2 International Hearing Loop

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24 Νοε 2013 (πριν από 3 χρόνια και 11 μήνες)

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2
nd

International Hearing Loop
Conference:
Telecoil

Panel

Linda Kozma
-
Spytek

Research Audiologist

Technology Access Program

Gallaudet University

RERC
-

Telecommunications Access

RERC


Hearing Enhancement

passive

amplified

Photo used with permission from Oticon, Inc.

Sensitivity
is
determined by its:


size and geometry


programming gain
(amplification) applied


Amplified
T
elecoils




consist of a coil and preamplifier



preamp increases sensitivity of the
telecoil



should have

RF
-
interference protection

Telecoils

A
telecoil

is a coil of wire around a
magnetic metal core that is sensitive to
magnetic fields.

Approximately 60% of hearing aid fittings in the US include a
telecoil
, and all cochlear implants have
telecoils
.

Telephones (directly)


Landline Phones (corded and cordless)


Wireless Devices (basic cell phones, feature phones and smart
phones)


Hearing Assistive Technology (HAT)


Induction Loop Systems (directly)


Other
HATs

(FM/IR) via


Neckloops


Silhouettes


Headsets


Audio Devices (telephones, music players, etc.) via


Neckloops


Silhouettes


Headsets



Telecoils

are used in hearing devices to connect to:

Programming

Fully programmable memory dedicated for
telecoil

use:




amplification characteristics can be independently adjusted by

the audiologist, including mixing input from

the
telecoil

and

microphone




amplification characteristics can also be preset

(manufacturer default
telecoil

program)








Manual:

Remote
Control

Touchless


Telecoil

Automatic:

+
Reduce acoustic background noise in all communication
settings

(
-

magnetic noise)


+
Reduce the effects of poor room acoustics (reverberation) in
all communication settings


+
Reduce the effects of distance (level of the speaker’s voice
remains constant regardless of the distance between the
hearing aid wearer and the speaker) in settings where the
telecoil

is part of a hearing assistive technology system

(
-

microphone location)


+
Eliminate acoustic feedback during telephone coupling


Why use
telecoil

coupling?

SPEECH

noise

noise

reflected

sound

Induction Loop (IL)

System

T

Acoustic
Loudspeakers

Telecoil

Orientation

Figures adapted with permission from
HyperPhysics



by Rod Nave,
www.phy
-
astr.gsu.edu

For best
coupling with a
telecoil
, a
magnetic field
should cut
across all turns
in the wire of the
telecoil

by
aligning with
the axis of the
core.

maximum

coupling

maximum

coupling

no

coupling

no

coupling

horizontal
telecoils

couple
best with axial

(horizontal)
magnetic
field
lines of a
telephone

vertical
telecoils

couple
best with

the weaker radial
(vertical) magnetic
field
lines of a telephone

vertical
telecoils

couple best with

the
vertical
magnetic field
lines of a room loop

`
`

Magnetic Field

Orientation

dB (SPL)
equivalent

dB (A/
m
)





90


0

highest axial field strength measured on cordless phone
samples

82

-

8

IEC 60118
-
4 specified

speech peak

field strength for induction
loop
systems
(400
mA/m
)

72

-
18

C63.19 required minimum axial and radial field strength for
wireless
devices

70

-
20

IEC 60118
-
4

resulting
long
-
term average level of speech for
induction loop
systems
(100
mA/m
)

68 [53]

-
22 [
-
37]

RS
-
504 required minimum axial field strength for landline
phones

[in
-
use levels

are ~
15
dB

lower]

63 [48]

-
27 [
-
42]

RS
-
504 required minimum radial field strength for landline
phones

[in
-
use levels are ~15
dB

lower]

60

-
30

lowest axial field strength measured on cordless phone samples

60

-
30


ANSI S3.22 (1996
)

-

HA quality assurance standard


reference

for
telecoil

sensitivity measurement
(31.6
mA/m
)

50

-
40

TIA 1083 specified A
-
weighted magnetic noise maximum

46

-
45

field strength of ambient magnetic noise (A
-
weighted)
measured in a parking lot, under power lines

27

-
63

field strength of ambient magnetic noise (A
-
weighted)
measured in a living room

Source Magnetic Field Strengths

Receiver

HA (amplified)

telecoil

+

+

Net
Frequency
Response

HA Signal
Processing

=

Net Frequency Response

Magnetic Source

Induction Loop
System

Telephone

Comparison of Magnetic Frequency Responses for
Telephones and Audio Loops

-35
-30
-25
-20
-15
-10
-5
0
5
10
15
100
1000
10000
dB

Hz

HA
Amplified
Telecoil

Frequency Response

-35
-30
-25
-20
-15
-10
-5
0
5
10
15
100
1000
dB

Hz

Magnetic Source Frequency Response

Audio Loop
Telephone
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
100
1000
dB

Hz

Net Frequency Response

Amplified Telecoil +
Audio Loop
Amplified Telecoil +
Telephone
What needs to be considered
for
telecoil

coupling capability?

Source (Magnetic)
Requirements
:


High enough signal strength


Low enough
noise/distortion
level


High enough signal to noise ratio


Usable field orientations


Large
enough

coverage area


Appropriate frequency
response

Receiver (
Telecoil
)
Requirements
:


Adequate sensitivity


Low enough noise/distortion
level


High enough signal to noise ratio


Usable
telecoil

orientation


Standard frequency response

System Verification Goals
:


To objectively quantify the real
-
ear performance of the hearing
aid in
telecoil

mode (when coupled to a telephone or hearing
assistive technology) in relation to a prescriptive target

Need: Level
-
controllable standard inductive signal sources

The contents of this PowerPoint presentation were developed
under grants from the Department of Education, NIDRR grant
numbers H133E080006 and 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.

Acknowledgements