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TR41.3-05-11-003. Cordless Telephones and Hearing Aids. A Presentation on the Work of TIA TR-41.3 to the ATIS HAC Incubator Group August 23, 2005. Ancient History. 1982 – Telecommunications for the Disabled Act requires “essential” telephones to be usable by persons with hearing aids

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Cordless telephones and hearing aids


Cordless Telephonesand Hearing Aids

A Presentation on the Work

of TIA TR-41.3 to the

ATIS HAC Incubator Group

August 23, 2005

Ancient history
Ancient History

  • 1982 – Telecommunications for the Disabled Act requires “essential” telephones to be usable by persons with hearing aids

  • 1983 – TR-41.3 creates EIA RS-504

    • Axial and radial field intensity

    • Axial frequency response

  • 1984 – FCC adopts RS-504 into Part 68.316

  • 1988 – Hearing Aid Compatibility Act requires virtually all wireline telephones to provide magnetic coupling

Recent history
Recent History

  • 4/2004 – Informal FCC Complaints begin

    • Digital cordless telephones

    • Industry wide

  • 6/2004 – TIA User Premises Equipment Division (UPED) forms Hearing Aid Compatibility (HAC) Task Force

  • 8/2004 – TR-41.3 begins work to understand and characterize cause of digital cordless telephone interference with hearing aids

  • 10/2004 – UPED meets with FCC and Self Help for Hard of Hearing People (SHHH) to inform them of TIA activities

Recent history cont
Recent History (cont)

  • 5/2005 – TR-41.3 completes preliminary work and launches SP-3-0219, Measurement Procedures and Performance Requirements for Handset Generated In-Band Magnetic Noise (to become TIA-1083)

  • 6/2005 – SHHH holds annual Convention in Washington, DC

    • Gallaudet subjective study involving 32 hearing aid users and 8 digital cordless telephones

    • TIA Member Companies show products intended to provide a solution

Gallaudet shhh study
Gallaudet SHHH Study

  • 32 subjects who normally use a hearing aid when talking on the telephone

    • 22 women and 10 men with ages from 43 to 79

    • 12 reported moderate to moderately severe hearing loss, 18 reported severe or profound hearing loss, and 2 were not sure

    • 27 used T-coil coupling and 5 used acoustic coupling

  • 8 digital cordless telephones

    • 5 off-the-shelf models and 3 potential solution models

    • 4 operating at 2.4 GHz and 4 operating at 5.8 GHz

    • 5 were frequency hoppers and 3 were direct sequence

  • 2500 set included in study for baseline reference

Gallaudet shhh study cont
Gallaudet SHHH Study (cont)

  • Subjects asked to rate

    • Loudness (1-7, inaudible to too loud)

    • Percent words understood (1-5, <20% to >80%)

    • Interference (0-5, none to unbearable)

    • Usability (1-4, highly usable to not usable)

  • Subjects also asked to provide a yes or no answer as to whether, based on the interference they perceived, they would purchase the phone

  • Study funded under Grant No. H133E040013 from the National Institute on Disability and Rehabilitation Research

Round robin measurements
Round Robin Measurements

  • SHHH study sets measured by 3 TR-41.3 members

    • Desired magnetic field axial signal level and frequency response using full band integrator as defined in draft revision of C63.19

    • Undesired magnetic field axial signal level and frequency response using half band integrator as defined in draft revision of C63.19.

  • Compared results for following metrics:

    • AFI (1 kHz) – desired axial field intensity at 1 kHz

    • A-Weighted Noise – undesired magnetic field (half band, A wtd)

    • Signal Quality – AFI(1 kHz) minus A-Weighted Noise

    • Highest SFI – field strength of highest amplitude noise component

    • Magnetic SFI – A-Weighted Noise minus Highest SFI

    • Signal-to-Highest SFI Ratio – AFI(1 kHz) minus Highest SFI

T coil coupling findings
T-Coil Coupling Findings

  • Subjective Interference rating correlates best with A-Weighted Noise and Highest SFI measures

  • Interference rating also shows correlation to Signal Quality and Signal-to-Highest SFI Ratio measures

  • Slightly lower correlation of Purchase question and Usability rating to objective measures

  • Poor correlation of Loudness and Percent Words ratings to any objective measures

  • Poor correlation of AFI (1 kHz) and Magnetic SFI to any subjective ratings

Current status
Current Status

  • Continuing to analyze Gallaudet SHHH subjective study data and objective measurements on same cordless phones by labs of 3 TR-41.3 members

  • Creating first draft of SP-3-0219 (to be TIA 1083)

  • Targeting committee ballot after 11/2005 meeting and industry ballot after 2/2006 meeting

Sp 3 0219 draft direction
SP-3-0219 Draft Direction

  • Addressing magnetic interference

    • All complaints seem to be related to T-coil use

    • RF power levels lower than for cell phones

    • Supported by SHHH study results

  • Relatively simple measurement procedure

    • Connect the probe coil normally used for Part 68 testing to a spectrum analyzer instead of a narrow-band tracking analyzer

    • Borrow the half-band integrator and A-weighting concepts from revision of C63.19 (Draft 3.1, October 7, 2004)

  • Set performance criteria to obtain high percentage of “Not Annoying” and “Highly Usable” ratings.

Further information
Further Information

  • Documentation available on TR-41.3 FTP site:

    • Publicly available (anonymous FTP)

    • Arranged in folders organized by meeting date

    • Alternative browser access (no password required)

  • Next TR-41 meeting is week of November 7-11, 2005 in Santa Fe, NM

    • TR-41.3 will meet on Thursday afternoon

    • Anyone may attend one meeting as a guest

    • Additional information available on TR-41 web page:


  • TR-41.3 Chair is James Bress of AST Technologies (

  • SP-3-0219 Document Editor is Al Baum of Uniden (

  • TR-41 Chair is Stephen R Whitesell of VTech (

  • SHHH study Research Audiologist is Linda Kozma-Spytek of Gallaudet University’s Technology Access Program (