The internationally acclaimed Hagen Quartett recently performed the 10 works of its Mozart cycle at the Tonhalle. The group had stretched the same repertoire over the whole concert season in Hamburg, reason enough for the Zurich audience to affectionately call the quartet’s offer – four concerts in two days – its “Mozart Marathon”, and I attended the first of the four concerts.

While in Mozart’s time, the string quartet was still an emerging musical genre, the Hagen marked the composer’s supreme achievement in the form with selected works from 1782-1790. Only Joseph Haydn had worked hitherto to establish the quartet as a reputable art, and the older composer was quick to show high regard for his junior’s achievements. To Leopold Mozart, Haydn was to say: “Before God, and as an honest man, I tell you that your son is the greatest composer known to me either in person or by name. He has taste, and, what is more, the most profound knowledge of composition.”

For the Zurich audience, the three siblings – Lukas Hagen (violin), Veronika Hagen (viola) and Clemens Hagen (cello) joined by the second violin Rainer Schmidt, performed in the same configuration that has played together since 1987. Schmidt attributes the group’s success to three factors: each musician shows the other three respect, none suffers the throes of “ego” and the group knows how to set the right priorities. But I found another strong attribute: communication among the players, picking up cues by watching and informing the others, as paramount to their high profile. They consistently raised eyebrows, glanced, stared, “sang to”, questioned, implied a “May I?” or a “Let me just…” and nodded to one another throughout. Particularly Veronika Hagen never showed the least aversion to pouting or grimaces, using them to give and take her instruction. She was a great communicator.

To their great advantage, the Hagens play on four famous Stradivarius instruments, formerly used by the Tokyo Quartet and the Paganini before them. In the right hands, the body of sound produced by such superb craftsmanship is as full and round as the finish of a fine Chippendale chair, as sensuous as the fleshy curves of a Bernini sculpture. In the String Quartet in G major, K387, one of the three “Haydn Quartets” featured, there was something almost three-dimensional about the Hagen’s rendition: the split second pauses injected before tackling a key note, for example, gave the “body” breath – even a physical presence – of its own. And while the first violin most often set the score, the others alternated the lead in a way that I, for one, have never experienced at another quartet’s performance. All four voices in perfect synchronicity made a true case for equality among the strings.

In the second movement, the first violin uncharacteristically zigzagged in fits and starts with an almost unsettling agitation, but set the pace for the wide variety in volume and timbre the Hagens brought to the work as each instrument played a vital and essential role. The slow movements and minuets made the “emotional core” of the work, but if music is to portray the full gamut of human emotion, there was good case for that here, too; the variety of expression called up everything from utter despair to playful jubilation, inescapable severity to light-hearted folly.

In the String Quartet in D minor, K421, Rainer Schmidt started his part in the first movement with a long look at the ceiling, as if to find something mystical out there that we couldn’t see. But in no time, the quartet entered an almost comical-sounding phase, puncuated by bold and down strokes of what sounded like a burly laugh. That in turn gave way to almost a Brahmsian sound, a soft shoe you were pleased to step into. And in the pizzicato of the final movement, there was an enthusiasm among the four players that seemed to say “Oh, boy!” So much for the variety of sounds and volumes.

After the interval, it was cellist Clemens Hagen who steered the first dynamic of the String Quartet in E flat major, K428. His playing in the first movement spanned a spectrum from the highly muscular to the temperate and highly restrained. He joined the others to give substance to the “squeezing” sensation at the start of the second movement; elaborating on a hunting theme where the folkloristic dance seemed to weigh against something almost schizophrenic in its volume and density. In the last movement, all the players drove hard and fast on the score’s downbeats, and I noted one comment only: Allegro assai − “an applecart alternating with a bullet train”. In sum, the versatility, timing, dialogues and superb technique of the Hagen made its achievement at the Tonhalle nothing short of four fine voices performing like a multifaceted one. Hands down, the quartet made for a magical moment that – not surprisingly – brought the thoroughly exhilarated audience to its feet.