Terpene cyclase that catalyzes the cyclization of farnesyl diphosphate (FPP) to the spirocyclic sesquiterpene alpha-acorenol. (2E,6E)-farnesyl diphosphate + H2O = (-)-alpha-acorenol + diphosphate Binds 3 Mg(2+) ions per monomer. Sesquiterpene biosynthesis. Homodimer. The 2 conserved active-site motifs D(D/E)XX(D/E) and NSE are required for coordinating the divalent metal ions that stabilize the PPi moiety of the substrate. The C-terminal WxxxxxRY motif is frequently found in terpene synthases and is important to guide product formation. Abolishes the production of the spirocyclic sesquiterpene alpha-acorenol. Belongs to the terpene synthase family.