Telecommunications Industry Association
TR41.3-05-11-XXX
Document Cover Sheet
Project Number
PN-3-0219
Document Title
Digital Cordless Phone and Hearing Aid Interference: Subjective and Objective
Studies
Source
RERC on Telecommunications Access
Contact
Name: Linda Kozma-Spytek
Complete Address: Gallaudet
University, 800 Florida Ave, NE,
Washington DC 20002
Distribution
TR-41.3
Intended Purpose
of Document
(Select one)
X
Phone: 202-651-5676
Fax:
202-651-5476
Email: linda.kozma@tap.gallaudet.edu
For Incorporation Into TIA Publication
For Information
Other (describe) -
The document to which this cover statement is attached is submitted to a Formulating Group or
sub-element thereof of the Telecommunications Industry Association (TIA) in accordance with the
provisions of Sections 6.4.1–6.4.6 inclusive of the TIA Engineering Manual dated March 2005, all of
which provisions are hereby incorporated by reference.
Abstract
Provide abstract of document here.
This power point presentation includes: 1) results from a statistical analysis of subjective ratings data on
digital cordless phone and hearing aid interference obtained during the 2005 SHHH convention and 2)
partial, preliminary results from an in-progress, objective study of the output of hearing aids coupled to
digital cordless phones.
v1.0 - 20050426
Digital Cordless Phone and
Hearing Aid Interference:
Subjective and Objective
Studies
Linda Kozma-Spytek
RERC on
Telecommunications Access
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-theshelf 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)
FHSS
2.4 GHz
4
5.8 GHz
1
DSSS
3
Differences between the RMS output of two digital BTE hearing aids
alone and when coupled to test phones on a live call/no signal
Microphone
Telecoil
(dB SPL)
(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, 1
14, 15
Off the Shelf Phone H
1, 4
18, 19
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=<20%; 3=41-60%; 5=>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
Overall Significance of Phone
for HA Mic & Telecoil Users
Test
Scale
Friedman
Friedman
Friedman
Loudness Intelligibility Interference
Mic
(n=5)
Telecoil
(n=27)
**sig. (p<0.01)
Friedman
Cochran
Usability
Purchase
.293
.052
.229
.127
.912
.000**
.000**
.000**
.000**
.000**
Significance Results for Pairwise Comparisons
between the Control Phone and Each Test Phone
Loudness
Intelligibility Interference Usability
Purchase
Phone A
0.01
0.00
0.03
0.00
0.32
Phone C
0.32
0.13
0.00
0.03
0.00
Phone D
0.10
0.00
0.00
0.03
0.00
Phone E
0.00
0.00
0.00
0.00
0.00
Phone F
1.00
0.00
0.00
0.00
0.00
Phone G
0.76
0.00
0.00
0.00
0.00
Phone B
0.00
0.00
0.00
0.00
0.00
Phone H
0.00
0.00
0.00
0.00
0.00
Friedman
Friedman
Friedman
Friedman
Cochran
sig. (p<0.01)
Loudness Ratings by Phone
** = sig. different from
Control phone (p<0.01)
100%
80%
**
60%
**
**
40%
20%
co
nt
ro
l
ph
on
e
A
Ph
on
e
C
Ph
on
e
D
Ph
on
e
E
Ph
on
e
F
Ph
on
e
G
Ph
on
e
B
Ph
on
e
H
0%
Soft - Inaudible
Comfortably Loud
Loud - Too Loud
Intelligibility Ratings by Phone
** = sig. different from
Control phone (p<0.01)
100%
80%
60%
**
**
40%
**
**
**
**
**
20%
0%
control phone Phone Phone Phone Phone Phone Phone Phone
A
C
D
E
F
G
B
H
<40%
40-60%
> 60%
Ratings of Annoyance due to Interference by Phone
** = sig. different from
Control phone (p<0.01)
100%
**
80%
**
60%
**
40%
**
**
**
**
20%
Co
nt
ro
l
Ph
on
e
A
Ph
on
e
C
Ph
on
e
D
Ph
on
e
E
Ph
on
e
F
Ph
on
e
G
Ph
on
e
B
Ph
on
e
H
0%
No Interference
Not Annoying
Mildly Annoying
Annoying - Unbearable
Ratings of Annoyance due to Interference by Phone
100%
**
** = sig. different from
Phones C&D (p<0.01)
**
80%
60%
**
40%
**
**
**
20%
0%
Control Phone Phone Phone Phone Phone Phone Phone Phone
A
C
D
E
F
G
B
H
No Interference - Not Annoying
Mildly Annoying
Annoying - Unbearable
Usability Ratings by Phone
100%
80%
60%
no sig. difference
40%
20%
0%
Control Phone Phone Phone Phone Phone Phone Phone Phone
A
C
D
E
F
G
B
H
Highly Usable
Minor Limitations
Major Lim. - Unusable
Spearman Correlations for Usability Ratings
** = sig.<0.01
Usability x
Loudness
Usability x
Intelligibility
Usability x
Interference
Wireline
0.207
0.639**
0.158
Phone A
0.616**
0.734**
0.276
Phone C
0.671**
0.839**
0.744**
Phone D
0.441
0.538**
0.496**
Purchase Decision by Phone
** = sig. different from
Control phone (p<0.01)
100%
**
**
80%
**
**
**
60%
**
**
yes
no
40%
20%
H
ne
Ph
o
Ph
o
ne
B
G
ne
Ph
o
Ph
o
ne
F
E
Ph
o
ne
D
ne
Ph
o
Ph
o
ne
C
A
ne
Ph
o
Co
n
tro
l
0%
Purchase Decision as a Function of Interference Rating
100%
80%
60%
40%
20%
7% - yes
yes
93% - no
no
77% - yes
23% - no
0%
No Interference - Not
Annoying
Mildly Annoying
Annoying Unbearable
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
Objective Testing
Hearing Aids
Analog
BTE
ITE
0
1
Digitally
Programmable
1
Fully Digital
3
ANSI C63.19
E-Field/H-Field
Frequency Range (MHz)
1800 - 2100
Dipole Position
Tip
Center
Hearing Aid 1 (D/ITE)
M4
M4
Hearing Aid 10 (D/ITE)
M4
M4
Hearing Aid 8 (D/ITE)
M3
M3
Hearing Aid 5 (D/BTE)
M3
M3
Hearing Aid 9 (D/BTE)
M2
M2
Hearing Aid 7 (D/BTE)
M2
M2
Hearing Aid 2 (A/ITE)
M1
M2
Failed
Failed
0
3
Hearing Aid 3 (DP/BTE)
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
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.
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
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.