Audiologist Dr. Steve Hallenbeck recommends you ‘go back to basics’ and address the steps before the verification. Here are his tips.
“Why does hearing aid x, y or z not quite match target at frequency a, b or c?”
This is a question I’ve been asked a lot over my career.
To address a question like this, I always think it’s best to go back to basics and address the fitting steps that come before verification. Often, if these steps are lined up, then verification goes smoothly.
Tips for a better fitting
1. Choose a receiver based on audibility
Maximizing effective hearing aid audibility might sound like a no-brainer, but all fittings have certain compromises that develop as part of the process.
Obviously, receiver size can influence comfort and tie your hands a little when making the best choice. But assuming that comfort and cosmetics are not the main drivers of your decision, often the receiver default of an M can be chosen, even when it’s not the best choice.
To dig a little deeper, let’s begin with a discussion on this tool, ‘the fitting range’. Fitting ranges can be helpful to eyeball and quickly estimate if a given hearing aid or receiver level will provide enough gain for a specific hearing loss.
Can you simply plot the loss on the audiogram, and then, bang your off to the races? The answer is No.
These are great estimates, but they are not the whole story. Fitting ranges across the industry are often based on manufacturers proprietary algorithms and assume an occluded earpiece.
As a rule of thumb, if thresholds generally fall in the grey area with about 10 dB of headroom, then you’re in pretty good shape. However, let’s say you’re trying to match NAL or DSL targets with an open fitting, the best next step in feeling confident with your choice of hearing aid is to simulate the fitting in the software using the intended dome and the fitting rule of your choice.
A little more work on the front end, but a few steps that will line up the process along the way nicely. If the target and gain curves don’t match in simulation, it’s time to move to a more powerful device or receiver.
2. Figure out the right coupling
After choosing the right power level, the next part of the puzzle is figuring out the right coupling, either a dome or custom earpiece.
Let’s categorize domes and earpieces based upon comfort, occlusion, and the hearing thresholds.
Based upon this criterion, the cap dome is the smallest, least occluding and feels the most like nothing is in the ear. Keep in mind a cap dome and open dome are intended for individuals with normal low frequency hearing and more ‘mild to moderately-severe’ losses in the high frequencies.
Vented domes and power domes have more contact points, become more occluding and are more appropriate for mild to moderate losses in the lows up to severe losses in the highs. As a rule of thumb, the vented dome is a great general starting point for many fittings.
Here are 3 more considerations:
- cShells and SlimTips have some comfort benefits given the custom fit.
- SlimTips can be beneficial for improved retention and when individuals have dexterity issues.
- cShells, while they can be made in any power level, are usually used for more severe to profound losses.
The coupling option will determine how much sound stays in the ear compared to how much leaks out of the ear. A good fitting balances all these components.
3. Run the feedback test
Every manufacturer is a little different and running a feedback test is a step where there is a fair amount of grey area.
When it comes to matching targets, I always advocate for running a feedback and real ear test, since they give you a nice cross check on your acoustic coupling and some data to build confidence.
The best cross check is to consider if the feedback curve intersects with the simulated gain curve and then decide on next steps accordingly.
4. Have realistic expectations
As they say, “the customer is always right” and “the hearing aid that’s worn is always the best”. Balance in a hearing aid fitting is all about realistic expectations for the audiologist as much as the hearing aid wearer.
For example, if you have a patient who cannot tolerate occlusion, you might choose the most open dome. But if they have 80 dB thresholds at 2K, they might need some give when matching certain targets. And in this example, if you’re going to chase the high frequency targets you might need to contend with feedback.
To that end, the role of the audiologist is to be the expert who knows how to balance the acoustic coupling options with the sound quality experience, occlusion abatement and speech audibility.
A great fitting does not have all the variables adding up to equal a matched target but includes target matching as part of the overall equation.
In my conversations with clinicians, many reported that these tips have helped clarify the process and upped their fitting game. I encourage you to give them a try and comment below on your experience.