The Occlusion Effect (OE) occurs when the ear canal is blocked by an object such as an earplug, noise-canceling earbud, or hearing aid. This phenomenon causes a person’s own voice, chewing, and footsteps to sound unnaturally loud. The discomfort of this internal amplification often leads people to question whether this sensation poses a genuine threat to hearing health. Understanding the underlying physics of the OE provides a clear answer regarding its safety.
Understanding the Occlusion Effect Sensation
The Occlusion Effect is the perception that internally generated sounds are amplified, often described as an echo or a “listening in a barrel” sensation. This amplification affects only low-frequency sounds, typically those below 1000 Hertz (Hz), with the most significant increase occurring around 250 Hz. For individuals wearing devices that seal the ear, simple actions such as speaking, swallowing, or walking suddenly become prominent.
This sensory distortion is a major reason why users may reject hearing devices. The experience is an unpleasant shift in sound quality that makes one’s own voice sound hollow and unnatural. The measurable increase in sound pressure within the ear canal confirms the physical reality behind the discomfort.
The Anatomical Cause of the Occlusion Effect
The Occlusion Effect is caused by the interaction between the body’s natural sound transmission mechanism and the blocked ear canal. Sounds generated internally, such as vocal cord vibrations, travel through the skull via bone conduction. This bone-conducted energy causes the walls of the ear canal to vibrate.
When the ear canal is open, this low-frequency vibrational energy radiates out and dissipates into the air, making internal sounds quiet. When an object seals the ear canal, it creates a small, closed acoustic cavity. The vibrating cartilaginous walls continue to generate sound pressure waves within this sealed space. Because the sound cannot escape, the pressure reflects back toward the eardrum, significantly boosting the intensity of low-frequency sounds. Measurements show this reflection can increase the sound pressure level (SPL) by approximately 20 to 25 decibels (dB) at frequencies around 250 Hz.
Assessing the Risk of Hearing Damage
Despite the increase in perceived loudness, the Occlusion Effect does not cause permanent hearing damage or noise-induced hearing loss. The internal amplification of self-generated sounds, even with the 20 to 25 dB boost, rarely reaches the sustained decibel levels required to physically harm the inner ear. The threshold for potential noise-induced hearing loss begins at sustained exposure to sound pressure levels of 85 dB and above.
Transient measurements have occasionally shown spikes near 100 dB at extremely low frequencies (under 40 Hz) in extreme blockage scenarios, but these are brief, non-sustained internal sounds. The primary consequence of the OE is psychological discomfort and annoyance that often leads users to stop wearing devices. The effect is considered a fitting problem rather than a safety hazard.
Methods for Eliminating the Effect
Manufacturers and audiologists employ several strategies to mitigate or eliminate the Occlusion Effect, primarily by disrupting the closed acoustic cavity. One common method is venting, which involves creating a small channel or hole in the earpiece. This vent allows excess low-frequency sound pressure to escape the sealed canal, preventing acoustic energy from reflecting back toward the eardrum.
Another solution involves altering the physical fit through deep insertion. The ear canal is composed of an outer cartilaginous section and an inner bony section. The softer cartilaginous walls vibrate more readily, which causes the OE. By inserting the earpiece deeper into the less compliant bony section, the device is positioned where the canal walls vibrate less, reducing the source of the sound pressure increase. Open-fit hearing aids and non-sealing domes also help by leaving the ear canal partially open, preventing the formation of a closed cavity.