Analyzing Sound Quality of Advanced Bone Anchored Hearing Aids

57 Pages·2012·3.07 MB·English

by  Tyler Wetter

University of Alberta

Analyzing Sound Quality of Advanced Bone Anchored Hearing Aids
by
Tyler Wetter

A thesis submitted to the Faculty of Graduate Studies and Research in partial fulfillment of the
requirements for the degree of

Master of Science
�in
Speech Language Pathology
Department of Speech Pathology and Audiology

©Tyler Wetter
Spring 2013
Edmonton, Alberta

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Abstract
In this study we explored whether differences in sound quality existed between new
advanced Bone Anchored Hearing Aids (BAHA). Three groups of subjects were tested. Two
groups, those with normal hearing and those with sufficient residual cochlear hearing, were
tested with Oticon’s Ponto Pro to Cochlear’s BP100. The third group had either mixed hearing
loss or single-sided deafness and they compared the more powerful devices (Oticon’s Ponto Pro
Power and Cochlear’s BP110). Some differences emerged within the normal hearing listeners
and the power user’s. However, no significant differences in sound quality were revealed in the
non-power users of the Ponto Pro and BP100. These limited results most likely reflect a lack of
power in the data due to the limited number of subjects per group. Continued data collection is
warranted.
Acknowledgements
First and foremost I would like to thank my supervisor, Dr. Hodgetts. Thank you for
your patience and support throughout this process. You told me early on that a great supervisor
is one who will be there come crunch time. You most definitely were and I know this project
could not have been successful without all your contributions. I also experienced a huge
learning curve with this thesis and you were always there to answer any questions or concerns
that I had. It was a pleasure working with you and getting to know you.
I would also like to thank Amberley Ostevik. You were so patient with me and willing to
answer questions I had about the project. I thank you for all your hard work with data collection
and teaching me what it means to do research. You were such a pleasure to work with and I feel
fortunate and grateful that I had the opportunity to work with you.
In addition, I have to thank Herman Lundgren and Dylan Scott. I know this project
would not have been possible without all the hard work and dedication you put into it. Thank
you so much for answering my questions with diagrams. You both were very supportive and
were always good for a few laughs. Thanks to both of you.
I also want to thank my committee for the time and effort they put into this project. Your
guidance and suggestions are greatly appreciated.
Lastly, I would like to thank my family and my girlfriend for always encouraging me to
keep going when times were tough. I know that this journey would not have been possible
without all your support. I’m very fortunate to have such wonderful people in my life.
Table of Contents
Introduction
 ..........................................................................................................................................
 1

Research
 Question(s)
 ...................................................................................................................................
 8

Method
 ....................................................................................................................................................
 9

Subjects
 .............................................................................................................................................................
 9

Group
 1
 –
 Normal
 Hearing
 Subjects
 ......................................................................................................................
 9

Groups
 2
 and
 3
 –
 BAHA
 Users.
 .................................................................................................................................
 9

Procedure
 .......................................................................................................................................................
 10

Phase
 1
 -­‐
 Hearing
 Testing,
 Device
 Setting
 and
 Recording
 ........................................................................
 10

Recordings
 .....................................................................................................................................................................
 12

De-­‐convolution
 Process
 ...........................................................................................................................................
 17

Phase
 2
 –
 Sound
 Quality
 Assessment
 .................................................................................................................
 21

Results
 ..................................................................................................................................................
 26

Normal
 Hearing
 Subjects
 ..........................................................................................................................
 26

Non-­‐Power
 Users:
 Ponto
 Pro
 and
 BP100
 .............................................................................................
 32

Power
 Users
 –
 Ponto
 Pro
 Power
 and
 BP110
 ......................................................................................
 36

Discussion
 ...........................................................................................................................................
 44

Normal
 Hearing
 Subjects
 ..........................................................................................................................
 44

Non-­‐power
 users
 ..........................................................................................................................................
 45

Power
 Users
 ...................................................................................................................................................
 47

Conclusion
 ..........................................................................................................................................
 48
List of Tables

Table
 1.
 Subject
 Details.
 .....................................................................................................................................
 10

Table
 2
 Correlations
 between
 scores
 with
 the
 different
 transducers
 (Ponto
 Pro
 and
 BP100)

for
 the
 non
 Power
 BAHA
 users.
 Bolded
 rows
 reached
 significance
 .....................................
 34

Table
 3.
 Correlations between scores with the different transducers (Ponto Pro Power and
BP110) for the Power BAHA users. Bolded rows reached significance.
 ..................................
 38
List of Figures
Figure
 1.
 Bone
 anchored
 hearing
 aid
 and
 titanium
 implant
 in
 the
 skull.
 ........................................
 2

Figure
 2.
 Devices
 used
 in
 the
 study.
 The
 top
 two
 are
 from
 Cochlear
 Corporation
 and
 the

bottom
 two
 are
 from
 Oticon
 Medical
 ....................................................................................................
 8

Figure
 3.
 Mean
 force
 level
 thresholds
 on
 a
 skull
 simulator
 for
 each
 subject
 group
 (non-­‐
power
 and
 power
 users)
 obtained
 with
 each
 of
 the
 manufacturer’s
 devices.
 .................
 11

Figure
 4.
 National
 Instruments
 data
 acquisition
 system
 (this
 is
 the
 same
 DAQ
 that
 has
 been

integrated
 into
 the
 test
 box)
 ..................................................................................................................
 13

Figure
 5.
 (a)
 Skull
 simulator
 and
 (b)
 internal
 components
 of
 skull
 simulator
 consisting
 of

an
 abutment,
 mass
 and
 accelerometer
 ..............................................................................................
 13

Figure
 6. SoundQual.vi recording software, designed using Labview
 ................................................
 14

Figure
 7.
 Audioscan
 Verifit,
 Skull
 Simulator
 and
 Sound
 Proofed
 Test
 Box
 .................................
 15

Figure
 8.
 DecovoluteMe.vi software program
 .............................................................................................
 16

Figure
 9.
 Schematic
 of
 de-­‐convolution
 process
 .......................................................................................
 18

Figure
 10.
 Comparisons
 of
 the
 original
 music
 .wav
 file
 to
 the
 recorded
 and
 the
 de-­‐
convoluted
 music
 .wav
 file
 for
 each
 processor.
 In
 addition,
 a
 difference
 waveform

between
 the
 original
 file
 and
 the
 final
 de-­‐convoluted
 file.
 (a)
 BP100,
 (b)
 Ponto
 Pro,
 (c)

BP110
 and
 the
 (d)
 Ponto
 Pro
 Power.
 .................................................................................................
 20

Figure
 11.
 Normalized,
 de-­‐convoluted
 spectra
 of
 each
 BAHA
 device
 compared
 to
 the

original
 music
 sample
 ...............................................................................................................................
 21

Figure
 12.
 SoundQualTestv2.vi
 software
 ...................................................................................................
 22

Figure
 13.
 Visual
 analog
 scale
 used
 to
 judge
 sound
 quality
 ...............................................................
 22

Figure
 14.
 Isolated
 (i.e.
 ,“naked”)
 Ponto
 Pro
 and
 BP100
 transducers
 ...........................................
 24

Figure
 15.
 Frequency/Output
 responses
 of
 the
 4
 naked
 BAHA
 transducers
 used
 in
 the

study.
 ................................................................................................................................................................
 25

Figure
 16.
 Main
 effect
 of
 mode
 of
 stimulation.
 Condition
 1
 is
 bone
 conduction
 and

condition
 2
 is
 air
 conduction.
 ................................................................................................................
 27

Figure
 17.
 Main
 effect
 of
 device.
 Device
 1
 is
 the
 Ponto
 Pro;
 device
 2
 is
 the
 BP100
 .................
 28

Figure
 18.
 Main
 effect
 of
 level.
 Level
 1
 is
 75
 dB
 SPL
 input
 and
 level
 2
 is
 60
 dB
 SPL
 input.
 ..
 29

Figure
 19.
 Main
 effect
 of
 stimulus
 type.
 Type
 1
 was
 male
 speech;
 type
 2
 was
 female
 speech

and
 type
 3
 was
 music.
 ...............................................................................................................................
 30

Figure
 20.
 Overall
 contrasts
 from
 the
 4-­‐way
 significant
 interaction
 from
 normal
 hearing

listeners.
 Error
 bars
 represent
 the
 95%
 confidence
 interval
 around
 the
 mean.
 ............
 32

Figure
 21.
 Frequency
 response/audibility
 curves
 for
 the
 60
 dB
 SPL
 male
 speech
 signals.
 .
 33

Figure
 22.
 Frequency
 response/audibility
 curves
 for
 the
 75
 dB
 SPL
 male
 speech
 signals..33

Figure
 23.
 Sound
 quality
 results
 when
 measured
 using
 the
 Ponto
 Pro
 naked
 transducer.
 .
 35

Figure
 24.
 Sound
 quality
 results
 when
 measured
 using
 the
 BP100
 naked
 transducer.
 ........
 36

Figure
 25.
 Frequency
 response/audibility
 curves
 for
 the
 60
 dB
 SPL
 male
 speech
 signals..37

Figure
 26.
 Frequency
 response/audibility
 curves
 for
 the
 75
 dB
 SPL
 male
 speech
 signals.
 .
 37

Figure
 27.
 Main
 effect
 of
 Device
 for
 the
 Ponto
 Pro
 Power
 transducer
 condition.
 Device
 1
 is

the
 Ponto
 Pro
 Power
 and
 Device
 2
 in
 the
 BP110.
 .........................................................................
 39

Figure
 28.
 Interaction
 between
 Device
 and
 Level
 for
 the
 Ponto
 Pro
 Power
 transducer

condition.
 Device
 1
 is
 the
 Ponto
 Pro
 Power
 and
 Device
 2
 is
 the
 BP110.
 Level
 1
 is
 75
 dB

SPL
 input
 and
 Level
 2
 is
 the
 60
 dB
 SPL
 input.
 ................................................................................
 40
Figure
 29.
 Means
 plus
 the
 95%
 CI
 for
 each
 of
 the
 twelve
 conditions
 under
 test
 with
 the

naked
 Ponto
 Pro
 Power
 transducer.
 ..................................................................................................
 41

Figure
 30.
 Main
 effect
 of
 Device
 when
 rated
 using
 the
 naked
 BP110
 transducer.
 Device
 1
 is

the
 Ponto
 Pro
 Power
 and
 Device
 2
 is
 the
 BP110.
 .........................................................................
 42

Figure
 31.
 Means
 plus
 the
 95%
 CI
 for
 each
 of
 the
 twelve
 conditions
 under
 test
 with
 the

naked
 BP110
 transducer.
 ........................................................................................................................
 43

Figure
 32.

 Differences
 in
 2
 non-­‐power
 subjects
 sound
 quality
 ratings.
 ......................................
 46
Introduction

Bone anchored hearing aids (BAHAs) have become increasingly popular for individuals
who have chronic otitis media (ear infections), atresia (absence of the ear canal), and single
sided deafness. BAHAs can be fitted for individuals with conductive or sensorineural hearing
loss. Traditionally, bone conduction hearing aid devices (BCHAs) were fitted to headbands or
eyeglasses. These techniques had limitations due to pressure, causing users to experience
discomfort, pressure sores and headaches (Bance et al., 2002). Bance and colleagues (2002) also
noted that even when these traditional devices had good skin contact, the skin and subcutaneous
tissue could dampen the signal by as much as 20 dB. This dampening, accompanied with the
need to continuously loosen the headband to avoid discomfort, resulted in significant sound
quality limitations. Others (Hakansson et al., 1994) noted that the appearance of the BCHAs on
a headband hindered these devices further and concluded they should be considered a last resort.
In contrast, the BAHA uses direct bone conduction. In order to achieve this, a surgically
implanted titanium screw is placed in the parietal/temporal region of the skull. Titanium has a
unique ability to promote osseointegration when placed into bone (Hakansson et al., 1994).
When enough time has passed (typically 6 weeks to 3 months) the screw will be stable and
capable of anchoring a BAHA. The BAHA is connected to the screw via a titanium abutment.
With this system, the BAHA delivers sound directly to the bone without any loss of energy to
the skin and subcutaneous tissue (Hakansson, 1994). Although the BAHA device is a more
expensive solution, Snik et al. (2005) claim that this can be justified by fewer trips to the clinic
and ultimately, improved communication performance. Snik and colleagues (2005) also
1
indicated that implantation of the screw is achieved in 90 - 98% of cases, with high degrees of
safety.

Figure 1. Bone anchored hearing aid and titanium implant in the skull.
Image source: http://ent.uci.edu/BAHA.htm
Reports indicate superior performance of BAHAs over conventional bone conduction
hearing aids because sound quality remains steady even at higher volume settings (Snik et al.,
2005). Snik and colleagues (2005) point to the fact that BAHAs are capable of more efficient
sound transmission (especially in the high frequencies) through direct bone conduction, which
ultimately results in better speech perception.
Bance et al. (2002) conducted a study that compared the audiometric performance of
BAHAs to air conduction hearing aids. They concluded that regardless of which hearing aid was
used, it never restored or rehabilitated the patients to the level of normal listeners. In all cases
aided hearing-impaired subjects performed worse than normal hearing individuals. In addition,
they concluded that both hearing aids produced very similar audiometric results. Sink et al.
(2005) echoed this finding, stating that ambiguous results were found for those individuals who
switched from air conduction devices to bone anchored hearing aids. They concluded that
BAHAs were not superior to air conduction aids. Mylanus et al. (1998) however, states that
once the air-bone gap is greater then approximately 30 dB SPL, better results should be
2
expected with BAHA devices. This is because air conduction hearing aids require higher gains,
which ultimately result in increased opportunities for feedback and poorer sound quality.
Mylanus et al. (1998) also stated that the majority of the patients in the study preferred the
BAHA device, when compared to their well-fitted air conduction aids. This appeared to be due
to a decreased number of visits to the outpatient clinic and a reduction in ear infections. The
study did indicate that neither type of hearing aid was preferred over the other when speech
recognition in noisy environments was evaluated.
Flynn et al. (2009) conducted a study that examined solutions available to those
individuals with severe mixed hearing loss. Their results confirmed those of Mylanus et al
(1998), concluding that BAHAs were superior devices once the air-bone gap exceeded 30 dB
SPL. The researchers examined ten subjects with mixed hearing loss who had worn a BAHA
device for at least a year. Mixed hearing loss was defined as an average sensorineural loss
greater than 25 dB SPL, in addition to an air-bone gap exceeding 30 dB SPL. In the study a
Baha Intenso was compared to an air conduction device, Oticon Sumo DM, which is a digital
superpower hearing aid. The results of the study indicated that all subjects increased speech
understanding in noise with the BAHA. Furthermore, all subjects reported that they preferred
the sound quality of the BAHA to that of the air conduction hearing aid. Although this study
indicates that BAHA users preferred the bone conduction device to an air conduction aid, it is
important to remember that this was only for people with severe mixed hearing loss and only
investigated one particular BAHA device. Further research is still needed in order to determine
what sound quality differences exist between various BAHAs.
Even though BAHA devices have been proven to be effective for individuals with
chronic otitis media (COM) and external auditory canal malformations, limited research has
3