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The CROS device (transmitter) is worn on the poorer-hearing ear. The CROS detects
sounds arriving at the poorer ear and transmits to the receiver of the device worn on the
normal-hearing ear, often utilizing NFMI ear-to-ear communication.
No amplification is added to the signal delivered to the normal-hearing ear.
n
A BICROS system is recommended for patients with an asymmetrical hearing loss where
the poorer ear cannot benefit from traditional amplification and the better-hearing ear
also requires amplification. Acoustic input reaching the poorer ear is routed to the betterhearing ear and presented along with the addition of gain prescribed for the loss in the
better-hearing ear.
n
Additional information about CROS and BICROS can be found in the comprehensive
literature review by Stewart and Woodward (2021).
n
A relatively new amplification option for those with asymmetrical hearing loss is AmpCROS.
With an AmpCROS system, the signal arriving at the device worn on the poorer-hearing
ear will be amplified and sent to both ears. The device on the better-hearing ear will deliver
the amplified signal from the other HA, along with a signal picked up from that HA. As this
amplification system is new to the market, additional research on its use and clinical value
is needed.
Hearing Aid Coupling
Earmolds
Noncustom HAs like the behind-the-ear (BTE; traditional, RICs, and slim tubes) require a method of
retention to channel sound from the HA into to the ear canal. The type of HA coupling selected must
consider degree of hearing loss and gain requirements, risk of feedback, and patient preference. HA
coupling can be a custom-made earmold or a non-custom modular fitting.
A modular fitting includes various sizes and shapes of small disposable domes. These can be used as
coupling options for RIC HAs and BTE HAs fit with a slim tube. Dome-style options include closed
dome, open dome, semi-open/tulip dome, and double/power dome.
n
A nonoccluding dome allows for a more open fit that can reduce occlusion effect and improve
patient comfort. The domes are easy and low cost to replace. Domes are also considered less
visible and more cosmetically appealing. With a non-custom dome, sound is more likely to
escape the ear canal, and therefore gain potential is limited.
n
Unfortunately, as gain requirements increase, the greater the likelihood of feedback occurring
when using a dome as compared to a more tightly fitting custom earmold option. Another
drawback to modular fittings includes ease of insertion. A patient with limited dexterity may
have more difficulty properly inserting a dome into the ear canal compared to a larger custom
earmold.
n
It should be noted that while modular fittings have the potential to reduce occlusion, certain
dome styles such as power/double domes can create a seal similar to that of a closed fit.
Therefore, the occlusion effect is still possible with a modular fitting depending on dome
characteristics.
A custom earmold begins with the creation of an earmold impression. There are several earmold
impression materials, including methyl methacrylate and silicone. Silicone, which is more commonly
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utilized, has a high viscosity and can result in a tighter-fitting earmold, which may be required for highgain applications (those with severe or severe-to-profound hearing loss). For a comprehensive review of
earmolds, their applications, acoustical properties, troubleshooting, and other pertinent information,
please refer to the Microsonic Custom Earmold Manual (https://store.microsonic-inc.com/manual/
earmolds_manual2.pdf).
AUDIOLOGY NUGGET
Some patients with chronic middle ear disease or other otologic disorders require
one or more otologic surgeries. These procedures may result in a change in the
size and shape of the ear canal and/or external auditory meatus. Increased care
and attention are needed when creating earmold impressions for this patient
population due to the changes in ear canal shape, which may create difficulty in
removing the impression material once it hardens. Collaboration with an otologist can be helpful to assist in packing the ear cavity prior to inserting impression
material. This can improve the resulting earmold and prevent complications
from earmold impressions.
The earmold may be created using a variety of materials, including acrylic, polyethylene, vinyl,
and silicone. The selection of earmold material may depend on texture of the ear, degree of hearing loss,
age of patient, and any known allergies to one of the earmold materials. See Table 9–3 for a list and
TABLE 9–3. Custom Earmold Styles
CUSTOM
EARMOLD DESCRIPTION
Full Shell Accommodates more severe hearing losses due to maximal retention. Most
common selection for infants and young children. May be slightly harder
to insert due to large size.
Half Shell Similar to full shell but top portion of canal is removed.
Skeleton Can accommodate a range of hearing loss severity. More cosmetically
appealing than full shell.
Canal Best for a mild to moderate hearing loss. With a well-fitted earmold,
accommodates more severe losses. May be easier to insert, but retention
may not be as secure.
Custom Open May be best for open fit BTE or CROS. Improved retention compared to a
noncustom coupling option.
Canal Lock Similar to a canal style with an added “lock” that lays posterior against the
Semi-Skeleton An open-fitting custom option.
concha bowl.
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description of custom earmold styles. Special considerations for earmolds should be made for pediatric
patients; these include:
n
The frequency of remakes needed and the durability of the earmold material.
Infants and young children grow quickly and will require new earmolds frequently.
More durable material may be required for smaller earmolds due to the size of the tubing
compared to the ear canal to prevent ripping with everyday use.
n
The warranty on the earmolds and the cost per mold
n
Color and design options
n
Tamperproof options such as cemented tubing and tube locks
Venting
When selecting custom earmolds for HA coupling, the audiologist must also select venting options.
Venting is used to manage the occlusion effect, increase comfort, and in some instances allow for
low-frequency sounds to enter the ear canal naturally. There are a number of vent options, including
parallel, diagonal, trench, select-a-vent (SAV), pressure, and acoustically optimized venting (AOV).
n
The use of a vent impacts the low-frequency response more than high-frequency response.
Specifically, the greater the vent diameter, the less low-frequency gain will reach the tympanic
membrane due to low-frequency signals escaping the ear canal and a mixing of natural sound
with processed sound.
n
A reduction in the low-frequency response can increase patient comfort by reducing unwanted
amplitude and occlusion. For many individuals with a downward-sloping high-frequency
hearing loss, with normal hearing in the low-frequency region, a larger vent can enable
low-frequency sounds to reach the ear more naturally. However, the greater the vent size, the
greater the chance of feedback, as more HA output will escape the ear canal.
n
Parallel venting (where the vent runs parallel to the sound bore) is typically preferred
to diagonal venting (where the vent intersects the sound bore) due to the possibility of
reducing the high-frequency output. Diagonal venting is often used with small ear sizes
where parallel venting is not possible. Trench venting involves creating a groove or channel
along the bottom of the HA or mold (near the bottom of the canal). Trenching a vent is
typically a last resort when significant occlusion is reported and other solutions prove to be
ineffective at reducing occlusion.
n
Occlusion can exist because of the physical presence of the HA in the ear or due to acoustic
features of HA programming. One way to quickly assess the source of occlusion is to have the
patient speak while the HA is in their ear and turned off. If the patient continues to report
the same concerns, the problem is physical occlusion. If the reported concerns are resolved,
this is acoustic occlusion. Physical occlusion can be addressed by modifications to the HA
like a different canal length or vent diameter. An acoustic occlusion may be addressed using
frequency modifications, such as a decrease in low-frequency gain. For more information on
dealing with occlusion and other related hearing aid sound quality troubleshooting, refer to
The Starkey Compression Handbook available on their website (https://order.starkeypro.com/
pdfs/The_Compression_Handbook.pdf).
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n
Venting is not appropriate for all HA users, especially those with greater degrees of hearing
435
loss. As a general rule, the greater severity of hearing gloss, the smaller the recommended
vent size due to the need to amplify low-frequency input as well as reduce the possibility of
feedback. A pressure vent is typically required for individuals with severe-to-profound losses if
venting is desired. Many manufacturers and earmold companies offer the option of requesting
what is often referred to as an AOV prescribed based on their experience and research. For
additional details related venting and its applications, please refer to the Microsonic Custom
Earmold Manual (https://store.microsonic-inc.com/manual/earmolds_manual2.pdf).
Ear Hooks
BTEs commonly utilize ear hooks, which aid in retention of the HA while also funneling sound from
the HA to the tubing. It is important for pediatric and adult patients that the size of the ear hook is
appropriate. Ear hooks may also be selected based on their acoustic characteristics, such as dampers.
n
Dampers are made of a screen-like material and are included in some ear hooks.
n
Damping is used to reduce resonant peaks in the mid-frequency region (approximately
1–3kHz) of the HA frequency response.
n
Wavelength resonances contribute to resonant peaks and while modern HA technology can
smooth peaks, the use of dampers provides additional smoothing.
n
The positioning of the dampers can also be manipulated for different acoustic effects. The
closer the damper is in relation to the tubing, the greater the effect of the damper.
Tubing
HA coupling also includes tubing selection. The National Association of Earmold Laboratories created
a naming convention for tubing based on tube diameter in 1979. The #13 tubing, also referred to as
standard tubing, is the most common tubing diameter, especially for traditional BTE fittings.
n
A thin tube (0.90–0.95 mm internal diameter) may be used for mini-BTEs in place of an
ear hook and traditional tubing configuration. Reducing the internal diameter of tubing will
lower both the frequencies of resonant peaks and the magnitude of the peaks. Thin tubing will
also create more roll-off (reduced frequency response) in the high-frequency region. Thus, a
slim tube coupled with a BTE and custom earmold may not be an appropriate tubing option
for a patient with a significant high-frequency hearing loss. Slim tubes may provide improved
aesthetics over standard tubing and may be considered with mild-to-moderate hearing losses
in the high-frequency region.
n
To naturally increase the high-frequency response (above 2–3 kHz), Libby Horns or belled
bores (sound bores that increase in diameter) can be utilized. To naturally reduce the highfrequency response, reverse horns can be utilized. It should be noted that due to the advent
of digital hearing aids and the ability to fine-tune the frequency response using programming
software, the use of earmold coupling to modify frequency responses is often less utilized.
However, modifying the acoustic coupling of a fitting to naturally alter the acoustic response
should not be discounted as a means of improving the quality of the fitting.
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Q & A
Question: Patient X is a 13-month-old with bilateral, moderately severe SNHL.
She is fit with traditional behind-the-ear HAs and a full-shell silicone earmold
with #13 tubing. Which venting selection would be best for this patient and why?
Answer: In this case, no venting should be added to the earmolds. This hearing
loss requires a high level of gain across the frequency range. The introduction
of a vent would allow some of that needed output power to escape out of the
ear canal (particularly in the low-frequency region). A vent in this case would
potentially create feedback. Additionally, venting should be used with caution
in pediatric patients as it allows another point for sound to escape and can
exacerbate feedback as the child outgrows their earmold. If this were an adult
patient, one might consider a pressure vent depending on certain fitting and
patient characteristics, but in the case of a child, venting is not advisable.
Hearing Aid Fitting
Programming
The means by which a HA is programmed related to gain and other signal processing considerations is
determined by its prescriptive fitting method. Each prescriptive method configures the HA programming to provide amplification based on audiometric and patient characteristics. Prescriptive fitting
methods can be divided into the following two categories:
n
Proprietary fitting strategies: these prescriptive fitting methods are specific to a particular HA
company and software. Each proprietary method uses algorithms developed based on research
by the HA company to program the signal processing features and gain characteristics of
the HA.
n
Device-independent (universal) fitting strategies: the use of thresholds and/or loudness
discomfort levels (LDLs) are used to calculate coupler or real ear targets. The targets can be
applied to any programmable HA and are not derived from the HA manufacturer.
With the foundations of loudness equalization and loudness normalization, a variety of deviceindependent fitting strategies were developed. Device-independent fitting strategies include the
following:
n
NAL-NL2: created by National Acoustic Laboratories, this strategy is designed to maximize
speech intelligibility while maintaining a comfortable level of loudness.
Loudness equalization, the method of amplifying speech so that all speech frequencies are
perceived as equal in loudness, is at the foundation of this strategy.
Provides less low-frequency gain compared to other listed strategies
NAL-NL2 provides more high-frequency emphasis compared to other methods (except
DSL).
Uses relatively low compression ratios.
When the entered age indicates a pediatric fitting, NAL-NL2 will increase the overall gain.
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n
DSL v5: created by faculty at the University of Western Ontario, this acronym in this strategy
stands for “desired sensation level.”
Loudness normalization (i.e., maintaining the natural amplitude differences across
frequencies) is at the foundation of this strategy.
This strategy was initially developed for pediatric HA fittings and is typically the preferred
fitting formula for pediatric HA fittings.
The goal of DSL v5 is to maximize speech information without creating discomfort.
Utilizes threshold data without needing LDL values.
There is a “pediatric” and “adult” version of the DSL v5, with the pediatric version
prescribing more gain overall.
n
IHAFF: the independent HA fitting formula is used to restore loudness perception across the
entire frequency range.
Loudness normalization is the foundation of this strategy.
n
FIG 6: The Figure 6 fitting strategy is used to calculate gain on a frequency-specific basis for
three input levels (40, 65, 90 dB).
Loudness normalization is the foundation of this strategy.
437
This strategy is not recommended for hearing losses with thresholds greater than 70 dB HL.
Q & A
Question: How do the amplification needs of children differ from those of
adults? Do clinicians need to modify the characteristics of amplification and
prescribed gain based on the patient’s age?
Answer: Unlike adults with acquired hearing loss who have significant language
experiences, children are actively developing speech and language. The success
of this development relies on adequate auditory access to speech sounds across
the frequency range. It is widely accepted that there is a greater importance of
both high-frequency and soft speech information for children due to the speech
spectra of their frequent communication partners (women and other children)
and the need for and benefits of incidental language learning. According to the
American Academy of Audiology (AAA, 2013) Pediatric Amplification Guidelines, “The primary goal of amplification is to provide, to the degree possible
given the hearing loss and limitation of hearing aid amplification, audibility
across the long-term average speech spectrum (LTASS), without delivering any
signal that is of an intensity that would be either uncomfortable or unsafe”
(p. 8). Additionally, children are at an increased risk for the adverse effects of
noise on speech recognition and they require a more favorable SNR (McCreery
et al., 2012). The American Speech-Language-Hearing Association’s (ASHA)
Working Group on Classroom Acoustics recommends a signal-to-noise ratio of
at least +15 dB at ear level. The use of appropriately fit HAs as well as remote
microphone technology in the classroom are both important to achieve this
recommendation.
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n
CAM 2: the Cambridge fitting formula focuses on speech levels of 65 and 85 dB SPL.
Loudness equalization is the foundation of this strategy.
Hearing Aid Verification
HA verification refers to a process of using objective measurements to ensure appropriate HA programming for a particular patient. Verification can be performed while the patient wears the HA, using
a probe microphone, or in a specialized test box using a coupler in place of the patient’s ear cavity.
The use of real ear (sometime referred to as probe microphone) or coupler measures to verify HAs is
considered best practice for device fittings. The following are terminology related to HA verification,
with expanded information provided for commonly utilized measurements.
n
Frequency response: total output of the HA measured in dB SPL
n
Gain: HA output level subtracted by HA input level
n
Real ear unaided response (REUR): SPL as a function of frequency measured in an unaided
and open ear canal
n
Real ear aided response (REAR): SPL as a function of frequency in a person’s ear canal with
the HA inserted and turned on
n
Real ear to coupler difference (RECD): difference between the output of a stimulus in the ear
canal compared to the output of the same stimulus in a 2-cc coupler
This value will vary based on the individual’s ear canal volume (the physical size of their ear
canal) and is useful in creating an improved HA fitting by correcting for the individual’s
ear canal volume in the fitting software. These values can be measured or estimated by the
verification equipment, with measured RECD values being the preferred method.
The use of RECD values is especially important in pediatric HA fittings as children’s ear
canal volumes will differ from a 2-cc coupler (and the estimated RECD values) more than
in adults. Children’s ear canal volumes are often smaller than the 2-cc coupler, and without
measured RECD values, HA fittings may be inappropriate if calculated in the coupler and
not using on-ear measures.
n
Real ear unaided gain (REUG): Gain created from the individual’s pinna and ear canal, as
measured in the ear canal; provides information regarding natural resonance of the ear
n
Real ear aided gain (REAG): HA gain measured in the ear canal
n
Real ear insertion gain (REIG): gain created by insertion of the HA calculated by subtracting
REUG from REAG
n
Even if real ear verification utilizing on-ear measurements is not possible, for example, due
to patient inability to sit still during the verification speech passage, the clinician should still
strive to obtain RECD to verify HA output in conjunction with test box verification. Test box
verification can be completed using HA couplers in conjunction with the patient’s RECD to
simulate the patient’s ear canal as an alternative to completing the entire verification on ear.
If RECD cannot be completed due to patient tolerance, ear drainage, occluding cerumen,
or other clinical contraindication, an age-specific estimation of RECD may be used. See
Table9–4 for a brief overview of available coupler types.
Real ear measures enable the clinician to:
n
Fine-tune and individualize HA output
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TABLE 9–4. Coupler Types
COUPLER
TYPE DESCRIPTION
HA-2 2 cc. Measures acoustic pressure generated by behind the ear
hearing aids. Hearing aid is connected to coupler via tubing.
HA-1 2cc. Measures acoustic pressure generated by ITE/ITC hearing
aids. Putty material is used to hold hearing aid in place.
HA-3 2 cc. Designed to test faceplates before they have been fully
assembled. Rarely used and difficult to acquire.
CIC Small volume of 0.4 cc representative of ear canal volume
associated with deeper insertion of CIC
n
Verify the in-situ HA response is meeting prescribed targets
n
Verify that in-situ performance is stable at annual evaluations
n
Verify output of HA is not exceeding uncomfortable levels (UCLs/LDLs), which are manually
entered or predicted based on the patient’s hearing loss
439
The first step in completing HA verification using real ear measures is to achieve a proper probe
tube placement in the ear canal. The tip of the probe tube should be placed within 5 mm of the
tympanic membrane. If the probe tube is not sufficiently deep in the canal, reflective interference and
radial waves can distort high-frequency measurements, leading to a reduced high-frequency response.
Newer verification equipment can emit a broadband signal and provide the clinician with an indication
as to when insertion depth is sufficient.
Q & A
Question: A 2-month-old baby is identified with a moderate sensorineural
hearing loss using auditory brainstem response (ABR) in both ears and hearing
aids are recommended. How do you use the ABR data to program the hearing
aids?
Answer: Hearing thresholds can be derived from ABR testing using tone-burst
stimuli to estimate hearing levels; however, the unit of measure for an ABR (dB
nHL) is different from behavioral hearing data (dB HL). These units differ for
a few reasons. The first is that dB nHL was developed using different referent
values from dB HL. Second, behavioral and electrophysiologic tests are not
evaluating the same region of the auditory system. Third, the stimuli are different between tone-burst ABRs and behavioral measures. For these reasons,
among others, a correction factor needs to be applied to convert dB nHL values
to estimated hearing levels for hearing aid fittings, referred to as dB eHL. Correction factors vary by frequency and fitting formula. For more information on
using correction factors for ABR thresholds, refer to Fuglholt (2010).
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Electroacoustic measurements can be completed with a verification system by using the test box.
These measurements include but are not limited to:
n
OSPL90: output sound pressure level assesses the maximum output of a HA by measuring the
response to a 90 dB SPL input stimulus.
n
Harmonic distortion: harmonic distortion occurs when a single frequency is presented
as input to the HA and the output contains the addition of an undesired frequency. The
harmonic distortion test provided in the Verifit2 measures harmonic distortion at the second
or third harmonics while varying input level and frequency.
n
Directionality: the directionality of HA microphones may be assessed by presenting noise to
the back microphone and speech stimuli to the front microphone. The intensity level of both
types of stimuli can be manipulated while the SPL is recorded.
n
Noise reduction: the output of the hearing aid is measured both before and during the
presentation of a broadband noise stimulus. A comparison can be made between the noise
and the hearing aid’s response to the noise, which provides a noise reduction value measured
in dB.
n
Input/output: a curve displaying HA output created based on the input stimulus intensity and
frequency.
n
ANSI test: a sequence of tests performed to assess HA regulations designated by ANSI
S3.22. The HA should be positioned in the test box as specifically directed by the verification
equipment protocol.
n
Battery drain test: measures the current of the battery while presenting varying inputs
frequencies and amplitudes. Battery life is estimated based on those measurements.
For additional details on various topics related to verification, please refer to the Audioscan Verifit2 Users
Guide (Audioscan, 2022).
KNOWLEDGE CHECKPOINT
The speech intelligibility index (SII) is an electroacoustic measurement that uses
a patient’s audiometric thresholds and the HA output to calculate a number
from 0.0 to 1.0, which is often converted to a percentage from 0% to 100%.
This percentage is correlated with the amount of speech that will be
audibility and potential for intelligibility. For example, an SII value of .5 or 50%
equates to 50% of average conversational speech being
The SII is a value that may be used to counsel patients and their families.
The aided SII value can be utilized to demonstrate how HAs improve speech
the need for amplification, as demonstrated by low unaided SII values. When
assessing HA programming, SII data may assist the audiologist in determining if
increasing gain levels to increase SII values (audibility) is required. For additional
information on the SII, please review Hornsby and Mueller (2004).
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CROS and BICROS Verification
Verification of a CROS or BICROS device is performed differently than traditional HAs. Probe microphone measures may be completed using a verification system to confirm that the CROS/BICROS is
able to overcome the head shadow effect while worn by the patient without over- or underamplifying
the better-hearing ear (i.e., does the system improve high-frequency output naturally reduced by the
head and torso). Most manufacturers offering CROS and BICROS technology provide detailed guides
to complete on-ear verification. Specific instructions for verification of CROS systems can be found in
the Verifit2 manual listed in the references.
Hearing Aid Validation
HA validation includes functional outcomes of HA use and subjective measures of performance. Validation measures include the following:
n
Aided threshold detection
This may be completed with the patient wearing their device(s) to respond to sounds via a
soundfield speaker utilizing age-appropriate audiometric test techniques.
This technique may have limitations related to the negative interaction between automated
HA systems such as compression, digital noise reduction, and expansion and the detection
of tonal signals. Currently, there is debate regarding the utility and accuracy of aided
threshold measurements.
For a comprehensive review of this topic, refer to Kuk and Ludvigsen (2003).
n
Speech perception testing
Speech perception measures can help determine device benefit by comparing speech
perception skill progression over time and the difference in speech perception with
and without amplification. Speech perception testing can occur in a variety of settings
including:
●
Testing with or without noise
●
Varying intensity levels (comparing soft speech to conversational speech intensities)
●
Closed-set testing versus open-set testing
Speech perception tests differ between adult and pediatric patients, and the patient’s
developmental status should be taken into consideration when choosing an assessment
measure.
n
Language outcomes
Language outcomes can be assessed in collaboration with a speech-language pathologist and
should be monitored in the pediatric population.
n
Quality of life outcomes
Assessing health-related quality of life (HRQOL) is a validation measure that can examine a
patient’s outcomes on a more global scale. HRQOL can include an individual’s perception
of their mental and physical health, as well as their social well-being (Yin et al., 2016).
A HRQOL outcome measure related to hearing loss and amplification is the Hearing
Environments and Reflection on Quality of Life (HEAR QL). These questionnaires were
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