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UDC 534
IS0
FOR STAND AR D I Z AT I O N
I N T ERN AT I O NA L O RG A N I ZAT I O N
IS0 RECOMMENDATION
R 389
STANDARD REFERENCE ZERO
FOR THE CALIBRATION OF PURE-TONE AUDIOMETERS
1st EDITION
November 1964
COPYRIGHT RESERVED
The copyright of IS0 Recommendations and IS0 Standards
belongs to IS0 Member Bodies. Reproduction of these
documents, in any country, may be authorized therefore only
by the national standards organization of that country, being
a member of ISO.
For each individual country the only valid standard is the national standard of that country.
Printed in Switzerland
Also issued in French and Russian. Copies to be obtained through the national standards organizations.
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BRIEF HISTORY
The IS0 Recommendation R 389, Standard Reference Zero for the Calibration oi
Pure-tone Audiometers, was drawn up by Technical Committee ISO/TC 43, Acoustics, the
is held by the British Standards Institution (BSI).
Secretariat of which
Work on this question by the Technical Committee began in 1955 and led, in 1962, to
the adoption of a Draft IS0 Recommendation.
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In January 1963, this Draft IS0 Recommendation (No. 554) was circulated to all the
IS0 Member Bodies for enquiry. It was approved by the following Member Bodies:
Australia
Germany Republic of South Africa
Austria Hungary Romania
Belgium India Sweden
Brazil Italy Switzerland
Chile Japan United Kingdom
Czechoslovakia Netherlands U.S.A.
Denmark Norway U.S.S.R.
Finland Poland Yugoslavia
France Portugal
No Member Body opposed the approval of the Draft.
The Draft IS0 Recommendation was then submitted by correspondence to the IS0
Council, which decided, in November 1964, to accept it as an IS0 RECOMMENDATION.
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ISO/R 389-1964 (E)
FOREWORD
The need has frequently been expressed, both by otologists and audiologists and the makers of
audiometers, for an internationally accepted basis of calibration for pure-tone audiometers of
the types commonly employed for diagnostic or screening purposes.
This IS0 Recommendation specifies a standard reference zero for the scale of hearing threshold
level applicable to pure-tone audiometers, which it is hoped will help to promote agreement and
uniformity in the expression of hearing threshold level measurements throughout the world.
This IS0 Recommendation states the information in a form suitable for direct application to
the calibration of audiometers, that is, in terms of the response of certain standard types of
earphone measured on an artificial ear or coupler of stated type. The earphone-coupler combina-
tions correspond with those currently used in a number of standardizing laboratories.
This IS0 Recommendation is based on an assessment of the information available from the
various standardizing laboratories responsible for audiometric standards, and from scientific
publications, up to the end of 1961. Some notes on the derivation and application of the recom-
mended reference levels are given in Appendix A to this IS0 Recommendation.
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ISO/R 389-1964 (E) m
IS0 Recommendation R 389 November 1964
STANDARD REFERENCE ZERO
FOR THE CALIBRATION OF PURE-TONE AUDIOMETERS
1. EXPLANATION OF TERMS
For the purpose of this IS0 Recommendation, the following terms are employed :
1 .ï Equivalent threshold soundpressure level (monaural earphone listening), of an ear at a specified
frequency and for a specified type of earphone and for a stated force of application of the
earphone to the human ear. Sound pressure level set up by the earphone at that frequency
in a specified artificial ear or coupler when the earphone is actuated by that voltage which,
with the earphone applied to the ear concerned, would correspond with the threshold of
hearing.
1.2 Reference equivalent threshold sound pressure level (monaural earphone listening), at a
specified frequency, for a specified type of earphone and for a specified pattern of artificial
ear. Modal value, at that frequency, of the equivalent threshold sound pressure levels of an
adequately large number of ears of otologically normal subjects within the age limits of
18 to 30 years inclusive.
NOTE. - For the purpose of this IS0 Recommendation, an ‘I otologically normal subject ” is understood to be a
person in a normal state of health who is free from all signs or symptoms of ear disease and from wax in the ear
canal, and has no history of undue exposure to noise.
2. SPECIFICATIONS
The reference equivalent threshold sound pressure level, for constant auditory threshold, is
dependent on the pattern of earphone and on the pattern of artificial ear employed for its cali-
bration. Usage in this respect may vary from one nation, or standardizing laboratory, to another.
The recommended standard values are given below in the Table, corresponding to the arrange-
ments adopted by different standardizing laboratories, in so far as these have been reported to
the International Organization for Standardization (ISO).
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