Semi-in-ear earbuds have long been favored for their lightweight, pressure-free comfort, making them a popular choice for extended listening. Yet from an engineering perspective, they also represent one of the most challenging form factors for noise cancellation. Unlike in-ear earbuds that rely on silicone ear tips to create a physical seal, the more open structure of semi-in-ear designs makes precise sound control significantly more difficult to achieve.
With Enco Air5s, OPPO set out to improve the semi-in-ear Active Noise Cancellation (ANC) experience by making it feel stable, natural, and comfortable in real-world use.
Creating Predictable Quietness with a Custom Acoustic Architecture
One of the greatest challenges for semi-in-ear ANC lies in the absence of a physical seal. Without silicone ear tips isolating the ear canal, environmental noise can enter through multiple acoustic paths, making the internal sound field far less predictable. Real-world noise is also inherently complex, spanning multiple frequency ranges, including human voices, traffic noise, and urban environmental sound, all of which make effective ANC that much harder to achieve.
To improve ANC consistency in an open acoustic structure, Enco Air5s features a specially engineered 1.4mm² acoustic short-circuit vent. In simple terms, this vent helps control how external sound and air pressure interact with the ear canal, giving the ANC system a more stable acoustic environment to work with. Rather than simply either blocking or allowing noise to pass through, the design carefully manages the pressure difference between the inside and outside of the ear canal, creating a sound field that is more controlled and predictable.
After extensive testing and tuning, the 1.4mm² configuration was selected to better balance noise cancellation performance across different frequency ranges, helping Enco Air5s deliver more consistent noise cancellation across low-frequency rumble, ambient sounds, and voice-related noise.
This acoustic architecture forms the foundation of the ANC system. By making the noise path more controllable, the noise cancellation algorithms can operate with greater precision and consistency.
Maintaining Stable ANC with Real-Time Adaptive Noise Cancellation
Compared with in-ear earbuds, semi-in-ear designs are naturally more susceptible to subtle changes in fit during everyday use. Even simple movements such as walking or speaking can slightly alter how the earbuds sit in the ear and thus how sound travels into the ear canal. And because ANC relies on precisely calibrated signals, even minor shifts like this may affect sound leakage, acoustic paths, and sound pressure inside the ear canal, making it more difficult for conventional ANC algorithms to maintain consistent cancellation performance.
To improve consistency across different wearing conditions, Enco Air5s combines OPPO’s Ergonomic Semi-in-Ear Fit Design with Real-time Adaptive Noise Cancellation technology, helping the earbuds both maintain a more stable fit and adjust noise cancellation performance in response to real-time acoustic changes.
The result is the Ergonomic Semi-in-Ear Fit Design of Enco Air5s, engineered with a larger contact area with the ear and a shallower insertion depth into the ear canal. By distributing contact more naturally across the ear while reducing pressure inside the ear canal, the design helps provide a comfortable fit, improve wearing stability, and reduce the likelihood of sound leakage during everyday movement.
Building on this ergonomic foundation, Enco Air5s applies OPPO’s Real-time Adaptive Noise Cancellation technology to dynamically respond to changing acoustic conditions. Powered by an ultra-high 800kHz sampling system, the earbuds continuously analyze how they’re worn, ear canal characteristics, and environmental noise in real time. This allows the system to detect subtle acoustic changes more rapidly and dynamically adjust filter parameters, anti-noise phase alignment, and cancellation depth with greater precision.
OPPO also optimized several key components within the ANC system, including low-frequency anti-noise output, phase stability, feedback microphone response, and anti-howling performance. Thanks to this close coordination of acoustic hardware and intelligent software algorithms, Enco Air5s is able to maintain more stable and natural noise cancellation even in constantly changing real-world environments.
Its ANC capability has also earned TÜV Rheinland Noise Cancellation Certification, further underscoring OPPO’s efforts to improve ANC performance in a semi-in-ear form factor.
Preserving Natural Sound with Adaptive Sound Enhancement
For OPPO, making semi-in-ear ANC work was not only about reducing noise. It was also about preserving the natural listening experience that users expect from open-fit earbuds.
To help preserve sound quality with ANC enabled, Enco Air5s introduces Adaptive Sound Enhancement technology. For the user, the upshot of all of this meticulous engineering is that Enco Air5s is able to maintain fuller bass, more natural vocals, and more consistent overall sound quality even with ANC enabled.
System-Level Engineering for a New Semi-In-Ear ANC Experience
More than simply being OPPO’s first semi-in-ear earbuds with ANC, Enco Air5s represents OPPO’s system-level approach to ANC in one of the industry’s most technically challenging earbud form factors.
By combining acoustic architecture, ergonomic engineering, real-time adaptive algorithms, and adaptive sound enhancement, Enco Air5s delivers a new generation of semi-in-ear listening experience that feels quieter, more stable, and more comfortable in everyday use.