HD 450.9 S1:1987

SLOVENSKI STANDARD
SIST HD 450.9 S1:2004
01-januar-2004
[Not translated]

Hearing aids - Part 9: Methods of measurement of characteristics of hearing aids with

Appareils de correction auditive - Partie 9: Méthodes de mesure des caractéristiques des

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in

sous que ce soit et par aucun any form or by any means, electronic or mechanical,

procédé, électronique ou mécanique, y compris la photo- including photocopying and microfilm, without permission in

Part 9: Methods of measurement of characteristics of hearing aids with bone vibrator output

1) The formal decisions or agreements of the IEC on technical matters, prepared by Technical Committees on which all the

National Committees having a special interest therein are represented, express, as nearly as possible, an international

They have the form of recommendations for international use and they are accepted by the National Committees in that sense.

In order to promote international unification, the IEC expresses the wish that all National Committees should adopt the text

of the IEC recommendation for their national rules in so far as national conditions will permit. Any divergence between the

IEC recommendation and the corresponding national rules should, as far as possible, be clearly indicated in the latter.

This standard has been prepared by IEC Technical Committee No.29: Electroacoustics.

Further information can be found in the Report on Voting, indicated in the table above.

Part 9: Methods of measurement of characteristics of hearing aids with bone vibrator output

IEC Publication 118-0: Hearing Aids, Part 0: Measurement of Electroacoustical Characteristics, gives

information on methods of test for air conduction hearing aids. The majority of hearing aids in use are of this

type but a small percentage use a bone vibrator instead of an earphone. The use of a bone vibrator requires a

different method of measuring the output from the hearing aid and also makes it impractical to measure

Amplification in the case of an air conduction hearing aid is expressed as the difference between the output

sound pressure level in an acoustic coupler or ear simulator and the input sound pressure level measured in a

specified manner. However, with bone conduction hearing aids the input is in terms of sound pressure level

but the output will be in terms of mechanical vibration measured as an alternating force or force level.

This standard defines a method of expressing the input/output ratio as an acousto-mechanical sensitivity

level measured .on a mechanical coupler according to the second edition of IEC Publication 373: Mechanical

By means of information provided in this standard the performance of hearing aids with bone vibrator

outputs which do not form an integral part of the hearing aid for example body worn hearing aids, may be

measured in a similar manner to aids with air conduction outputs as described in IEC Publication 118-0.

Where the bone vibrator forms an integral part of the hearing aid, or where it is attached in some fixed

manner to the hearing aid (e.g. a headband type bone conduction hearing aid), performance cannot be

measured in the same way as for body-worn aids, due to the large dimensions of the mechanical coupler

having to be in contact with the spectacle arm. This standard recommends a pressure method of controlling

The second edition of IEC Publication 373, describes the means of measuring the output from a bone

This standard specifies methods of measurement of the characteristics of hearing aids using bone

The methods described will produce a suitable basis for the exchange of information or for direct

comparison of the electroacoustical characteristics of hearing aids using bone vibrator output. These

methods are chosen to be practical and reproducible and are based on selected fixed parameters.

The results obtained by the methods specified herein express the performance under the conditions

of the test, but will not necessarily agree exactly with the performance of the hearing aid under practical

3.1 Throughout this standard all sound pressure levels specified are referred to 20 µPa. When appropriate,

Publication 118-0 (1983): Hearing Aids, Part 0: Measurement of Electroacoustical Characteristics.

Publication 118-7 (1983): Hearing Aids, Part 7: Measurement of the Performance Characteristics of

Publication 263 (1982): Scales and Sizes for Plotting Frequency Characteristics and Polar Diagrams.

An electromechanical transducer intended to produce the sensation of hearing by vibrating the

A device designed to present a specified mechanical impedance to a vibrator applied with a specified

static force and equipped with a mechano-electric transducer to enable the alternating force level at the

Twenty times the logarithm to the base 10 of the ratio of the r.m.s. value of the force transmitting the

The vibratory force level produced at a specified frequency on a mechanical coupler by the bone

The OFL produced on the mechanical coupler by the hearing aid expressed as a function of fre-

The OFL at a specified frequency produced with an input sound pressure level of 90 dB and the

A point on the hearing aid chosen for the purpose of defining its position, normally the centre of the

At a specified frequency and under specified operating conditions the quotient of the vibratory force

produced on the mechanical coupler by the hearing aid and the sound pressure at the reference point of

Twenty times the logarithm to the base 10 of the ratio of the acousto-mechanical sensitivity to the

To calculate the acousto-mechanical sensitivity level (AMSL) from measurements made in this standard the

where OFL is expressed in decibels ref. 1 µN and sound pressure level to the hearing aid microphone in decibels

The setting of the hearing aid gain control that provides an output force level on the mechanical

coupler 15 ± 1 dB less than OFL 90 for an input sound pressure level of 60 dB at the reference test

frequency of 1600 Hz. For certain hearing aids for which a higher reference test frequency is more

appropriate (so called high-tone hearing aids) 2500 Hz shall be used. If 2500 Hz is used this shall be

clearly stated. If the acousto-mechanical sensitivity level available will not permit this, the full on gain

The output force level frequency response curve obtained with the gain control in the reference test

The equipment used for measurement of OFL on the mechanical coupler produced by the hearing

5.1.1 For all measurements a mechanical coupler in accordance with the second edition of IEC Publication

5.1.2 The output force level corresponding to hum, vibration, thermal agitation and other noise sources

shall be sufficiently low to ensure that the reading shall drop at least 10 dB when the test signal is

For this purpose a high-pass filter not affecting frequencies of 200 Hz and above may be employed.

5.1.3 The output indicator used shall give the r.m.s. indication within a tolerance of ±0.5 dB at a signal

Under certain conditions it is necessary to use a selective measuring system in order to ensure that the response

of the hearing aid to the signal can be differentiated from inherent noise in the hearing aid. The use of the

It is well known that the type of output indicator employed may influence the test results significantly if a non-

sinusoidal voltage is being measured. Such non-sinusoidal voltages may be present when making measurements

5.1.4 The overall accuracy of the electronic measuring system following the mechanical coupler shall be

5.1.5 The calibration of the mechanical coupler shall be in accordance with the second edition of IEC

The calibration of the mechanical coupler should be repeated sufficiently often, preferably at least once a year, to