BS EN IEC 60118‑9 specifies methods for the measurement of bone conduction hearing aid characteristics. The methods described produce a suitable basis for the exchange of information or for direct comparison of the electroacoustical characteristics of bone conduction hearing aids. These methods are chosen to be practical, and reproducible, and are based on selected fixed parameters.
The results obtained by the methods specified in BS EN IEC 60118‑9 express the performance under the conditions of measurement, however, the performance of the hearing aid under practical conditions of use will depend upon a number of factors (e.g. effective load impedance, environmental conditions, acoustical environment, etc.).
BS EN IEC 60118‑9 defines methods of measurement of characteristics of bone conduction hearing aids both for:
Throughout BS EN IEC 60118‑9, all sound pressure levels specified are referred to as 20 μPa. When appropriate, the sound pressure level will be abbreviated to SPL.
BS EN IEC 60118‑9 on hearing aids is helpful for:
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. BS EN IEC 60118‑9 gives information on methods of measurement 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 directly in terms of acoustic gain.
By means of the information provided in BS EN IEC 60118‑9, the performance of hearing aids with bone vibrator outputs that do not form an integral part of the hearing aid, for example body worn, behind-the-ear hearing aids, or bone conduction implant systems with an external bone vibrator is measured in a similar manner to aids with air conduction outputs. BS EN IEC 60118‑9 recommends a pressure method of controlling the input sound pressure level to the hearing aid microphone. As an alternative to the pressure method, storage of a test enclosure frequency response correction curve can be used. This method is referred to as the "substitution method". BS EN IEC 60118‑9 provides a wearable instrument intended to aid a person with impaired hearing using an electromechanical transducer intended to produce the sensation of hearing by vibrating the cranial bones.
Overall, BS EN IEC 60118‑9 is useful as it assists with the acoustic measurement procedure which is based on a method of measurement in which the sound pressure level at the bone conduction hearing aid reference point is kept constant to simulate free field conditions. This method is referred to as the "constant entrance sound pressure method" or shortened to the "pressure method" throughout BS EN IEC 60118‑9.
BS EN IEC 60118‑9:2019 supersedes BS 6083‑9:1986, which is withdrawn. BS EN IEC 60118‑9:2019 constitutes a technical revision. BS EN IEC 60118‑9:2019 includes the following significant technical changes with respect to the previous edition:
EN 60118-9
IEC 60118-9