Leveraging its experience in engineering services and product development for many of the world’s audio brands, StreamUnlimited created a completely modular approach for active speaker systems with built-in streaming and audio processing. A modular hardware and software architecture, designed to minimize integration complexity and reduce time to market.
For decades, speakers have been the most crucial part of any premium audio system, as they ultimately generate the sound that consumers enjoy. Despite significant advancements in speaker drivers and acoustics, speakers remain the most stable component of such systems. A premium passive speaker from two decades ago is still regarded as a good product, something that few people would claim about a 20-year-old audio streaming amplifier.
Conversely, there are distinct technical advantages to positioning amplifiers as close as possible to the speaker drivers and bringing the crossover to the digital domain. A digital filter calculated with 32-bit precision offers a fidelity that a crossover filter made of analog components cannot match. The audio signal stays lossless, regardless of the cable's quality or cost, and shortening the cable enhances the audio quality. Additionally, powerful network-enabled devices not only deliver audio content but also offer significant processing power and a richer and more user-friendly interface. This enables loudspeaker designers to optimize sound performance for various environments and potentially allow end-users to adjust settings for specific listening conditions and room characteristics.
With all that in mind, the transition from passive speaker boxes to network-enabled, smart active speakers should be a logical step. However, it is a far more difficult task than one would expect due to multiple factors.
First, even highly efficient speaker drivers convert most of the energy they receive into heat. A powerful audio amplifier, a power supply, and a high-performance network processor, wireless chipset, and high-end op-amp and analog-to-digital (AD) and digital-to-analog (DA) conversion stage create additional heat inside an enclosure, which is mostly airtight and made of sturdy MDF that forms a good thermal isolator.
Second, the inner volume is crucial for the acoustics of the speaker. Especially for compact designs, creating a separate compartment for electronics would reduce the volume significantly. And placing electronics into the acoustical compartment may cause undesired resonances or vibrations.
Another challenge is the fact that users want to have multiple inputs and outputs on the back panel of active speakers—but these must be air-sealed. Even small openings could form a kind of whistle, blown by the significant internal air pressure that is generated when playing at high volume.
Adding wireless input options adds another level of complexity. Certification of a wireless product is a costly and risky process, creating a major hurdle for high-end audio brands that do not sell high quantities per year.
And while designing high-end speaker boxes requires acoustical and manufacturing know-how, the design of high-end audio electronics requires knowledge of AD/DA conversion, handling of fast clock and data bus signal integrity, and more. Fast data buses should not form an antenna for undesired spurious emissions while the wireless audio transfer relies on optimized antennas and receiver/transmit paths.
And with a product functionality mainly defined by software, the stability, feature-richness, and responsiveness of the user-interface becomes a crucial aspect for customer satisfaction. The effort involved with the creation of a feature-rich audio streaming software stack can be extreme. Choosing a stack from a third party is the only viable option. Yet, the product should still have a different look and feel than other products with similar features.
A Modular System Approach
To address these challenges and simplify the transition to active networked speaker designs, the ideal solution would be to have a modular system where streaming functionality, DSP, and amplification would be integrated into a compact, flexible unit (Photo 1). StreamUnlimited developed the StreamAmp platform as an example of how such an architecture can be realized in practice.
The same module can be adapted to a variety of speaker enclosures while preserving flexibility for manufacturers to implement their own acoustic designs and product-specific features.
The StreamSDK software stack, which is used in millions of shipping products, was heavily customized for the StreamAmp module to address the specifics of this product category.
Figure 1 shows an overview of the default features StreamAmp currently provides out of the box. Photo 2 shows a reference active speaker design created by the StreamUnlimited team.
System Architecture and Core Features
Based on their extensive experience with countless custom projects, the StreamUnlimited development team embraced the choice of a sophisticated real-time architecture, which would be able to do things such as instantly process volume changes initiated by the user by controlling the DA converter without the main processor involved. In this example, feedback is then provided to the
main processor, which forwards those changes to the remote user interface (UI) on the iOS/Android app for control and setup.
This architecture is made possible by StreamUnlimited’s flagship networking module Stream1955 (Photo 3), offering ample processing power through a quad-core processor, combined with a 2x2 Wi-Fi 6 wireless chipset along with Ethernet and Bluetooth/BLE interfaces for enhanced connectivity. The Stream1955 module also supports online updates for all its system components, ensuring long-term functionality and the ability to accommodate future feature enhancements.
Audio Processing and Amplification
StreamUnlimited partners with Illusonic, a Swiss company specializing in audio processing technologies. The Illusonic team provides extensive expertise in this area and can be involved for specific customizations, supporting project-specific requirements where needed.
The StreamAmp module offers a centralized architecture where the host speaker acts as the single processing hub for all audio channels. This design simplifies system management and maintenance while enabling full processing of up to eight audio channels with advanced filtering capabilities.
A/D and D/A conversion is handled using ESS Technology's 32-bit SABRE Reference DACs and ADCs, with analog buffers and filters implemented via OPA1502 operational amplifiers.
For the amplifier and power supply part, StreamUnlimited selected the Hyper-N-core family of modules, which is a well-known and popular choice among Hi-Fi enthusiasts.
It also provides excellent frequency response as well as ultra-low harmonic distortion and noise, independently of the load impedance. These features make the Hyper-N-core modules well suited as generic building blocks that fit different configurations.
Currently, the StreamAmp platform offers a choice between 100W, 125W, 250W, and 500W per channel in terms of default options for amplifier output power.
Recognizing that amplifier topology does shape the sonic character, StreamAmp offers the flexibility to integrate external amplification or combine it with Hyper-N-Core modules as part of the system design.
Below Image: Block diagram of a StreamAmp stereo pair configuration with up to four channels per speaker.
Speaker Configurations and Connectivity
In its most basic configuration, the StreamAmp module provides two channel outputs. One output is routed internally to the speaker drivers; the crossover is still analog. The second output is routed via an analog speaker cable connector to a passive speaker. Even in the basic configuration, the acoustic designer retains full DSP control over all output channels.
The more advanced configuration offers amplification in every speaker of the stereo pair. The second speaker ("client") has the very same amplifier and D/A converter built-in and receives four channels of 32-bit at 192kHz audio from the "host" speaker via a proprietary bit-transparent low-latency digital link--nicknamed "StreamLink." This way, each speaker can have up to four amplifier channels (Figure 2).
For those brands that do not want to route a cable, there is an option to transmit 24-bit/96kHz uncompressed audio wirelessly from the host speaker to the client speaker using WISA technology.
The StreamAmp module was designed to be applied inside the acoustical compartment without causing undesirable problems for the speaker designers. The StreamAmp enclosure structure prevents undesired resonances and allows all volume that is not occupied by the electronics to be used as acoustical volume. It also allows the heat to spread and prevent hotspots.
Since all electronics are based on high-efficiency parts and the metal back plate allows heat to exit the product while being airtight, no special thermal measures are required when integrating the StreamAmp module.
User Interface and Control Options
A critical element in active speaker configurations is the design of control options on the panel or remotely. The optional local user interface, which consists of touch buttons for source and volume control and visual feedback via an LED bar, can be customized by re-assigning the buttons or even by replacing the entire UI board with a custom version.
Since the StreamAmp module may be controlled via Bluetooth LE, a custom wireless remote control may also be designed for a dedicated look and feel.
An alternative native remote user interface can be realised by using the StreamAmp's network API. This allows manufacturers to incorporate full remote features on a dedicated remote control unit with modern design elements, or even to incorporate those features in an external system component.
StreamUnlimited created a demo implementation using a popular Wi-Fi microcontroller, which displays source and volume information on its display while allowing volume and source to be changed via a rotary and pushbutton integrated in the display (Photo 4).
Design Options
The simplest means of design customization of the StreamAmp module is by re-arranging I/O connections on the back plate. This is easily possible since the electronics are split between a mainboard with generic interfaces and I/O boards that can be customized or re-arranged without touching the mainboard. Further customization is possible by only using the mainboard and designing dedicated I/O boards to provide different or additional analog and digital interfaces (Photo 5).
Certification and Compliance
To address the certification challenges, the StreamAmp module was fully FCC and CE certified in a reference product at a leading test lab. Depending on how close the actual product is to the reference speaker, the scope of additional testing for the end product can be reduced significantly compared to other (even pre-certified) building blocks, especially if handling certifications in the same test lab that already certified the StreamAmp module.
Figure 3: Illusonic test and configuration software.
A second part of the product certification process is the streaming services, which also require their own certification testing and official approval. To address this, the StreamAMP module was pre-certified for AirPlay 2, Spotify Connect, Roon, Qobuz Connect, and TIDAL Connect.
To allow speaker brands to optimize the sound and acoustical properties according to their own signature approach, Illusonic provides a PC tool for tuning of all parameters (Figure 3). This software runs on Linux, Windows, and macOS and allows direct download onto the StreamAmp and/or simulating the audio processing on any PC. This tool also offers different profiles to manage different sets of features according to the demands of each application (Figure 4).
Final Build Process
Once all hardware and software configurations are finalized and the product has passed all required certifications, product-specific keys from service providers and custom settings can be applied to the final design using a PC-based tool. This tool generates the final software release and any future updates.
This custom software release can be customized in multiple ways. The key elements in each software image include product-specific settings (Manufacturer Name, Model Name), firmware update URL, Illusonic configuration file (created using the aforementioned Illusonic tool), WebClient content/user interface, and button mapping of the capacitive touch buttons. The software image also includes audio files for startup sound, shutdown sound, notifications for button presses, sound for entering network standby, Wi-Fi setup, Bluetooth pairing, and more.
Balancing the ability for brands to create unique products with the need to avoid excessive technical variations or costly NRE for custom hardware and software remains a key challenge. The StreamAmp modular platform provides a flexible solution for such challenges, allowing brands to maintain a solid portfolio, supported by a long-term hardware roadmap, and enabling consistent sourcing and product lifecycle planning.
StreamAmp Expansions
Depending on quantities, additional options are available for the StreamAmp platform, such as single or dual subwoofer outputs, Dante Receiver, Amazon Music HD support, Dirac room correction, USB audio input, Phono input, and more.
The modular hardware and software architecture of the StreamAmp platform also allows for any configurations to be maintained and updated for many years. Products based on this platform may truly be considered future-proof.
It is inevitable that electronics and software will eventually become outdated. For brands and high-end enthusiasts who still prefer passive speaker boxes, the StreamAmp boards may be used in a different encasing to create a Streaming Amplifier. This also allows brands to offer their own streaming hubs as an add-on to existing product ranges, expanding the value of the brand by future-proofing and rewarding user investment.
To demonstrate these concepts, StreamUnlimited accordingly showcases demo products, as shown in Photo 6. For this demonstration, only the LED/Button board needed to be customised: a rotary encoder with button press function was added for volume and play/pause control, while an LED bar provides volume and source information. Additionally, it features two high-quality pre-out channels, fully configurable via the Illusonic software plugin for any application, whether driving subwoofers or powering external amplifiers dedicated to the mid/high frequency sections of high-end speakers.
Meeting Real Demand
Initial products within the StreamAmp platform are already on the market, with further designs currently in development. StreamUnlimited is seeing growing interest in this modular hardware and software architecture that allows flexible adaptation to various use cases. For active speaker designs, this is an exciting new concept as more users recognize the value of fully integrated systems in their lifestyles, while not compromising on audio quality. This new approach also requires ensuring a consistent and stable supply chain. The StreamAmp module is designed and manufactured in Europe, and all integrated services are actively maintained by StreamUnlimited, with regular updates.
The flexibility of the StreamAmp platform allows manufacturers to adapt the hardware and software configuration to meet specific product requirements, whether through integration into speaker enclosures or by developing dedicated streaming amplifier products. This modularity supports a broad range of applications and future updates, providing a reliable foundation for the development of high-end, network-enabled active loudspeakers.