DALI Callisto 2C Active Digital Speaker System

All Together Now

Equipment report
Music servers and computer audio
DALI Callisto 2C
DALI Callisto 2C Active Digital Speaker System

When Robert Harley asked me to return to high-end audio reviewing after a many-year hiatus, he had a product in mind. Oh sure, he stated it was a “new class of product” that TAS would “like to have more coverage of in the future.” But really it was the ultimate system to lure an audiophile back into the fold after a long period of stagnation.

According to DALI (Danish Audiophile Loudspeaker Industries): “The Callisto 2 C is the stand-mount solution in our new wireless ecosystem that empowers you to easily access all your high-res music directly from your smart device.” A couple of tidbits in there might have put me off in the past, “wireless” and “smart device” traditionally have not been associated with the best sound. However, it turns out that the way DALI implements these into its all-in-one design is quite different. There is no downside and a good bit of upside. That ecosystem includes the DALI Sound Hub, which functions as a preamp. Inputs are in many formats including Bluetooth, WiFi, LAN, and wired digital and analog; the signal then goes to the speakers through DALI’s proprietary wireless standard. I reviewed the Callisto with the BluOS NPM-1 module, which handles networking and streaming, installed in one of the Sound Hub’s two bays. The speakers themselves include mono D/A converters, preamps, power amps, and drivers. You simply plug in the speakers and connect a wired or wireless source to the Sound Hub and start listening. Why would DALI pack so much technology into a single product? Does it sound “high-end”? Do the cost savings of including all these components inside the speaker cabinet outweigh potential sonic compromises? Or are such integrated systems an inherently superior architecture to component audio?

Parts of the Whole
Looking at individual parts of this highly integrated system, the first component in the signal path is a 50MIPS digital signal processor. This manages control signals and digital-domain crossovers for the speaker drivers. The DSP is connected through I2S to a Burr-Brown PCM1796 DAC capable of 123dB dynamic range, with differential current outputs for lower noise. Volume control is performed in the analog domain just before the amps, for good S/N ratio and true 24-bit resolution. There are then two separate amps, one for the tweeters and one for the woofer. DALI states that “the 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.” One of its benefits is that distortion stays low at all frequencies, as opposed to traditional amps which have higher distortion at higher frequencies. Rated at only 30W for continuous signals, DALI says these amps can put out 250W for periods of up to five seconds.

Then there are only minimal crossover parts needed between amp and drivers, thanks to filtering accomplished in the DSP. The speakers are technically three- or two-and-a-half-way, though DALI calls them two-way, grouping the two tweeters together as a “hybrid tweeter.” There is a 3/4"-by-2" planar-magnetic ribbon super-tweeter with response beyond 30kHz and a 1-1/8" dome tweeter with a membrane so thin it’s partially transparent, which handles frequencies down to 2kHz. The single 6-1/2" woofer uses a lightweight wood-fiber cone. DALI also claims it has been designed to stay linear at large excursions, keeping distortion low at high output levels. This partly results from DALI’s patented Soft Magnetic Compound (SMC) in the pole piece, which supports magnetic penetration while reducing electrical crosscurrents. The cabinets employ thick 25mm (1") MDF, with internal bracing to reduce side-wall vibrations. The Callistos themselves are built in DALI’s factory in Denmark, and the Sound Hub is made in a DALI-owned factory in China.

The stands recommended for the Callisto 2Cs were the DALI Connect M-600s. They were easy to assemble, sturdy, and good-looking in their shiny black finish. They have a thick steel top plate, one-piece extruded-aluminum stem,  a thick glass bottom plate, and aluminum cone spikes that attach to the underside with sticky material. My floor is concrete slab on top of earth, so it does not vibrate. The top plates were a bit small; I would have preferred a size that fit the Callisto more closely, perhaps with bolt holes to connect with the threaded spike holes in the bottom of the speaker. I did not use spikes on the Callisto, but rather attached the tiny rubber bumpers that were included.

Features and Functionality
Via the BluOS module in the Sound Hub, the system can join a multi-room network that includes many types of BluOS-equipped audio gear. The speakers can also interface with many major-brand home-control systems. Playback can be controlled through the BluOS app on different platforms, iOS and Android, Windows and Mac. The platform supports hi-res PCM audio up to 24/192, as well as quite a few other audio formats, including master-quality MQA. The whole system is MQA-certified all the way from the internet to the speaker drivers.

The Sound Hub features auto-sensing source selection. It will turn on and switch to the active input when a connected source is detected. It will also automatically go into sleep mode, as will the speakers, a few minutes after the input goes silent. So super-easy to use—created for music lovers and not just audiophiles. I was able to install the BluOS app on Kindle and Android tablets, as well as on a Windows 10 laptop and Win 7 desktop PC. All of them controlled playback just fine. In addition to the front-panel controls on the Sound Hub, there is an included remote and a volume strip on top of the speakers. Goodness, has anyone seen a system that could be controlled from so many places? My only quibble was the BluOS app volume slider is too sensitive. Tapping on the upper or lower part of the scale didn’t work for small level steps. It would be good to make the scale longer in the future. A major addition I noticed after a firmware update was a “home theater” mode available for setup in the speaker-connection menu.

For streaming I installed the Win Tidal app for the first time on my home-built desktop PC. Honestly, I did not expect much, as I was using a basic Soundblaster Audigy LE PCIE sound card running analog signals to an old cheap ($80) pair of PC speakers. Well, surprise! The Labtec Edge 418 with Slab flat-panel technology can sound quite good with Tidal. Mind you, only at low levels. My sole previous streaming-audio experience was YouTube HD music videos. What YouTube calls “high definition” is really not so high, compared to Tidal. Not only on the MQA tracks, but also on the “CD-quality” ones, the sound was really fantastic! I absolutely had to hook up the DALI Callistos if I was getting sound this good from basic PC speakers.

Listening and Tweaking
I installed the speakers in a different room, and gave them some break in. The Sound Hub was off in my main listening room, though DALI does not recommend this. It states that the 5.8GHz wireless band is less crowded with other devices, though it does not go through walls very well. I found it went through one interior drywall/wood frame wall just fine, though the distance between the Hub and speakers was not more than 24 feet. (DALI has the maximum reliable distance at 60 feet in the same room.) The first thing I noticed was the incredible amount of detail. The next thing was that the top octave was too forward on many recordings. Leaving the front grilles on helped (and that is how I did most of my listening). Then adding recording-studio egg-carton foam on the wall behind the speakers (two 2'-by-4' pieces) helped ease the brightness a bit. I always use this type of acoustic treatment, but you can use the less visually obtrusive room treatment of your choice to achieve similar results. As I continued listening, I realized it was not so much a frequency spike in the top octave, but rather that the Callistos were brutally revealing of characteristics of the recording. This is a quality that I like.

So if we want to adjust the frequency balance for the system we… substitute some different cables? Negative, there are no cables in the Callisto system! Adding my Audioprism Power Foundation III for AC conditioning helped a little. When all you have to work with is AC conditioning, power cords, and room treatment, you certainly should address all of those areas.