DALI Sound Hub

The DALI Sound Hub features a huge range of digital and analogue inputs and an auto source sensing system. The Sound Hub automatically activates the right input the moment you start playing music or turn on your TV – so you can just sit back and enjoy exquisite audio.

The retro feel volume knob on the front of the hub embeds a LED display, which combines tradition with convenience. The LED display shows the current audio source as well as the volume level, and you can even adjust the light intensity of the display. This is supported by a light display on top of the Sound Hub, which indicates the location of the paired CALLISTO speakers in the pairing process.

So you only need to worry about adjusting the volume using CALLISTO’s Bluetooth remote or directly via the touch panels built into the top plate of each speaker.

Expansion ports

One of the most innovative features of the DALI Sound Hub is actually hidden away from view. The two modular expansion ports on the back panel open up the hub to a world of possibilities. Via the DALI designed open standard connector, any type of audio module can integrate 100% with the Sound Hub system. 

This enables a total seamless addition of extra hub functions - allowing for streaming, multi-room or even multi-channel expansions, but also future proofing the Sound Hub. This includes any connected speakers by separating the quickly evolving music delivery technologies from the more robust and time durable speaker technology. 

Our first expansion module integrates Bluesound’s incredible BluOS hi-res multi-room platform. BluOS is devised by audiophiles for audiophiles to deliver the best digital sound quality imaginable throughout your house. And because BlueSound is compatible with speakers from a variety of audiophile manufacturers, it delivers flexibility, convenience and choice as well as unparalleled quality. Which makes it a natural extension to the CALLISTO wireless family.

Wireless audio transfer

The wireless connection between the Sound Hub and the speakers,  is an extremely stable digital connection, made on either the 2.4 GHz or the 5.8 GHz band depending on location and quality of the connection. The proprietary 30 bit audio protocol transfers an uncompressed audio signal in 24 bit 96 kHz, utilising the remaining bits to control volume, speaker ID and other control data. Because it works on a less trafficked band, and the protocol is specially designed for transporting an audio signal, the connection is highly stable introducing next to no packet loss. The protocol uses forward error correction to remove the result of packet loss should they occur. The high bandwidth low latency protocol functions as a point to multipoint connection. This allows for multiple speakers to connect to the same stereo signal. With latency below 25 ms, sync between video and audio from a movie or TV source is obtained well within conventionally acceptable limits.

Sound Hub inputs

Bluetooth

Bluetooth is built into the DALI Sound Hub as standard, offering the possibility to transfer sound to the CALLISTO system from almost any device - supporting AAC and Apt-X HD quality. AAC is an improved audio protocol that despite still being lossy, supports a larger amount of audio data to be transferred via the Bluetooth connection. It’s the highest quality of Bluetooth transfer for an Apple product. Apt-X HD is a well-known audio protocol, allowing for compression of up to 24 bit 48 kHz audio streams and a wider bandwidth transfer than Apt-X. This allows for high quality playback of not just traditional audio files, but also HD quality music over Bluetooth, along with full backward compatibility with Apt-X. 

Optical

The Sound Hub features two optical inputs that are controlled differently - with a clear focus on TV and audio use. The TV input is activated by the carrier signal. This enables the Sound Hub to power up the CALLISTO speaker system the second the TV is turned on. The audio input is activated by an audio signal, and by analysing the audio signal, the Sound Hub can determine if audio is played back, and if not, will automatically power off the system, turning it back on again when a signal is detected. 

The optical input accepts any data rate from 16 bit / 32 kHz to 24 bit / 192 kHz. The signal will be converted to work optimally with the 24 bit / 96 kHz wireless transfer audio protocol before being passed on to the connected speakers. 

Coaxial RCA

For direct digital connection between an audio device and the Sound Hub. Like the optical input, it will accept from 16 bit / 32 kHz to 24 bit / 192 kHz.

Analogue (RCA and mini/jack)

The high-quality ADC samples the analogue signal in 24 bit / 96 kHz using the system master clock for optimal wireless transfer to the CALLISTO speakers.

Sound Hub outputs

Sub-out

LFE type subwoofer output. When a subwoofer is connected, everything below 100 Hz is sent through this output to a connected subwoofer.

Pre-out

Line level RCA output. This output allows you to use the DALI Sound Hub as a pre-amplifier for your existing setup, making it possible to enjoy the benefits of the modular extensions and the auto source sensing capabilities. The Pre-out can also be used to connect to the CALLISTO speakers via a cable in cases where wireless transfer is not preferable.

USB

The built in USB A port delivers a 5V 1.2A output to power connected devices like a Google Chromecast Audio, or charge a mobile device whilst playing. It is also used to update the Sound Hub’s firmware. The built in USB port does not offer the ability to playback audio stored on a connected device.

Amplifier

Designing a ‘best in class’ active speaker system is the sum of many parts. One truly important part is the amplifier, or more correctly the amplifier module. Any quality amplifier module consists of three equally important parts that need to be designed to work together in perfect harmony: the amplifier itself, the PSU and the signal processing. The delivery from the signal processing and the PSU to the amplifier circuitry must adhere precisely to the amplifiers needs and demands. Only in this way can you achieve an undistorted, uncoloured and coherent amplification.

The amplifier

The CALLISTO Class D amplifier is based on patented state-of-the-art technology with a global feedback, self-oscillating design chosen for its very musical properties. Being able to deliver 250 Watts for up to 5 seconds, there is plenty of power to ensure more than enough sound pressure even in complex musical passages or massive explosions in movies.

The self-oscillating loop PWM amplifier enjoys improved performance over conventional fixed-frequency triangle-based PWM amplifiers because the bandwidth of the feedback loop is higher than that of a conventional feedback loop which must obey conservative stability criteria. The post filter feedback reduces distortion and provides best in class load invariance. To keep control of the self-oscillating switching frequency and to ensure fast recovery after a clipping situation, the limiter circuit acts whenever the voltage difference between the input and output of the error amplifier exceeds a hardware defined threshold. This threshold is tuned so that THD levels will not exceed approximately 1% at the speaker output.

The Total Harmonic Distortion (THD) of the amplifier is below 0.005% across the audio bandwidth 20-20 kHz measured at 1W output power into 4Ω. At 30W output power the amplifier meets THD levels between 0.015% and 0.03% which is successfully independent of frequency. Traditional amplifiers typically show increasing levels of THD towards higher frequencies.

A large study presented in 2014 analysed more than 400 different musical tracks, and concluded that there needs to be a 10x peak-to-average power in an amplifier to ensure the dynamics of music without limiting and in worst case clipping. The amplifier in CALLISTO delivers 30 Watts continuous power, and up to 300 Watts power for very short bursts, delivering perfectly on the 10x peak-to-average power ratio. The obvious advantage of leveraging this knowledge is the amplifier design draws less running power, and thereby reduces the risk of introducing PSU noise leaks and shutdowns due to overheating.

The Power Supply Unit

The power supply for the system is a universal mains input switch mode PSU, capable of delivering 50 Watts continuous and 250 Watts power for 5 seconds. The voltage regulation is done from both the negative and positive rail voltage to suppress uneven bus pumping on the rails through the half-bridge amplifier design.

The power supply is a 130 kHz switching fly-back type, making use of the alternating energy stored in the transformer. The size of the transformer is optimized for the power dynamics of the amplifier, maintaining stable operation from 300W down to less than 1 W.

The Signal processing

The core of the signal processing is comprised of a 50MIPS Digital Signal Processor, and an audiophile 24bit Digital to Analogue Converter.

The DSP boasts an audio processor capable of up to 1024 instructions per cycle. On the output side the DSP is connected through I2S to a Burr Brown DAC that makes use of advanced segment architecture to achieve excellent 123 dB dynamic range performance. Differential current outputs are provided to suppress common mode noise and, by nature of the analogue interface, clock jitter is eliminated on the audio interface to the class D power amplifier. The current to voltage conversion is done at the power amplifier input, securing the shortest possible signal path without the need of sound quality degrading AC-coupling capacitors.

The master volume control takes effect in the signal chain just before the analogue amplification stage, to ensure optimal Signal-to-Noise-Ratio at all volume levels. This means that no matter which of the many possible volume controls is used for adjusting the master volume, the actual volume change is done in the same position in the signal chain.

The amplifier output is connected directly to the driver, with all of the crossover filtering done in DSP. Having complete control over every step of the audio handling has the clear benefit of being able to maximize the utilisation of every component in the audio chain. Optimising the crossover parameters with the knowledge of precisely how the driver is going to react, pushing the performance of the individual driver right to the limit without ever going beyond. Combined with the well-known DALI driver performance, this is a large part of the ‘best in class’ sound of the CALLISTO speakers