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Two-way driver architecture in modern TWS: enabling next-generation acoustic performance
Evolving Acoustic Demands in Earphone Design
The modern TWS market demands more than just sound reproduction. Advanced features such as active noise cancellation (ANC) and sound personalization are now standard expectations. These functionalities significantly raise the performance requirements on earphone driver systems.
For example, effective ANC demands robust low-frequency output, which in turn requires high-compliance suspensions. At the same time, the trend toward personalized audio experiences requires linear and repeatable high-frequency performance, which is crucial for the application of digital filters that adapt sound output to individual hearing profiles.
However, fulfilling these diverse demands with a single driver often results in performance trade-offs. Optimizing for low-frequency reproduction typically compromises high-frequency behaviour, introducing undesirable sharp resonance peaks. These resonances not only degrade sound quality but also make precise digital filtering more complex and less effective.
The Case for Multi-Driver Architectures
The need to balance acoustic performance across the full frequency spectrum is not new. As early as the 1930s, engineers at Bell Labs addressed similar challenges in loudspeakers through the introduction of two-way systems, separating low and high-frequency reproduction across specialized transducers.
The same basic principle can be applied to earphones. In a typical two-way earphone design, a woofer handles the low-end frequencies. At the same time, a tweeter manages the highs, resulting in smoother SPL curves and improved fidelity across and beyond the audible range.
Miniaturization Unlocks Mass Market Potential
Recent advances in component miniaturization—especially with MEMS (Micro-Electro-Mechanical Systems) technology—have now made two-way designs viable for mass market consumer earphones.
A prime example is the Greip 1.1 UAM-C1011, a compact, fully integrated dual-speaker audio module. It combines an electrodynamic woofer with a MEMS tweeter, integrating onboard driving electronics and a passive crossover. This module delivers high-performance output while streamlining system integration for OEMs.
This type of dual-speaker integration is no longer limited to prototypes—brands like QCY have already adopted MEMS tweeter technology in their MeloBuds N70 true wireless earbuds, demonstrating that mass-market deployment at scale is now a reality.
Why Acoustic Design Matters
Even with cutting-edge transducer technology, a well-engineered acoustic design remains essential to unlock the drivers’ acoustic potential fully. By leveraging two independent acoustic pathways, each tuned to the needs of the specific driver, multi-driver architectures allow for greater design flexibility.
These pathways are carefully tuned as Helmholtz resonators, which act as targeted acoustic filters. For the woofer, the resonator limits high-frequency leakage and helps create an acoustic low-pass effect, while the tweeter’s path is tuned for enhanced response in the upper midrange and high-frequency bands. This ensures that each driver operates within its optimal range without interference. It allows for the electrical crossover to be directly integrated into the speaker module.
The following figure shows a cross-sectional view of the air volumes within such a design.
This separation also benefits system-level design. For instance:
- The woofer channel can accommodate an ANC microphone without affecting the tweeter’s output.
- The tweeter’s cavity can be minimized to reduce acoustic mass and preserve high-frequency responsiveness.
This targeted optimization improves not only raw output but also enables more precise and reliable digital signal processing by creating a smooth frequency response.
Measurement Results
Examining the figure below, we can observe the impact of this acoustic design on the performance of an earphone featuring the Greip 1.1 UAM-C1011. Also shown is the SPL of the audio module, built into the reference earphone shell, measured at 0.126 VRMS on an IEC 60318-4 Coupler (black curve). The green dashed line shows the performance without the earphone design (directly on the coupler, at 0.126 VRMS).
The increased high-frequency performance above 5 kHz allows for a variety of acoustic sound signatures to be implemented using digital filtering. And, also clearly visible, the strong performance in the near ultrasound region allows for the implementation of smart sensing technologies like heart rate sensing or wear detection.
Summary
Two-way driver configurations represent a transformative leap in earphone performance. By combining them with optimized acoustic architecture, simulation-backed design processes, and tightly integrated modules, manufacturers can deliver products that exceed user expectations on both sound and feature sets.
The successful launch of QCY’s MeloBuds N70, powered by USound MEMS tweeters, highlights how two-way driver architectures can deliver high-resolution sound in compact, cost-sensitive consumer designs.
USound offers more than just innovative components—we support our customers with simulation-driven acoustic design services and integration expertise for applications ranging from high-fidelity sound reproduction to advanced AI-powered biosensing.
Contact our Sales Team to learn how we can improve your customers’ acoustic satisfaction.
About the author
Fabian Bachl is an Acoustic Engineer at USound GmbH, a leading developer of MEMS-based audio solutions. He is responsible for the design, simulation, and characterization of acoustic systems, contributing to the advancement of miniature speaker technologies. His expertise lies in the intersection of acoustics and microsystems technology, with a focus on high-performance audio applications in consumer electronics and hearing technologies. LinkedIn
