In-Ear headphones Active Noise Cancellation: how Oppo eliminate noise

In-ear headphones remain one of the most popular form factors due to their lightweight design, comfortable fit, and all-day comfort. However, this design is considered one of the most challenging to implement active noise cancellation (ANC). Unlike in-ear models with silicone ear tips, which provide a tight seal to the ear canal, earbuds have an open fit, making it significantly more difficult to control acoustic processes. Oppo explained how it solved this problem.

What is Active Noise Cancelling (ANC)

Active Noise Cancelling (ANC) is an active noise cancellation technology. It cancels out unwanted external sounds by generating counter-waves of sound.

Types of ANC

• Feedforward: Microphones are located outside the earcups. They capture high and mid frequencies well, but they don’t know what your ear is hearing inside.
• Feedback: Microphones are located inside the earcup. They hear what you hear, are better at attenuating low frequencies, but are more difficult to tune. This is the most effective, but also the most expensive option.
• Hybrid: combines external and internal microphones. This is the most effective, but also the most expensive option.

What types of in-ear headphones are there?

In-ear headphones (also often called “tablet” headphones) are a type Headphones that fit into the outer ear canal but don’t extend deep into the ear canal. Their design leaves the ear partially open to outside sounds.

The Main Types of In-Ear Headphones By Design

• Classic Earbuds (Open-fit): These have a rounded shape and fit snugly into the ear. They do not have silicone tips.
• Anatomical Earbuds: They feature small plastic or silicone tips that direct sound more clearly into the ear canal without clogging it.
• Earbuds with extra retention have special silicone spacers or ear hooks. They are designed for sports, so the headphones won’t fall out during active movements.

Specialized Acoustic Architecture

The main challenge in developing noise cancellation for earbuds is the lack of a seal within the ear canal. Without silicone tips, external sounds penetrate through multiple pathways, creating an unstable acoustic environment. A variety of ambient noises—from human conversations to traffic noise and urban background noise—create additional challenges.

To improve the system’s efficiency, Oppo engineers developed a special 1.4 mm² ventilation hole. Its purpose isn’t simply to isolate external noise, but to control air pressure and the interaction of sound waves within the ear canal. This allows the ANC system to operate more predictably and more accurately compensate for external sounds.

After a series of tests, the 1.4 mm² size was found to be optimal. This design provides more consistent low-frequency noise cancellation, reduces environmental influences, and more effectively handles human speech. This engineering feature forms the foundation of the Enco Air5s’ active noise cancellation system.

Real-Time Adaptive Noise Cancellation

Unlike in-ear models, in-ear headphones are more responsive to even slight changes in position. While walking, talking, or other normal activities, the fit may shift slightly, altering the acoustic characteristics and impacting noise cancellation effectiveness.

When developing the case shape, specialists used a large database of user ear anatomies and conducted extensive testing with people with different auricular structures and listening habits.

The result is a design with an increased contact area and reduced depth within the ear canal. This solution provides a more stable fit, evenly distributes pressure, and reduces the likelihood of acoustic leakage during movement.

Additionally, the noise-cancelling system continuously analyzes the fit, ear canal parameters, and ambient noise levels. Thanks to an ultra-high sampling rate of 800 kHz, the algorithms are able to respond almost instantly to any changes, adjusting filtering, phase alignment, and noise-cancellation intensity.

Natural sound even with active noise cancellation

When developing the Enco Air5s, Oppo’s engineers aimed not only to minimize ambient noise but also to preserve the natural sound characteristic of open-back headphones.

This task is especially challenging in earbuds, where the open design simultaneously impacts both noise isolation and playback quality.

To address this issue, the Enco Air5s employ Adaptive Sound Enhancement technology. Algorithms continuously analyze both the reproduced signal and the acoustic loss caused by the open fit. The system then automatically adjusts individual frequency ranges, paying particular attention to the low frequencies that are most susceptible to dispersion.