Hearing aid feedback is the common, high-pitched whistling or squealing sound that can occasionally disrupt the use of the device. This noise is simply an unwanted sound loop created when amplified sound escapes the ear canal and is unintentionally re-captured. Understanding how this sound loop forms is the first step in addressing the issue, which often stems from physical fit issues or internal device settings.
The Mechanism of Acoustic Feedback
Acoustic feedback in a hearing aid is a form of instability that occurs when sound cycles continuously between the speaker and the microphone. The hearing aid’s microphone picks up sound from the environment and sends it to an amplifier. The receiver, or speaker, then outputs this amplified sound into the ear canal to assist hearing.
The system works as intended unless some of the amplified sound leaks out of the ear canal and is picked up again by the microphone. This leakage creates a closed-loop system where the sound is re-amplified, leaks again, and is picked up repeatedly. This rapid, continuous cycling of sound quickly escalates into the recognizable, high-pitched whistle.
Physical Causes Related to Ear Canal Leakage
The most frequent source of feedback is a problem with the physical seal between the hearing aid and the ear canal, allowing amplified sound to escape. A poor fit is a primary cause, often resulting from an earmold or dome that is either too small or improperly seated. If the device does not create a snug seal, a small gap allows sound to leak out and travel back to the microphone, restarting the amplification loop.
Changes in the shape of the ear canal, which can happen naturally over time due to aging or body weight fluctuations, may cause a previously well-fitting device to become loose. Inserting the hearing aid incorrectly can also temporarily break the seal, causing immediate feedback until it is properly situated. Even normal movements like chewing, yawning, or talking can momentarily shift the ear canal and break the seal, leading to temporary whistling.
Another common physical obstruction is an excessive buildup of cerumen, or earwax, in the ear canal. This blockage prevents the amplified sound from traveling effectively to the eardrum, causing the sound waves to reflect off the wax and bounce back toward the hearing aid’s microphone. Placing any object near the ear, such as a hand, a hat, or a phone, can also reflect sound directly back into the microphone, triggering the feedback cycle.
Device-Specific and Programming Factors
Feedback can also stem from the hearing aid’s internal settings or mechanical condition, even when the fit is perfect. Setting the volume too high for the required gain increases the chance of sound leakage, as the system reaches its maximum stable gain limit. When the volume exceeds this limit, the amplified signal is too powerful to be contained by the physical seal, pushing sound out and back to the microphone.
Physical wear and tear on the device can also create new pathways for sound to escape internally before it reaches the ear canal. Small cracks in the casing, loose receiver components, or hardened tubing in behind-the-ear models can allow amplified sound to leak and be picked up by the microphone. These internal issues require professional repair or component replacement to resolve.
Modern hearing aids utilize digital feedback cancellation systems that work by generating an opposite sound wave to neutralize the detected feedback signal. If the device is incorrectly programmed or the cancellation algorithm malfunctions, the system may fail to suppress the whistling sound effectively. A hearing professional can adjust the programming to reduce the amplification of specific frequencies that are most prone to feedback, lowering the risk of the whistle occurring.