Sesquiterpene synthase involved in the biosynthesis of volatile organic compounds (PubMed:25956881). Mediates the conversion of (2E,6E)-farnesyl diphosphate (FPP) into beta-ylangene, beta-copaene and beta-cubebene (PubMed:25956881). Does not use (2E)-geranyl diphosphate (GPP) as substrate (PubMed:25956881). (2E,6E)-farnesyl diphosphate = beta-ylangene + diphosphate (2E,6E)-farnesyl diphosphate = beta-copaene + diphosphate (2E,6E)-farnesyl diphosphate = beta-cubebene + diphosphate Binds 3 Mg(2+) ions per subunit. Secondary metabolite biosynthesis; terpenoid biosynthesis. Monomer. The Asp-Asp-Xaa-Xaa-Asp/Glu (DDXXD/E) motif is important for the catalytic activity, presumably through binding to Mg(2+). Belongs to the terpene synthase family. Tpsa subfamily.