He combined his love for travel and music to turn the Long Island Youth Orchestra into a globe-trotting powerhouse.Martin C. Dreiwitz, who drew on his twin passions for travel and classical music to found the globe-trotting Long Island Youth Orchestra, conducting his student musicians before audiences as close as Great Neck and Brookville and as far away as Karachi and Kathmandu, died on June 20 at a hospital near his home in Oyster Bay, N.Y. He was 91.Steven Behr, the president of the orchestra’s board of directors, said the cause was a heart attack.The orchestra may have counted some 100 performers, but Mr. Dreiwitz (pronounced DRY-witz) was practically a one-man show: He raised the funds, he scouted for new members, he cajoled parents to bring snacks on rehearsal days, and he conducted every performance from its founding in 1962 to his retirement in 2012.He was also the orchestra’s travel agent. In addition to playing four concerts a year, mostly at a performance hall on the campus of Long Island University Post in Brookville, N.Y., the orchestra went on a summer tour, almost always abroad, with multiple stops and often on multiple continents. One trip, in 1977, took them to Greece, Kenya, the Seychelles, India, Sri Lanka and Israel, with every detail arranged by Mr. Dreiwitz.Though he trained as a classical clarinetist, Mr. Dreiwitz was, in fact, a travel agent by trade, and he used his skills and connections to plot intricate journeys that even a professional orchestra might shrink from. He took pride in being among the first Western orchestras to play in places like Pakistan and Nepal, performing sold-out shows with students who often had never before left Long Island.He treated his musicians like adults, and saw his mission as one less about pedagogy than about preparation for a professional music career. He eschewed the typical youth orchestra fare — Aaron Copland’s “Fanfare for the Common Man,” Samuel Barber’s “Adagio for Strings” — in favor of deep cuts from Mozart and Rossini and avant-garde composers like Virgil Thomson (a personal friend, who sometimes used the orchestra to test-run his latest work).He also tended to steer clear of Broadway scores, though he did have a soft spot for the music of George Gershwin, especially “Porgy and Bess,” and often included selections from that opera on the orchestra’s summer tour.Mr. Dreiwitz saw travel as another form of preparation. It was, he insisted, important for budding violists and clarinetists to learn how to perform at their best in strange new venues, in strange new cities, in front of strange new audiences.But he also simply loved the challenge of planning, say, a five-week trip for 85 students across five countries in East Asia. In between raising money and running rehearsals, during the school year he would dash off on reconnaissance trips, scouting each site for an upcoming tour — arranging hotels (or just as often private homes), checking out venues, even taste-testing restaurants. When the students arrived, months later, everything would be perfect.The orchestra ran on a shoestring budget, especially early on, when Mr. Dreiwitz refused to charge tuition. Instead, funds came from family donations, annual candy sales and, quite often, his own pocket. Every spring he offered a $2,500 scholarship to be split among the three best high school seniors, as judged by an outside panel.The Long Island Youth Orchestra in 1974. Alumni have gone on to play in most of the country’s major symphonies, and they populate countless chamber groups and academic music departments.Lester Paverman for The New York TimesMr. Dreiwitz’s hard work paid off. The orchestra’s 4,000 (and counting) alumni have gone on to play in many of the country’s major companies, including the Boston Symphony Orchestra, the New York Philharmonic, and the Philadelphia Orchestra, and they populate countless chamber groups and academic music departments.Mr. Dreiwitz could be stern and exacting on the podium, but, many of his former musicians said, he ran the orchestra like a family, fostering a vibe of collegiality instead of competitiveness.“I don’t twist anyone’s arm to join,” he told The New York Times in 1964. “They’re giving up their own time because they love music and want an opportunity to play. I don’t think you can find a more enthusiastic group of musicians any place.”Martin Charles Dreiwitz was born in Weehawken, N.J, on June 15, 1931, and raised in Brooklyn. His father, Samuel Dreiwitz, worked in the fur industry, and his mother, Charlotte (Silver) Dreiwitz, was a homemaker.He is survived by his two sons, Tuan Dinh and Dung Dinh.A gifted musician even as a child, he played clarinet and graduated from the High School of Music and Art in Manhattan (now the Fiorello H. LaGuardia High School of Music & the Arts), and he majored in music at the University of Chicago. Along the way he studied under woodwind luminaries like Simeon Bellison, the principal clarinetist for New York Philharmonic, and Anthony Gugliotti, who held the same post with the Philadelphia Orchestra.After graduating from college in 1953, he moved to Europe, where he traveled and studied to be a conductor, including a stint with Wilhelm Furtwängler in Vienna.He returned to the United States in the early 1960s and settled in suburban Long Island, hoping to find a job conducting. To make ends meet, he took a job as a travel agent and offered private clarinet lessons on the side.One day in 1962, one of his particularly talented students put down his instrument and frowned.“I’ve gotten this far,” Mr. Dreiwitz recalled the student saying, “and now I must wait years, until I get into a major orchestra, before I get some really good experience. Where do I go from here?”The seed was planted, and took root: Mr. Dreiwitz held auditions for what he initially called the North Shore Symphony Orchestra in September 1962. He started with just 52 musicians, and they held a concert the next spring. A few years later, he took them on their first trip, to Chicopee, Mass.It was stop and go in the early years, with Mr. Dreiwitz hitting up Nassau County music teachers to find promising players. But by the end of the 1960s, he no longer needed to. Eager students lined up outside his travel agency to audition, and every year he had a wait list. The orchestra went on its first overseas trip, to Europe, in 1971.He took emeritus status in 2012, handing the baton to Scott Dunn, a former student. He continued to come in to rehearsals at L.I.U. Post, though less and less often, and then not at all.But Mr. Dreiwitzhad one more hurrah. In 2018, hundreds of alumni returned for a concert in his honor, and he even mounted the podium, to conduct a selection from his beloved “Porgy and Bess.” More