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Loop systems – T-coil

Loop systems – T-coil

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Loop systems – T-coil

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  1. Loop systems – T-coil Conny Andersson IEC 60118-4 Conny.Andersson@edin.se

  2. Loop System – Wireless system • Receiver = T-coil in Hearing Instrument (HI) • No current consumption • Transmitter = Loop Amplifier and Loop • World Wide Standard

  3. Acoustic and T-coil input AcousticOutput Input Gain +60dB Hearing Instrument 130dB Speech level=70dB @1m distance M T Loop Level: Fixed @ 400mA/m for all signals switch 130dB Coil Sensitivity Same output level for M and T-position

  4. Relative T-coil sensitivity • Switching between M and T will give approximately the same output level It could be stated differently: • 0dB difference between M and T-position • Related to acoustic level: The acoustic output is the same for T and M-position with a 70dB acoustical input signal

  5. International Standards, IEC • Hearing Instrument (HI) • Many parameters are fitted for the individual. Can not be standardized • Hearing Loop system • All parameters are standardized International Electrotechnical Commission

  6. ANSI S3.22-2009 • American National Standard Institute has many abbreviations for T-coil functions 3.4 Terms relating to measurements with inductive inputs 3.4.1 high frequency average SPL for an inductive telephone simulator (HFA-SPLITS). The high frequency average of the SPLITS levels (see Clause 3.4.5). The abbreviation for this term is HFASPLITS. 3.4.2 high frequency average SPL in a vertical magnetic field (HFA-SPLIV). The high-frequency average of the SPLIV levels (see Clause 3.4.6). The abbreviation for this term is HFA-SPLIV. 3.4.3 relative simulated equivalent telephone sensitivity (RSETS). Difference in decibels obtained by subtracting the RTG + 60 dB SPL from the HFA-SPLITS. The abbreviation for this term is RSETS. 3.4.4 relative test loop sensitivity (RTLS). Difference in decibels obtained by subtracting the RTG + 60 dB SPL from the HFA-SPLIV. The abbreviation for this term is RTLS. 3.4.5 sound pressure level for an inductive telephone simulator (SPLITS). Sound pressure level developed in the coupler by a hearing aid with the gain control at the RTS when the input is the magnetic field generated by a Telephone Magnetic Field Simulator (refer to Clause 3.2.5). The abbreviation for this term is SPLITS. 3.4.6 sound pressure level in a vertical magnetic field (SPLIV). Sound pressure level developed in the coupler by a hearing aid with the gain control at the RTS when the input is a 31.6 mA/m sinusoidal alternating magnetic field parallel to the vertical reference and the input selector of the hearing aid set to T-position. The abbreviation for this term is SPLIV. • Good News, ANSI S3.22 committee has decided to make T-coil specification mandatory for quality test inspection

  7. Standardized Parameters Magnetic Field Strength, 400mA/m Coverage area/space (sitting and standing), Should have minimum variations (+-3dB)

  8. Field distribution – level/coverage Variation less than +-3dB

  9. Standardized Parameters (hum) • Magnetic field strength from electrical appliances • Received directly by the T-coilNOT by the hearing loop system • Less problematic due to stronger regulations of electrical environment

  10. Hearing Instr. frequency response Hearing instrument, microphone/telecoil response Mic T-coil

  11. Often reduced low freq. T-coil Hearing instrument, microphone/telecoil response Reduced low frequency sensitivity Mic 25dB Tele-coil

  12. HI has large variation in freq resp Hearing instrument, microphone/telecoil response Hearing intrument, microphone/telecoil response Mic Tele-coil

  13. Loop frequency response is flat Hearing instrument, microphone/telecoil response Within +-3dB +-3dB Mic Tele-coil

  14. Loop specifications is regulated • It is therefore impossible to judge the full quality of a loop system by using a Hearing Instrument • Measurements are mandatory

  15. Vertical Field Strength • The specifications for most of the parameters for loops are for vertical directions • This corresponds to HI manufacturers placing the T-coil in vertical position

  16. Conventional loops - tilt angel -3dB (@45°)‏ -3dB (@45°)‏ Vertical field 0dB=full level Silence! Silence!

  17. Loops/T-coil with TWO directions Vertical AND Horizontal Field 0dB=full level -3dB (@45°)‏ -3dB (@45°)‏ full level full level

  18. Conclusion and a `T-coil wish` • Increased low frequency response • Hum harmonics remover • Default sensitivity should follow the standard of 400mA/m (125ms, RMS) If the sensitivity is set higher in the Hearing Instrument there is a strong risk for high distortion, clipping/saturation when entering a correct installed Loop System. A weak loop must not be compensated by increasing the T-coil sensitivity with a decreased Signal to Noise ratio.

  19. Conclusion and a `T-coil wish` • Several channels and modulated/coded loop system. • One “standard loop system for world wide use in theatres etc • Other channels for school and domestic use. Decreased Signal to Noise ratio.

  20. Thank you for your attention!

  21. Thank you for your attention!

  22. Acoustic and T-coil input AcousticOutput Input Gain +60dB Hearing Instrument 130dB Speech level=70dB @1m distance M T Loop Level: Fixed @ 400mA/m for all signals switch 130dB Coil Sensitivity Same output level for M and T-position

  23. Acoustic and T-coil input AcousticOutput Input Gain +60dB Long-term signals: Hearing Instrument 130dB Speech level=70dB @1m distance M T Loop Level: Fixed @ 100mA/m for all signals switch 130dB Coil Sensitivity Same output level for M and T-position

  24. Acoustic and T-coil input AcousticOutput Input Gain +60dB Long-term signals: Hearing Instrument 120dB Speech level=60dB @1m distance M T Loop Level: Fixed @ 31.6 mA/m for all signals switch 120dB Coil Sensitivity Same output level for M and T-position