In addition to archaeology, ancient art, and classical philology, music was another of James Loeb’s great passions. His mother, Betty Loeb (née Gallenberg), came from a family of musicians in Mannheim (her father was the first violinist in the Grand Ducal Orchestra in Mannheim). She was a pianist and violinist who had trained at the Paris Conservatoire to concert level. At the Loeb home in Cincinnati and later in New York, she fostered a rich and high-quality musical life through regular chamber music matinees featuring family members (excluding the father) and guests. 

James Loeb received early instruction in cello (as his primary instrument), piano, and organ. According to his nephew James Paul Warburg, he was the only one among his siblings with true musical talent. An excellent cellist throughout his life and a pianist of nearly equal skill, he was involved in the public musical life of his American homeland from an early age and long after his move to Germany. He is known for his contributions to the founding of the Institute of Musical Art (together with Frank Damrosch) and for preserving its successor institution, the later world-famous Juilliard School of Music.

The large-format volumes and slipcases, bound in black with gold embossing, contain primarily sheet music from the late 19th and early 20th centuries. Among them are several valuable first editions of chamber music works by composers such as Brahms, Dvořák, Tchaikovsky, Rimsky-Korsakov, Richard Strauss, and others, as well as many other chamber music rarities in rare early editions.

However, Loeb clearly did not act as a bibliophile collector in this field (sheet music), but rather—despite his keen sense of quality and historical value—approached the acquisition and care of his music collection from a practical, performance-oriented perspective: works for the same instrumentation are bound together into complete sets. Prints that have become valuable over time can be found there alongside plain, run-of-the-mill editions (some of which are still sold today).

The music collection clearly did not form part of his official scholarly library. Rather, given its origin and intended purpose, it was of a purely private nature. Not a single music volume bears his bookplate with the well-known motto “Opes adipiscendae ut dignis largiamur” (Acquire wealth so that we may give to those who are worthy). Many, however, bear his personal signature. Some volumes, if not the majority of the collection, may have come from his mother’s music collection in the Loeb family home. This is suggested by bindings elegantly ornamented in the style of the late 19th century (Example 2) as well as license stamps from American representatives of German music publishers (e.g., Schirmer, Example 3) found in some old editions.

Notwithstanding Loeb’s preference for the string quartets of the Viennese Classics (see above), the focus of the Augsburg collection—as well as of Loeb’s chamber music collection as a whole—is clearly on chamber music for strings with piano. On the one hand, the focus was on composers of the generation around 1830–1840 (Brahms, Dvořák, Tchaikovsky, etc.), who, during Loeb’s youth, were among the established and leading figures in the American music scene (thanks, in part, to the transatlantic presence of their European publishers). On the other hand, there was also a specifically German repertoire, cultivated in the bourgeois salons of the late 19th century and largely unfamiliar today. The collection was thus clearly shaped by the musical tastes of his mother’s family tradition.

Concerts are still held based on James Loeb’s collection of sheet music. In recent years, there have been regular concerts at Murnau Castle or at the James Loeb Villa at the Hochried Clinic.