By Manuel Arias Ruiz,Head of Hardware Design & Testing at USound, Jakob Spötl ,Head of Acoustics at USound.

Revolutionizing Sound Quality and Mechanical Integration.

Luxshare-ICT and USound have developed Gemini, an innovative audio module that offers numerous advantages through its coaxial 2-way audio technology. With a combination of high sound quality, improved ANC-capability, and easy integration, this dual-driver module allows manufacturers to differentiate their products from the competition.

Introduction

USound and Luxshare-ICT have recently unveiled a joint innovation, an integrated dual-driver module for true wireless stereo (TWS) earbuds. In this article, we delve into the benefits of combining multiple speaker technologies this way.

The Innovation: Gemini

In the increasingly competitive market of TWS earphones, consumers expect further acoustic optimization. Wireless earbuds should not only be small and lightweight but should also deliver exceptional audio quality. As already described in another article (Two-way TWS: Why USound MEMS speakers are the ideal tweeter to maximize sound quality), MEMS speakers can facilitate this.

This module was named Gemini after the Latin word for “twins”, showcasing the use of two (non-identical) combined speakers. The core of the innovation is the integration of USound’s Conamara MEMS tweeter inside a toroidal electrodynamic woofer, creating a 2-way system. Aside from the two loudspeakers, the Gemini module also includes:

• USound’s amplifier ASIC, Tarvos 1.0, designed for MEMS speakers.
• Inward-facing microphone, e.g. for feedback-ANC.
• A combined input for all signals (in and out) with an FPC board-to-board connector.
• A sound tube element designed to bring the tweeter signal directly to the earphone output, avoiding detrimental resonances.

Benefits of Dual Driver Audio Modules:

The Gemini audio module offers a multitude of advantages that set them apart from conventional solutions:

• Optimized Speaker Bandwidth: Using a dual-driver module allows each speaker to be optimized for a specific frequency range. For example, the woofer can be designed with a more flexible diaphragm, improving the sound pressure level (SPL) in high-leak scenarios. While this would result in a loss of SPL at high frequencies, this is compensated by USound’s Conamara UA-C0601-2T MEMS tweeter. Without the need to produce SPL at low frequencies, the MEMS tweeter is designed with greater stiffness to achieve ideal performance at high frequencies, extending well above 20 kHz into Hi-Res territory.

• Optimized for ANC: Since the woofer only needs to reproduce low and mid frequencies, it can be designed with lower acoustic impedance, yielding better performance in high-leak scenarios. This makes it ideal for high-performance ANC earphones, where consistent performance, regardless of quality of fit, is achieved with controlled leakage.

• More Possibilities for tuning the sound: The dual driver module unlocks more possibilities for achieving the desired sound characteristic. Customers can fine-tune their products to deliver the exact audio experience they envision by using different damping on the woofer and MEMS tweeter sound paths.

Benefits of Coaxial Speakers

USound’s and Luxshare’s dual driver audio module employs a patented coaxial speaker design where the MEMS tweeter is not placed in front of but inside the woofer, which introduces additional benefits:

• Thinner Product Profile: By integrating the MEMS tweeter within the woofer, the thickness of the module is greatly reduced compared to simply stacking two speakers on top of each other. This feature is particularly advantageous when space is limited, such as in thin earphones or wearables. The reduced height of the speaker module allows for that space to be used by other components – or alternatively allows for a smaller overall product form factor.

• Seamless Integration: As the acoustic output ports of the two speakers are on the same plane, integrating the module into an earphone design is much easier. The electronic design is made simple by having all the I/O of the module on a single board-to-board connector as well.

• Elimination of Comb-Filtering: Comb-filtering is a common challenge in multi-driver speaker systems, as the sound waves are not emitted from the same reference plane. USound’s coaxial speakers eliminate this issue by aligning the soundwaves from both speakers on the same plane. This alignment results in improved sound coherence, ensuring a clean and accurate audio reproduction.

• High Sound Pressure Level (SPL) Output: The 12.5 mm diameter dynamic speaker from Luxshare-ICT delivers very high SPL output, which, when used in ANC applications, allows it to cancel out even very loud impulse noises.

Figure 1: Nominal SPL performance of the woofer and MEMS tweeter separately. The tweeter path also includes the amplifier. Nominal input voltage: 179 mVrms; also shown is the maximum SPL achievable by the tweeter (880 mVrms into the amplifier). Measurement condition: 60318-4 Coupler (‘711’) including ear-mould adapter.

• Ideal for High-Leak Applications: In earphones that use ANC it’s vital to have a consistent acoustic performance. To ensure this, typically, a controlled leakage path is integrated, connecting the acoustic volume to the outside. With Gemini’s 12.5 mm dynamic speaker, the module can provide the necessary headroom to deliver undistorted sound pressure even in these challenging conditions.

• Simplified Integration with the Tweeter Amplifier: The Gemini module includes the MEMS speaker amplifier Tarvos 1.0, facilitating seamless integration and synergy between the MEMS tweeter and woofer. This integration simplifies the design process, reduces engineering efforts, and ensures optimal acoustic performance. By incorporating the tweeter amplifier within the module, USound allows customers to focus on other critical aspects of their product development.

• Optimal Size for High-End Noise Canceling: The 12.5 mm diameter of the dynamic speaker in the Gemini module strikes the perfect balance between size and performance. This size allows for a high level of acoustic output and headroom, crucial for achieving top-notch noise-canceling performance.

• Flexibility for Differentiation: The Gemini module’s versatility and flexibility offers customers the opportunity to differentiate their products from others in the market. By leveraging the module’s unique capabilities, manufacturers can create innovative audio solutions that captivate users and provide a competitive edge. With the Gemini module, customization and differentiation becomes easy.

Conclusion

USound’s and Luxshare’s dual driver audio modules are show many benefits in sound quality, ease of integration and size. By combining cutting-edge technology with customer-centric design, USound solidifies its position as an innovation leader in the audio industry.