A group of xylophones is commonly called an Ensemble. Other collective nouns you may see include Group and Set.
Collective nouns are unique terms used to describe a group or collection of people, animals, or things. This particular category, however, lacks an official collective noun dedicated solely to xylophones. We often use "set" or "ensemble" as general terms to describe a group of musical instruments, including xylophones. However, to revamp the conventional naming scheme and provide an imaginative collective noun, we suggest "harmony" as a potential descriptor to represent a delightful assemblage of xylophones playing harmoniously together. The overlapping harmonies created by a unity of xylophones form a captivating and melodious collective – a "harmony" of xylophones.
Known collective nouns for Xylophones include: