Martin, Robert L. PhD
Robert L. Martin, PhD, has been a Dispensing Audiologist in private practice in the San Diego area for more than 30 years. He has been writing Nuts & Bolts since 1989.
Let me start by asking a trick question: If a patient returns to your office with a pair of new hearing aids, and says, “I don't like these hearing aids. The loud noises bother me,” what do you do?
Figure. Robert L. Ma...Image Tools
Your response probably depends on how long you have been working in this field. A novice may assume the output is too high and adjust the output limiting circuits. An experienced professional would most likely ask the patient, “What do you mean ‘too loud’? Show me.”
It takes years to learn how to understand patients’ comments. Recently, a patient said her hearing aid kept making “that noise.” It took some time before I realized “that noise” was the alert tone that sounded every time she changed programs.
When we solve problems, we need to engage the patient, spouse, and other family members in productive conversation. We want to make sure we are all talking about the same thing. It helps to double-check all parts of the fitting, look at the most recent hearing test, listen to the hearing aids, and look in the ears and sound tubes. The problem may be technical, or there may be a problem with the insertion or the use-gain level. On the other hand, the problem the patient is reporting may have nothing to do with the instruments.
If the patient is using the instruments correctly, but some sounds are actually too loud, be careful when you adjust the hearing aids. Many practitioners simply increase the automatic gain control (AGC) compression ratios across the total frequency range to deal with the reported loudness or noise issue. In my opinion, this is a mistake. You want to solve all problems, not trade one problem (excess loudness) for another (a decrease in clarity and word understanding). If a patient says the hearing aids are too loud or too noisy, I ask the patient to tell me about it. We need to be careful not to jump to conclusions.
Let's look at some examples of loud sounds and noise, and work through the remedies to these problems.
* Noise from a distant freeway: If a patient lives near a major highway, they will hear the low frequency noise that reaches their house unless you are cautious when you select the gain and AGC values. Patients often attempt to close the doors and windows of the house to reduce this noise, which helps, but is not a real solution.When I run into this type of problem, I reduce the gain in the low frequencies, and I have the patient use their noise reduction program at home. Directional microphones are typically used in restaurants or noisy groups, but they can also reduce distant freeway noise.
* A man with a very loud voice: If the patient lives with a man who has an extra-loud voice and speech therapy is not an option (I have an uncle like this), I use less-than-normal gain in the lower frequencies, very low compression thresholds, and moderate compression ratios in the lower frequencies—not the higher. I see this as an extra-energy-in-the-low-frequencies problem, not a broadband energy problem. Reducing gain in the lows is helpful because the unwanted sound is in that zone.
* Dogs barking: The noise intensity level of a dog barking in the house is often high. Increasing compression in this instance is usually beneficial for the patient because the perceived noise is changed from painful or extremely loud to tolerable.When the problem is dogs barking in the yard next door, you are dealing with a very different type of acoustical event—an annoyance rather than a high-intensity noise surge. If it's the patient's dog, he usually loves the dog and adjustments in AGC can make the noise acceptable. When dogs live next door, and the patient reports hearing them bark all the time, the patient usually hates the dogs, and wants to get rid of the noise. Modifying the AGC setting in this case typically does not solve the problem. Reducing the volume level or removing the hearing aids is the typical response.
* Rustling noises: The rustle of the newspaper and a small fan a few feet away are quite similar. Patients who complain about these noises are generally becoming accustomed to amplification and other technical considerations. Some patients are married to small fans, others to their morning newspapers. In both cases, we are dealing with softer, higher-pitched noises, not intense levels of sound.Increasing the overall compression ratio will not reduce the sounds significantly (remember: these are soft sounds). Rather than using AGC to reduce the sounds, I prefer a simple reduction in gain. Make sure the patient also has an easy-to-operate volume control—the new small remote controls are wonderful—and have the patient reduce the volume to a comfortable level while reading the paper. I usually talk to the patient about getting used to amplification, and reducing and increasing the volume setting for special occasions. A volume control used by a knowledgeable user is a powerful noise reduction tool.
* Feedback from the hearing aid: If patients are adjusting volume levels to help with perceived noise, it helps to have the patient and spouse agree when they want to talk. The spouse says, “Honey…,” and the patient responds, “Just a moment, dear.” Then the patient increases the volume to the best communication level. This technique reduces the annoyance of wearing hearing aids while providing good hearing when needed.
* Floor noise in the hearing aid: If the patient is able to hear the floor noise in the instrument, something is obviously wrong with the instrument or its programming code. A repair may be needed or technical support from the manufacturer should be consulted for help in adjusting the code.
A huge amount of research has been done to determine the best type of amplification for each audiometric configuration. As yet, there is no agreement on what “best” is, and there is no best way to solve these problems.
Some professionals instinctively use modifications in broadband AGC to remediate loud noise problems, and this works sometimes. I often prefer to modify the frequency response before I adjust the AGC. Without question, marked increases in AGC can make certain sounds more comfortable, but the indiscriminate use of AGC to solve noise issues often results in a significant decrease in clarity and word understanding.
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