1. v1.0 - 20050426 Telecommunications Industry AssociationTR41.3-05-11-XXX

2. Digital Cordless Phone and Hearing Aid Interference: Subjective and Objective Studies Linda Kozma-Spytek RERC on Telecommunications Access

3. Phone Selection Select cordless phones that produce varying amounts of interference at the output of hearing aids coupled in microphone and telecoil modes Select cordless phones that represent current off-the- shelf models as well as solution phones from different manufacturers Select cordless phones that represent current digital transmission frequencies and technologies (i.e., 2.4 & 5.8 GHz; DSSS & FHSS) FHSSDSSS 2.4 GHz4 5.8 GHz13

4. Microphone (dB SPL) Telecoil (dB SPL) Solution Phone A 0, -1-1, 2 Off the Shelf Phone B 1, 2 3, 5 Solution Phone C-2, 1 5, 6 Solution Phone D 1, 2 7, 7 Off the Shelf Phone E-1, 2 8, 10 Off the Shelf Phone F 2, 2 9, 12 Off the Shelf Phone G 0, 114, 15 Off the Shelf Phone H 1, 418, 19 Differences between the RMS output of two digital BTE hearing aids alone and when coupled to test phones on a live call/no signal

5. Participants: 5 HA Microphone users; 27 HA Telecoil users Stimuli: long recorded phone conversation between a male and female speaker hearing aid and/or telephone VC was adjusted in order to achieve a comfortable listening level for speech using the preferred ear for telephone listening Procedure: One training run using the corded, landline control phone with a rotary dial handset VC Randomized presentation of the control and test phones For each phone condition, participants rated their listening experience on 4 scales Loudness of Speech (7 pt scale; 1=inaudible, 4=comfortably loud, 7=too loud) Intelligibility - %age of words understood in the conversation (5 pt scale; 1= 80%) Annoyance due to Interference (6 pt scale; 0=no interference, 3=annoying, 5=unbearable) Usability (4 pt scale; 1=highly usable, 4=not usable) For each phone condition, participants were asked whether they would purchase the phone under test given the amount of interference perceived

6. Test Friedman Cochran Scale LoudnessIntelligibilityInterferenceUsabilityPurchase Mic (n=5).293.052.229.127.912 Telecoil (n=27).000** Overall Significance of Phone for HA Mic & Telecoil Users **sig. (p<0.01)

7. LoudnessIntelligibilityInterferenceUsabilityPurchase Phone A0.010.000.030.000.32 Phone C0.320.130.000.030.00 Phone D0.100.00 0.030.00 Phone E0.00 Phone F1.000.00 Phone G0.760.00 Phone B0.00 Phone H0.00 sig. (p<0.01) Friedman Cochran Significance Results for Pairwise Comparisons between the Control Phone and Each Test Phone

8. ** Loudness Ratings by Phone ** = sig. different from Control phone (p<0.01)

9. ** Intelligibility Ratings by Phone ** = sig. different from Control phone (p<0.01)

10. Ratings of Annoyance due to Interference by Phone ** ** = sig. different from Control phone (p<0.01)

11. ** Ratings of Annoyance due to Interference by Phone ** = sig. different from Phones C&D (p<0.01)

12. Usability Ratings by Phone no sig. difference

13. ** = sig.<0.01 Usability x Loudness Usability x Intelligibility Usability x Interference Wireline0.2070.639**0.158 Phone A0.616**0.734**0.276 Phone C0.671**0.839**0.744** Phone D0.4410.538**0.496** Spearman Correlations for Usability Ratings

14. Purchase Decision by Phone ** ** = sig. different from Control phone (p<0.01)

15. 7% - yes 93% - no 77% - yes 23% - no Purchase Decision as a Function of Interference Rating

16. Data for the sample of HA users tested suggest that: 1)cordless telephone interference is likely to be primarily a baseband magnetic problem affecting hearing aid telecoil users 2)the annoyance ratings and purchase decisions due to interference by hearing aid telecoil users for Phone A are not significantly different from those of the control phone 3)the solution implemented in Phone A either eliminates perceived interference or reduces perceived interference to a level that is detectable, but not annoying for hearing aid telecoil users 4)an objective measure correlating to an interference rating of 1 (Not Annoying – I can detect interference but it is not at all annoying.) would establish a performance requirement for cordless telephones that will produce a subjective experience with regard to interference equivalent to landline corded phones 5)Phone A provides evidence for the technical feasibility of designing a digital cordless phone to meet this performance requirement

17. ANSI C63.19E-Field/H-Field Frequency Range (MHz)1800 - 2100 Dipole PositionTipCenter Hearing Aid 1 (D/ITE)M4 Hearing Aid 10 (D/ITE)M4 Hearing Aid 8 (D/ITE)M3 Hearing Aid 5 (D/BTE)M3 Hearing Aid 9 (D/BTE)M2 Hearing Aid 7 (D/BTE)M2 Hearing Aid 2 (A/ITE)M1M2 Hearing Aid 3 (DP/BTE)Failed Hearing AidsBTEITE Analog01 Digitally Programmable 10 Fully Digital33 Objective Testing

18. Objective Measurements Characterize hearing aid output when coupled to the control and test phones Hearing Aids (programmed/constant VC)  Microphone & Telecoil coupling modes Phones (normal use position re HA)  Off, Minimum VC & Maximum VC Measures (w/o speech through phones)  RMS (dB SPL)  Spectrum Measures (w/ speech through phones at Min. VC only)  SIR Replications for select conditions

19. Preliminary results from the objective measures suggest: Cordless telephone interference appears to be primarily an audioband magnetic problem for hearing aids in telecoil coupling mode. However, it appears that for some hearing aids with very low RF immunity (i.e., M1 or poorer re ANSI C63.19 in the high band), interference may be generated in hearing aids using microphone coupling.

20. Considerations re the development of the in-band magnetic noise standard for telephone wireless handsets: 1)Implementation of the standard by industry 2)Product identification/labeling 3)Dissemination of information for consumers and consumer organizations 4)Participation in C63.19 5)Monitoring new/emerging technologies for the potential to produce interference in hearing aids – either in-band magnetic or RF generated

21. This research was supported by the Rehabilitation Engineering Research Center on Telecommunications Access. The RERC on Telecommunications Access is a joint project of the Trace Center, University of Wisconsin, and the Technology Access Program, Gallaudet University. The RERC is funded by the National Institute on Disability and Rehabilitation Research in the U.S. Department of Education, under grant number H133E040013. However, the opinions and content are those of the grantees and do not necessarily represent the policy of the U.S. Department of Education.