Hearing aid fitting is a discipline within hearing care. It includes both the physical fit and the software fit of a new hearing aid. The goal of hearing aid fitting is to ensure your client's ability to hear sounds in everyday listening situations. It may take several follow-up evaluations to achieve this goal.
The fitting process begins with identifying your client’s hearing loss using audiometry. It is also essential to discuss your client’s lifestyle and hearing needs. Following this, you will recommend a new hearing aid for your client’s hearing needs. Fitting a hearing aid involves adjusting the fitting software so the hearing aid provides the proper amount of sound amplification. This may take place over the course of multiple follow-up visits.
You need to adjust your client’s hearing aids according to your client’s audiogram before or during the first fitting appointment. So, before the first appointment, you perform a hearing test to measure hearing thresholds and uncomfortable sound levels. Based on this, you use fitting software to limit uncomfortably loud sounds and to amplify sounds your client cannot hear. This functions as the initial programming.
The first appointment generally takes an hour. Firstly, you make sure the selected hearing aid and earmold fits comfortably on or in your client’s ear. If you have not already done the initial programming before the appointment, you will do it during the first appointment. The initial programming can seldom be enough and will typically require adjustment. During this appointment, you should also teach the hearing aid user how to use, care for and clean the hearing aid.
A successful hearing aid fitting depends on creating a personalized client journey. It is a collaboration between the hearing care professional, the client and any present family members. Together, you work towards a correct and comfortable listening experience. However, it is also crucial that you are good at managing your client’s expectations. It is also important to explain the limitations of persistent background noise. This may be work-related.
Hearing care professionals use real-ear measurement (REM) for objective adjustments of hearing aids. While your client is wearing the hearing aid, you place a probe microphone in your client’s ear canal. Take care to place the end within 5 mm of the eardrum. This microphone objectively measures the hearing aid’s performance in response to sound stimuli. You can then fit against recognized third-party algorithms.
Hearing tests determine the degree of hearing loss. Audiograms thereby inform you which hearing aid is suitable for your client. You may also discuss your client’s everyday listening situations, expectations, preferences and previous experience with hearing instruments. Preference may include items such as design, volume control and rechargeable batteries. Your client may also prefer a certain hearing aid style. For example, behind-the-ear (BTE) devices or in-the-ear (ITE) devices.
Populations with unilateral hearing loss may benefit from only using a hearing aid on one ear, also called monaural fitting. Populations with bilateral hearing loss may benefit from using a hearing aid on both ears. As the severity of the hearing loss may deviate on each ear, binaural fitting refers to fitting each aid individually. A severity that equates deafness will deem amplification, and thereby hearing aid devices, irrelevant.
Hearing instrument testing (HIT) is a branch within fitting. It is a technical measurement of a hearing instrument. You compare this measurement with the hearing instrument manufacturer's data sheet. Most hearing instrument manufacturers use international specifications for their data sheets. This includes the ANSI and IEC standards. You perform HIT to determine whether a hearing instrument functions as it should. You usually perform HIT after a hearing aid fitting using real-ear measurements or during a repair appointment. An anechoic test box provides an ideal acoustic environment for HIT.
HIT software often enables coupler-based fitting. This includes the real-ear-to-coupler difference (RECD) measurement. RECD is a standard ANSI measurement. It measures the difference in dB SPL produced in a real-ear aided response (REAR) and in a 2cc coupler. This is beneficial in pediatric testing, where the ear canal varies greatly for each client. In addition, most of the measurement takes place away from the client. This is an added benefit when dealing with young or difficult clients.
You can measure harmonic distortion by presenting a pure tone to a hearing device. You then evaluate the waveform of the output. This is to measure the distortion components relative to the total power of the input signal. Total harmonic distortion (THD) is the total sum of all harmonics. THD is expressed as a percentage value relative to the wanted output signal component. Distortion in moderate to severe amounts will negatively impact speech intelligibility (SI).
The compression attack time is the time it takes for the hearing aid compressor to react to an increase in input level. The compression recovery time is the time it takes for the hearing aid compressor to react to a decrease in input level. Testing the attack and recovery times gives you an idea of the time constants within the hearing aid. It also determines how fast the device reacts to incoming sounds.
Unwanted noise is provided by many sources in daily life. It can come from many different directions. Fortunately, many digital hearing aids have directional microphones. They suppress noise coming from some directions while maintaining a good sensitivity to sounds coming from another direction.
Directional microphones provide hearing aid users with the signals they prefer. From a hearing-instrument-testing (HIT) perspective, electroacoustic directionality testing evaluates how hearing aid directionality functions in certain acoustic environments. HIT test results can also provide good verification from a technical standpoint.
It can be difficult to understand feedback from your client. This may concern how his or her hearing aid performs. Affinity Compact has a feature that allows you to listen directly to the probe microphone or the coupler microphone. This enables you to hear exactly what the hearing aid is doing in your client's ear. In turn, this will aid in fitting the hearing aid.
Test boxes, also called test chambers, are an ideal tool to achieve the best conditions for hearing aid verification. This is important for the validity of hearing instrument testing (HIT) measurements. Test boxes can either be standalone or be embedded within a hearing aid fitting solution. Test boxes are usually constructed using sound-isolating materials. These help to prevent sound coming in and any sound from leaking out.
A test box has a closable lid, in which couplers and hearing aids rest on a sound-absorbing material. Foam is often used to absorb any sound output within the test box. This prevents noise from slipping out. On the base you will often find plugs for microphones, battery drain meters and external telecoil.
Test boxes help to provide the correct test environment for measurements to comply with the prescriptive ANSI and IEC standards. Hearing instrument testing (HIT) measurements that live up to the prescriptive ANSI and IEC standards provide verification of a hearing aid's performance.
Test boxes are used to conduct valid measurements of a hearing aid's performance. This includes digital signal processing (DSP) functions such as directionality, noise reduction and feedback suppression. You can also use test boxes to evaluate bone-anchored hearing instruments. You can do this with a tool such as the SKS10 Skull Simulator coupler. Finally, you can use test boxes for coupler‑based fitting such as real-ear-to-coupler difference (RECD).
A common user scenario is when testing a hearing aid that a client has reported to be faulty. In this circumstance, you can choose to program the hearing aid according to the standard ANSI or IEC settings. Afterwards, you compare the measured performance with the manufacturer's data sheet. If the measurements match the data sheet, then the hearing aid does not have any issues. If they do not, then you need to send the device for service or repair.
An alternative application is to run a hearing instrument testing (HIT) measurement following the client's hearing aid fitting. This would require the hearing aid to remain in the user settings. It would also allow you to keep a record of the hearing aid's performance on file. Should the client complain that the hearing aid does not sound as it had before, you can quickly run a new measurement and compare its performance against the initial hearing aid fitting. Replacing a lost hearing aid can also be done without a further appointment. Instead, you can program a new aid based on the prior fitting.
You use real-ear measurement for objective verification of what a hearing aid is doing in your client's ear canal. You do this by using a thin probe microphone placed within 5 mm of the eardrum. The microphone measures the sound pressure level (SPL) provided by the hearing aid and the resonance effect of your client's ear canal. In the real-ear measurement process, you match the measured sound to a third-party prescriptive target. This could be the NAL-NL1 or NAL-NL2 targets. You use this to achieve proper audibility across all frequencies of the hearing device. Real-ear measurement is also referred to as hearing aid verification.
Hearing aid verification can be divided into two branches: ear-based measurement and coupler‑based measurement. The first is typically used on adult populations and consists of the real-ear insertion gain (REIG) and real-ear aided response (REAR) measurements. The latter is typically used on pediatric populations or adults with special needs and consists of the real-ear-to-coupler difference (RECD) measurement. Most of RECD testing is performed away from the patient.
The shape and size of an ear canal have a large effect on the sound achieved close to the eardrum. It is therefore crucial to include your client's auditory effects in the hearing aid fitting. The condition of your client's ear canal is also important. For example, too much earwax must be removed ahead of performing real-ear measures. This obstacle can cause acoustic artefacts within your results. Contraindications, such as a perforated eardrum, may lead you to perform alternative steps to achieve the best fitting.
Beyond a hearing aid fitting solution, you need a loudspeaker. This produces the sounds that you verify the hearing device against. Secondly, you need a reference microphone. This sits outside your client’s ear and collects the sound from the loudspeaker to ensure correct intensity levels. Finally, you need a probe microphone, which you insert into your client's ear, and real‑ear measurement software. Typically, the probe and reference microphones are built into the real-ear measurement headset.
Following audiometry, you will probably use the manufacturer's first-fit as a starting point. This is achieved using your client's audiogram. Thereafter, real-ear measures verify what the hearing device is doing and displays this on screen. You measure the effects of your client's ear and the hearing aid with a probe microphone. The goal is to match the hearing aid's real-ear amplification to target. You achieve this target match by manually altering the gain trimmers in the fitting software.
Hearing aid fitting begins once your client's hearing aid amplification has achieved a target match. This is a starting point that demonstrates to your client how her hearing aid should perform for her hearing loss and lifestyle. However, the loudness can be overwhelming for your client. She may prefer a softer amplification strategy to acclimatize to. It is crucial that you include your client's subjective feedback in the fitting process. This could be the difference between the acceptance or the rejection of a hearing instrument.
Real-ear measurement provides a tailor-made approach to the fitting. Real-ear measurement can also help you to demonstrate how a hearing aid works and how to accommodate for this in daily life. It allows you, your client and support to visualize the hearing aid's performance. This demonstration can help your client to understand the limitations her hearing loss and lifestyle incur. Generally, real-ear measurement can have a positive psychological impact on your client. It can increase your client's perceived quality of care. It can also increase your client's confidence in the benefit of the hearing aid.
Make sure to get the client into a position 0.5 – 1 m from the loudspeaker, with the loudspeaker at ear level. If this is not possible, angle the loudspeaker upwards, pointing in direction of the ear. Your client should look directly at the loudspeaker (0⁰) or slightly away (45⁰). In addition, it is important your client is sat roughly 1 m away from reflective surfaces.
REAR is the output of a hearing aid in the ear in response to an external stimulus, expressed in dB SPL. REAR testing requires your client to remain still. This means certain patients are more suitable for RECD testing. Real-ear insertion gain (REIG) is a relative measure. It is the difference between the real-ear unaided response (REUR) and REAR. REUR is the same as the real-ear unaided gain (REUG) but is displayed in dB SPL.
Place a marker on the probe tube so it sits at the end of the ear canal. In normal adults, the British Society of Audiology (BSA) recommends 28 mm (women) or 30 mm (men) between the marker and the end of the probe tube.
VSPM gives you a live view of a hearing aid's performance against your client's hearing loss. This allows you to accurately determine your client's audibility. VSPM allows you to map out how a hearing aid reacts to different sounds, such as the ISTS speech signal, across the frequency and intensity domains. You can thereby better explain the benefits of amplification to your client. You perform VSM in a real-ear aided response (REAR) dB SPL domain.
The primary goal of VSPM is to match hearing aid output to a research-based prescriptive target. This is similar to what you do in the real-ear measurement (REM) process. In addition to the prescriptive match to target, there are other helpful tools, such as the speech intelligibility index (SII) score. This is an indicator of the percentage of speech information that is audible and usable for your client.
VSPM is a real-ear aided response (REAR) measurement. It expresses the amplification output at the eardrum in dB SPL. After placing an in-situ headset on your client's ear, VSPM consists of four easy steps:
When performing VSPM, you can match to target while showing the benefit via a simultaneous unaided and aided display.
A major advantage of VSPM is that you can verify the amplification provided by a hearing instrument. You do this by using realistic sounds such as speech or music. VSPM can help you to understand how the device is operating. It can also help you to troubleshoot deviances between your client's experienced hearing and the fitting software. The combination of auditory and visual cues is essential to help you understand which rehabilitation techniques to implement during the hearing journey. You can also monitor effects on the hearing aid when you amplify it. This maximizes you and your client's satisfaction.
In the display, you will find an upper limit. This displays your client's uncomfortable loudness level (ULL). Secondly, you will find a lower limit. This displays your client's audiometric threshold. The area between the two limits is the dynamic fitting range. This is audible and meaningful sound whilst not being too loud. The dynamic fitting range can help you to explain the limitations of your client's hearing loss. Thirdly, you will see a solid red line. This expresses the average intensity for a given acoustic stimulus. Finally, you will notice a shaded area within the dynamic range. This is a percentile analysis.
VSPM is an important part of hearing aid fitting. It makes hearing aid performance visible for your client and your client's support. This can help you to explain how your client's hearing aid is performing and to manage your client's expectations. VSPM combines the objective aspect of the verification and the subjective counseling component. Combining these helps to save time and make verification a positive experience for your client. Together with real-ear measurement (REM), VSPM can also reduce the amount of follow-up calibrations. This is a win-win situation for the clinician and his or her client.
"Affinity Compact is beautifully designed. The box is wonderful. It has a sweet touch and you have this new changing light. Affinity Compact brings more specificity at the high frequencies, and this is where we find most of the hearing loss among our patients. It gives you a good feeling when you have all the materials to make the best fitting and your patient feels happy about your job. What more could you want?"
B.Sc. Audiologist at Sonance Audition, Castries, France