This standard applies to audio induction loops that generate alternating magnetic fields and provide input signals to hearing aids with induction pickup coils. GB/T 11454-1989 Magnetic field strength of audio induction loops for hearing aids GB/T11454-1989 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Magnetic field strength in audio-frequency induction loops for hearing aids This standard is equivalent to IEC J18-4 Magnetic field strength in audio-frequency induction loops for hearing aids. 1 Scope
GB 11454-- 89
This standard is applicable to audio-frequency induction loops that generate alternating magnetic fields and provide input signals to hearing aids with induction pickup coils. 2 Purpose
The purpose of this standard is to specify the value of the magnetic field strength of the audio-frequency induction loop for hearing aids, so that the hearing aids can provide a sufficient signal-to-noise ratio without overloading.
3 Explanation of terms
3.1 The average value of the recommended magnetic field strengthwww.bzxz.net
The magnetic field strength of the long-term average value of the speech signal applied to the system within the specified area. 3.2 Maximum magnetic field strength
The magnetic field strength corresponding to the maximum average value of the speech signal applied to the system in a short time average (about 0.125 s for the integration time used in the averaging process) within the specified area. 3.3 Specified magnetic field area
The area required for the hearing aid to be placed under normal use and its induction coil. Within this area, there is the magnetic field strength required to meet the recommended specifications.
Note: The specified magnetic field strength area is not necessarily the geometric area of ​​the induction loop plane. 3.4 Specified vector components of magnetic field strength
3.4.1 For many uses. For example, in the space where the hearing aid user is standing or sitting upright, the vertical component of the magnetic field is the main quantity, and the specified vector component refers to the vertical component. If other magnetic field components are also important, they are also stated together with their directions. 3.4.2 For other cases, such as small transmitting coils used for close contact coupling, the direction of the maximum sensitivity of the coil can be used. In this case, the vector component now specified refers to the field strength at the location and the direction of maximum sensitivity of the user's induction pickup line. 3.5 Specified Magnetic Field Frequency Response
The change in magnetic field strength relative to a frequency of 1 000 Hz when the system is fed with a constant input level. 4 Recommended Magnetic Field Strength
4.1 Recommended Magnetic Field Strength within the Specified Magnetic Field Area - The recommended average magnetic field strength is -20±3 dB, with 1A/m as the reference. The voltage generated by a 1000 Hz sinusoidal input signal is equal to the long-term average speech signal level applied to the system input. Note: The maximum magnetic field strength of this quasi-recommended magnetic field system is approximately -8 dB, with 1A/m as the symbol. Approved by the State Administration of Technical Supervision on 1989-0T-04 and implemented on 1990-04-01
GB 11454-89
This maximum magnetic field strength is based on the difference between the shortest time (about 0.125 s) average speech signal level and the long-term average level being approximately 12 dB.
4.2 The recommended magnetic field frequency should be within the frequency range of 100 to -5 000 Hz. When the system is fed with a constant value of the electrical input signal, the deviation of the magnetic field frequency response of the entire range from the value of 1000H7 is no more than ±3 dB. Note: In the case of hearing-impaired children, a low-frequency boost can be used to compensate for the low-frequency response of the induction loop transmission. Interference
Interference may occur when communication equipment or connections are very close to the induction loop, especially when the loop covers a large area. In order to limit this interference to an acceptable level, it is necessary to provide special measures. Additional remarks:
This standard was proposed by the National Technical Committee for Electroacoustics Standardization. This standard is under the jurisdiction of the State Administration of Technical Supervision. This standard is compiled by the China National Institute of Metrology. The main drafters of this standard are Zhang Jucai, Jiu Yang, Shuai Zhengping, and Zhang Yongqiang.
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