclusive. and sound pressure level. One example of another sound field configuration is a diffuse field. The relation between frontal in- The relations are expressed by means of an equation in bilinear cidence and diffuse field together with the resulting equal- form, with the sound pressure level as the independent variable loudness level function for narrow bands of noise in a diffuse and the loudness level as the dependent variable, for the pre- sound field are specified in annex C to this International Stan- ferred frequencies in the one-third octave series from 20 to dard. 12 500 Hz inclusive. NOTE - The relation between frontal incidence and diffuse field was NOTES given in IS0 454; with the inclusion of this relation in this edition of IS0 226, IS0 454 has become superfluous and has been withdrawn 1 In accordance with convention, the reference dependent variable is (see the “Foreword”). 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 The hearing threshold may be considered as a special case of remains unchanged (but with transformed coefficients) if the variables equal-loudness level, and the corresponding threshold sound .are interchanged or if a tone of another frequency in the preferred one- pressure levels [minimum audible field (MAF)] are included in third octave series is taken as the reference. this International Standard. It should be emphasized that the 2 The data in this International Standard are approximately equal to minimum audible field differs from the audiometric zero equal-loudness level relations between narrow bands of random noise, specified in IS0 389, since the latter refers to monaural listen- not exceeding the auditory critical bandwidth. ing through earphones with sound pressure levels referred to 3 Without extrapolation of the experimental data, the upper limit of specified couplers and artificial ears. Direct comparison be- the frequency range could not be extended to the next preferred fre- tween the data in IS0 389 and in this International Standard is quency in the one-third octave series. For further information regarding therefore not appropriate. the range from 12 500 to 15 000 Hz, see [ll. 1 IS0 226 : 1987 (El Graphical and short tabular presentations of the relations are 3.7 hearing threshold : The level of a sound at which, given in annexes A and B. under specified conditions, a person gives 50 % of correct detection responses on repeated trials. Annex C specifies the correction to be applied to obtain the equal-loudness level relations for narrow bands of random 3.8 otologically normal person : A person in a normal noise in a diffuse sound field and the resulting equal-loudness state of health who is free from all signs or symptoms of ear level function. disease and from excess wax in the ear canals, and who has no history of undue exposure to noise. 2 References 39 minimum audible field (MAF) : At a specified fre- IS0 131, Acoustics - Expression of physical and subjective quency the sound pressure level of a pure tone or a narrow magnitudes of sound or noise in air. band of noise corresponding to the modal value of the binaural hearing threshold of otologically normal persons within the age IS0 266, Acoustics - Preferred frequencies for measurements. limits from I8 to 30 years inclusive. IS0 389, Acoustics - Standard reference zero for the call’- 3.10 critical bandwidth : The widest frequency band bration of pure tone air conduction audiometers. within which the loudness of a band of continuously distributed random noise of constant band sound pressure level is indepen- dent of its bandwidth. 3 Definitions For the purposes of this International Standard, the following definitions are used, the conditions of applicability stated in 4 Specification clause I being understood, where appropriate. The loudness level, LN, in phons, of a pure tone of frequencyf, in hertz, is given by the equation 3.1 loudness : That attribute of auditory sensation in terms of which sounds may be ordered oni Ta scaleeh extending STA fromN Dsoft ARD PREVIspyEW - Tf) to loud. LN = 4,2 + . (1) (standards.iteh.ai) I + bf(Lf - Tf) 3.2 loudness level : Of a given sound, the sound pressure level of a reference sound, consisting of a sinusoidal plane pro-ISO 226:19where87 gressive wave of frequency I 000 Hz coming from directly in https://standards.iteh.ai/catalog/standards/sist/7919f81c-7cad-4a4f-824c- front of the listener, which is judged by otologically normal per- Lf is the sound pressure level of the tone, expressed in sons to be equally loud to the given sound. Loudnessdb3 cleveld56 2is45 0e/iso-226decibels-1987 (reference : 20 PPa); expressed in phons. 7’~ is the threshold sound pressure level of the tone, ex- 3.3 equal-loudness level function : For a pure tone of pressed in decibels, as given in table I; given frequency or for a narrow band of noise of a given fre- quency band, the relation between loudness level, expressed in afand bf are frequency-dependent parameters, as given in phons, and sound pressure level, expressed in decibels. table I. 3.4 equal-loudness level contour : A curve in the sound Equation (I 1 applies, at each frequency, for values of Lffrom pressure level/frequency plane, connecting points the co- the lower limit Tf to the following upper limits : ordinates of which represent pure tones or narrow bands of noise judged equally loud. 20 to I 000 Hz : 120 dB 125oto 8 000 Hz : 110 dB 3.5 normal equal-loudness level function : The equal- IO 000 and I2 500 Hz : 100 dB loudness level function corresponding to the modal judgement I of otologically normal persons within the age limits from I8 to NOTES 30 years inclusive.