The occlusion effect is a common auditory phenomenon that occurs when the external ear canal is partially or completely blocked by an object. This blockage leads to an altered perception of sounds generated from inside the body, particularly the sound of one’s own voice. The effect is frequently experienced by individuals wearing in-ear devices, such as earplugs, headphones, or hearing aids, which physically occupy space within the canal. The sensation is a direct result of the acoustic change caused by the obstruction, rather than a change in the original sound source.
Understanding the Sensation
The experience of the occlusion effect is generally described as an increase in the loudness of self-generated sounds. People often report their own voice sounding “booming,” “hollow,” “muffled,” or like they are speaking into a barrel. This distortion is most prominent with low-frequency sounds, typically those below 1000 Hertz (Hz), and sometimes most intense around 200 to 400 Hz. The increased sound pressure level in the ear canal can be measured to be as high as 20 to 30 decibels (dB) in this low-frequency range.
The amplified sensation is not limited to speech; it also affects other internally produced noises. Activities like chewing, swallowing, or even the sound of one’s own footsteps can seem abnormally loud or thumping. The phenomenon is most noticeable when the ear canal is suddenly sealed, such as when placing a finger in the ear or when first beginning to use a custom-fitted hearing device or earplug.
The Biomechanical Cause
The physical mechanism behind the occlusion effect is rooted in the way sound energy travels through the body, primarily through bone conduction. When a person speaks or chews, vibrations are generated by the skull and surrounding tissues, traveling through the head to the ear canal walls. When the ear canal is unblocked, this internally generated, low-frequency sound energy is able to escape into the open air and dissipate.
The problem arises when an object, like an earmold or earplug, is placed into the ear canal, especially in the outer, cartilaginous portion. This object acts as a physical barrier, plugging the natural escape route for the internal vibrations. Instead of exiting the ear, the low-frequency acoustic energy is trapped and reflected back toward the eardrum, significantly increasing the sound pressure level in the now-closed cavity.
It is important to differentiate this from air conduction, which is the process of sound waves traveling through the air from an external source. The outer two-thirds of the ear canal are surrounded by soft tissue and cartilage, which vibrate readily with internal sounds. Blocking this vibrating section forces the low-frequency energy to take the path of least resistance, which becomes the eardrum, leading to the sensation of increased loudness.
Solutions for Hearing Devices
Managing the occlusion effect is a significant part of ensuring comfort and satisfaction for users of hearing aids and other in-ear devices. Two primary categories of solutions exist: physical modifications to the device and acoustic adjustments through programming.
One effective physical solution is deep insertion, where the device is placed far enough into the ear canal to pass the cartilaginous section and rest in the bony portion. The bony section vibrates much less than the cartilage, which minimizes the amount of internal sound energy that gets trapped and reflected. Another common physical strategy is the use of venting, which involves creating a small channel or tube through the device’s shell.
This vent allows the trapped low-frequency sound energy to escape, restoring the natural dissipation path. The size and length of the vent must be carefully calibrated, as a vent that is too large can compromise the device’s ability to amplify external sounds or lead to acoustic feedback. For many modern hearing aids, especially Receiver-in-Canal (RIC) models, an open-fit design with a soft dome is used, which acts as a large, continuous vent that significantly reduces the effect.
Beyond physical changes, digital signal processing (DSP) in advanced hearing aids allows for acoustic solutions. A hearing care professional can adjust the device’s programming to reduce the amplification gain specifically in the low-frequency range where the occlusion effect is most pronounced.