I can’t count the number of times I have sat at my computer, opened YouTube and typed a strange phrase into the search box: “knee 1.”


“Knee 1” is the title of the opening section of “Einstein on the Beach,” Philip Glass and Robert Wilson’s 1976 operatic spectacle, a work that until last week at the Brooklyn Academy of Music, where it has returned after 20 years, I had known exclusively through recordings.


From the time I first heard about “Einstein,” while growing up just outside New York — the city whose 1970s downtown avant-garde it epitomized, and where it had its American premiere at the Metropolitan Opera House in 1976 — I knew that it was a seminal event in opera history. The work represented the culmination of centuries of experiments in the union of image and sound, and a new way to think about plot, or rather the absence of one. It was through this reputation that I admired it, but it was through recordings — through Mr. Glass’s alternately creeping and churning score — that I loved it.


For me the long-desired prospect of combining that score with Mr. Wilson’s design and direction, along with Lucinda Childs’s choreography, held the promise of a dream come to life. But the experience fell short of my imaginings.


I was surprised to discover that for all those years I had been missing so little. The really important component of the opera turns out to be the music, the part that has always been with us, preserved on those recordings. The other, more evanescent elements — the eternally open horizons of Mr. Wilson’s blue-lighted backdrops; his twitchy movement vocabulary; Ms. Childs’s swirling dances — feel, in the final estimation, dazzling yet dispensable.


There is nothing dispensable about the sound world of “Einstein.” That opening, for one thing. Like Wagner’s “Ring” cycle, Mr. Glass’s score begins with a deep drone, descending through three subterranean pitches. Voices — first a spoken solo, then a singing choir — crisply recite numbers. Then another group of singers comes in, echoing the initial low, elegiac melody in solfège syllables: “la, sol, do.”


Last week at the Brooklyn Academy the drone was more like a rumble; the voices were clear and piercing. It was astonishing: the difference between the live experience and listening on my laptop was like the difference between hearing the beginning of the “Ring” on records and hearing it in the theater, where its long, low E flat is less sound than texture, less audible than felt as a fine vibration.


There was also the visual component that I had always imagined but never thought I would see in person: the choir singing with eerie yet charming smiles from the pit, and the two female soloists illuminated in a downstage corner, sitting at desks and staring forward as they made strange, focused motions with their hands, scribbling with invisible pencils.


The sequence makes an impact. But even after seeing two performances of the opera in close succession (having returned on Sunday), I missed what I had so long been prepared for, what an opera more than four hours long ideally provides: a sense of accumulated power. In 1985 Jonathan Lieberson wrote in The New York Review of Books that “one is constantly struck by the impression that Wilson does not really know what to do with his images once he has presented them.”


It is true that the visual component of “Einstein,” which regularly astounds at the outset, rarely deepens with time. Extended scenes tend to explode with a live-wire burst of Mr. Glass’s music, then dissipate; not one ends with more intensity than when it began. I responded to certain moments, like the slow rotation of a bar of light from horizontal to vertical near the end of the opera, with indifference, as if I were checking off a box.


I found myself, as I never have when listening to a recording of the work, growing bored. A few times I closed my eyes and just listened, and the show immediately turned stranger and more riveting.


Why is the music of “Einstein” moving and satisfying in a way that the full production is not? It may be that profound sense of strangeness in Mr. Glass’s score, which upends most of the expectations of Western drama and embraces Eastern values of repetition, meditation, drone.