Alvin Lucier, an acclaimed composer of the perpetual avant-garde who found music in everything, including the opening and closing of an umbrella over a ticking alarm clock as well as the overtones of a triangle being struck repeatedly for 15 minutes, died Dec. 1 at his home in Middletown, Conn. He was 90.

His wife, Wendy Stokes, said he had Parkinsonism and recently had a fall.

During a career spanning six decades, Lucier moved from a respectable position as a traditional composer with impeccable training (he studied at Tanglewood with Lukas Foss and Aaron Copland) to the near-personification of experimentalism in music. Beginning in the mid-1960s, he began writing pieces for brain waves, birdcalls, electronic devices, resonant bowls and, every so often, standard classical instruments mostly used in unconventional ways.

Lucier was best known for “I Am Sitting in a Room” (1970), regarded as a seminal masterpiece of the 20th century. Although it can be presented live – 90 different artists offered their own versions for a celebration of the composer’s last birthday – it is best known for the recorded version Lucier made himself in his living room almost 52 years ago.

On that long-ago afternoon, Lucier read a halting speech into one tape recorder, then played the recording back into another tape recorder, then played that dub back into the first tape recorder, repeating the process until there were 32 versions of the speech. He was inspired by his then-wife, the video artist Mary Lucier, who had become known for her “Xerox art,” effectively making a photocopy of a photocopy of a photocopy until almost all semblance of the original was distorted beyond recognition.

The speech read in part: “I am sitting in a room different from the one you are in now. I am recording the sound of my speaking voice and I am going to play it back into the room again and again until the resonant frequencies of the room reinforce themselves so that any semblance of my speech, with perhaps the exception of rhythm, is destroyed.”

After listening to Lucier’s recording for 20 minutes, you can scarcely make out what he is saying. By the end of the piece, all that is left is a mercurial patina of sonic residue – call it the “ghost” of the speech. On paper, it could sound arty and pretentious, but many critics and audiences found it lovely, especially as the distortion moves in to stay. Words become music, sound becomes shimmer and a natural process of acoustics is demonstrated in the most elegant and strangely beautiful fashion.

It is an ideal piece for teaching students to write about music. The musically trained may respond favorably or unfavorably, but even those who know nothing at all about music are often inspired to wax poetic. One university-level music student, asked to write about “I Am Sitting in a Room,” handed in his “paper” by purchasing two cheap mirrors and handing them in. He had written “I Am Looking In a Mirror” in black marker on one of them.

Alvin Augustus Lucier Jr. was born in Nashua, N.H., on May 14, 1931. His father, a lawyer who became mayor, was an amateur violinist. His mother played piano. For his part, young Alvin had no interest in learning piano or violin but instead took up the drums. His main interest was jazz but his discovery of a recording of Arnold Schoenberg’s “Serenade” drew him into contemporary classical music.

He began formal studies at Yale University, where he graduated in 1954. He then moved on to Brandeis, where he received a master of fine arts degree in 1960 and studied under composers Harold Shapero and Irving Fine before joining the faculty in 1963. During that period, he also was awarded a Fulbright scholarship to travel through Europe where, he later said, he “went to all the festivals” and admired much of the music but did not feel at home working in the same manner.

He tried to make a tape piece in the electronic studio in Milan. “The sounds were okay, but the narrative of the piece was wrong,” he later recalled to the Irish Times. “It was the old-fashioned thing: low, high, contrast. It didn’t satisfy me.”

There followed an arid period, where he pondered the future of his own work. “If I continued doing neoclassical music, or atonal music, I’d be imitating someone, I wouldn’t be truly myself,” he said. “So I waited.”

The breakthrough came in 1965, when a scientist friend interested Lucier in a sound amplifier that he had just created to measure and reflect alpha waves. “I made a piece for brain waves and percussion,” he told the Irish Times. “The process of making that piece is that you cannot move around or do much activity, when you’re trying to produce alpha brain waves. So I sat there passively. I thought that was a lovely way to make music, where you’re not forcing things. If you do, nothing happens.”

His next work was entitled “Music for Solo Performer for Enormously Amplified Brain Waves and Percussion.”

In 1970, Lucier was appointed composition professor at Wesleyan University. He would remain in Middletown the rest of his life, serving at times as the head of the music department. His marriage to Mary Glosser ended in divorce. In addition to Stokes, survivors include their daughter, Amanda Lucier of Portland, Ore.

Lucier was a mentor and was widely admired in musical circles that ranged from tenured professors at universities to indie rock bands. In 2016, he presented a concert in New York with the band Yo La Tengo.

“I must confess that I am executing crazy ideas I have had in my mind for years but never have had the courage to realize,” he said earlier this year to the New York Times. One of those, which went unfulfilled, was what he called “a duet with a bat who lives in the belfry of the Wesleyan Memorial Chapel.”

“One of my fondest compliments,” he reflected, “was when our plumber, as he was leaving my house after having finished a job at my home, remarked as he was walking out the door: ‘Are you the guy who wrote the piece about sitting in a room? My kids love it. You are ahead of your time.’ “