T-coil Loop System

Document Sample
T-coil Loop System Powered By Docstoc
					                Conny Andersson
                    IEC 60118-4


                    Conny.Andersson@edin.se



www.univox.eu
                 Receiver = T-coil in Hearing Instrument (HI)
                   No current consumption


                 Transmitter = Loop Amplifier and Loop



                 World Wide Standard


www.univox.eu
                  Input                                            Acoustic
                                                                   Output
                                        Gain +60dB
                                               Hearing             130dB
                Speech level=70dB              Instrument
                @1m distance
                                                 M
                Loop Level:
                                                 T
                Fixed @ 400mA/m                switch
                for all signals
                                                                   130dB
                                       Coil Sensitivity

                          Same output level for M and T-position

www.univox.eu
                 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

www.univox.eu
                       Hearing Instrument (HI)
                                  Many parameters are fitted for the
                                   individual. Can not be standardized


                       Hearing Loop system
                                  All parameters are standardized


                International
                Electrotechnical
                Commission


www.univox.eu
                 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-

                 Good News, ANSI S3.22 committee
                    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

                 has decided to make T-coil
                    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
                 specification mandatory for quality
                    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
                 test inspection
                    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.



www.univox.eu
           Magnetic Field Strength, 400mA/m




           Coverage area/space (sitting and standing),
           Should have minimum variations (+-3dB)




www.univox.eu
    Variation less
    than +-3dB




www.univox.eu
                 Magnetic field strength from electrical
                 appliances

                 Received directly by the T-coil
                 NOT by the hearing loop system

                 Less problematic due to stronger
                 regulations of electrical environment

www.univox.eu
                Hearing instrument, microphone/telecoil response




                        Mic




                         T-coil




www.univox.eu
                         Hearing instrument, microphone/telecoil response




                                 Mic
    Reduced low
    frequency     25dB
    sensitivity
                                  Tele-coil




www.univox.eu
                 Hearing intrument,
                Hearing instrument, microphone/telecoil response




                        Mic




                         Tele-coil




www.univox.eu
                Hearing instrument, microphone/telecoil response

      Within
                                 +-3dB
      +-3dB

                        Mic




                         Tele-coil




www.univox.eu
                 It is therefore impossible to judge
                 the full quality of a loop system by
                 using a Hearing Instrument

                 Measurements are mandatory




www.univox.eu
                 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



www.univox.eu
                                          Vertical field
                                          0dB=full level



                           -3dB (@45°)‫‏‬                    -3dB (@45°)‫‏‬




                Silence!                                             Silence!




www.univox.eu
                                Vertical AND Horizontal Field
                                            0dB=full level


                             -3dB (@45°)‫‏‬                    -3dB (@45°)‫‏‬




                full level                                              full level




www.univox.eu
                 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.
www.univox.eu
                 Several channels and modulated/coded
                 loop system.

                 One‫“‏‬standard‫‏‬loop‫‏‬system‫‏‬for‫‏‬world‫‏‬
                 wide use in theatres etc

                 Other channels for school and domestic
                 use. Decreased Signal to Noise ratio.


www.univox.eu
www.univox.eu
www.univox.eu
                  Input                                            Acoustic
                                                                   Output
                                        Gain +60dB
                                               Hearing             130dB
                Speech level=70dB              Instrument
                @1m distance
                                                 M
                Loop Level:
                                                 T
                Fixed @ 400mA/m                switch
                for all signals
                                                                   130dB
                                       Coil Sensitivity

                          Same output level for M and T-position

www.univox.eu
                  Input                                            Acoustic
                                                                   Output
                                        Gain +60dB
           Long-term signals:
                                               Hearing             130dB
                Speech level=70dB              Instrument
                @1m distance
                                                 M
                Loop Level:
                                                 T
                Fixed @ 100mA/m                switch
                for all signals
                                                                   130dB
                                       Coil Sensitivity

                          Same output level for M and T-position

www.univox.eu
                  Input                                            Acoustic
                                                                   Output
                                        Gain +60dB
           Long-term signals:
                                               Hearing             120dB
                Speech level=60dB              Instrument
                @1m distance
                                                 M
                Loop Level:
                                                 T
                Fixed @ 31.6 mA/m              switch
                for all signals
                                                                   120dB
                                       Coil Sensitivity

                          Same output level for M and T-position

www.univox.eu

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:5/7/2013
language:
pages:24