Hearing aids have undergone remarkable transformation over the past 25 years. Today’s devices incorporate cutting edge technologies that deliver individualized amplification, advanced noise reduction, and a range of intelligent features.
However, no matter how sophisticated the internal electronics are, the sound ultimately reaches the ear through the earpiece. This earpiece plays a crucial role in shaping the effectiveness of the entire hearing solution through what we call acoustic coupling.
In this article, part of the Shaping Sound series, we focus on occlusion - one of the most common yet misunderstood challenges in hearing aid fittings - and explore how anatomy, insertion depth, and modern digital design workflows can help reduce its impact on own voice perception and long term user satisfaction.
Figure 1: Occlusion problems are often described as “talking in a barrel”. AI-generated image.
Even highly sophisticated devices can feel uncomfortable or unnatural to users if their own voice sounds boomy, echoey, or simply “not like themselves.” As with comfort and retention, the earpiece, not the electronics, often becomes the deciding factor between a successful fitting and a device abandoned in a drawer.
From a fitting perspective, occlusion also interacts with other performance aspects:
The key point is that occlusion is largely manageable when we look at it as an anatomy and acoustics problem, rather than just something customers complain about.
Occlusion matters because it sits at the intersection of acoustics, anatomy, and user acceptance. In simple terms, when the ear canal is sealed by an earmould or device, low frequency energy from the user’s own voice - largely transmitted through bone conduction - builds up as sound pressure in the residual ear canal volume. Classic modelling work by Stenfelt and Reinfeldt (2007) shows that this effect is strongly dependent on where the occlusion occurs (shallow vs. deep) and the acoustic coupling of the ear canal, and that even deep occlusions can still produce noticeable occlusion effects rather than eliminating them completely. Complementing this, Hansen's (1998) detailed investigation emphasizes that the occlusion effect is not a single “yes/no” phenomenon - it is shaped by earmould properties and the way the canal is acoustically coupled.
A key reason occlusion is hard to solve consistently is that the seal is not just a design choice, it is an anatomical decision. The ear canal transitions from a soft, mobile cartilaginous section to a rigid bony section at the cartilage–bone junction (CBJ). Work by Nielsen and Darkner (2011) shows that this junction is not located at a fixed “standard depth”: across individuals it typically lies medial to the second bend and varies by several millimetres, meaning a “deep” fit in one ear may still be a “cartilage seal” in another.
This is important because the cartilaginous portion is more elastic, so it vibrates more and amplifies low-frequency sound from canal wall motion. In practice, this is why two fittings that look similar externally can yield very different own voice outcomes - especially when insertion depth, seal location, and stability differ between insertions.
At the design level, the strongest lever clinicians and labs have is how open the ear canal is acoustically. While ventilation size is often seen as the main parameter to steer how open the canal is, the correct notion is in fact acoustic mass, which is how much air resists being moved when sound pressure pushes on it. In their controlled comparison of multiple earmould geometries, Denk et al. (2023) show that the vent’s acoustic mass (a function of vent length and cross section) is the prime predictor of both the occlusion effect and coupling behaviour. Critically, they also demonstrate that the physical location of the medial seal zone influences the magnitude of the occlusion effect, with shallower seals exposing more of the cartilaginous canal and often increasing occlusion despite larger vents. The study also shows that instant‑fit domes are inconsistent: their variable insertion depth leads to unpredictable occlusion from day to day.
Figure 3: Occlusion effect as a function of Insertion/Occlusion Depth for different frequencies. Results derived by the model of Stenfelt and Reinfeldt (2007).
Finally, it’s important to recognize that users’ complaints about their own voice are not always explained by occlusion alone. Laugesen et al. (2011) developed the Own Voice Qualities (OVQ) approach specifically because clinical experience suggested that hearing aid users report multiple own voice issues beyond classic occlusion effect, affecting sound quality, control of voice level, and the ability to “speak and hear” naturally in interaction. Their data show that even users not expected to have occlusion problems can still report meaningful own voice difficulties compared to normally hearing controls, reinforcing that solving occlusion is necessary but not sufficient for truly natural own voice experiences. Taken together, these studies sharpen the “Understanding the Problem” message: occlusion is a real physical mechanism, but what the user experiences is the combined result of seal placement, vent acoustic mass, earmould properties, and broader own voice perception factors.
Closing the canal is not a mistake, it is often a requirement for audibility, stable gain, and effective processing, especially when users struggle in noise.
This is why “open fittings” should be framed as a targeted solution, not a default. Open fittings can be excellent for a specific profile: typically, mild-to-moderate high frequency loss with relatively normal low frequency thresholds, where comfort and own voice naturalness are priority and the required low frequency gain is limited.
But when a user’s core complaint includes speech in noise, an open fitting can be the wrong trade off because it can reduce the effectiveness of directionality/noise reduction and limit stable gain. Even in open fittings, additional acoustic interactions can occur: direct sound mixing with amplified sound may create response irregularities and perceptual artifacts unless the fitting strategy compensates for the open ear acoustics.
This is exactly why occlusion management must be treated as optimization, not elimination: we reduce occlusion effects enough for comfort while maintaining the coupling needed for performance.
Occlusion is not a minor comfort issue; it directly affects device acceptance and wearing time. Users who perceive their own voice as unnatural often reduce usage or stop wearing their hearing aids altogether, even when speech understanding with external sounds is otherwise good.
Open fittings provide a low impedance escape path for low frequency energy and can be very effective for users with normal or near normal low frequency hearing. However, “open” should not be treated as a universal solution. Increased openness also reduces available low frequency output and limits maximum gain before feedback.
Custom open designs offer an advantage over instant fit solutions by providing stable positioning and repeatable venting, reducing variability in occlusion and sound quality.
Occlusion may appear to be a simple consequence of “blocking the ear,” but it is the result of a complex interaction between anatomy, insertion depth, seal location, and vent geometry. Understanding where and how the ear canal vibrates, and designing earpieces accordingly, makes a measurable difference in own voice perception and long term device acceptance.
With precise scanning, controlled vent design, and anatomically informed insertion strategies, modern digital workflows make it possible to reduce occlusion while preserving comfort, audibility, and acoustic stability. They also enable consistent control and reproduction of vent geometry and insertion depth, reducing trial and error and improving first-fit success.
