Innovative Wi-Fi Streaming for High-End Headphones

As digital integration deepens across all aspects of life, consumers increasingly seek audio experiences that blend seamlessly with wireless connectivity. As a leading developer in the audio streaming sector, StreamUnlimited is continuously pushing the boundaries to transform traditional audio systems into smart, connected devices without sacrificing sound quality. Recognizing this trend, StreamUnlimited developed an innovative Wi-Fi solution tailored for both high-end and mainstream headphones, redefining the wireless listening experience.
 

This innovative approach not only addresses the limitations often associated with Bluetooth connections, such as dependency on phone proximity and interruptions from phone calls and notifications but also sets a new standard for audiophiles seeking a seamless and uninterrupted audio experience, with the ability to default to Bluetooth for added convenience.

Wi-Fi headphones can handle advanced audio formats with sampling rates up to 192kHz, well beyond the limits of Bluetooth (when using USB-Audio, sampling rates up to 384kHz can be supported). This major advantage allows for high-resolution audio playback on a headphone, supporting all the standard formats, both compressed and uncompressed/lossless.

At the core of StreamUnlimited’s Wi-Fi headphones solution is the Stream210 module, optimized for low-power, high-connectivity applications. This small footprint (25.4mm×27.5mm), self-contained module can be directly powered from a single-cell Li-Ion battery and already features an integrated audio ADC and DAC. The module features a dual-core ARM Cortex-A32 at 1.3GHz and 2Gb of DDR3 memory, ensuring efficient data handling with minimal power drain. It is powerful enough to run audio streaming services locally on the device yet significantly lower in power consumption than 64-bit Cortex-A53 or A55 platforms, which are commonly used. Notably for battery-powered applications, it supports host-less operation using the internal MCU, which allows the module to remain active while main processor and memory is hibernated.

 

In terms of wireless connectivity, the Stream210 is a fully certified solution that offers integrated Wi-Fi6 wireless interface with support for 2.4GHz and 5GHz bands. In this wireless mode, it provides up to 114Mbps throughput using 20MHz channels, far more than even the most demanding audio streaming services require, while keeping power consumption low. The integrated Bluetooth 5.3 interface offers Bluetooth classic, Low Energy, and LE Audio and co-exists well with Wi-Fi due to completely separate RF paths and antennas for Wi-Fi and Bluetooth.

Enhancing the hardware capabilities of the Stream210, StreamUnlimited also offers StreamSDK, a comprehensive software stack for music streaming services. This SDK supports leading music services such as Spotify Connect, AirPlay, TIDAL, and Google Cast, as well as multiple audio codecs, smart home protocols, and voice assistant integrations. The solution also caters to the high-end audio market, enabling HD audio streaming from services such as Spotify HiFi (24-bit audio), TIDAL HiFi and others.

This development introduces a new product segment in the headphone market, offering direct access to advanced streaming services — features previously unavailable in Bluetooth — only models. Stream210’s versatility extends beyond wireless headphones. It is an ideal solution for a variety of devices, including digital radios, wireless speakers, streaming audio receivers, and more.

This flexibility makes Stream210 a preferred choice for manufacturers looking to incorporate reliable Wi-Fi connectivity into diverse product form factors. Stream210 supports dual-band 802.11ax with 20MHz channel bandwidth and could support even higher throughput by using MIMO and channel bandwidth of 40MHz, 80MHz, or even 160MHz. This is important for a router and may still be of importance for a laptop, which needs to manipulate large files on a network drive or stream 4K video. For an audio product that has to run from a battery, fitting into headphones, the additional power consumption related to higher channel bandwidth is a no-go.

 

Supporting MIMO would not only increase power consumption but also require at least two antennas for Wi-Fi only. Also, this does not go well with the very limited space available in headphone products. On the CPU, Stream210 actually uses a quad-core processor, the two Cortex-A32 cores that are used by the Linux OS and application run on 1.3GHz while the two RTOS cores run on 333MHz and 40MHz, respectively. Same as for Wi-Fi, we are talking about a low-power architecture, which means that even though average power consumption is low, current peaks may well occur within the audio frequency range.

Same as for Wi-Fi, the internal DAC design is a decent compromise between low power and high quality, as shown in Figure 1 and Figure 2. Should the performance of the internal DAC be deemed insufficient, an external DAC can be connected via I2S. The I2S interfaces provided by Stream210 support up to 384kHz and 2×32 bit per stereo sample. This is twice the sampling frequency of 192kHz supported by the internal DAC. 

Common streaming services, however, do not provide content at 384kHz and the related data rate can be problematic in end-customer wireless environments even when playing from a local DLNA server. Anyway, the I2S interface is not the bottleneck for audio quality. Multiple data lines would be available to output multiple channels, which is however hardly needed on headphones.

The internal HiFi phase-locked loop (PLL) and I2S silicon implementation doesn’t limit the audio performance, and jitter is extremely low (Figure 3). 

 

Challenges in Wi-Fi Headphones
The ability to receive 24-bit/192kHz uncompressed audio means that all design aspects of a high-end audio product need to be covered in a very small system to get the related audio quality up to the transducers. While the Wi-Fi interface operates at a frequency far above the audio spectrum, the Wi-Fi packets are received at a rate that falls within the audio spectrum. The current consumed by the Wi-Fi interface thus shows spikes which can be audible if the power and GND is not well separated between the audio output stages and the supply part.

The same applies to the processor cores and memory. They consume little power when not loaded but can produce steep transitions in the supply current when their full capability is demanded. While Bluetooth headsets transmit little RF energy and are thus usually exempted from specific absorption rate (SAR) testing, the Wi-Fi interface transmits higher energy levels. StreamUnlimited performed SAR testing on a prototype at a third-party lab to ensure that the solution may be used without endangering the health of users or legal compliance.

Apart from health and legal aspects, defining the antenna geometry to fit the product and at the same time provide good range, while supporting a co-existence between Wi-Fi and Bluetooth is a challenge of its own.

Current spikes need to be filtered such that they do not propagate to the audio output stages, coils and capacitors in the supply section are just a few millimeters away from the ear of the audiophile customer and must thus not produce any mechanical noise. The battery will usually be on the other side of the product than the electronics to balance the weight, cables connecting the battery to the electronics must not couple any disturbances to the cables returning the audio signal to the second transducer. Wi-Fi antennas do transmit RF energy also when receiving data, and RF energy may couple to analog output stages, get demodulated there and appear as low-level disturbance in the audio signal.

 

In Conclusion
Integrating Wi-Fi and a strong processor into headphones has its technical challenges but if done right, results in far superior performance than what can be achieved on Bluetooth headphones. StreamUnlimited designed a reference platform to support the evaluation for these headphone applications, including battery charging. The demonstration board was integrated into commercially available headphones, allowing full testing to experience and solving all resulting challenges. This knowledge, combined with StreamUnlimited’s experience in designing high-end audio products, is now available. StreamUnlimited is available to provide full custom board design or simply review and support in-house design efforts. aX
www.streamunlimited.com

This article was originally published in in the printed edition of audioXpress, April 2025