loop systems – t-coil
DESCRIPTION
Loop systems – T-coil. Conny Andersson IEC 60118-4. [email protected]. Loop System – Wireless system. Receiver = T-coil in Hearing Instrument (HI) No current consumption Transmitter = Loop Amplifier and Loop World Wide Standard. Acoustic and T-coil input. Acoustic Output. Input. - PowerPoint PPT PresentationTRANSCRIPT
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Loop System – Wireless system
Receiver = T-coil in Hearing Instrument (HI)No current consumption
Transmitter = Loop Amplifier and Loop
World Wide Standard
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Input
Acoustic and T-coil inputAcousticOutput
switch
MT
HearingInstrument
Loop Level:Fixed @ 400mA/mfor all signals
Speech level=70dB@1m distance
130dB
Gain +60dB
Coil Sensitivity130dB
Same output level for M and T-position
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Relative T-coil sensitivitySwitching 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
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International Standards, IEC
Hearing Instrument (HI) Many parameters are fitted for the
individual. Can not be standardized
Hearing Loop system All parameters are standardized
InternationalElectrotechnicalCommission
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ANSI S3.22-2009American National Standard Institute has
many abbreviations for T-coil functions3.4 Terms relating to measurements with inductive inputs3.4.1 high frequency average SPL for an inductive telephone simulator (HFA-SPLITS). The high frequencyaverage 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-frequencyaverage 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 obtainedby 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 leveldeveloped in the coupler by a hearing aid with the gain control at the RTS when the input is themagnetic field generated by a Telephone Magnetic Field Simulator (refer to Clause 3.2.5). Theabbreviation for this term is SPLITS.3.4.6 sound pressure level in a vertical magnetic field (SPLIV). Sound pressure level developed inthe coupler by a hearing aid with the gain control at the RTS when the input is a 31.6 mA/m sinusoidalalternating magnetic field parallel to the vertical reference and the input selector of the hearing aid setto 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
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Standardized Parameters
Magnetic Field Strength, 400mA/m
Coverage area/space (sitting and standing),Should have minimum variations (+-3dB)
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Field distribution – level/coverage
Variation less than +-3dB
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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
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Hearing Instr. frequency response
Mic
T-coil
Hearing instrument, microphone/telecoil response
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Often reduced low freq. T-coil
Mic
Tele-coil
Reduced low frequency sensitivity
25dB
Hearing instrument, microphone/telecoil response
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HI has large variation in freq resp
Mic
Tele-coil
Hearing intrument, microphone/telecoil response Hearing instrument, microphone/telecoil response
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Loop frequency response is flat
Mic
Tele-coil
Hearing instrument, microphone/telecoil response
Within +-3dB +-3dB
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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
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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
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-3dB (@45°)-3dB (@45°)
Conventional loops - tilt angel
0dB=full level
Silence!
Vertical field
Silence!
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Loops/T-coil with TWO directions
full levelfull level
Vertical AND Horizontal Field0dB=full level
-3dB (@45°)-3dB (@45°)
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Conclusion and a `T-coil wish`Increased low frequency responseHum harmonics removerDefault 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.
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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.
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Thank you for your attention!
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Thank you for your attention!
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Input
Acoustic and T-coil inputAcousticOutput
switch
MT
HearingInstrument
Loop Level:Fixed @ 400mA/mfor all signals
Speech level=70dB@1m distance
130dB
Gain +60dB
Coil Sensitivity130dB
Same output level for M and T-position
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Input
Acoustic and T-coil inputAcousticOutput
switch
MT
HearingInstrument
Loop Level:Fixed @ 100mA/mfor all signals
Speech level=70dB@1m distance
130dB
Gain +60dB
Coil Sensitivity130dB
Same output level for M and T-position
Long-term signals:
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Input
Acoustic and T-coil inputAcousticOutput
switch
MT
HearingInstrument
Loop Level:Fixed @ 31.6 mA/mfor all signals
Speech level=60dB@1m distance
120dB
Gain +60dB
Coil Sensitivity120dB
Same output level for M and T-position
Long-term signals: