CENTRA Active: A new receiver-in-canal solution designed to ...

Background information on RIC technology
Corporate Audiology, Siemens Audiologische Technik GmbH, Germany
www.siemens.com/hearing
CENTRA Active:
A new receiver-in-canal
solution designed to enhance
patient satisfaction
Page 2 I Introduction
Page 2 II A style and substance solution
Page 5 III Product information
Page 7 IV Acoustic advantages
Page 8 V Research results
Page 9 VI Fitting guidelines
Page 10 VII Summary
Page 11 References
Abstract
One of the biggest fitting challenges for hearing care professionals is handling the
high expectations of both new and experienced hearing instrument wearers. With
modern technology, wearers seek high speech intelligibility in noise and a high level
of overall listening comfort in a variety of acoustic environments. In addition, research
indicates that consumers want hearing instruments that are discrete, easy to use,
comfortable to wear, and robust. CENTRA Active combines the latest advancements
in signal processing with receiver-in-canal (RIC) technology and a series of proprietary
innovations to meet these requirements. This approach allows a feedback-free and
occlusion-free fitting for a wide range of hearing losses. Behavioral studies show that
CENTRA Active also provides an outstanding spontaneous acceptance. The special
acoustics of CENTRA Active are discussed in detail and guidelines for fitting and
handling are given.

I
Introduction
II
A style and
substance
solution
2
Introduction
One major advancement in hearing instrument technology
over the years has been observed in the introduction
of new algorithms in the digital signal
processing. Notable examples of this from Siemens
are e2e wireless technology (Powers & Burton
2005), SoundSmoothing (Keidser et al. 2007,
Chalupper & Powers 2007) and the Learning Volume
Control (“DataLearning”) (Dillon et al. 2006, Chalupper
& Powers 2006). Research has shown that these
advancements enhance patient benefit.
In addition to innovations in signal processing, there
is a need for advancements that will increase patient
acceptance of hearing instruments. Consumer surveys
(Kochkin 2002), indicate that many hearing aid
users desire hearing instruments which are discrete,
easy to use, comfortable to wear and provide overall
listening comfort. It is therefore important, that advancements
in signal processing be combined with
other innovations – for example in style and ease of
use – to accommodate the other desired attributes
of hearing instruments and ultimately lead to increased
use and benefit.
A style and substance solution
A new hearing instrument from Siemens, CENTRA
Active, combines the advanced and clinically proven
signal processing strategies of the CENTRA hearing
instrument family with new design and handling
features to enhance cosmetics, usability and patient
wearing comfort. CENTRA Active includes the following
digital signal processing features from the successful
CENTRA product family:
• SoundSmoothing
• Learning Volume Control (“DataLearning”)
• e2e wireless
• Automatic, multichannel adaptive directional
microphone
• Speech and noise management with Wiener Filter
and modulation-based digital noise reduction
• Adaptive high-speed feedback cancellation system
• Data logging
• ePocket option
• 16-channel compression system
CENTRA Active also employs other new unique features
designed to enhance user acceptance. In recent
years, the behind-the-ear (BTE) open canal (OC)
hearing instrument has enjoyed increased popularity.
As reviewed by Mueller (Mueller 2006), there
are many advantages to OC fittings, and patient surveys
have shown that these instruments provide improved
benefit and satisfaction (Gnewikow and Moss
2006; Taylor 2006). One advantage of the OC fitting
is in regard to cosmetics – an important concern for
most consumers. With receiver-in-canal BTEs, the
BTE itself can be relatively small since the receiver,
one of the largest components, is placed outside the
instrument’s housing into the ear canal. This of
course makes the hearing instrument less visible and
more cosmetically appealing. The thin wire used to
transfer the signal to the receiver in the ear canal is
also thinner and less conspicuous than typical earmold
tubing.
When receivers are placed in the ear canal, as in custom
instruments and the RIC design, it is critical that
an effective and efficient wax protection device is
used (Branda & Chalupper 2007). Such a device,
referred to as “C-Guard,” is a standard feature for all
CENTRA Active products. C-Guard is one of the three
unique components of CENTRA Active’s AquaProtect
(Siemens 2007) feature. In combination with a
unique GORE exchangeable microphone cover and
nanocoating, AquaProtect shields CENTRA Active
from perspiration, water and dirt. This provides additional
wearing comfort and reliability when used
outside, or for participating in sports or other activities
where there is a high moisture level surrounding
the hearing instrument.
CENTRA Active also includes a rechargeable feature.
CENTRA Active’s charger option provides additional
handling comfort and ease of use as there is no need
to change batteries.
These innovations unite the style and substance required
for a modern hearing instrument that meets
the requirements for today’s active wearers.
CENTRA Active combines the clinically proven signal
processing strategies of CENTRA with new design
and handling features.

Product information
While CENTRA Active contains the same technology as
the proven CENTRA family, there are some unique aspects
to its design and the method by which it is fitted
in the ear canal.
Fig. 1 Components of the external
receiver
Figure 1: Components of the external receiver including the
dome with C-Guard and the receiver housing.
CENTRA Active’s receiver unit and dome are shown
in Figure 1. The receiver unit consists of the receiver
wire, the housing spout, the receiver and the receiver
housing all integrated into one piece that securely
attaches to the instrument body with a click
and turn connection. The CENTRA Active dome tip
includes an integrated C-Guard barrier membrane.
This membrane prevents even liquid cerumen from
impacting the receiver (Branda & Chalupper 2007).
The C-Guard membrane is slightly recessed from
the tip of the dome to prevent damage to the membrane.
Domes are easily but securely attached to the
receiver spout tip, so that they can be changed as
needed. CENTRA Active can be fit with either open
or closed earpieces. Open domes are available in
three sizes (6, 8 and 10 mm) and closed domes are
available in two sizes (8 and 10 mm).
CENTRA Active’s receiver housing is ergonomically
bent to assure easy insertion and a comfortable fit in
the ear canal. In addition to comfort, the receiver
housing was carefully designed so that it fits appropriately
around the bend of the ear canal, and the
outlet is maintained in the center of the canal. With
a straight receiver housing, as is the case with other
systems, there is a risk that the tip may be pushed
against the canal wall. In addition to discomfort, this
may cause increased feedback risk, reduction in the
amplified signal, cerumen accumulation, and cause
the receiver to work its way out of the canal.
Acoustic advantages
Spout
Dome with integrated
C-Guard membrane
Receiver housing
In addition to the cosmetic and “ease of use” benefits
of CENTRA Active, there also are important acoustic
advantages that have been optimized in the Active
design.
Enhanced high frequencies
As reviewed by Mueller (Mueller 2006), improved
high frequency amplification is a desired attribute
of OC fittings. Mueller and Ricketts (Mueller and
Ricketts 2006) demonstrate that when the coupling
in the ear canal allows for a residual ear canal resonance,
this resonance then contributes to the amplified
signal. That is, in the region of the residual
resonance, less amplifier gain is needed to achieve
desired ear canal SPL. This residual ear canal resonance
usually is in the 2000-3000 Hz range – important
frequencies for speech understanding, especially
in background noise.
Acoustics of RIC and conventional BTE systems
III
Transmission to eardrum
Feedback path
Figure 2: Illustration of the sound transmission paths for
the RIC and a conventional BTE, showing both the transmission
of the amplified sounds to the eardrum (REAR),
and also the path of the sound back to the hearing aid
microphone (feedback path).
The receiver-in-canal design most obviously
differs from traditional BTEs because of the receiver
location in the ear canal. However, the
schematic drawings in Figure 2 show that the
acoustic sound transmission paths to the eardrum
and to the hearing instrument’s microphone
are very similar for traditional BTEs and
receiver-in-canal instruments. Because of this
similarity, the probability of acoustic feedback
with a receiver-in-canal instrument as compared
to a traditional BTE will also be similar. Factors
that influence the occurrence of feedback include:
the intensity of the input signal, the intensity
of the amplified signal in the ear canal,
individual anatomy of the ear canal and outer
ear, the openness of the fitting, and the location
of the hearing aid microphone. As shown
in Figure 2, all of these contributing factors are
essentially the same for hearing instruments
with an external receiver and for traditional
BTEs using the same earmold and microphone
location. Similar considerations apply for the
sound pressure level delivered to the eardrum.
Product
information
IV
Acoustic
advantages
3

IV
Acoustic
advantages
4
Gain / dB
Fig. 3 REOG of open and closed dome
20
15
10
5
0
-5
-10
-15
REUG
Dome closed
Dome open
-20
100 500 1000 4000 10000
Figure 3: Illustration of the real ear occluded gain (REOG) for
both the open and closed domes of CENTRA Active. The real
ear unaided gain (REUG) is shown for comparison.
Figure 3 shows the real ear unaided gain (REUG) for
the open ear canal. Observe that there is 13-17 dB
peak in the 2000 to 4000 Hz range. In a closed hearing
aid fitting this open ear advantage is eliminated,
as the canal is closed and resonant properties are
altered. However, observe in the dark blue curve of
Figure 3, when the receiver fitted in the open dome
is placed in the canal, all the open ear effects remain.
The curve for the closed dome shows that there is
nearly no difference to the REUG below 1 kHz, but
significant attenuation at higher frequencies. The
following sections examine the consequences of
these acoustic properties on occlusion and feedback
stability.
Occlusion reduction
Frequency / Hz
In addition to improved high frequency amplification,
another desired benefit of CENTRA Active is the
reduction of the occlusion effect. The occlusion effect,
often described as a “hollowness” of one’s own
voice, is known to be bothersome, and in some instances,
prevents individuals from using amplification.
Physically, the occlusion effect relates to an in
increase of sound pressure level at low frequencies
inside the ear canal. While the curves shown in Figure
3 suggest that the ear canal is not significantly
occluded below 1 kHz, this is not a direct measure of
the “occlusion effect,” as REOG is measured with an
external signal.
Fig. 4 Occlusion with open and
closed dome
Occlusion / dB
12
10
8
6
4
2
0
-2
250 500
Figure 4: Occlusion measurements for CENTRA Active fitted
with both the open and closed dome. Results from MacKenzie
2006 for occluded, 2 mm and OC tips shown for comparison.
To confirm that CENTRA Active’s ear pieces do not
cause an occlusion effect, testing was conducted
with ten individuals (five males and five females).
Each subject was fitted with the most appropriate
dome size and wire length. The amount of occlusion
was measured by subtracting the level in the
open ear canal from the level in the test condition
(open dome, closed dome). Subjects vocalized an
“ee” during the measurements to generate an “internal”
test signal. The results of this testing, using
the open and closed dome are shown in Figure 4.
For comparison, these mean findings are displayed
with the mean data from MacKenzie and colleagues
(MacKenzie et al. 2004), which illustrate the expected
amount of occlusion for an occluded and open
fitting, and a vented fitting (2-mm vent). No significant
differences between female and male subjects
were observed. Note that with CENTRA Active, negligible
occlusion is present. Even with the tighter fitting
closed dome, average occlusion is no more than
2-3 dB – a value that would not be bothersome nor
even noticeable for most patients.
Smooth frequency response
Frequency / Hz
Occluded
2 mm vent
Open canal
Dome open
Dome closed
1000
There is a direct relationship between sound quality
and the smoothness of the frequency response. The
receiver and coupling system of CENTRA Active were
optimized to provide a smooth response, with extended
amplification in the higher frequencies.
Figure 5 illustrates measures taken in the ear of the
KEMAR for both the open and closed domes. Notice
that the frequency response of CENTRA Active is
smooth throughout the frequency range, with high
frequency amplification extending to 8000 Hz.

Insertion gain / dB
Fig. 5 Maximum insertion gain for open
and closed dome
50
40
30
20
10
0
Dome closed
Dome open
-10
100 500 1000 4000 10000
Figure 5: Measured maximum insertion gain (IG) for both the
open and closed domes of CENTRA Active.
Observe that for both domes, gain in the higher frequencies
is similar. Because there is less ear canal leakage
with the closed dome, gain with this fitting option
is 10 to 15 dB higher in the lower frequencies.
Feedback stability
Frequency / Hz
Maximum insertion gain, displayed for CENTRA
Active in Figure 5, can be practically applied only
if feedback is absent. To accomplish this, the maximum
gain without feedback (also known as “critical
gain” or “maximum stable gain”) must be larger than
the maximum insertion gain. A commonly used
method to determine the critical gain for a given individual
is an open loop gain (“OLG”) measurement 1
(see Dillon 2001 for review).
Figure 6 shows the range (i.e. minimum and maximum
values) and mean of the OLG measurements
for 50 subjects with CENTRA Active fitted with the
closed dome. Observe that there is an extremely
large individual variance – up to 40 dB for some frequencies!
Some patients, especially in the low frequencies,
have stable gain values much larger than
the maximum gain of CENTRA Active. Note that the
average OLG at 3000 Hz is about 30 dB; this is the
frequency region where the SPL is typically the highest
in the ear canal, and hence the probability of
feedback is highest. The mean OLG in this region
is about 10 dB below the maximum insertion gain
shown in Figure 5. Due to the large individual variability,
OLG measurements are recommended. Because
the open dome is less occluding (see Figure 3),
the average stable gain will be somewhat less at all
frequencies than shown in Figure 6 for the closed
dome.
1 The critical gain measurement in CONNEXX also applies the open
loop gain technique
Fig. 6 OLG measurements: Range and
mean for closed dome
Open loop gain / dB
80
70
60
50
40
30
20
10
0
Dome closed
Dome open
500 1000 4000
Figure 6: The mean open loop gain for CENTRA Active (closed
dome), with minimum and maximum values.
With any OC fitting, the risk of feedback is higher
than that of a closed fitting. This feedback risk indicates
the need for an effective feedback cancellation
system. CENTRA Active’s feedback cancellation system
provides between 10 and 20 dB additional stable
gain. Factors that influence this are individual hearing
loss, individual anatomy and the acoustical situa-
tion. Since the feedback path can vary by up to 20 dB
in daily life conditions (e.g. due to chewing or proximity
to windows), a combination of OLG optimization
(e.g. by using OPEN) and an adaptive feedback
canceller is able to provide feedback-free listening
for most patients in daily life (Chalupper & Kasanmascheff
2005).
Research results
Frequency / Hz
As discussed, the acoustic benefits of CENTRA Active
are numerous. Therefore, whether these design attributes
would translate to improved patient satisfaction
was the subject of a recent study conducted
at the Hörzentrum in Oldenburg, Germany. Twenty
experienced hearing instrument wearers with moderate
symmetrical hearing loss participated in the
study. CENTRA Active was compared to three other
premium OC hearing instruments from major manufacturers.
One of the comparative products also employed
RIC technology, while the other two were traditional
BTE designs with the receivers located in the
instrument housing.
Each of the four hearing instruments was fitted to
the subjects, and ear canal recordings were made
for three different sound examples: speech in quiet,
speech in a background noise babble, and music
(flute).
IV
Acoustic
advantages
V
Research results
5

V
Research results
VI
Fitting
guidelines
6
Open loop gain (OLG) measurement
To understand the OLG technique, refer back to
Figure 2. This illustration shows that the sound
travels through the hearing aid to the receiver
and after it is delivered in the ear canal, a portion
of the sound leaks back to the microphone
and is picked up again. It is possible, therefore
to think of sound as a “closed loop” (from microphone
to microphone) for all types of hearing
instruments. When the OLG testing is con-
ducted, however, the hearing aid signal processing
path is split between microphone and
receiver. That is, the microphone signal is not
forwarded to the receiver. Hence, the loop
is opened, which is why it’s referred to as an
“open loop” measure.
Now imagine what happens in the “closed loop”
if there is no attenuation of the sound that
leaves the receiver. As soon as any amount of
gain is applied, the sound will be amplified by
this amount in each run through the closed
loop. Because of the speed of sound, this continuous
looping effect quickly drives the gain
to the maximum output of the hearing instrument.
If there is a dominant frequency, there
will be a whistle, or what has come to be
known as feedback.
Given this knowledge of the physics of sound,
it becomes clear that the amount of attenuation
in the feedback path directly indicates how
much gain can be applied without feedback.
Hence, if we simply measure the attenuation
between the ear canal SPL and the microphone,
we know the maximum stable gain; this in fact
is the OLG measurement. For example, if a tone
was generated with a known output of 80 dB
SPL, and the microphone picks up this tone via
the feedback path and measures its level to be
10 dB SPL, then, the maximum stable gain
would be 70 dB at this frequency. It’s important
to understand that this value is unrelated to the
maximum gain provided by the hearing aid
used to conduct the measurement. It simply indicates
the maximum stable gain that potentially
could be delivered, given the ear acoustics,
earmold plumbing and the microphone
location of that particular fitting.
These recordings were then played back-to-back to
the participants using a paired-comparison paradigm.
By using recordings, the participants were blinded to
the products themselves, and factors such as size of
the hearing instrument, comfort of the fitting, etc.,
were not confounding variables. In each round, all
products were compared to each other, and in each
comparison, the participant was instructed to pick
a “winner” (the hearing instrument that they would
prefer to use). In the case that two instruments
sounded the same, the subject was to indicate that
as well. The complete round-robin procedure was
repeated two times, resulting in a total of 18 comparisons
for each hearing instrument.
Fig. 7 Preference in direct comparison
Wins / %
50
40
30
20
10
0
Figure 7: Percent of wins in paired comparison test for three
different listening conditions. Data represents pairings where
differences were noted.
The results of this research are illustrated in Figure 7.
Shown are the percent of wins for each product for
each listening condition. As all devices were premium
products, in several of the comparisons, no difference
could be detected. However, observe that
when differences were noted, CENTRA Active consistently
had the most wins for all three listening conditions.
These findings reveal that even when compared
to the highest level of competition, the signal
processing and acoustics of CENTRA Active have a
distinct advantage.
Fitting guidelines
In general, fitting decisions and procedures concerning
CENTRA Active are similar to other members of
the CENTRA family. There are some specific issues to
consider for CENTRA Active, however, that will be
discussed in this section.
Fitting range
CENTRA
Active
HI #2
Speech in noise
Speech in quiet
Music
HI #3
HI #4
As shown in Figure 8, CENTRA Active is appropriate
for a wide range of hearing losses. In observing the
fitting range, it’s important to consider that the upper
limit of the fitting range for Siemens hearing

instruments is calculated based on NAL-NL1, Acclimatization
Level 2 – including 5-10 dB headroom to
allow for the peaks of speech, temporary VC adjustments,
and/or progressive hearing loss.
Fig. 8 Fitting range
Hearing loss / dB HL
dB
0
20
40
60
80
100
120
Closed domes
Open domes
125 250 500 1k 2k 4k 8k
Frequency / Hz
Figure 8: The shaded areas on the audiogram represent the
recommended fitting range for CENTRA Active with open and
closed domes.
Receiver selection and replacement
The receiver unit is available in three different wire
lengths; the most appropriate length can be easily
determined for each patient using the CENTRA Active
measuring gauge. The receiver assembly is easy to
attach and remove (see Figure 9). To remove, simply
rotate the “turn-and-click” connection counter-clockwise
(noticeable click). To attach, take the new re-
Summary
ceiver and then turn the connection clockwise (noticeable
click). This easy process is also used to replace
damaged receivers in office and eliminates the need
to send out the hearing aid for receiver repair.
Fig. 9 Receiver selection & replacement
Figure 9: Illustration of the procedure for replacing the external
receiver of CENTRA Active.
Prescriptive algorithm
to open
Programming CENTRA Active requires Siemens fitting
software CONNEXX 5.4, Sifit database 5.4.2. First Fit
can be performed using the following fitting algorithms:
Siemens OPEN (Chalupper & Kasanmascheff
2005), NAL-NL1 or DSL. The OPEN algorithm uses
NAL-NL1 as the audiologic rationale to calculate input
frequency-specific gain and output values. In
addition, the OPEN formula automatically optimizes
the frequency response if it is predicted that the
NAL-NL1 output values will exceed critical gain. In
most cases because of CENTRA Active’s fast-acting
feedback cancellation system, the NAL-NL1 targets
can be met, so the OPEN algorithm is a conservative
approach to further guard against unwanted feedback.
Research and anecdotal evidence alike indicate that hearing instrument wearers desire hearing instruments
that are discrete, easy to use, comfortable to wear, provide overall listening comfort and
perform in a variety of acoustic environments. Research also indicates that these patients receive
significant benefit from the latest algorithms and special features available with modern hearing instruments.
The goal, therefore, when a new product is introduced, is to couple the new advanced algorithms
with new appealing hearing aid designs as well as ergonomic advances. CENTRA Active meets
this goal by accommodating all these desired attributes, and more.
Using the latest receiver-in-canal technology, this innovative product provides a wide range of gain and
output, a smooth extended frequency response and an occlusion-free fitting. Innovations in handling,
robustness and design have also been achieved. Moreover, clinical trial results have supported patient’s
preference of CENTRA Active over other premium solutions. In summary, CENTRA Active meets the requirements
of a wide range of patients, and its design and features are expected to further enhance
patient benefit and satisfaction.
VI
Fitting
guidelines
VII
Summary
7

Siemens
Audiologische Technik GmbH
Gebbertstrasse 125
91058 Erlangen
Germany
Phone +49 (9131) 308-0
www.siemens.com/hearing
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Open is in.
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Real-world satisfaction and benefit with open-canal fittings.
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