Two 30W class-D amplifiers drive the tweeter module and the woofers. DALI says these amplifiers are rated for 10 times the peak-to-average power required in normal use and can deliver 250W for up to 5 seconds. The crossover is implemented in the digital domain, and volume control takes place just before the speaker's Burr-Brown PCM1796 balanced-output DACs to maintain 24-bit resolution.
Callisto 6 Cs are assembled in Denmark with a Danish cabinet and components manufactured in the DALI factory in Ningbo, China.
Setup
Once the Sound Hub and Callistos are powered up, connecting each speaker to the Hub is a simple matter of first pressing the button at the top of the Hub's rear panel then pressing the connect button at the base of the speaker's rear surface, above the inset connection panel. (A display next to the speaker's button allows you to choose whether the speaker is the left or the right.) Each speaker emits a reassuring low-pitched chime when the connection to the Sound Hub is confirmed. The Sound Hub's analog and digital inputs can then be used, the Hub automatically switching to whichever source is connected (other than the 3.5mm jack). For this review, I connected the Sound Hub to my network and activated it as a Zone in the Roon 1.6 app running on my iPad Mini.
I started my listening with the DALI speakers in the positions where the Joseph Perspective2 Graphenes had worked well when I reviewed them for the July 2019 Stereophile. The woofers of both were 75" from the wall behind; those of the left speaker were 30" from the LPs that line its sidewall; the right speaker's woofers were 45" from the books that line its sidewall. (A small raised platform at the front right of my room mandates the asymmetrical placement.) The Callistos produced a superbly even bass balance in these positions, so I left them there.
The speakers were initially toed-in to the listening position, but in that orientation I found the high frequencies excessive. I then tried the speakers firing straight ahead, as recommended by DALI, but ended up with a slight, 5° toe-in, which gave the smoothest mid-treble balance. A fairly bulky, cloth-covered plastic grille plugs into the upper section of the Callisto 6 C's front baffle; I left the grilles off for my auditioning.
Sound quality
DALI says in their user manual that the Callisto 6 C will take about 100 hours to break in. I therefore used the speakers for a couple of weeks before I started my serious auditioning. At first, I used the Callistos with their analog inputs connected to the single-ended outputs of my PS Audio DirectStream D/A converter.
Listening to the dual-mono pink noise track on my Editor's Choice CD (Stereophile STPH016-2), the Callistos produced a stable, narrow central image, though with some of what the late J. Gordon Holt used to call "vertical venetian blinding" as I moved my head a few inches from side to side. (This is due to narrow-band cancellations in the treble between the sounds from the two speakers.) The image of the noise wasn't quite as narrow as that offered by the KEF LS50s, which I confirmed by listening to Nathan Milstein's 1951 performance of Dvorák's Violin Concerto in A minor (Op.53) with Antal Doráti conducting the Minneapolis Symphony Orchestra (16/44.1 AIFF file, Naxos 8110975). The violin was recorded too loud in relation to the orchestra, but its image was stable, ie, didn't wander with frequency. And I was surprised at the amount of image depth apparent on this mono recording, the horns, for example, sounding a long way behind the soloist.
The pink noise track sounded a little top-heavy if I sat up straight so that my ears were just above the ribbon supertweeter, which is 37" from the floor. With my ears level with the ribbon unit, the balance was more even, though still with perhaps a touch too much top-octave energy.
At the other end of the spectrum, low frequencies sounded powerful. The 1/3-octave bass warble tones on Editor's Choice were produced with good weight down to the 40Hz band, with then the 32Hz warble tone exaggerated by the lowest mode in my room. At my typical listening level, the 25Hz band was just audible but the 20Hz band was missing in action. Commendably, there was no audible wind noise or "chuffing" from the ports with the lowest-frequency tones. Overall, the warble tones sounded extremely clean, with no audible distortion. The half-step–spaced tonebursts on Editor's Choice spoke clearly and evenly down to their 32Hz lower limit, but with a slight emphasis to the leading edges of the tonebursts.
I doubt that the Callisto 6 Cs will be used without their companion Sound Hub; all my subsequent auditioning was therefore performed with the Hub sending data wirelessly to the speakers. Like the Callisto speaker, the Sound Hub digitizes its single-ended analog inputs. To examine how an analog signal fed to the Sound Hub's analog inputs compared with the original digital data, I sent the same data to the Hub's BluOS module and to the PS Audio DAC via Roon over my network. Playing the 1kHz warble tone from Editor's Choice and with the DirectStream's volume set to its maximum, I had to increase the Sound Hub's volume control by three "clicks" to give an spl within 0.5dB of that with the digital connection.
With this housework done, the dotted rhythm of the opening "Komm, ihr Töchter, helft mir klagen" from Bach's St. Matthew Passion, with John Butt directing the Dunedin Consort (24/88.2 Studio Master download, Linn CKD 313P), sounded equally compelling from both sources. The soundstaging on this excellent recording, however, was wider and deeper with the direct connection to the Sound Hub. The soloists sounded a little shut-in with the analog connection from the PS Audio DAC. Repeating this comparison using my Ayre disc player as a source, sending AES/EBU CD data first to an antique Digital Domain VSP format converter to convert it to S/PDIF, then sending the data simultaneously to both the PS Audio DAC and the Sound Hub, gave a similar result. The drums and cymbals on "Maybe You'll Be There" from Diana Krall's Live in Paris (CD, Verve 065 109-2) were set farther back in the soundstage with the direct S/PDIF feed. The image of Krall's voice on her hauntingly beautiful treatment of Joni Mitchell's "A Case of You" was more palpable with the digital connection to the Hub.
The Sound Hub's analog inputs are useful, but the digital inputs get the best from the Callistos for serious listening. I continued my auditioning using Roon to send digital data to the Sound Hub via my network. I downloaded and installed the BluOS app on my iPad Mini, but as this integrates the Roon functionality, including controlling the Sound Hub's volume, I stuck with the familiar Roon interface. (Perhaps I am too easily amused, but I did find it intriguing that when I was running Roon on my laptop while the BluOS app ran on my iPad, adjustments to the Callisto system's volume level via the laptop slider were reflected in changes in the Sound Hub's numeric display, by the bargraphs on the fronts of both speakers, and by the volume control in the BluOS app.)
For this ex-pat, Vaughan Williams' The Lark Ascending always conjures a vision of the English countryside. My favorite performance is from violinist Nigel Kennedy, with Simon Rattle conducting the City of Birmingham Symphony Orchestra (16/44.1 ALAC file, from EMI Classics 72435 56413 2 8). The works starts with hushed strings murmuring behind the soloist as he moves up the fingerboard of his instrument, the lark into the air. The Callistos sent shivers down my spine with this recording. The image of Kennedy's violin moved slightly from side to side, but I suspect this is an artifact of the miking, as the image of Milstein's instrument in the Dvorák concerto was stable with frequency. Rosin noise from Kennedy's bow was a little more audible than I am used to, but not to the extent that it distracted from the music making. The woodwinds were set well back in the soundstage, the orchestral image wide and stable.
The Callisto's midrange was natural-sounding. After the Vaughan Williams, Roon Radio selected a track I hadn't played for a long time, Hyperion Knight performing Earl Wild's arrangement for piano of the Grand Fantasy on Porgy and Bess, from Rhapsody (16/44.1 ALAC file, Stereophile STPH010-2, footnote 1). The 9' Steinway D nicely illuminated the acoustic of Albuquerque's First United Methodist Church, where I had made the recording in 1997. The sound of the piano and its image via the DALIs was true to my memories of the sessions, and the instrument's lowest notes were played back with an excellent combination of weight and articulation.
I suspect that the claims made for the low distortion of Callisto's woofers are correct: My Fender bass guitar on the channel identification tracks on Editor's Choice had superb weight and articulation. The deep if overcooked bass notes that underpin "Cast Off" on Bruce Hornsby's relatively new Absolute Zero (16/44.1 ALAC file, Zappo Productions Zappo001) were reproduced with impressive heft but without undercontrolled boom.
A recent purchase and a contender for Stereophile's 2020 "Records 2 Die 4" is the complete set of Beethoven Symphonies with Simon Rattle conducting the Berlin Philharmonic (24/192 WAV files, Berliner Philharmoniker BPHR 160091). The soundstage on Symphony 7 was reproduced with good depth. The double-bass notes that punctuate this symphony's second movement, Allegretto, were both superbly well articulated and reproduced with good weight.
Downsampling
What about the fact that even though the Sound Hub will accept PCM data sampled at 192kHz, it downsamples the rate to 96kHz before transmitting them to the Callistos? A favorite test track for assessing transparency is "Die Tänzerin" from German singer Ulla Meinecke's Wenn Schon Nicht für Immer, dann Wenigstens für Ewig (24/192 needledrop made with the Ayre QA-9 A/D converter from LP, German RCA 426124). Though Meinecke is balanced relatively upfront in the mix, the recording has tremendous dynamic range, and both the voice and the stereo keyboard are accompanied by generous helpings of reverberation and repeat echo. Playing this track, I literally count how many echoes I can hear before they are obscured. Some systems dry out the reverb to a noticeable degree, but the Callistos did well, lighting up a deep dome of artificial ambience at the appropriate times. The dry-sounding finger snaps on "Die Tänzerin" were pushed a little more forward in the soundstage than I am used to, but not to the extent that it mattered. And the differences between the Ayre QA-9 and the Benchmark A/D converter with which I had made an alternative needle drop were well-resolved. The Callisto's necessary downsampling of high–sample-rate data would therefore seem to be reasonably benign. Conclusion
I found that the treble balance requires some care with setup in the owner's room, but when that is optimized, at $5750 with the Sound Hub and BluOS network module, DALI's Callisto 6 C system is competitively priced when you take into consideration its fit'n'forget nature and its excellent sound quality. I enjoyed my time with this system. You will too. It is the very model of a self-contained music reproduction system.
Footnote 1: The booklet notes for this CD feature some of the best writing Wes Phillips, who died on August 27, 2016, contributed to Stereophile.
Once the Sound Hub and Callistos are powered up, connecting each speaker to the Hub is a simple matter of first pressing the button at the top of the Hub's rear panel then pressing the connect button at the base of the speaker's rear surface, above the inset connection panel. (A display next to the speaker's button allows you to choose whether the speaker is the left or the right.) Each speaker emits a reassuring low-pitched chime when the connection to the Sound Hub is confirmed. The Sound Hub's analog and digital inputs can then be used, the Hub automatically switching to whichever source is connected (other than the 3.5mm jack). For this review, I connected the Sound Hub to my network and activated it as a Zone in the Roon 1.6 app running on my iPad Mini.
I started my listening with the DALI speakers in the positions where the Joseph Perspective2 Graphenes had worked well when I reviewed them for the July 2019 Stereophile. The woofers of both were 75" from the wall behind; those of the left speaker were 30" from the LPs that line its sidewall; the right speaker's woofers were 45" from the books that line its sidewall. (A small raised platform at the front right of my room mandates the asymmetrical placement.) The Callistos produced a superbly even bass balance in these positions, so I left them there.
The speakers were initially toed-in to the listening position, but in that orientation I found the high frequencies excessive. I then tried the speakers firing straight ahead, as recommended by DALI, but ended up with a slight, 5° toe-in, which gave the smoothest mid-treble balance. A fairly bulky, cloth-covered plastic grille plugs into the upper section of the Callisto 6 C's front baffle; I left the grilles off for my auditioning.
Sound qualityDALI says in their user manual that the Callisto 6 C will take about 100 hours to break in. I therefore used the speakers for a couple of weeks before I started my serious auditioning. At first, I used the Callistos with their analog inputs connected to the single-ended outputs of my PS Audio DirectStream D/A converter.
At the other end of the spectrum, low frequencies sounded powerful. The 1/3-octave bass warble tones on Editor's Choice were produced with good weight down to the 40Hz band, with then the 32Hz warble tone exaggerated by the lowest mode in my room. At my typical listening level, the 25Hz band was just audible but the 20Hz band was missing in action. Commendably, there was no audible wind noise or "chuffing" from the ports with the lowest-frequency tones. Overall, the warble tones sounded extremely clean, with no audible distortion. The half-step–spaced tonebursts on Editor's Choice spoke clearly and evenly down to their 32Hz lower limit, but with a slight emphasis to the leading edges of the tonebursts.
The Sound Hub's analog inputs are useful, but the digital inputs get the best from the Callistos for serious listening. I continued my auditioning using Roon to send digital data to the Sound Hub via my network. I downloaded and installed the BluOS app on my iPad Mini, but as this integrates the Roon functionality, including controlling the Sound Hub's volume, I stuck with the familiar Roon interface. (Perhaps I am too easily amused, but I did find it intriguing that when I was running Roon on my laptop while the BluOS app ran on my iPad, adjustments to the Callisto system's volume level via the laptop slider were reflected in changes in the Sound Hub's numeric display, by the bargraphs on the fronts of both speakers, and by the volume control in the BluOS app.)
I suspect that the claims made for the low distortion of Callisto's woofers are correct: My Fender bass guitar on the channel identification tracks on Editor's Choice had superb weight and articulation. The deep if overcooked bass notes that underpin "Cast Off" on Bruce Hornsby's relatively new Absolute Zero (16/44.1 ALAC file, Zappo Productions Zappo001) were reproduced with impressive heft but without undercontrolled boom.
DownsamplingWhat about the fact that even though the Sound Hub will accept PCM data sampled at 192kHz, it downsamples the rate to 96kHz before transmitting them to the Callistos? A favorite test track for assessing transparency is "Die Tänzerin" from German singer Ulla Meinecke's Wenn Schon Nicht für Immer, dann Wenigstens für Ewig (24/192 needledrop made with the Ayre QA-9 A/D converter from LP, German RCA 426124). Though Meinecke is balanced relatively upfront in the mix, the recording has tremendous dynamic range, and both the voice and the stereo keyboard are accompanied by generous helpings of reverberation and repeat echo. Playing this track, I literally count how many echoes I can hear before they are obscured. Some systems dry out the reverb to a noticeable degree, but the Callistos did well, lighting up a deep dome of artificial ambience at the appropriate times. The dry-sounding finger snaps on "Die Tänzerin" were pushed a little more forward in the soundstage than I am used to, but not to the extent that it mattered. And the differences between the Ayre QA-9 and the Benchmark A/D converter with which I had made an alternative needle drop were well-resolved. The Callisto's necessary downsampling of high–sample-rate data would therefore seem to be reasonably benign. Conclusion
I found that the treble balance requires some care with setup in the owner's room, but when that is optimized, at $5750 with the Sound Hub and BluOS network module, DALI's Callisto 6 C system is competitively priced when you take into consideration its fit'n'forget nature and its excellent sound quality. I enjoyed my time with this system. You will too. It is the very model of a self-contained music reproduction system.
Footnote 1: The booklet notes for this CD feature some of the best writing Wes Phillips, who died on August 27, 2016, contributed to Stereophile.
